FreeBSD/Linux Kernel Cross Reference
sys/block/cfq-iosched.c

     /*
      *  CFQ, or complete fairness queueing, disk scheduler.
      *
      *  Based on ideas from a previously unfinished io
      *  scheduler (round robin per-process disk scheduling) and Andrea Arcangeli.
      *
      *  Copyright (C) 2003 Jens Axboe <axboe@kernel.dk>
      */
     #include <linux/module.h>
    #include <linux/slab.h>
    #include <linux/blkdev.h>
    #include <linux/elevator.h>
    #include <linux/jiffies.h>
    #include <linux/rbtree.h>
    #include <linux/ioprio.h>
    #include <linux/blktrace_api.h>
    #include "blk.h"
    #include "blk-cgroup.h"
    
    /*
     * tunables
     */
    /* max queue in one round of service */
    static const int cfq_quantum = 8;
    static const int cfq_fifo_expire[2] = { HZ / 4, HZ / 8 };
    /* maximum backwards seek, in KiB */
    static const int cfq_back_max = 16 * 1024;
    /* penalty of a backwards seek */
    static const int cfq_back_penalty = 2;
    static const int cfq_slice_sync = HZ / 10;
    static int cfq_slice_async = HZ / 25;
    static const int cfq_slice_async_rq = 2;
    static int cfq_slice_idle = HZ / 125;
    static int cfq_group_idle = HZ / 125;
    static const int cfq_target_latency = HZ * 3/10; /* 300 ms */
    static const int cfq_hist_divisor = 4;
    
    /*
     * offset from end of service tree
     */
    #define CFQ_IDLE_DELAY          (HZ / 5)
    
    /*
     * below this threshold, we consider thinktime immediate
     */
    #define CFQ_MIN_TT              (2)
    
    #define CFQ_SLICE_SCALE         (5)
    #define CFQ_HW_QUEUE_MIN        (5)
    #define CFQ_SERVICE_SHIFT       12
    
    #define CFQQ_SEEK_THR           (sector_t)(8 * 100)
    #define CFQQ_CLOSE_THR          (sector_t)(8 * 1024)
    #define CFQQ_SECT_THR_NONROT    (sector_t)(2 * 32)
    #define CFQQ_SEEKY(cfqq)        (hweight32(cfqq->seek_history) > 32/8)
    
    #define RQ_CIC(rq)              icq_to_cic((rq)->elv.icq)
    #define RQ_CFQQ(rq)             (struct cfq_queue *) ((rq)->elv.priv[0])
    #define RQ_CFQG(rq)             (struct cfq_group *) ((rq)->elv.priv[1])
    
    static struct kmem_cache *cfq_pool;
    
    #define CFQ_PRIO_LISTS          IOPRIO_BE_NR
    #define cfq_class_idle(cfqq)    ((cfqq)->ioprio_class == IOPRIO_CLASS_IDLE)
    #define cfq_class_rt(cfqq)      ((cfqq)->ioprio_class == IOPRIO_CLASS_RT)
    
    #define sample_valid(samples)   ((samples) > 80)
    #define rb_entry_cfqg(node)     rb_entry((node), struct cfq_group, rb_node)
    
    struct cfq_ttime {
            unsigned long last_end_request;
    
            unsigned long ttime_total;
            unsigned long ttime_samples;
            unsigned long ttime_mean;
    };
    
    /*
     * Most of our rbtree usage is for sorting with min extraction, so
     * if we cache the leftmost node we don't have to walk down the tree
     * to find it. Idea borrowed from Ingo Molnars CFS scheduler. We should
     * move this into the elevator for the rq sorting as well.
     */
    struct cfq_rb_root {
            struct rb_root rb;
            struct rb_node *left;
            unsigned count;
            unsigned total_weight;
            u64 min_vdisktime;
            struct cfq_ttime ttime;
    };
    #define CFQ_RB_ROOT     (struct cfq_rb_root) { .rb = RB_ROOT, \
                            .ttime = {.last_end_request = jiffies,},}
    
    /*
     * Per process-grouping structure
     */
    struct cfq_queue {
            /* reference count */
           int ref;
           /* various state flags, see below */
           unsigned int flags;
           /* parent cfq_data */
           struct cfq_data *cfqd;
           /* service_tree member */
           struct rb_node rb_node;
           /* service_tree key */
           unsigned long rb_key;
           /* prio tree member */
           struct rb_node p_node;
           /* prio tree root we belong to, if any */
           struct rb_root *p_root;
           /* sorted list of pending requests */
           struct rb_root sort_list;
           /* if fifo isn't expired, next request to serve */
           struct request *next_rq;
           /* requests queued in sort_list */
           int queued[2];
           /* currently allocated requests */
           int allocated[2];
           /* fifo list of requests in sort_list */
           struct list_head fifo;
   
           /* time when queue got scheduled in to dispatch first request. */
           unsigned long dispatch_start;
           unsigned int allocated_slice;
           unsigned int slice_dispatch;
           /* time when first request from queue completed and slice started. */
           unsigned long slice_start;
           unsigned long slice_end;
           long slice_resid;
   
           /* pending priority requests */
           int prio_pending;
           /* number of requests that are on the dispatch list or inside driver */
           int dispatched;
   
           /* io prio of this group */
           unsigned short ioprio, org_ioprio;
           unsigned short ioprio_class;
   
           pid_t pid;
   
           u32 seek_history;
           sector_t last_request_pos;
   
           struct cfq_rb_root *service_tree;
           struct cfq_queue *new_cfqq;
           struct cfq_group *cfqg;
           /* Number of sectors dispatched from queue in single dispatch round */
           unsigned long nr_sectors;
   };
   
   /*
    * First index in the service_trees.
    * IDLE is handled separately, so it has negative index
    */
   enum wl_prio_t {
           BE_WORKLOAD = 0,
           RT_WORKLOAD = 1,
           IDLE_WORKLOAD = 2,
           CFQ_PRIO_NR,
   };
   
   /*
    * Second index in the service_trees.
    */
   enum wl_type_t {
           ASYNC_WORKLOAD = 0,
           SYNC_NOIDLE_WORKLOAD = 1,
           SYNC_WORKLOAD = 2
   };
   
   struct cfqg_stats {
   #ifdef CONFIG_CFQ_GROUP_IOSCHED
           /* total bytes transferred */
           struct blkg_rwstat              service_bytes;
           /* total IOs serviced, post merge */
           struct blkg_rwstat              serviced;
           /* number of ios merged */
           struct blkg_rwstat              merged;
           /* total time spent on device in ns, may not be accurate w/ queueing */
           struct blkg_rwstat              service_time;
           /* total time spent waiting in scheduler queue in ns */
           struct blkg_rwstat              wait_time;
           /* number of IOs queued up */
           struct blkg_rwstat              queued;
           /* total sectors transferred */
           struct blkg_stat                sectors;
           /* total disk time and nr sectors dispatched by this group */
           struct blkg_stat                time;
   #ifdef CONFIG_DEBUG_BLK_CGROUP
           /* time not charged to this cgroup */
           struct blkg_stat                unaccounted_time;
           /* sum of number of ios queued across all samples */
           struct blkg_stat                avg_queue_size_sum;
           /* count of samples taken for average */
           struct blkg_stat                avg_queue_size_samples;
           /* how many times this group has been removed from service tree */
           struct blkg_stat                dequeue;
           /* total time spent waiting for it to be assigned a timeslice. */
           struct blkg_stat                group_wait_time;
           /* time spent idling for this blkcg_gq */
           struct blkg_stat                idle_time;
           /* total time with empty current active q with other requests queued */
           struct blkg_stat                empty_time;
           /* fields after this shouldn't be cleared on stat reset */
           uint64_t                        start_group_wait_time;
           uint64_t                        start_idle_time;
           uint64_t                        start_empty_time;
           uint16_t                        flags;
   #endif  /* CONFIG_DEBUG_BLK_CGROUP */
   #endif  /* CONFIG_CFQ_GROUP_IOSCHED */
   };
   
   /* This is per cgroup per device grouping structure */
   struct cfq_group {
           /* must be the first member */
           struct blkg_policy_data pd;
   
           /* group service_tree member */
           struct rb_node rb_node;
   
           /* group service_tree key */
           u64 vdisktime;
           unsigned int weight;
           unsigned int new_weight;
           unsigned int dev_weight;
   
           /* number of cfqq currently on this group */
           int nr_cfqq;
   
           /*
            * Per group busy queues average. Useful for workload slice calc. We
            * create the array for each prio class but at run time it is used
            * only for RT and BE class and slot for IDLE class remains unused.
            * This is primarily done to avoid confusion and a gcc warning.
            */
           unsigned int busy_queues_avg[CFQ_PRIO_NR];
           /*
            * rr lists of queues with requests. We maintain service trees for
            * RT and BE classes. These trees are subdivided in subclasses
            * of SYNC, SYNC_NOIDLE and ASYNC based on workload type. For IDLE
            * class there is no subclassification and all the cfq queues go on
            * a single tree service_tree_idle.
            * Counts are embedded in the cfq_rb_root
            */
           struct cfq_rb_root service_trees[2][3];
           struct cfq_rb_root service_tree_idle;
   
           unsigned long saved_workload_slice;
           enum wl_type_t saved_workload;
           enum wl_prio_t saved_serving_prio;
   
           /* number of requests that are on the dispatch list or inside driver */
           int dispatched;
           struct cfq_ttime ttime;
           struct cfqg_stats stats;
   };
   
   struct cfq_io_cq {
           struct io_cq            icq;            /* must be the first member */
           struct cfq_queue        *cfqq[2];
           struct cfq_ttime        ttime;
           int                     ioprio;         /* the current ioprio */
   #ifdef CONFIG_CFQ_GROUP_IOSCHED
           uint64_t                blkcg_id;       /* the current blkcg ID */
   #endif
   };
   
   /*
    * Per block device queue structure
    */
   struct cfq_data {
           struct request_queue *queue;
           /* Root service tree for cfq_groups */
           struct cfq_rb_root grp_service_tree;
           struct cfq_group *root_group;
   
           /*
            * The priority currently being served
            */
           enum wl_prio_t serving_prio;
           enum wl_type_t serving_type;
           unsigned long workload_expires;
           struct cfq_group *serving_group;
   
           /*
            * Each priority tree is sorted by next_request position.  These
            * trees are used when determining if two or more queues are
            * interleaving requests (see cfq_close_cooperator).
            */
           struct rb_root prio_trees[CFQ_PRIO_LISTS];
   
           unsigned int busy_queues;
           unsigned int busy_sync_queues;
   
           int rq_in_driver;
           int rq_in_flight[2];
   
           /*
            * queue-depth detection
            */
           int rq_queued;
           int hw_tag;
           /*
            * hw_tag can be
            * -1 => indeterminate, (cfq will behave as if NCQ is present, to allow better detection)
            *  1 => NCQ is present (hw_tag_est_depth is the estimated max depth)
            *  0 => no NCQ
            */
           int hw_tag_est_depth;
           unsigned int hw_tag_samples;
   
           /*
            * idle window management
            */
           struct timer_list idle_slice_timer;
           struct work_struct unplug_work;
   
           struct cfq_queue *active_queue;
           struct cfq_io_cq *active_cic;
   
           /*
            * async queue for each priority case
            */
           struct cfq_queue *async_cfqq[2][IOPRIO_BE_NR];
           struct cfq_queue *async_idle_cfqq;
   
           sector_t last_position;
   
           /*
            * tunables, see top of file
            */
           unsigned int cfq_quantum;
           unsigned int cfq_fifo_expire[2];
           unsigned int cfq_back_penalty;
           unsigned int cfq_back_max;
           unsigned int cfq_slice[2];
           unsigned int cfq_slice_async_rq;
           unsigned int cfq_slice_idle;
           unsigned int cfq_group_idle;
           unsigned int cfq_latency;
           unsigned int cfq_target_latency;
   
           /*
            * Fallback dummy cfqq for extreme OOM conditions
            */
           struct cfq_queue oom_cfqq;
   
           unsigned long last_delayed_sync;
   };
   
   static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd);
   
   static struct cfq_rb_root *service_tree_for(struct cfq_group *cfqg,
                                               enum wl_prio_t prio,
                                               enum wl_type_t type)
   {
           if (!cfqg)
                   return NULL;
   
           if (prio == IDLE_WORKLOAD)
                   return &cfqg->service_tree_idle;
   
           return &cfqg->service_trees[prio][type];
   }
   
   enum cfqq_state_flags {
           CFQ_CFQQ_FLAG_on_rr = 0,        /* on round-robin busy list */
           CFQ_CFQQ_FLAG_wait_request,     /* waiting for a request */
           CFQ_CFQQ_FLAG_must_dispatch,    /* must be allowed a dispatch */
           CFQ_CFQQ_FLAG_must_alloc_slice, /* per-slice must_alloc flag */
           CFQ_CFQQ_FLAG_fifo_expire,      /* FIFO checked in this slice */
           CFQ_CFQQ_FLAG_idle_window,      /* slice idling enabled */
           CFQ_CFQQ_FLAG_prio_changed,     /* task priority has changed */
           CFQ_CFQQ_FLAG_slice_new,        /* no requests dispatched in slice */
           CFQ_CFQQ_FLAG_sync,             /* synchronous queue */
           CFQ_CFQQ_FLAG_coop,             /* cfqq is shared */
           CFQ_CFQQ_FLAG_split_coop,       /* shared cfqq will be splitted */
           CFQ_CFQQ_FLAG_deep,             /* sync cfqq experienced large depth */
           CFQ_CFQQ_FLAG_wait_busy,        /* Waiting for next request */
   };
   
   #define CFQ_CFQQ_FNS(name)                                              \
   static inline void cfq_mark_cfqq_##name(struct cfq_queue *cfqq)         \
   {                                                                       \
           (cfqq)->flags |= (1 << CFQ_CFQQ_FLAG_##name);                   \
   }                                                                       \
   static inline void cfq_clear_cfqq_##name(struct cfq_queue *cfqq)        \
   {                                                                       \
           (cfqq)->flags &= ~(1 << CFQ_CFQQ_FLAG_##name);                  \
   }                                                                       \
   static inline int cfq_cfqq_##name(const struct cfq_queue *cfqq)         \
   {                                                                       \
           return ((cfqq)->flags & (1 << CFQ_CFQQ_FLAG_##name)) != 0;      \
   }
   
   CFQ_CFQQ_FNS(on_rr);
   CFQ_CFQQ_FNS(wait_request);
   CFQ_CFQQ_FNS(must_dispatch);
   CFQ_CFQQ_FNS(must_alloc_slice);
   CFQ_CFQQ_FNS(fifo_expire);
   CFQ_CFQQ_FNS(idle_window);
   CFQ_CFQQ_FNS(prio_changed);
   CFQ_CFQQ_FNS(slice_new);
   CFQ_CFQQ_FNS(sync);
   CFQ_CFQQ_FNS(coop);
   CFQ_CFQQ_FNS(split_coop);
   CFQ_CFQQ_FNS(deep);
   CFQ_CFQQ_FNS(wait_busy);
   #undef CFQ_CFQQ_FNS
   
   static inline struct cfq_group *pd_to_cfqg(struct blkg_policy_data *pd)
   {
           return pd ? container_of(pd, struct cfq_group, pd) : NULL;
   }
   
   static inline struct blkcg_gq *cfqg_to_blkg(struct cfq_group *cfqg)
   {
           return pd_to_blkg(&cfqg->pd);
   }
   
   #if defined(CONFIG_CFQ_GROUP_IOSCHED) && defined(CONFIG_DEBUG_BLK_CGROUP)
   
   /* cfqg stats flags */
   enum cfqg_stats_flags {
           CFQG_stats_waiting = 0,
           CFQG_stats_idling,
           CFQG_stats_empty,
   };
   
   #define CFQG_FLAG_FNS(name)                                             \
   static inline void cfqg_stats_mark_##name(struct cfqg_stats *stats)     \
   {                                                                       \
           stats->flags |= (1 << CFQG_stats_##name);                       \
   }                                                                       \
   static inline void cfqg_stats_clear_##name(struct cfqg_stats *stats)    \
   {                                                                       \
           stats->flags &= ~(1 << CFQG_stats_##name);                      \
   }                                                                       \
   static inline int cfqg_stats_##name(struct cfqg_stats *stats)           \
   {                                                                       \
           return (stats->flags & (1 << CFQG_stats_##name)) != 0;          \
   }                                                                       \
   
   CFQG_FLAG_FNS(waiting)
   CFQG_FLAG_FNS(idling)
   CFQG_FLAG_FNS(empty)
   #undef CFQG_FLAG_FNS
   
   /* This should be called with the queue_lock held. */
   static void cfqg_stats_update_group_wait_time(struct cfqg_stats *stats)
   {
           unsigned long long now;
   
           if (!cfqg_stats_waiting(stats))
                   return;
   
           now = sched_clock();
           if (time_after64(now, stats->start_group_wait_time))
                   blkg_stat_add(&stats->group_wait_time,
                                 now - stats->start_group_wait_time);
           cfqg_stats_clear_waiting(stats);
   }
   
   /* This should be called with the queue_lock held. */
   static void cfqg_stats_set_start_group_wait_time(struct cfq_group *cfqg,
                                                    struct cfq_group *curr_cfqg)
   {
           struct cfqg_stats *stats = &cfqg->stats;
   
           if (cfqg_stats_waiting(stats))
                   return;
           if (cfqg == curr_cfqg)
                   return;
           stats->start_group_wait_time = sched_clock();
           cfqg_stats_mark_waiting(stats);
   }
   
   /* This should be called with the queue_lock held. */
   static void cfqg_stats_end_empty_time(struct cfqg_stats *stats)
   {
           unsigned long long now;
   
           if (!cfqg_stats_empty(stats))
                   return;
   
           now = sched_clock();
           if (time_after64(now, stats->start_empty_time))
                   blkg_stat_add(&stats->empty_time,
                                 now - stats->start_empty_time);
           cfqg_stats_clear_empty(stats);
   }
   
   static void cfqg_stats_update_dequeue(struct cfq_group *cfqg)
   {
           blkg_stat_add(&cfqg->stats.dequeue, 1);
   }
   
   static void cfqg_stats_set_start_empty_time(struct cfq_group *cfqg)
   {
           struct cfqg_stats *stats = &cfqg->stats;
   
           if (blkg_rwstat_sum(&stats->queued))
                   return;
   
           /*
            * group is already marked empty. This can happen if cfqq got new
            * request in parent group and moved to this group while being added
            * to service tree. Just ignore the event and move on.
            */
           if (cfqg_stats_empty(stats))
                   return;
   
           stats->start_empty_time = sched_clock();
           cfqg_stats_mark_empty(stats);
   }
   
   static void cfqg_stats_update_idle_time(struct cfq_group *cfqg)
   {
           struct cfqg_stats *stats = &cfqg->stats;
   
           if (cfqg_stats_idling(stats)) {
                   unsigned long long now = sched_clock();
   
                   if (time_after64(now, stats->start_idle_time))
                           blkg_stat_add(&stats->idle_time,
                                         now - stats->start_idle_time);
                   cfqg_stats_clear_idling(stats);
           }
   }
   
   static void cfqg_stats_set_start_idle_time(struct cfq_group *cfqg)
   {
           struct cfqg_stats *stats = &cfqg->stats;
   
           BUG_ON(cfqg_stats_idling(stats));
   
           stats->start_idle_time = sched_clock();
           cfqg_stats_mark_idling(stats);
   }
   
   static void cfqg_stats_update_avg_queue_size(struct cfq_group *cfqg)
   {
           struct cfqg_stats *stats = &cfqg->stats;
   
           blkg_stat_add(&stats->avg_queue_size_sum,
                         blkg_rwstat_sum(&stats->queued));
           blkg_stat_add(&stats->avg_queue_size_samples, 1);
           cfqg_stats_update_group_wait_time(stats);
   }
   
   #else   /* CONFIG_CFQ_GROUP_IOSCHED && CONFIG_DEBUG_BLK_CGROUP */
   
   static inline void cfqg_stats_set_start_group_wait_time(struct cfq_group *cfqg, struct cfq_group *curr_cfqg) { }
   static inline void cfqg_stats_end_empty_time(struct cfqg_stats *stats) { }
   static inline void cfqg_stats_update_dequeue(struct cfq_group *cfqg) { }
   static inline void cfqg_stats_set_start_empty_time(struct cfq_group *cfqg) { }
   static inline void cfqg_stats_update_idle_time(struct cfq_group *cfqg) { }
   static inline void cfqg_stats_set_start_idle_time(struct cfq_group *cfqg) { }
   static inline void cfqg_stats_update_avg_queue_size(struct cfq_group *cfqg) { }
   
   #endif  /* CONFIG_CFQ_GROUP_IOSCHED && CONFIG_DEBUG_BLK_CGROUP */
   
   #ifdef CONFIG_CFQ_GROUP_IOSCHED
   
   static struct blkcg_policy blkcg_policy_cfq;
   
   static inline struct cfq_group *blkg_to_cfqg(struct blkcg_gq *blkg)
   {
           return pd_to_cfqg(blkg_to_pd(blkg, &blkcg_policy_cfq));
   }
   
   static inline void cfqg_get(struct cfq_group *cfqg)
   {
           return blkg_get(cfqg_to_blkg(cfqg));
   }
   
   static inline void cfqg_put(struct cfq_group *cfqg)
   {
           return blkg_put(cfqg_to_blkg(cfqg));
   }
   
   #define cfq_log_cfqq(cfqd, cfqq, fmt, args...)  do {                    \
           char __pbuf[128];                                               \
                                                                           \
           blkg_path(cfqg_to_blkg((cfqq)->cfqg), __pbuf, sizeof(__pbuf));  \
           blk_add_trace_msg((cfqd)->queue, "cfq%d%c %s " fmt, (cfqq)->pid, \
                             cfq_cfqq_sync((cfqq)) ? 'S' : 'A',            \
                             __pbuf, ##args);                              \
   } while (0)
   
   #define cfq_log_cfqg(cfqd, cfqg, fmt, args...)  do {                    \
           char __pbuf[128];                                               \
                                                                           \
           blkg_path(cfqg_to_blkg(cfqg), __pbuf, sizeof(__pbuf));          \
           blk_add_trace_msg((cfqd)->queue, "%s " fmt, __pbuf, ##args);    \
   } while (0)
   
   static inline void cfqg_stats_update_io_add(struct cfq_group *cfqg,
                                               struct cfq_group *curr_cfqg, int rw)
   {
           blkg_rwstat_add(&cfqg->stats.queued, rw, 1);
           cfqg_stats_end_empty_time(&cfqg->stats);
           cfqg_stats_set_start_group_wait_time(cfqg, curr_cfqg);
   }
   
   static inline void cfqg_stats_update_timeslice_used(struct cfq_group *cfqg,
                           unsigned long time, unsigned long unaccounted_time)
   {
           blkg_stat_add(&cfqg->stats.time, time);
   #ifdef CONFIG_DEBUG_BLK_CGROUP
           blkg_stat_add(&cfqg->stats.unaccounted_time, unaccounted_time);
   #endif
   }
   
   static inline void cfqg_stats_update_io_remove(struct cfq_group *cfqg, int rw)
   {
           blkg_rwstat_add(&cfqg->stats.queued, rw, -1);
   }
   
   static inline void cfqg_stats_update_io_merged(struct cfq_group *cfqg, int rw)
   {
           blkg_rwstat_add(&cfqg->stats.merged, rw, 1);
   }
   
   static inline void cfqg_stats_update_dispatch(struct cfq_group *cfqg,
                                                 uint64_t bytes, int rw)
   {
           blkg_stat_add(&cfqg->stats.sectors, bytes >> 9);
           blkg_rwstat_add(&cfqg->stats.serviced, rw, 1);
           blkg_rwstat_add(&cfqg->stats.service_bytes, rw, bytes);
   }
   
   static inline void cfqg_stats_update_completion(struct cfq_group *cfqg,
                           uint64_t start_time, uint64_t io_start_time, int rw)
   {
           struct cfqg_stats *stats = &cfqg->stats;
           unsigned long long now = sched_clock();
   
           if (time_after64(now, io_start_time))
                   blkg_rwstat_add(&stats->service_time, rw, now - io_start_time);
           if (time_after64(io_start_time, start_time))
                   blkg_rwstat_add(&stats->wait_time, rw,
                                   io_start_time - start_time);
   }
   
   static void cfq_pd_reset_stats(struct blkcg_gq *blkg)
   {
           struct cfq_group *cfqg = blkg_to_cfqg(blkg);
           struct cfqg_stats *stats = &cfqg->stats;
   
           /* queued stats shouldn't be cleared */
           blkg_rwstat_reset(&stats->service_bytes);
           blkg_rwstat_reset(&stats->serviced);
           blkg_rwstat_reset(&stats->merged);
           blkg_rwstat_reset(&stats->service_time);
           blkg_rwstat_reset(&stats->wait_time);
           blkg_stat_reset(&stats->time);
   #ifdef CONFIG_DEBUG_BLK_CGROUP
           blkg_stat_reset(&stats->unaccounted_time);
           blkg_stat_reset(&stats->avg_queue_size_sum);
           blkg_stat_reset(&stats->avg_queue_size_samples);
           blkg_stat_reset(&stats->dequeue);
           blkg_stat_reset(&stats->group_wait_time);
           blkg_stat_reset(&stats->idle_time);
           blkg_stat_reset(&stats->empty_time);
   #endif
   }
   
   #else   /* CONFIG_CFQ_GROUP_IOSCHED */
   
   static inline void cfqg_get(struct cfq_group *cfqg) { }
   static inline void cfqg_put(struct cfq_group *cfqg) { }
   
   #define cfq_log_cfqq(cfqd, cfqq, fmt, args...)  \
           blk_add_trace_msg((cfqd)->queue, "cfq%d " fmt, (cfqq)->pid, ##args)
   #define cfq_log_cfqg(cfqd, cfqg, fmt, args...)          do {} while (0)
   
   static inline void cfqg_stats_update_io_add(struct cfq_group *cfqg,
                           struct cfq_group *curr_cfqg, int rw) { }
   static inline void cfqg_stats_update_timeslice_used(struct cfq_group *cfqg,
                           unsigned long time, unsigned long unaccounted_time) { }
   static inline void cfqg_stats_update_io_remove(struct cfq_group *cfqg, int rw) { }
   static inline void cfqg_stats_update_io_merged(struct cfq_group *cfqg, int rw) { }
   static inline void cfqg_stats_update_dispatch(struct cfq_group *cfqg,
                                                 uint64_t bytes, int rw) { }
   static inline void cfqg_stats_update_completion(struct cfq_group *cfqg,
                           uint64_t start_time, uint64_t io_start_time, int rw) { }
   
   #endif  /* CONFIG_CFQ_GROUP_IOSCHED */
   
   #define cfq_log(cfqd, fmt, args...)     \
           blk_add_trace_msg((cfqd)->queue, "cfq " fmt, ##args)
   
   /* Traverses through cfq group service trees */
   #define for_each_cfqg_st(cfqg, i, j, st) \
           for (i = 0; i <= IDLE_WORKLOAD; i++) \
                   for (j = 0, st = i < IDLE_WORKLOAD ? &cfqg->service_trees[i][j]\
                           : &cfqg->service_tree_idle; \
                           (i < IDLE_WORKLOAD && j <= SYNC_WORKLOAD) || \
                           (i == IDLE_WORKLOAD && j == 0); \
                           j++, st = i < IDLE_WORKLOAD ? \
                           &cfqg->service_trees[i][j]: NULL) \
   
   static inline bool cfq_io_thinktime_big(struct cfq_data *cfqd,
           struct cfq_ttime *ttime, bool group_idle)
   {
           unsigned long slice;
           if (!sample_valid(ttime->ttime_samples))
                   return false;
           if (group_idle)
                   slice = cfqd->cfq_group_idle;
           else
                   slice = cfqd->cfq_slice_idle;
           return ttime->ttime_mean > slice;
   }
   
   static inline bool iops_mode(struct cfq_data *cfqd)
   {
           /*
            * If we are not idling on queues and it is a NCQ drive, parallel
            * execution of requests is on and measuring time is not possible
            * in most of the cases until and unless we drive shallower queue
            * depths and that becomes a performance bottleneck. In such cases
            * switch to start providing fairness in terms of number of IOs.
            */
           if (!cfqd->cfq_slice_idle && cfqd->hw_tag)
                   return true;
           else
                   return false;
   }
   
   static inline enum wl_prio_t cfqq_prio(struct cfq_queue *cfqq)
   {
           if (cfq_class_idle(cfqq))
                   return IDLE_WORKLOAD;
           if (cfq_class_rt(cfqq))
                   return RT_WORKLOAD;
           return BE_WORKLOAD;
   }
   
   
   static enum wl_type_t cfqq_type(struct cfq_queue *cfqq)
   {
           if (!cfq_cfqq_sync(cfqq))
                   return ASYNC_WORKLOAD;
           if (!cfq_cfqq_idle_window(cfqq))
                   return SYNC_NOIDLE_WORKLOAD;
           return SYNC_WORKLOAD;
   }
   
   static inline int cfq_group_busy_queues_wl(enum wl_prio_t wl,
                                           struct cfq_data *cfqd,
                                           struct cfq_group *cfqg)
   {
           if (wl == IDLE_WORKLOAD)
                   return cfqg->service_tree_idle.count;
   
           return cfqg->service_trees[wl][ASYNC_WORKLOAD].count
                   + cfqg->service_trees[wl][SYNC_NOIDLE_WORKLOAD].count
                   + cfqg->service_trees[wl][SYNC_WORKLOAD].count;
   }
   
   static inline int cfqg_busy_async_queues(struct cfq_data *cfqd,
                                           struct cfq_group *cfqg)
   {
           return cfqg->service_trees[RT_WORKLOAD][ASYNC_WORKLOAD].count
                   + cfqg->service_trees[BE_WORKLOAD][ASYNC_WORKLOAD].count;
   }
   
   static void cfq_dispatch_insert(struct request_queue *, struct request *);
   static struct cfq_queue *cfq_get_queue(struct cfq_data *cfqd, bool is_sync,
                                          struct cfq_io_cq *cic, struct bio *bio,
                                          gfp_t gfp_mask);
   
   static inline struct cfq_io_cq *icq_to_cic(struct io_cq *icq)
   {
           /* cic->icq is the first member, %NULL will convert to %NULL */
           return container_of(icq, struct cfq_io_cq, icq);
   }
   
   static inline struct cfq_io_cq *cfq_cic_lookup(struct cfq_data *cfqd,
                                                  struct io_context *ioc)
   {
           if (ioc)
                   return icq_to_cic(ioc_lookup_icq(ioc, cfqd->queue));
           return NULL;
   }
   
   static inline struct cfq_queue *cic_to_cfqq(struct cfq_io_cq *cic, bool is_sync)
   {
           return cic->cfqq[is_sync];
   }
   
   static inline void cic_set_cfqq(struct cfq_io_cq *cic, struct cfq_queue *cfqq,
                                   bool is_sync)
   {
           cic->cfqq[is_sync] = cfqq;
   }
   
   static inline struct cfq_data *cic_to_cfqd(struct cfq_io_cq *cic)
   {
           return cic->icq.q->elevator->elevator_data;
   }
   
   /*
    * We regard a request as SYNC, if it's either a read or has the SYNC bit
    * set (in which case it could also be direct WRITE).
    */
   static inline bool cfq_bio_sync(struct bio *bio)
   {
           return bio_data_dir(bio) == READ || (bio->bi_rw & REQ_SYNC);
   }
   
   /*
    * scheduler run of queue, if there are requests pending and no one in the
    * driver that will restart queueing
    */
   static inline void cfq_schedule_dispatch(struct cfq_data *cfqd)
   {
           if (cfqd->busy_queues) {
                   cfq_log(cfqd, "schedule dispatch");
                   kblockd_schedule_work(cfqd->queue, &cfqd->unplug_work);
           }
   }
   
   /*
    * Scale schedule slice based on io priority. Use the sync time slice only
    * if a queue is marked sync and has sync io queued. A sync queue with async
    * io only, should not get full sync slice length.
    */
   static inline int cfq_prio_slice(struct cfq_data *cfqd, bool sync,
                                    unsigned short prio)
   {
           const int base_slice = cfqd->cfq_slice[sync];
   
           WARN_ON(prio >= IOPRIO_BE_NR);
   
           return base_slice + (base_slice/CFQ_SLICE_SCALE * (4 - prio));
   }
   
   static inline int
   cfq_prio_to_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
   {
           return cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio);
   }
   
   static inline u64 cfq_scale_slice(unsigned long delta, struct cfq_group *cfqg)
   {
           u64 d = delta << CFQ_SERVICE_SHIFT;
   
           d = d * CFQ_WEIGHT_DEFAULT;
           do_div(d, cfqg->weight);
           return d;
   }
   
   static inline u64 max_vdisktime(u64 min_vdisktime, u64 vdisktime)
   {
           s64 delta = (s64)(vdisktime - min_vdisktime);
           if (delta > 0)
                   min_vdisktime = vdisktime;
   
           return min_vdisktime;
   }
   
   static inline u64 min_vdisktime(u64 min_vdisktime, u64 vdisktime)
   {
           s64 delta = (s64)(vdisktime - min_vdisktime);
           if (delta < 0)
                   min_vdisktime = vdisktime;
   
           return min_vdisktime;
   }
   
   static void update_min_vdisktime(struct cfq_rb_root *st)
   {
           struct cfq_group *cfqg;
   
           if (st->left) {
                   cfqg = rb_entry_cfqg(st->left);
                   st->min_vdisktime = max_vdisktime(st->min_vdisktime,
                                                     cfqg->vdisktime);
           }
   }
   
   /*
    * get averaged number of queues of RT/BE priority.
    * average is updated, with a formula that gives more weight to higher numbers,
    * to quickly follows sudden increases and decrease slowly
    */
   
   static inline unsigned cfq_group_get_avg_queues(struct cfq_data *cfqd,
                                           struct cfq_group *cfqg, bool rt)
   {
           unsigned min_q, max_q;
           unsigned mult  = cfq_hist_divisor - 1;
           unsigned round = cfq_hist_divisor / 2;
           unsigned busy = cfq_group_busy_queues_wl(rt, cfqd, cfqg);
   
           min_q = min(cfqg->busy_queues_avg[rt], busy);
           max_q = max(cfqg->busy_queues_avg[rt], busy);
           cfqg->busy_queues_avg[rt] = (mult * max_q + min_q + round) /
                   cfq_hist_divisor;
           return cfqg->busy_queues_avg[rt];
   }
   
   static inline unsigned
   cfq_group_slice(struct cfq_data *cfqd, struct cfq_group *cfqg)
   {
           struct cfq_rb_root *st = &cfqd->grp_service_tree;
   
           return cfqd->cfq_target_latency * cfqg->weight / st->total_weight;
   }
   
   static inline unsigned
   cfq_scaled_cfqq_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
   {
           unsigned slice = cfq_prio_to_slice(cfqd, cfqq);
           if (cfqd->cfq_latency) {
                   /*
                    * interested queues (we consider only the ones with the same
                    * priority class in the cfq group)
                    */
                   unsigned iq = cfq_group_get_avg_queues(cfqd, cfqq->cfqg,
                                                   cfq_class_rt(cfqq));
                   unsigned sync_slice = cfqd->cfq_slice[1];
                   unsigned expect_latency = sync_slice * iq;
                   unsigned group_slice = cfq_group_slice(cfqd, cfqq->cfqg);
   
                   if (expect_latency > group_slice) {
                           unsigned base_low_slice = 2 * cfqd->cfq_slice_idle;
                           /* scale low_slice according to IO priority
                            * and sync vs async */
                           unsigned low_slice =
                                   min(slice, base_low_slice * slice / sync_slice);
                           /* the adapted slice value is scaled to fit all iqs
                            * into the target latency */
                           slice = max(slice * group_slice / expect_latency,
                                       low_slice);
                   }
           }
           return slice;
   }
   
   static inline void
   cfq_set_prio_slice(struct cfq_data *cfqd, struct cfq_queue *cfqq)
   {
           unsigned slice = cfq_scaled_cfqq_slice(cfqd, cfqq);
   
           cfqq->slice_start = jiffies;
           cfqq->slice_end = jiffies + slice;
           cfqq->allocated_slice = slice;
           cfq_log_cfqq(cfqd, cfqq, "set_slice=%lu", cfqq->slice_end - jiffies);
   }
   
   /*
    * We need to wrap this check in cfq_cfqq_slice_new(), since ->slice_end
    * isn't valid until the first request from the dispatch is activated
    * and the slice time set.
    */
   static inline bool cfq_slice_used(struct cfq_queue *cfqq)
   {
           if (cfq_cfqq_slice_new(cfqq))
                   return false;
           if (time_before(jiffies, cfqq->slice_end))
                   return false;
   
           return true;
   }
   
   /*
    * Lifted from AS - choose which of rq1 and rq2 that is best served now.
    * We choose the request that is closest to the head right now. Distance
    * behind the head is penalized and only allowed to a certain extent.
    */
   static struct request *
   cfq_choose_req(struct cfq_data *cfqd, struct request *rq1, struct request *rq2, sector_t last)
   {
           sector_t s1, s2, d1 = 0, d2 = 0;
           unsigned long back_max;
   #define CFQ_RQ1_WRAP    0x01 /* request 1 wraps */
   #define CFQ_RQ2_WRAP    0x02 /* request 2 wraps */
           unsigned wrap = 0; /* bit mask: requests behind the disk head? */
   
           if (rq1 == NULL || rq1 == rq2)
                   return rq2;
           if (rq2 == NULL)
                   return rq1;
   
           if (rq_is_sync(rq1) != rq_is_sync(rq2))
                   return rq_is_sync(rq1) ? rq1 : rq2;
   
           if ((rq1->cmd_flags ^ rq2->cmd_flags) & REQ_PRIO)
                   return rq1->cmd_flags & REQ_PRIO ? rq1 : rq2;
   
           s1 = blk_rq_pos(rq1);
           s2 = blk_rq_pos(rq2);
  
          /*
           * by definition, 1KiB is 2 sectors
           */
          back_max = cfqd->cfq_back_max * 2;
  
          /*
           * Strict one way elevator _except_ in the case where we allow
           * short backward seeks which are biased as twice the cost of a
           * similar forward seek.
           */
          if (s1 >= last)
                  d1 = s1 - last;
          else if (s1 + back_max >= last)
                  d1 = (last - s1) * cfqd->cfq_back_penalty;
          else
                  wrap |= CFQ_RQ1_WRAP;
  
          if (s2 >= last)
                  d2 = s2 - last;
          else if (s2 + back_max >= last)
                  d2 = (last - s2) * cfqd->cfq_back_penalty;
          else
                  wrap |= CFQ_RQ2_WRAP;
  
          /* Found required data */
  
          /*
           * By doing switch() on the bit mask "wrap" we avoid having to
           * check two variables for all permutations: --> faster!
           */
          switch (wrap) {
          case 0: /* common case for CFQ: rq1 and rq2 not wrapped */
                  if (d1 < d2)
                          return rq1;
                  else if (d2 < d1)
                          return rq2;
                  else {
                          if (s1 >= s2)
                                  return rq1;
                          else
                                  return rq2;
                  }
  
          case CFQ_RQ2_WRAP:
                  return rq1;
          case CFQ_RQ1_WRAP:
                  return rq2;
          case (CFQ_RQ1_WRAP|CFQ_RQ2_WRAP): /* both rqs wrapped */
          default:
                  /*
                   * Since both rqs are wrapped,
                   * start with the one that's further behind head
                   * (--> only *one* back seek required),
                   * since back seek takes more time than forward.
                   */
                  if (s1 <= s2)
                          return rq1;
                  else
                          return rq2;
          }
  }
  
  /*
   * The below is leftmost cache rbtree addon
   */
  static struct cfq_queue *cfq_rb_first(struct cfq_rb_root *root)
  {
          /* Service tree is empty */
          if (!root->count)
                  return NULL;
  
          if (!root->left)
                  root->left = rb_first(&root->rb);
  
          if (root->left)
                  return rb_entry(root->left, struct cfq_queue, rb_node);
  
          return NULL;
  }
  
  static struct cfq_group *cfq_rb_first_group(struct cfq_rb_root *root)
  {
          if (!root->left)
                  root->left = rb_first(&root->rb);
  
          if (root->left)
                  return rb_entry_cfqg(root->left);
  
          return NULL;
  }
  
  static void rb_erase_init(struct rb_node *n, struct rb_root *root)
  {
          rb_erase(n, root);
          RB_CLEAR_NODE(n);
  }
  
  static void cfq_rb_erase(struct rb_node *n, struct cfq_rb_root *root)
  {
          if (root->left == n)
                  root->left = NULL;
          rb_erase_init(n, &root->rb);
          --root->count;
  }
  
  /*
   * would be nice to take fifo expire time into account as well
   */
  static struct request *
  cfq_find_next_rq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                    struct request *last)
  {
          struct rb_node *rbnext = rb_next(&last->rb_node);
          struct rb_node *rbprev = rb_prev(&last->rb_node);
          struct request *next = NULL, *prev = NULL;
  
          BUG_ON(RB_EMPTY_NODE(&last->rb_node));
  
          if (rbprev)
                  prev = rb_entry_rq(rbprev);
  
          if (rbnext)
                  next = rb_entry_rq(rbnext);
          else {
                  rbnext = rb_first(&cfqq->sort_list);
                  if (rbnext && rbnext != &last->rb_node)
                          next = rb_entry_rq(rbnext);
          }
  
          return cfq_choose_req(cfqd, next, prev, blk_rq_pos(last));
  }
  
  static unsigned long cfq_slice_offset(struct cfq_data *cfqd,
                                        struct cfq_queue *cfqq)
  {
          /*
           * just an approximation, should be ok.
           */
          return (cfqq->cfqg->nr_cfqq - 1) * (cfq_prio_slice(cfqd, 1, 0) -
                         cfq_prio_slice(cfqd, cfq_cfqq_sync(cfqq), cfqq->ioprio));
  }
  
  static inline s64
  cfqg_key(struct cfq_rb_root *st, struct cfq_group *cfqg)
  {
          return cfqg->vdisktime - st->min_vdisktime;
  }
  
  static void
  __cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
  {
          struct rb_node **node = &st->rb.rb_node;
          struct rb_node *parent = NULL;
          struct cfq_group *__cfqg;
          s64 key = cfqg_key(st, cfqg);
          int left = 1;
  
          while (*node != NULL) {
                  parent = *node;
                  __cfqg = rb_entry_cfqg(parent);
  
                  if (key < cfqg_key(st, __cfqg))
                          node = &parent->rb_left;
                  else {
                          node = &parent->rb_right;
                          left = 0;
                  }
          }
  
          if (left)
                  st->left = &cfqg->rb_node;
  
          rb_link_node(&cfqg->rb_node, parent, node);
          rb_insert_color(&cfqg->rb_node, &st->rb);
  }
  
  static void
  cfq_update_group_weight(struct cfq_group *cfqg)
  {
          BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node));
          if (cfqg->new_weight) {
                  cfqg->weight = cfqg->new_weight;
                  cfqg->new_weight = 0;
          }
  }
  
  static void
  cfq_group_service_tree_add(struct cfq_rb_root *st, struct cfq_group *cfqg)
  {
          BUG_ON(!RB_EMPTY_NODE(&cfqg->rb_node));
  
          cfq_update_group_weight(cfqg);
          __cfq_group_service_tree_add(st, cfqg);
          st->total_weight += cfqg->weight;
  }
  
  static void
  cfq_group_notify_queue_add(struct cfq_data *cfqd, struct cfq_group *cfqg)
  {
          struct cfq_rb_root *st = &cfqd->grp_service_tree;
          struct cfq_group *__cfqg;
          struct rb_node *n;
  
          cfqg->nr_cfqq++;
          if (!RB_EMPTY_NODE(&cfqg->rb_node))
                  return;
  
          /*
           * Currently put the group at the end. Later implement something
           * so that groups get lesser vtime based on their weights, so that
           * if group does not loose all if it was not continuously backlogged.
           */
          n = rb_last(&st->rb);
          if (n) {
                  __cfqg = rb_entry_cfqg(n);
                  cfqg->vdisktime = __cfqg->vdisktime + CFQ_IDLE_DELAY;
          } else
                  cfqg->vdisktime = st->min_vdisktime;
          cfq_group_service_tree_add(st, cfqg);
  }
  
  static void
  cfq_group_service_tree_del(struct cfq_rb_root *st, struct cfq_group *cfqg)
  {
          st->total_weight -= cfqg->weight;
          if (!RB_EMPTY_NODE(&cfqg->rb_node))
                  cfq_rb_erase(&cfqg->rb_node, st);
  }
  
  static void
  cfq_group_notify_queue_del(struct cfq_data *cfqd, struct cfq_group *cfqg)
  {
          struct cfq_rb_root *st = &cfqd->grp_service_tree;
  
          BUG_ON(cfqg->nr_cfqq < 1);
          cfqg->nr_cfqq--;
  
          /* If there are other cfq queues under this group, don't delete it */
          if (cfqg->nr_cfqq)
                  return;
  
          cfq_log_cfqg(cfqd, cfqg, "del_from_rr group");
          cfq_group_service_tree_del(st, cfqg);
          cfqg->saved_workload_slice = 0;
          cfqg_stats_update_dequeue(cfqg);
  }
  
  static inline unsigned int cfq_cfqq_slice_usage(struct cfq_queue *cfqq,
                                                  unsigned int *unaccounted_time)
  {
          unsigned int slice_used;
  
          /*
           * Queue got expired before even a single request completed or
           * got expired immediately after first request completion.
           */
          if (!cfqq->slice_start || cfqq->slice_start == jiffies) {
                  /*
                   * Also charge the seek time incurred to the group, otherwise
                   * if there are mutiple queues in the group, each can dispatch
                   * a single request on seeky media and cause lots of seek time
                   * and group will never know it.
                   */
                  slice_used = max_t(unsigned, (jiffies - cfqq->dispatch_start),
                                          1);
          } else {
                  slice_used = jiffies - cfqq->slice_start;
                  if (slice_used > cfqq->allocated_slice) {
                          *unaccounted_time = slice_used - cfqq->allocated_slice;
                          slice_used = cfqq->allocated_slice;
                  }
                  if (time_after(cfqq->slice_start, cfqq->dispatch_start))
                          *unaccounted_time += cfqq->slice_start -
                                          cfqq->dispatch_start;
          }
  
          return slice_used;
  }
  
  static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,
                                  struct cfq_queue *cfqq)
  {
          struct cfq_rb_root *st = &cfqd->grp_service_tree;
          unsigned int used_sl, charge, unaccounted_sl = 0;
          int nr_sync = cfqg->nr_cfqq - cfqg_busy_async_queues(cfqd, cfqg)
                          - cfqg->service_tree_idle.count;
  
          BUG_ON(nr_sync < 0);
          used_sl = charge = cfq_cfqq_slice_usage(cfqq, &unaccounted_sl);
  
          if (iops_mode(cfqd))
                  charge = cfqq->slice_dispatch;
          else if (!cfq_cfqq_sync(cfqq) && !nr_sync)
                  charge = cfqq->allocated_slice;
  
          /* Can't update vdisktime while group is on service tree */
          cfq_group_service_tree_del(st, cfqg);
          cfqg->vdisktime += cfq_scale_slice(charge, cfqg);
          /* If a new weight was requested, update now, off tree */
          cfq_group_service_tree_add(st, cfqg);
  
          /* This group is being expired. Save the context */
          if (time_after(cfqd->workload_expires, jiffies)) {
                  cfqg->saved_workload_slice = cfqd->workload_expires
                                                  - jiffies;
                  cfqg->saved_workload = cfqd->serving_type;
                  cfqg->saved_serving_prio = cfqd->serving_prio;
          } else
                  cfqg->saved_workload_slice = 0;
  
          cfq_log_cfqg(cfqd, cfqg, "served: vt=%llu min_vt=%llu", cfqg->vdisktime,
                                          st->min_vdisktime);
          cfq_log_cfqq(cfqq->cfqd, cfqq,
                       "sl_used=%u disp=%u charge=%u iops=%u sect=%lu",
                       used_sl, cfqq->slice_dispatch, charge,
                       iops_mode(cfqd), cfqq->nr_sectors);
          cfqg_stats_update_timeslice_used(cfqg, used_sl, unaccounted_sl);
          cfqg_stats_set_start_empty_time(cfqg);
  }
  
  /**
   * cfq_init_cfqg_base - initialize base part of a cfq_group
   * @cfqg: cfq_group to initialize
   *
   * Initialize the base part which is used whether %CONFIG_CFQ_GROUP_IOSCHED
   * is enabled or not.
   */
  static void cfq_init_cfqg_base(struct cfq_group *cfqg)
  {
          struct cfq_rb_root *st;
          int i, j;
  
          for_each_cfqg_st(cfqg, i, j, st)
                  *st = CFQ_RB_ROOT;
          RB_CLEAR_NODE(&cfqg->rb_node);
  
          cfqg->ttime.last_end_request = jiffies;
  }
  
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
  static void cfq_pd_init(struct blkcg_gq *blkg)
  {
          struct cfq_group *cfqg = blkg_to_cfqg(blkg);
  
          cfq_init_cfqg_base(cfqg);
          cfqg->weight = blkg->blkcg->cfq_weight;
  }
  
  /*
   * Search for the cfq group current task belongs to. request_queue lock must
   * be held.
   */
  static struct cfq_group *cfq_lookup_create_cfqg(struct cfq_data *cfqd,
                                                  struct blkcg *blkcg)
  {
          struct request_queue *q = cfqd->queue;
          struct cfq_group *cfqg = NULL;
  
          /* avoid lookup for the common case where there's no blkcg */
          if (blkcg == &blkcg_root) {
                  cfqg = cfqd->root_group;
          } else {
                  struct blkcg_gq *blkg;
  
                  blkg = blkg_lookup_create(blkcg, q);
                  if (!IS_ERR(blkg))
                          cfqg = blkg_to_cfqg(blkg);
          }
  
          return cfqg;
  }
  
  static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg)
  {
          /* Currently, all async queues are mapped to root group */
          if (!cfq_cfqq_sync(cfqq))
                  cfqg = cfqq->cfqd->root_group;
  
          cfqq->cfqg = cfqg;
          /* cfqq reference on cfqg */
          cfqg_get(cfqg);
  }
  
  static u64 cfqg_prfill_weight_device(struct seq_file *sf,
                                       struct blkg_policy_data *pd, int off)
  {
          struct cfq_group *cfqg = pd_to_cfqg(pd);
  
          if (!cfqg->dev_weight)
                  return 0;
          return __blkg_prfill_u64(sf, pd, cfqg->dev_weight);
  }
  
  static int cfqg_print_weight_device(struct cgroup *cgrp, struct cftype *cft,
                                      struct seq_file *sf)
  {
          blkcg_print_blkgs(sf, cgroup_to_blkcg(cgrp),
                            cfqg_prfill_weight_device, &blkcg_policy_cfq, 0,
                            false);
          return 0;
  }
  
  static int cfq_print_weight(struct cgroup *cgrp, struct cftype *cft,
                              struct seq_file *sf)
  {
          seq_printf(sf, "%u\n", cgroup_to_blkcg(cgrp)->cfq_weight);
          return 0;
  }
  
  static int cfqg_set_weight_device(struct cgroup *cgrp, struct cftype *cft,
                                    const char *buf)
  {
          struct blkcg *blkcg = cgroup_to_blkcg(cgrp);
          struct blkg_conf_ctx ctx;
          struct cfq_group *cfqg;
          int ret;
  
          ret = blkg_conf_prep(blkcg, &blkcg_policy_cfq, buf, &ctx);
          if (ret)
                  return ret;
  
          ret = -EINVAL;
          cfqg = blkg_to_cfqg(ctx.blkg);
          if (!ctx.v || (ctx.v >= CFQ_WEIGHT_MIN && ctx.v <= CFQ_WEIGHT_MAX)) {
                  cfqg->dev_weight = ctx.v;
                  cfqg->new_weight = cfqg->dev_weight ?: blkcg->cfq_weight;
                  ret = 0;
          }
  
          blkg_conf_finish(&ctx);
          return ret;
  }
  
  static int cfq_set_weight(struct cgroup *cgrp, struct cftype *cft, u64 val)
  {
          struct blkcg *blkcg = cgroup_to_blkcg(cgrp);
          struct blkcg_gq *blkg;
          struct hlist_node *n;
  
          if (val < CFQ_WEIGHT_MIN || val > CFQ_WEIGHT_MAX)
                  return -EINVAL;
  
          spin_lock_irq(&blkcg->lock);
          blkcg->cfq_weight = (unsigned int)val;
  
          hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
                  struct cfq_group *cfqg = blkg_to_cfqg(blkg);
  
                  if (cfqg && !cfqg->dev_weight)
                          cfqg->new_weight = blkcg->cfq_weight;
          }
  
          spin_unlock_irq(&blkcg->lock);
          return 0;
  }
  
  static int cfqg_print_stat(struct cgroup *cgrp, struct cftype *cft,
                             struct seq_file *sf)
  {
          struct blkcg *blkcg = cgroup_to_blkcg(cgrp);
  
          blkcg_print_blkgs(sf, blkcg, blkg_prfill_stat, &blkcg_policy_cfq,
                            cft->private, false);
          return 0;
  }
  
  static int cfqg_print_rwstat(struct cgroup *cgrp, struct cftype *cft,
                               struct seq_file *sf)
  {
          struct blkcg *blkcg = cgroup_to_blkcg(cgrp);
  
          blkcg_print_blkgs(sf, blkcg, blkg_prfill_rwstat, &blkcg_policy_cfq,
                            cft->private, true);
          return 0;
  }
  
  #ifdef CONFIG_DEBUG_BLK_CGROUP
  static u64 cfqg_prfill_avg_queue_size(struct seq_file *sf,
                                        struct blkg_policy_data *pd, int off)
  {
          struct cfq_group *cfqg = pd_to_cfqg(pd);
          u64 samples = blkg_stat_read(&cfqg->stats.avg_queue_size_samples);
          u64 v = 0;
  
          if (samples) {
                  v = blkg_stat_read(&cfqg->stats.avg_queue_size_sum);
                  do_div(v, samples);
          }
          __blkg_prfill_u64(sf, pd, v);
          return 0;
  }
  
  /* print avg_queue_size */
  static int cfqg_print_avg_queue_size(struct cgroup *cgrp, struct cftype *cft,
                                       struct seq_file *sf)
  {
          struct blkcg *blkcg = cgroup_to_blkcg(cgrp);
  
          blkcg_print_blkgs(sf, blkcg, cfqg_prfill_avg_queue_size,
                            &blkcg_policy_cfq, 0, false);
          return 0;
  }
  #endif  /* CONFIG_DEBUG_BLK_CGROUP */
  
  static struct cftype cfq_blkcg_files[] = {
          {
                  .name = "weight_device",
                  .read_seq_string = cfqg_print_weight_device,
                  .write_string = cfqg_set_weight_device,
                  .max_write_len = 256,
          },
          {
                  .name = "weight",
                  .read_seq_string = cfq_print_weight,
                  .write_u64 = cfq_set_weight,
          },
          {
                  .name = "time",
                  .private = offsetof(struct cfq_group, stats.time),
                  .read_seq_string = cfqg_print_stat,
          },
          {
                  .name = "sectors",
                  .private = offsetof(struct cfq_group, stats.sectors),
                  .read_seq_string = cfqg_print_stat,
          },
          {
                  .name = "io_service_bytes",
                  .private = offsetof(struct cfq_group, stats.service_bytes),
                  .read_seq_string = cfqg_print_rwstat,
          },
          {
                  .name = "io_serviced",
                  .private = offsetof(struct cfq_group, stats.serviced),
                  .read_seq_string = cfqg_print_rwstat,
          },
          {
                  .name = "io_service_time",
                  .private = offsetof(struct cfq_group, stats.service_time),
                  .read_seq_string = cfqg_print_rwstat,
          },
          {
                  .name = "io_wait_time",
                  .private = offsetof(struct cfq_group, stats.wait_time),
                  .read_seq_string = cfqg_print_rwstat,
          },
          {
                  .name = "io_merged",
                  .private = offsetof(struct cfq_group, stats.merged),
                  .read_seq_string = cfqg_print_rwstat,
          },
          {
                  .name = "io_queued",
                  .private = offsetof(struct cfq_group, stats.queued),
                  .read_seq_string = cfqg_print_rwstat,
          },
  #ifdef CONFIG_DEBUG_BLK_CGROUP
          {
                  .name = "avg_queue_size",
                  .read_seq_string = cfqg_print_avg_queue_size,
          },
          {
                  .name = "group_wait_time",
                  .private = offsetof(struct cfq_group, stats.group_wait_time),
                  .read_seq_string = cfqg_print_stat,
          },
          {
                  .name = "idle_time",
                  .private = offsetof(struct cfq_group, stats.idle_time),
                  .read_seq_string = cfqg_print_stat,
          },
          {
                  .name = "empty_time",
                  .private = offsetof(struct cfq_group, stats.empty_time),
                  .read_seq_string = cfqg_print_stat,
          },
          {
                  .name = "dequeue",
                  .private = offsetof(struct cfq_group, stats.dequeue),
                  .read_seq_string = cfqg_print_stat,
          },
          {
                  .name = "unaccounted_time",
                  .private = offsetof(struct cfq_group, stats.unaccounted_time),
                  .read_seq_string = cfqg_print_stat,
          },
  #endif  /* CONFIG_DEBUG_BLK_CGROUP */
          { }     /* terminate */
  };
  #else /* GROUP_IOSCHED */
  static struct cfq_group *cfq_lookup_create_cfqg(struct cfq_data *cfqd,
                                                  struct blkcg *blkcg)
  {
          return cfqd->root_group;
  }
  
  static inline void
  cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) {
          cfqq->cfqg = cfqg;
  }
  
  #endif /* GROUP_IOSCHED */
  
  /*
   * The cfqd->service_trees holds all pending cfq_queue's that have
   * requests waiting to be processed. It is sorted in the order that
   * we will service the queues.
   */
  static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                                   bool add_front)
  {
          struct rb_node **p, *parent;
          struct cfq_queue *__cfqq;
          unsigned long rb_key;
          struct cfq_rb_root *service_tree;
          int left;
          int new_cfqq = 1;
  
          service_tree = service_tree_for(cfqq->cfqg, cfqq_prio(cfqq),
                                                  cfqq_type(cfqq));
          if (cfq_class_idle(cfqq)) {
                  rb_key = CFQ_IDLE_DELAY;
                  parent = rb_last(&service_tree->rb);
                  if (parent && parent != &cfqq->rb_node) {
                          __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
                          rb_key += __cfqq->rb_key;
                  } else
                          rb_key += jiffies;
          } else if (!add_front) {
                  /*
                   * Get our rb key offset. Subtract any residual slice
                   * value carried from last service. A negative resid
                   * count indicates slice overrun, and this should position
                   * the next service time further away in the tree.
                   */
                  rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;
                  rb_key -= cfqq->slice_resid;
                  cfqq->slice_resid = 0;
          } else {
                  rb_key = -HZ;
                  __cfqq = cfq_rb_first(service_tree);
                  rb_key += __cfqq ? __cfqq->rb_key : jiffies;
          }
  
          if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
                  new_cfqq = 0;
                  /*
                   * same position, nothing more to do
                   */
                  if (rb_key == cfqq->rb_key &&
                      cfqq->service_tree == service_tree)
                          return;
  
                  cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
                  cfqq->service_tree = NULL;
          }
  
          left = 1;
          parent = NULL;
          cfqq->service_tree = service_tree;
          p = &service_tree->rb.rb_node;
          while (*p) {
                  struct rb_node **n;
  
                  parent = *p;
                  __cfqq = rb_entry(parent, struct cfq_queue, rb_node);
  
                  /*
                   * sort by key, that represents service time.
                   */
                  if (time_before(rb_key, __cfqq->rb_key))
                          n = &(*p)->rb_left;
                  else {
                          n = &(*p)->rb_right;
                          left = 0;
                  }
  
                  p = n;
          }
  
          if (left)
                  service_tree->left = &cfqq->rb_node;
  
          cfqq->rb_key = rb_key;
          rb_link_node(&cfqq->rb_node, parent, p);
          rb_insert_color(&cfqq->rb_node, &service_tree->rb);
          service_tree->count++;
          if (add_front || !new_cfqq)
                  return;
          cfq_group_notify_queue_add(cfqd, cfqq->cfqg);
  }
  
  static struct cfq_queue *
  cfq_prio_tree_lookup(struct cfq_data *cfqd, struct rb_root *root,
                       sector_t sector, struct rb_node **ret_parent,
                       struct rb_node ***rb_link)
  {
          struct rb_node **p, *parent;
          struct cfq_queue *cfqq = NULL;
  
          parent = NULL;
          p = &root->rb_node;
          while (*p) {
                  struct rb_node **n;
  
                  parent = *p;
                  cfqq = rb_entry(parent, struct cfq_queue, p_node);
  
                  /*
                   * Sort strictly based on sector.  Smallest to the left,
                   * largest to the right.
                   */
                  if (sector > blk_rq_pos(cfqq->next_rq))
                          n = &(*p)->rb_right;
                  else if (sector < blk_rq_pos(cfqq->next_rq))
                          n = &(*p)->rb_left;
                  else
                          break;
                  p = n;
                  cfqq = NULL;
          }
  
          *ret_parent = parent;
          if (rb_link)
                  *rb_link = p;
          return cfqq;
  }
  
  static void cfq_prio_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          struct rb_node **p, *parent;
          struct cfq_queue *__cfqq;
  
          if (cfqq->p_root) {
                  rb_erase(&cfqq->p_node, cfqq->p_root);
                  cfqq->p_root = NULL;
          }
  
          if (cfq_class_idle(cfqq))
                  return;
          if (!cfqq->next_rq)
                  return;
  
          cfqq->p_root = &cfqd->prio_trees[cfqq->org_ioprio];
          __cfqq = cfq_prio_tree_lookup(cfqd, cfqq->p_root,
                                        blk_rq_pos(cfqq->next_rq), &parent, &p);
          if (!__cfqq) {
                  rb_link_node(&cfqq->p_node, parent, p);
                  rb_insert_color(&cfqq->p_node, cfqq->p_root);
          } else
                  cfqq->p_root = NULL;
  }
  
  /*
   * Update cfqq's position in the service tree.
   */
  static void cfq_resort_rr_list(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          /*
           * Resorting requires the cfqq to be on the RR list already.
           */
          if (cfq_cfqq_on_rr(cfqq)) {
                  cfq_service_tree_add(cfqd, cfqq, 0);
                  cfq_prio_tree_add(cfqd, cfqq);
          }
  }
  
  /*
   * add to busy list of queues for service, trying to be fair in ordering
   * the pending list according to last request service
   */
  static void cfq_add_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          cfq_log_cfqq(cfqd, cfqq, "add_to_rr");
          BUG_ON(cfq_cfqq_on_rr(cfqq));
          cfq_mark_cfqq_on_rr(cfqq);
          cfqd->busy_queues++;
          if (cfq_cfqq_sync(cfqq))
                  cfqd->busy_sync_queues++;
  
          cfq_resort_rr_list(cfqd, cfqq);
  }
  
  /*
   * Called when the cfqq no longer has requests pending, remove it from
   * the service tree.
   */
  static void cfq_del_cfqq_rr(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          cfq_log_cfqq(cfqd, cfqq, "del_from_rr");
          BUG_ON(!cfq_cfqq_on_rr(cfqq));
          cfq_clear_cfqq_on_rr(cfqq);
  
          if (!RB_EMPTY_NODE(&cfqq->rb_node)) {
                  cfq_rb_erase(&cfqq->rb_node, cfqq->service_tree);
                  cfqq->service_tree = NULL;
          }
          if (cfqq->p_root) {
                  rb_erase(&cfqq->p_node, cfqq->p_root);
                  cfqq->p_root = NULL;
          }
  
          cfq_group_notify_queue_del(cfqd, cfqq->cfqg);
          BUG_ON(!cfqd->busy_queues);
          cfqd->busy_queues--;
          if (cfq_cfqq_sync(cfqq))
                  cfqd->busy_sync_queues--;
  }
  
  /*
   * rb tree support functions
   */
  static void cfq_del_rq_rb(struct request *rq)
  {
          struct cfq_queue *cfqq = RQ_CFQQ(rq);
          const int sync = rq_is_sync(rq);
  
          BUG_ON(!cfqq->queued[sync]);
          cfqq->queued[sync]--;
  
          elv_rb_del(&cfqq->sort_list, rq);
  
          if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list)) {
                  /*
                   * Queue will be deleted from service tree when we actually
                   * expire it later. Right now just remove it from prio tree
                   * as it is empty.
                   */
                  if (cfqq->p_root) {
                          rb_erase(&cfqq->p_node, cfqq->p_root);
                          cfqq->p_root = NULL;
                  }
          }
  }
  
  static void cfq_add_rq_rb(struct request *rq)
  {
          struct cfq_queue *cfqq = RQ_CFQQ(rq);
          struct cfq_data *cfqd = cfqq->cfqd;
          struct request *prev;
  
          cfqq->queued[rq_is_sync(rq)]++;
  
          elv_rb_add(&cfqq->sort_list, rq);
  
          if (!cfq_cfqq_on_rr(cfqq))
                  cfq_add_cfqq_rr(cfqd, cfqq);
  
          /*
           * check if this request is a better next-serve candidate
           */
          prev = cfqq->next_rq;
          cfqq->next_rq = cfq_choose_req(cfqd, cfqq->next_rq, rq, cfqd->last_position);
  
          /*
           * adjust priority tree position, if ->next_rq changes
           */
          if (prev != cfqq->next_rq)
                  cfq_prio_tree_add(cfqd, cfqq);
  
          BUG_ON(!cfqq->next_rq);
  }
  
  static void cfq_reposition_rq_rb(struct cfq_queue *cfqq, struct request *rq)
  {
          elv_rb_del(&cfqq->sort_list, rq);
          cfqq->queued[rq_is_sync(rq)]--;
          cfqg_stats_update_io_remove(RQ_CFQG(rq), rq->cmd_flags);
          cfq_add_rq_rb(rq);
          cfqg_stats_update_io_add(RQ_CFQG(rq), cfqq->cfqd->serving_group,
                                   rq->cmd_flags);
  }
  
  static struct request *
  cfq_find_rq_fmerge(struct cfq_data *cfqd, struct bio *bio)
  {
          struct task_struct *tsk = current;
          struct cfq_io_cq *cic;
          struct cfq_queue *cfqq;
  
          cic = cfq_cic_lookup(cfqd, tsk->io_context);
          if (!cic)
                  return NULL;
  
          cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
          if (cfqq) {
                  sector_t sector = bio->bi_sector + bio_sectors(bio);
  
                  return elv_rb_find(&cfqq->sort_list, sector);
          }
  
          return NULL;
  }
  
  static void cfq_activate_request(struct request_queue *q, struct request *rq)
  {
          struct cfq_data *cfqd = q->elevator->elevator_data;
  
          cfqd->rq_in_driver++;
          cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "activate rq, drv=%d",
                                                  cfqd->rq_in_driver);
  
          cfqd->last_position = blk_rq_pos(rq) + blk_rq_sectors(rq);
  }
  
  static void cfq_deactivate_request(struct request_queue *q, struct request *rq)
  {
          struct cfq_data *cfqd = q->elevator->elevator_data;
  
          WARN_ON(!cfqd->rq_in_driver);
          cfqd->rq_in_driver--;
          cfq_log_cfqq(cfqd, RQ_CFQQ(rq), "deactivate rq, drv=%d",
                                                  cfqd->rq_in_driver);
  }
  
  static void cfq_remove_request(struct request *rq)
  {
          struct cfq_queue *cfqq = RQ_CFQQ(rq);
  
          if (cfqq->next_rq == rq)
                  cfqq->next_rq = cfq_find_next_rq(cfqq->cfqd, cfqq, rq);
  
          list_del_init(&rq->queuelist);
          cfq_del_rq_rb(rq);
  
          cfqq->cfqd->rq_queued--;
          cfqg_stats_update_io_remove(RQ_CFQG(rq), rq->cmd_flags);
          if (rq->cmd_flags & REQ_PRIO) {
                  WARN_ON(!cfqq->prio_pending);
                  cfqq->prio_pending--;
          }
  }
  
  static int cfq_merge(struct request_queue *q, struct request **req,
                       struct bio *bio)
  {
          struct cfq_data *cfqd = q->elevator->elevator_data;
          struct request *__rq;
  
          __rq = cfq_find_rq_fmerge(cfqd, bio);
          if (__rq && elv_rq_merge_ok(__rq, bio)) {
                  *req = __rq;
                  return ELEVATOR_FRONT_MERGE;
          }
  
          return ELEVATOR_NO_MERGE;
  }
  
  static void cfq_merged_request(struct request_queue *q, struct request *req,
                                 int type)
  {
          if (type == ELEVATOR_FRONT_MERGE) {
                  struct cfq_queue *cfqq = RQ_CFQQ(req);
  
                  cfq_reposition_rq_rb(cfqq, req);
          }
  }
  
  static void cfq_bio_merged(struct request_queue *q, struct request *req,
                                  struct bio *bio)
  {
          cfqg_stats_update_io_merged(RQ_CFQG(req), bio->bi_rw);
  }
  
  static void
  cfq_merged_requests(struct request_queue *q, struct request *rq,
                      struct request *next)
  {
          struct cfq_queue *cfqq = RQ_CFQQ(rq);
          struct cfq_data *cfqd = q->elevator->elevator_data;
  
          /*
           * reposition in fifo if next is older than rq
           */
          if (!list_empty(&rq->queuelist) && !list_empty(&next->queuelist) &&
              time_before(rq_fifo_time(next), rq_fifo_time(rq)) &&
              cfqq == RQ_CFQQ(next)) {
                  list_move(&rq->queuelist, &next->queuelist);
                  rq_set_fifo_time(rq, rq_fifo_time(next));
          }
  
          if (cfqq->next_rq == next)
                  cfqq->next_rq = rq;
          cfq_remove_request(next);
          cfqg_stats_update_io_merged(RQ_CFQG(rq), next->cmd_flags);
  
          cfqq = RQ_CFQQ(next);
          /*
           * all requests of this queue are merged to other queues, delete it
           * from the service tree. If it's the active_queue,
           * cfq_dispatch_requests() will choose to expire it or do idle
           */
          if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list) &&
              cfqq != cfqd->active_queue)
                  cfq_del_cfqq_rr(cfqd, cfqq);
  }
  
  static int cfq_allow_merge(struct request_queue *q, struct request *rq,
                             struct bio *bio)
  {
          struct cfq_data *cfqd = q->elevator->elevator_data;
          struct cfq_io_cq *cic;
          struct cfq_queue *cfqq;
  
          /*
           * Disallow merge of a sync bio into an async request.
           */
          if (cfq_bio_sync(bio) && !rq_is_sync(rq))
                  return false;
  
          /*
           * Lookup the cfqq that this bio will be queued with and allow
           * merge only if rq is queued there.
           */
          cic = cfq_cic_lookup(cfqd, current->io_context);
          if (!cic)
                  return false;
  
          cfqq = cic_to_cfqq(cic, cfq_bio_sync(bio));
          return cfqq == RQ_CFQQ(rq);
  }
  
  static inline void cfq_del_timer(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          del_timer(&cfqd->idle_slice_timer);
          cfqg_stats_update_idle_time(cfqq->cfqg);
  }
  
  static void __cfq_set_active_queue(struct cfq_data *cfqd,
                                     struct cfq_queue *cfqq)
  {
          if (cfqq) {
                  cfq_log_cfqq(cfqd, cfqq, "set_active wl_prio:%d wl_type:%d",
                                  cfqd->serving_prio, cfqd->serving_type);
                  cfqg_stats_update_avg_queue_size(cfqq->cfqg);
                  cfqq->slice_start = 0;
                  cfqq->dispatch_start = jiffies;
                  cfqq->allocated_slice = 0;
                  cfqq->slice_end = 0;
                  cfqq->slice_dispatch = 0;
                  cfqq->nr_sectors = 0;
  
                  cfq_clear_cfqq_wait_request(cfqq);
                  cfq_clear_cfqq_must_dispatch(cfqq);
                  cfq_clear_cfqq_must_alloc_slice(cfqq);
                  cfq_clear_cfqq_fifo_expire(cfqq);
                  cfq_mark_cfqq_slice_new(cfqq);
  
                  cfq_del_timer(cfqd, cfqq);
          }
  
          cfqd->active_queue = cfqq;
  }
  
  /*
   * current cfqq expired its slice (or was too idle), select new one
   */
  static void
  __cfq_slice_expired(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                      bool timed_out)
  {
          cfq_log_cfqq(cfqd, cfqq, "slice expired t=%d", timed_out);
  
          if (cfq_cfqq_wait_request(cfqq))
                  cfq_del_timer(cfqd, cfqq);
  
          cfq_clear_cfqq_wait_request(cfqq);
          cfq_clear_cfqq_wait_busy(cfqq);
  
          /*
           * If this cfqq is shared between multiple processes, check to
           * make sure that those processes are still issuing I/Os within
           * the mean seek distance.  If not, it may be time to break the
           * queues apart again.
           */
          if (cfq_cfqq_coop(cfqq) && CFQQ_SEEKY(cfqq))
                  cfq_mark_cfqq_split_coop(cfqq);
  
          /*
           * store what was left of this slice, if the queue idled/timed out
           */
          if (timed_out) {
                  if (cfq_cfqq_slice_new(cfqq))
                          cfqq->slice_resid = cfq_scaled_cfqq_slice(cfqd, cfqq);
                  else
                          cfqq->slice_resid = cfqq->slice_end - jiffies;
                  cfq_log_cfqq(cfqd, cfqq, "resid=%ld", cfqq->slice_resid);
          }
  
          cfq_group_served(cfqd, cfqq->cfqg, cfqq);
  
          if (cfq_cfqq_on_rr(cfqq) && RB_EMPTY_ROOT(&cfqq->sort_list))
                  cfq_del_cfqq_rr(cfqd, cfqq);
  
          cfq_resort_rr_list(cfqd, cfqq);
  
          if (cfqq == cfqd->active_queue)
                  cfqd->active_queue = NULL;
  
          if (cfqd->active_cic) {
                  put_io_context(cfqd->active_cic->icq.ioc);
                  cfqd->active_cic = NULL;
          }
  }
  
  static inline void cfq_slice_expired(struct cfq_data *cfqd, bool timed_out)
  {
          struct cfq_queue *cfqq = cfqd->active_queue;
  
          if (cfqq)
                  __cfq_slice_expired(cfqd, cfqq, timed_out);
  }
  
  /*
   * Get next queue for service. Unless we have a queue preemption,
   * we'll simply select the first cfqq in the service tree.
   */
  static struct cfq_queue *cfq_get_next_queue(struct cfq_data *cfqd)
  {
          struct cfq_rb_root *service_tree =
                  service_tree_for(cfqd->serving_group, cfqd->serving_prio,
                                          cfqd->serving_type);
  
          if (!cfqd->rq_queued)
                  return NULL;
  
          /* There is nothing to dispatch */
          if (!service_tree)
                  return NULL;
          if (RB_EMPTY_ROOT(&service_tree->rb))
                  return NULL;
          return cfq_rb_first(service_tree);
  }
  
  static struct cfq_queue *cfq_get_next_queue_forced(struct cfq_data *cfqd)
  {
          struct cfq_group *cfqg;
          struct cfq_queue *cfqq;
          int i, j;
          struct cfq_rb_root *st;
  
          if (!cfqd->rq_queued)
                  return NULL;
  
          cfqg = cfq_get_next_cfqg(cfqd);
          if (!cfqg)
                  return NULL;
  
          for_each_cfqg_st(cfqg, i, j, st)
                  if ((cfqq = cfq_rb_first(st)) != NULL)
                          return cfqq;
          return NULL;
  }
  
  /*
   * Get and set a new active queue for service.
   */
  static struct cfq_queue *cfq_set_active_queue(struct cfq_data *cfqd,
                                                struct cfq_queue *cfqq)
  {
          if (!cfqq)
                  cfqq = cfq_get_next_queue(cfqd);
  
          __cfq_set_active_queue(cfqd, cfqq);
          return cfqq;
  }
  
  static inline sector_t cfq_dist_from_last(struct cfq_data *cfqd,
                                            struct request *rq)
  {
          if (blk_rq_pos(rq) >= cfqd->last_position)
                  return blk_rq_pos(rq) - cfqd->last_position;
          else
                  return cfqd->last_position - blk_rq_pos(rq);
  }
  
  static inline int cfq_rq_close(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                                 struct request *rq)
  {
          return cfq_dist_from_last(cfqd, rq) <= CFQQ_CLOSE_THR;
  }
  
  static struct cfq_queue *cfqq_close(struct cfq_data *cfqd,
                                      struct cfq_queue *cur_cfqq)
  {
          struct rb_root *root = &cfqd->prio_trees[cur_cfqq->org_ioprio];
          struct rb_node *parent, *node;
          struct cfq_queue *__cfqq;
          sector_t sector = cfqd->last_position;
  
          if (RB_EMPTY_ROOT(root))
                  return NULL;
  
          /*
           * First, if we find a request starting at the end of the last
           * request, choose it.
           */
          __cfqq = cfq_prio_tree_lookup(cfqd, root, sector, &parent, NULL);
          if (__cfqq)
                  return __cfqq;
  
          /*
           * If the exact sector wasn't found, the parent of the NULL leaf
           * will contain the closest sector.
           */
          __cfqq = rb_entry(parent, struct cfq_queue, p_node);
          if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
                  return __cfqq;
  
          if (blk_rq_pos(__cfqq->next_rq) < sector)
                  node = rb_next(&__cfqq->p_node);
          else
                  node = rb_prev(&__cfqq->p_node);
          if (!node)
                  return NULL;
  
          __cfqq = rb_entry(node, struct cfq_queue, p_node);
          if (cfq_rq_close(cfqd, cur_cfqq, __cfqq->next_rq))
                  return __cfqq;
  
          return NULL;
  }
  
  /*
   * cfqd - obvious
   * cur_cfqq - passed in so that we don't decide that the current queue is
   *            closely cooperating with itself.
   *
   * So, basically we're assuming that that cur_cfqq has dispatched at least
   * one request, and that cfqd->last_position reflects a position on the disk
   * associated with the I/O issued by cur_cfqq.  I'm not sure this is a valid
   * assumption.
   */
  static struct cfq_queue *cfq_close_cooperator(struct cfq_data *cfqd,
                                                struct cfq_queue *cur_cfqq)
  {
          struct cfq_queue *cfqq;
  
          if (cfq_class_idle(cur_cfqq))
                  return NULL;
          if (!cfq_cfqq_sync(cur_cfqq))
                  return NULL;
          if (CFQQ_SEEKY(cur_cfqq))
                  return NULL;
  
          /*
           * Don't search priority tree if it's the only queue in the group.
           */
          if (cur_cfqq->cfqg->nr_cfqq == 1)
                  return NULL;
  
          /*
           * We should notice if some of the queues are cooperating, eg
           * working closely on the same area of the disk. In that case,
           * we can group them together and don't waste time idling.
           */
          cfqq = cfqq_close(cfqd, cur_cfqq);
          if (!cfqq)
                  return NULL;
  
          /* If new queue belongs to different cfq_group, don't choose it */
          if (cur_cfqq->cfqg != cfqq->cfqg)
                  return NULL;
  
          /*
           * It only makes sense to merge sync queues.
           */
          if (!cfq_cfqq_sync(cfqq))
                  return NULL;
          if (CFQQ_SEEKY(cfqq))
                  return NULL;
  
          /*
           * Do not merge queues of different priority classes
           */
          if (cfq_class_rt(cfqq) != cfq_class_rt(cur_cfqq))
                  return NULL;
  
          return cfqq;
  }
  
  /*
   * Determine whether we should enforce idle window for this queue.
   */
  
  static bool cfq_should_idle(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          enum wl_prio_t prio = cfqq_prio(cfqq);
          struct cfq_rb_root *service_tree = cfqq->service_tree;
  
          BUG_ON(!service_tree);
          BUG_ON(!service_tree->count);
  
          if (!cfqd->cfq_slice_idle)
                  return false;
  
          /* We never do for idle class queues. */
          if (prio == IDLE_WORKLOAD)
                  return false;
  
          /* We do for queues that were marked with idle window flag. */
          if (cfq_cfqq_idle_window(cfqq) &&
             !(blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag))
                  return true;
  
          /*
           * Otherwise, we do only if they are the last ones
           * in their service tree.
           */
          if (service_tree->count == 1 && cfq_cfqq_sync(cfqq) &&
             !cfq_io_thinktime_big(cfqd, &service_tree->ttime, false))
                  return true;
          cfq_log_cfqq(cfqd, cfqq, "Not idling. st->count:%d",
                          service_tree->count);
          return false;
  }
  
  static void cfq_arm_slice_timer(struct cfq_data *cfqd)
  {
          struct cfq_queue *cfqq = cfqd->active_queue;
          struct cfq_io_cq *cic;
          unsigned long sl, group_idle = 0;
  
          /*
           * SSD device without seek penalty, disable idling. But only do so
           * for devices that support queuing, otherwise we still have a problem
           * with sync vs async workloads.
           */
          if (blk_queue_nonrot(cfqd->queue) && cfqd->hw_tag)
                  return;
  
          WARN_ON(!RB_EMPTY_ROOT(&cfqq->sort_list));
          WARN_ON(cfq_cfqq_slice_new(cfqq));
  
          /*
           * idle is disabled, either manually or by past process history
           */
          if (!cfq_should_idle(cfqd, cfqq)) {
                  /* no queue idling. Check for group idling */
                  if (cfqd->cfq_group_idle)
                          group_idle = cfqd->cfq_group_idle;
                  else
                          return;
          }
  
          /*
           * still active requests from this queue, don't idle
           */
          if (cfqq->dispatched)
                  return;
  
          /*
           * task has exited, don't wait
           */
          cic = cfqd->active_cic;
          if (!cic || !atomic_read(&cic->icq.ioc->active_ref))
                  return;
  
          /*
           * If our average think time is larger than the remaining time
           * slice, then don't idle. This avoids overrunning the allotted
           * time slice.
           */
          if (sample_valid(cic->ttime.ttime_samples) &&
              (cfqq->slice_end - jiffies < cic->ttime.ttime_mean)) {
                  cfq_log_cfqq(cfqd, cfqq, "Not idling. think_time:%lu",
                               cic->ttime.ttime_mean);
                  return;
          }
  
          /* There are other queues in the group, don't do group idle */
          if (group_idle && cfqq->cfqg->nr_cfqq > 1)
                  return;
  
          cfq_mark_cfqq_wait_request(cfqq);
  
          if (group_idle)
                  sl = cfqd->cfq_group_idle;
          else
                  sl = cfqd->cfq_slice_idle;
  
          mod_timer(&cfqd->idle_slice_timer, jiffies + sl);
          cfqg_stats_set_start_idle_time(cfqq->cfqg);
          cfq_log_cfqq(cfqd, cfqq, "arm_idle: %lu group_idle: %d", sl,
                          group_idle ? 1 : 0);
  }
  
  /*
   * Move request from internal lists to the request queue dispatch list.
   */
  static void cfq_dispatch_insert(struct request_queue *q, struct request *rq)
  {
          struct cfq_data *cfqd = q->elevator->elevator_data;
          struct cfq_queue *cfqq = RQ_CFQQ(rq);
  
          cfq_log_cfqq(cfqd, cfqq, "dispatch_insert");
  
          cfqq->next_rq = cfq_find_next_rq(cfqd, cfqq, rq);
          cfq_remove_request(rq);
          cfqq->dispatched++;
          (RQ_CFQG(rq))->dispatched++;
          elv_dispatch_sort(q, rq);
  
          cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]++;
          cfqq->nr_sectors += blk_rq_sectors(rq);
          cfqg_stats_update_dispatch(cfqq->cfqg, blk_rq_bytes(rq), rq->cmd_flags);
  }
  
  /*
   * return expired entry, or NULL to just start from scratch in rbtree
   */
  static struct request *cfq_check_fifo(struct cfq_queue *cfqq)
  {
          struct request *rq = NULL;
  
          if (cfq_cfqq_fifo_expire(cfqq))
                  return NULL;
  
          cfq_mark_cfqq_fifo_expire(cfqq);
  
          if (list_empty(&cfqq->fifo))
                  return NULL;
  
          rq = rq_entry_fifo(cfqq->fifo.next);
          if (time_before(jiffies, rq_fifo_time(rq)))
                  rq = NULL;
  
          cfq_log_cfqq(cfqq->cfqd, cfqq, "fifo=%p", rq);
          return rq;
  }
  
  static inline int
  cfq_prio_to_maxrq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          const int base_rq = cfqd->cfq_slice_async_rq;
  
          WARN_ON(cfqq->ioprio >= IOPRIO_BE_NR);
  
          return 2 * base_rq * (IOPRIO_BE_NR - cfqq->ioprio);
  }
  
  /*
   * Must be called with the queue_lock held.
   */
  static int cfqq_process_refs(struct cfq_queue *cfqq)
  {
          int process_refs, io_refs;
  
          io_refs = cfqq->allocated[READ] + cfqq->allocated[WRITE];
          process_refs = cfqq->ref - io_refs;
          BUG_ON(process_refs < 0);
          return process_refs;
  }
  
  static void cfq_setup_merge(struct cfq_queue *cfqq, struct cfq_queue *new_cfqq)
  {
          int process_refs, new_process_refs;
          struct cfq_queue *__cfqq;
  
          /*
           * If there are no process references on the new_cfqq, then it is
           * unsafe to follow the ->new_cfqq chain as other cfqq's in the
           * chain may have dropped their last reference (not just their
           * last process reference).
           */
          if (!cfqq_process_refs(new_cfqq))
                  return;
  
          /* Avoid a circular list and skip interim queue merges */
          while ((__cfqq = new_cfqq->new_cfqq)) {
                  if (__cfqq == cfqq)
                          return;
                  new_cfqq = __cfqq;
          }
  
          process_refs = cfqq_process_refs(cfqq);
          new_process_refs = cfqq_process_refs(new_cfqq);
          /*
           * If the process for the cfqq has gone away, there is no
           * sense in merging the queues.
           */
          if (process_refs == 0 || new_process_refs == 0)
                  return;
  
          /*
           * Merge in the direction of the lesser amount of work.
           */
          if (new_process_refs >= process_refs) {
                  cfqq->new_cfqq = new_cfqq;
                  new_cfqq->ref += process_refs;
          } else {
                  new_cfqq->new_cfqq = cfqq;
                  cfqq->ref += new_process_refs;
          }
  }
  
  static enum wl_type_t cfq_choose_wl(struct cfq_data *cfqd,
                                  struct cfq_group *cfqg, enum wl_prio_t prio)
  {
          struct cfq_queue *queue;
          int i;
          bool key_valid = false;
          unsigned long lowest_key = 0;
          enum wl_type_t cur_best = SYNC_NOIDLE_WORKLOAD;
  
          for (i = 0; i <= SYNC_WORKLOAD; ++i) {
                  /* select the one with lowest rb_key */
                  queue = cfq_rb_first(service_tree_for(cfqg, prio, i));
                  if (queue &&
                      (!key_valid || time_before(queue->rb_key, lowest_key))) {
                          lowest_key = queue->rb_key;
                          cur_best = i;
                          key_valid = true;
                  }
          }
  
          return cur_best;
  }
  
  static void choose_service_tree(struct cfq_data *cfqd, struct cfq_group *cfqg)
  {
          unsigned slice;
          unsigned count;
          struct cfq_rb_root *st;
          unsigned group_slice;
          enum wl_prio_t original_prio = cfqd->serving_prio;
  
          /* Choose next priority. RT > BE > IDLE */
          if (cfq_group_busy_queues_wl(RT_WORKLOAD, cfqd, cfqg))
                  cfqd->serving_prio = RT_WORKLOAD;
          else if (cfq_group_busy_queues_wl(BE_WORKLOAD, cfqd, cfqg))
                  cfqd->serving_prio = BE_WORKLOAD;
          else {
                  cfqd->serving_prio = IDLE_WORKLOAD;
                  cfqd->workload_expires = jiffies + 1;
                  return;
          }
  
          if (original_prio != cfqd->serving_prio)
                  goto new_workload;
  
          /*
           * For RT and BE, we have to choose also the type
           * (SYNC, SYNC_NOIDLE, ASYNC), and to compute a workload
           * expiration time
           */
          st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
          count = st->count;
  
          /*
           * check workload expiration, and that we still have other queues ready
           */
          if (count && !time_after(jiffies, cfqd->workload_expires))
                  return;
  
  new_workload:
          /* otherwise select new workload type */
          cfqd->serving_type =
                  cfq_choose_wl(cfqd, cfqg, cfqd->serving_prio);
          st = service_tree_for(cfqg, cfqd->serving_prio, cfqd->serving_type);
          count = st->count;
  
          /*
           * the workload slice is computed as a fraction of target latency
           * proportional to the number of queues in that workload, over
           * all the queues in the same priority class
           */
          group_slice = cfq_group_slice(cfqd, cfqg);
  
          slice = group_slice * count /
                  max_t(unsigned, cfqg->busy_queues_avg[cfqd->serving_prio],
                        cfq_group_busy_queues_wl(cfqd->serving_prio, cfqd, cfqg));
  
          if (cfqd->serving_type == ASYNC_WORKLOAD) {
                  unsigned int tmp;
  
                  /*
                   * Async queues are currently system wide. Just taking
                   * proportion of queues with-in same group will lead to higher
                   * async ratio system wide as generally root group is going
                   * to have higher weight. A more accurate thing would be to
                   * calculate system wide asnc/sync ratio.
                   */
                  tmp = cfqd->cfq_target_latency *
                          cfqg_busy_async_queues(cfqd, cfqg);
                  tmp = tmp/cfqd->busy_queues;
                  slice = min_t(unsigned, slice, tmp);
  
                  /* async workload slice is scaled down according to
                   * the sync/async slice ratio. */
                  slice = slice * cfqd->cfq_slice[0] / cfqd->cfq_slice[1];
          } else
                  /* sync workload slice is at least 2 * cfq_slice_idle */
                  slice = max(slice, 2 * cfqd->cfq_slice_idle);
  
          slice = max_t(unsigned, slice, CFQ_MIN_TT);
          cfq_log(cfqd, "workload slice:%d", slice);
          cfqd->workload_expires = jiffies + slice;
  }
  
  static struct cfq_group *cfq_get_next_cfqg(struct cfq_data *cfqd)
  {
          struct cfq_rb_root *st = &cfqd->grp_service_tree;
          struct cfq_group *cfqg;
  
          if (RB_EMPTY_ROOT(&st->rb))
                  return NULL;
          cfqg = cfq_rb_first_group(st);
          update_min_vdisktime(st);
          return cfqg;
  }
  
  static void cfq_choose_cfqg(struct cfq_data *cfqd)
  {
          struct cfq_group *cfqg = cfq_get_next_cfqg(cfqd);
  
          cfqd->serving_group = cfqg;
  
          /* Restore the workload type data */
          if (cfqg->saved_workload_slice) {
                  cfqd->workload_expires = jiffies + cfqg->saved_workload_slice;
                  cfqd->serving_type = cfqg->saved_workload;
                  cfqd->serving_prio = cfqg->saved_serving_prio;
          } else
                  cfqd->workload_expires = jiffies - 1;
  
          choose_service_tree(cfqd, cfqg);
  }
  
  /*
   * Select a queue for service. If we have a current active queue,
   * check whether to continue servicing it, or retrieve and set a new one.
   */
  static struct cfq_queue *cfq_select_queue(struct cfq_data *cfqd)
  {
          struct cfq_queue *cfqq, *new_cfqq = NULL;
  
          cfqq = cfqd->active_queue;
          if (!cfqq)
                  goto new_queue;
  
          if (!cfqd->rq_queued)
                  return NULL;
  
          /*
           * We were waiting for group to get backlogged. Expire the queue
           */
          if (cfq_cfqq_wait_busy(cfqq) && !RB_EMPTY_ROOT(&cfqq->sort_list))
                  goto expire;
  
          /*
           * The active queue has run out of time, expire it and select new.
           */
          if (cfq_slice_used(cfqq) && !cfq_cfqq_must_dispatch(cfqq)) {
                  /*
                   * If slice had not expired at the completion of last request
                   * we might not have turned on wait_busy flag. Don't expire
                   * the queue yet. Allow the group to get backlogged.
                   *
                   * The very fact that we have used the slice, that means we
                   * have been idling all along on this queue and it should be
                   * ok to wait for this request to complete.
                   */
                  if (cfqq->cfqg->nr_cfqq == 1 && RB_EMPTY_ROOT(&cfqq->sort_list)
                      && cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
                          cfqq = NULL;
                          goto keep_queue;
                  } else
                          goto check_group_idle;
          }
  
          /*
           * The active queue has requests and isn't expired, allow it to
           * dispatch.
           */
          if (!RB_EMPTY_ROOT(&cfqq->sort_list))
                  goto keep_queue;
  
          /*
           * If another queue has a request waiting within our mean seek
           * distance, let it run.  The expire code will check for close
           * cooperators and put the close queue at the front of the service
           * tree.  If possible, merge the expiring queue with the new cfqq.
           */
          new_cfqq = cfq_close_cooperator(cfqd, cfqq);
          if (new_cfqq) {
                  if (!cfqq->new_cfqq)
                          cfq_setup_merge(cfqq, new_cfqq);
                  goto expire;
          }
  
          /*
           * No requests pending. If the active queue still has requests in
           * flight or is idling for a new request, allow either of these
           * conditions to happen (or time out) before selecting a new queue.
           */
          if (timer_pending(&cfqd->idle_slice_timer)) {
                  cfqq = NULL;
                  goto keep_queue;
          }
  
          /*
           * This is a deep seek queue, but the device is much faster than
           * the queue can deliver, don't idle
           **/
          if (CFQQ_SEEKY(cfqq) && cfq_cfqq_idle_window(cfqq) &&
              (cfq_cfqq_slice_new(cfqq) ||
              (cfqq->slice_end - jiffies > jiffies - cfqq->slice_start))) {
                  cfq_clear_cfqq_deep(cfqq);
                  cfq_clear_cfqq_idle_window(cfqq);
          }
  
          if (cfqq->dispatched && cfq_should_idle(cfqd, cfqq)) {
                  cfqq = NULL;
                  goto keep_queue;
          }
  
          /*
           * If group idle is enabled and there are requests dispatched from
           * this group, wait for requests to complete.
           */
  check_group_idle:
          if (cfqd->cfq_group_idle && cfqq->cfqg->nr_cfqq == 1 &&
              cfqq->cfqg->dispatched &&
              !cfq_io_thinktime_big(cfqd, &cfqq->cfqg->ttime, true)) {
                  cfqq = NULL;
                  goto keep_queue;
          }
  
  expire:
          cfq_slice_expired(cfqd, 0);
  new_queue:
          /*
           * Current queue expired. Check if we have to switch to a new
           * service tree
           */
          if (!new_cfqq)
                  cfq_choose_cfqg(cfqd);
  
          cfqq = cfq_set_active_queue(cfqd, new_cfqq);
  keep_queue:
          return cfqq;
  }
  
  static int __cfq_forced_dispatch_cfqq(struct cfq_queue *cfqq)
  {
          int dispatched = 0;
  
          while (cfqq->next_rq) {
                  cfq_dispatch_insert(cfqq->cfqd->queue, cfqq->next_rq);
                  dispatched++;
          }
  
          BUG_ON(!list_empty(&cfqq->fifo));
  
          /* By default cfqq is not expired if it is empty. Do it explicitly */
          __cfq_slice_expired(cfqq->cfqd, cfqq, 0);
          return dispatched;
  }
  
  /*
   * Drain our current requests. Used for barriers and when switching
   * io schedulers on-the-fly.
   */
  static int cfq_forced_dispatch(struct cfq_data *cfqd)
  {
          struct cfq_queue *cfqq;
          int dispatched = 0;
  
          /* Expire the timeslice of the current active queue first */
          cfq_slice_expired(cfqd, 0);
          while ((cfqq = cfq_get_next_queue_forced(cfqd)) != NULL) {
                  __cfq_set_active_queue(cfqd, cfqq);
                  dispatched += __cfq_forced_dispatch_cfqq(cfqq);
          }
  
          BUG_ON(cfqd->busy_queues);
  
          cfq_log(cfqd, "forced_dispatch=%d", dispatched);
          return dispatched;
  }
  
  static inline bool cfq_slice_used_soon(struct cfq_data *cfqd,
          struct cfq_queue *cfqq)
  {
          /* the queue hasn't finished any request, can't estimate */
          if (cfq_cfqq_slice_new(cfqq))
                  return true;
          if (time_after(jiffies + cfqd->cfq_slice_idle * cfqq->dispatched,
                  cfqq->slice_end))
                  return true;
  
          return false;
  }
  
  static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          unsigned int max_dispatch;
  
          /*
           * Drain async requests before we start sync IO
           */
          if (cfq_should_idle(cfqd, cfqq) && cfqd->rq_in_flight[BLK_RW_ASYNC])
                  return false;
  
          /*
           * If this is an async queue and we have sync IO in flight, let it wait
           */
          if (cfqd->rq_in_flight[BLK_RW_SYNC] && !cfq_cfqq_sync(cfqq))
                  return false;
  
          max_dispatch = max_t(unsigned int, cfqd->cfq_quantum / 2, 1);
          if (cfq_class_idle(cfqq))
                  max_dispatch = 1;
  
          /*
           * Does this cfqq already have too much IO in flight?
           */
          if (cfqq->dispatched >= max_dispatch) {
                  bool promote_sync = false;
                  /*
                   * idle queue must always only have a single IO in flight
                   */
                  if (cfq_class_idle(cfqq))
                          return false;
  
                  /*
                   * If there is only one sync queue
                   * we can ignore async queue here and give the sync
                   * queue no dispatch limit. The reason is a sync queue can
                   * preempt async queue, limiting the sync queue doesn't make
                   * sense. This is useful for aiostress test.
                   */
                  if (cfq_cfqq_sync(cfqq) && cfqd->busy_sync_queues == 1)
                          promote_sync = true;
  
                  /*
                   * We have other queues, don't allow more IO from this one
                   */
                  if (cfqd->busy_queues > 1 && cfq_slice_used_soon(cfqd, cfqq) &&
                                  !promote_sync)
                          return false;
  
                  /*
                   * Sole queue user, no limit
                   */
                  if (cfqd->busy_queues == 1 || promote_sync)
                          max_dispatch = -1;
                  else
                          /*
                           * Normally we start throttling cfqq when cfq_quantum/2
                           * requests have been dispatched. But we can drive
                           * deeper queue depths at the beginning of slice
                           * subjected to upper limit of cfq_quantum.
                           * */
                          max_dispatch = cfqd->cfq_quantum;
          }
  
          /*
           * Async queues must wait a bit before being allowed dispatch.
           * We also ramp up the dispatch depth gradually for async IO,
           * based on the last sync IO we serviced
           */
          if (!cfq_cfqq_sync(cfqq) && cfqd->cfq_latency) {
                  unsigned long last_sync = jiffies - cfqd->last_delayed_sync;
                  unsigned int depth;
  
                  depth = last_sync / cfqd->cfq_slice[1];
                  if (!depth && !cfqq->dispatched)
                          depth = 1;
                  if (depth < max_dispatch)
                          max_dispatch = depth;
          }
  
          /*
           * If we're below the current max, allow a dispatch
           */
          return cfqq->dispatched < max_dispatch;
  }
  
  /*
   * Dispatch a request from cfqq, moving them to the request queue
   * dispatch list.
   */
  static bool cfq_dispatch_request(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          struct request *rq;
  
          BUG_ON(RB_EMPTY_ROOT(&cfqq->sort_list));
  
          if (!cfq_may_dispatch(cfqd, cfqq))
                  return false;
  
          /*
           * follow expired path, else get first next available
           */
          rq = cfq_check_fifo(cfqq);
          if (!rq)
                  rq = cfqq->next_rq;
  
          /*
           * insert request into driver dispatch list
           */
          cfq_dispatch_insert(cfqd->queue, rq);
  
          if (!cfqd->active_cic) {
                  struct cfq_io_cq *cic = RQ_CIC(rq);
  
                  atomic_long_inc(&cic->icq.ioc->refcount);
                  cfqd->active_cic = cic;
          }
  
          return true;
  }
  
  /*
   * Find the cfqq that we need to service and move a request from that to the
   * dispatch list
   */
  static int cfq_dispatch_requests(struct request_queue *q, int force)
  {
          struct cfq_data *cfqd = q->elevator->elevator_data;
          struct cfq_queue *cfqq;
  
          if (!cfqd->busy_queues)
                  return 0;
  
          if (unlikely(force))
                  return cfq_forced_dispatch(cfqd);
  
          cfqq = cfq_select_queue(cfqd);
          if (!cfqq)
                  return 0;
  
          /*
           * Dispatch a request from this cfqq, if it is allowed
           */
          if (!cfq_dispatch_request(cfqd, cfqq))
                  return 0;
  
          cfqq->slice_dispatch++;
          cfq_clear_cfqq_must_dispatch(cfqq);
  
          /*
           * expire an async queue immediately if it has used up its slice. idle
           * queue always expire after 1 dispatch round.
           */
          if (cfqd->busy_queues > 1 && ((!cfq_cfqq_sync(cfqq) &&
              cfqq->slice_dispatch >= cfq_prio_to_maxrq(cfqd, cfqq)) ||
              cfq_class_idle(cfqq))) {
                  cfqq->slice_end = jiffies + 1;
                  cfq_slice_expired(cfqd, 0);
          }
  
          cfq_log_cfqq(cfqd, cfqq, "dispatched a request");
          return 1;
  }
  
  /*
   * task holds one reference to the queue, dropped when task exits. each rq
   * in-flight on this queue also holds a reference, dropped when rq is freed.
   *
   * Each cfq queue took a reference on the parent group. Drop it now.
   * queue lock must be held here.
   */
  static void cfq_put_queue(struct cfq_queue *cfqq)
  {
          struct cfq_data *cfqd = cfqq->cfqd;
          struct cfq_group *cfqg;
  
          BUG_ON(cfqq->ref <= 0);
  
          cfqq->ref--;
          if (cfqq->ref)
                  return;
  
          cfq_log_cfqq(cfqd, cfqq, "put_queue");
          BUG_ON(rb_first(&cfqq->sort_list));
          BUG_ON(cfqq->allocated[READ] + cfqq->allocated[WRITE]);
          cfqg = cfqq->cfqg;
  
          if (unlikely(cfqd->active_queue == cfqq)) {
                  __cfq_slice_expired(cfqd, cfqq, 0);
                  cfq_schedule_dispatch(cfqd);
          }
  
          BUG_ON(cfq_cfqq_on_rr(cfqq));
          kmem_cache_free(cfq_pool, cfqq);
          cfqg_put(cfqg);
  }
  
  static void cfq_put_cooperator(struct cfq_queue *cfqq)
  {
          struct cfq_queue *__cfqq, *next;
  
          /*
           * If this queue was scheduled to merge with another queue, be
           * sure to drop the reference taken on that queue (and others in
           * the merge chain).  See cfq_setup_merge and cfq_merge_cfqqs.
           */
          __cfqq = cfqq->new_cfqq;
          while (__cfqq) {
                  if (__cfqq == cfqq) {
                          WARN(1, "cfqq->new_cfqq loop detected\n");
                          break;
                  }
                  next = __cfqq->new_cfqq;
                  cfq_put_queue(__cfqq);
                  __cfqq = next;
          }
  }
  
  static void cfq_exit_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          if (unlikely(cfqq == cfqd->active_queue)) {
                  __cfq_slice_expired(cfqd, cfqq, 0);
                  cfq_schedule_dispatch(cfqd);
          }
  
          cfq_put_cooperator(cfqq);
  
          cfq_put_queue(cfqq);
  }
  
  static void cfq_init_icq(struct io_cq *icq)
  {
          struct cfq_io_cq *cic = icq_to_cic(icq);
  
          cic->ttime.last_end_request = jiffies;
  }
  
  static void cfq_exit_icq(struct io_cq *icq)
  {
          struct cfq_io_cq *cic = icq_to_cic(icq);
          struct cfq_data *cfqd = cic_to_cfqd(cic);
  
          if (cic->cfqq[BLK_RW_ASYNC]) {
                  cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_ASYNC]);
                  cic->cfqq[BLK_RW_ASYNC] = NULL;
          }
  
          if (cic->cfqq[BLK_RW_SYNC]) {
                  cfq_exit_cfqq(cfqd, cic->cfqq[BLK_RW_SYNC]);
                  cic->cfqq[BLK_RW_SYNC] = NULL;
          }
  }
  
  static void cfq_init_prio_data(struct cfq_queue *cfqq, struct cfq_io_cq *cic)
  {
          struct task_struct *tsk = current;
          int ioprio_class;
  
          if (!cfq_cfqq_prio_changed(cfqq))
                  return;
  
          ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio);
          switch (ioprio_class) {
          default:
                  printk(KERN_ERR "cfq: bad prio %x\n", ioprio_class);
          case IOPRIO_CLASS_NONE:
                  /*
                   * no prio set, inherit CPU scheduling settings
                   */
                  cfqq->ioprio = task_nice_ioprio(tsk);
                  cfqq->ioprio_class = task_nice_ioclass(tsk);
                  break;
          case IOPRIO_CLASS_RT:
                  cfqq->ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
                  cfqq->ioprio_class = IOPRIO_CLASS_RT;
                  break;
          case IOPRIO_CLASS_BE:
                  cfqq->ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
                  cfqq->ioprio_class = IOPRIO_CLASS_BE;
                  break;
          case IOPRIO_CLASS_IDLE:
                  cfqq->ioprio_class = IOPRIO_CLASS_IDLE;
                  cfqq->ioprio = 7;
                  cfq_clear_cfqq_idle_window(cfqq);
                  break;
          }
  
          /*
           * keep track of original prio settings in case we have to temporarily
           * elevate the priority of this queue
           */
          cfqq->org_ioprio = cfqq->ioprio;
          cfq_clear_cfqq_prio_changed(cfqq);
  }
  
  static void check_ioprio_changed(struct cfq_io_cq *cic, struct bio *bio)
  {
          int ioprio = cic->icq.ioc->ioprio;
          struct cfq_data *cfqd = cic_to_cfqd(cic);
          struct cfq_queue *cfqq;
  
          /*
           * Check whether ioprio has changed.  The condition may trigger
           * spuriously on a newly created cic but there's no harm.
           */
          if (unlikely(!cfqd) || likely(cic->ioprio == ioprio))
                  return;
  
          cfqq = cic->cfqq[BLK_RW_ASYNC];
          if (cfqq) {
                  struct cfq_queue *new_cfqq;
                  new_cfqq = cfq_get_queue(cfqd, BLK_RW_ASYNC, cic, bio,
                                           GFP_ATOMIC);
                  if (new_cfqq) {
                          cic->cfqq[BLK_RW_ASYNC] = new_cfqq;
                          cfq_put_queue(cfqq);
                  }
          }
  
          cfqq = cic->cfqq[BLK_RW_SYNC];
          if (cfqq)
                  cfq_mark_cfqq_prio_changed(cfqq);
  
          cic->ioprio = ioprio;
  }
  
  static void cfq_init_cfqq(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                            pid_t pid, bool is_sync)
  {
          RB_CLEAR_NODE(&cfqq->rb_node);
          RB_CLEAR_NODE(&cfqq->p_node);
          INIT_LIST_HEAD(&cfqq->fifo);
  
          cfqq->ref = 0;
          cfqq->cfqd = cfqd;
  
          cfq_mark_cfqq_prio_changed(cfqq);
  
          if (is_sync) {
                  if (!cfq_class_idle(cfqq))
                          cfq_mark_cfqq_idle_window(cfqq);
                  cfq_mark_cfqq_sync(cfqq);
          }
          cfqq->pid = pid;
  }
  
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
  static void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio)
  {
          struct cfq_data *cfqd = cic_to_cfqd(cic);
          struct cfq_queue *sync_cfqq;
          uint64_t id;
  
          rcu_read_lock();
          id = bio_blkcg(bio)->id;
          rcu_read_unlock();
  
          /*
           * Check whether blkcg has changed.  The condition may trigger
           * spuriously on a newly created cic but there's no harm.
           */
          if (unlikely(!cfqd) || likely(cic->blkcg_id == id))
                  return;
  
          sync_cfqq = cic_to_cfqq(cic, 1);
          if (sync_cfqq) {
                  /*
                   * Drop reference to sync queue. A new sync queue will be
                   * assigned in new group upon arrival of a fresh request.
                   */
                  cfq_log_cfqq(cfqd, sync_cfqq, "changed cgroup");
                  cic_set_cfqq(cic, NULL, 1);
                  cfq_put_queue(sync_cfqq);
          }
  
          cic->blkcg_id = id;
  }
  #else
  static inline void check_blkcg_changed(struct cfq_io_cq *cic, struct bio *bio) { }
  #endif  /* CONFIG_CFQ_GROUP_IOSCHED */
  
  static struct cfq_queue *
  cfq_find_alloc_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
                       struct bio *bio, gfp_t gfp_mask)
  {
          struct blkcg *blkcg;
          struct cfq_queue *cfqq, *new_cfqq = NULL;
          struct cfq_group *cfqg;
  
  retry:
          rcu_read_lock();
  
          blkcg = bio_blkcg(bio);
          cfqg = cfq_lookup_create_cfqg(cfqd, blkcg);
          cfqq = cic_to_cfqq(cic, is_sync);
  
          /*
           * Always try a new alloc if we fell back to the OOM cfqq
           * originally, since it should just be a temporary situation.
           */
          if (!cfqq || cfqq == &cfqd->oom_cfqq) {
                  cfqq = NULL;
                  if (new_cfqq) {
                          cfqq = new_cfqq;
                          new_cfqq = NULL;
                  } else if (gfp_mask & __GFP_WAIT) {
                          rcu_read_unlock();
                          spin_unlock_irq(cfqd->queue->queue_lock);
                          new_cfqq = kmem_cache_alloc_node(cfq_pool,
                                          gfp_mask | __GFP_ZERO,
                                          cfqd->queue->node);
                          spin_lock_irq(cfqd->queue->queue_lock);
                          if (new_cfqq)
                                  goto retry;
                  } else {
                          cfqq = kmem_cache_alloc_node(cfq_pool,
                                          gfp_mask | __GFP_ZERO,
                                          cfqd->queue->node);
                  }
  
                  if (cfqq) {
                          cfq_init_cfqq(cfqd, cfqq, current->pid, is_sync);
                          cfq_init_prio_data(cfqq, cic);
                          cfq_link_cfqq_cfqg(cfqq, cfqg);
                          cfq_log_cfqq(cfqd, cfqq, "alloced");
                  } else
                          cfqq = &cfqd->oom_cfqq;
          }
  
          if (new_cfqq)
                  kmem_cache_free(cfq_pool, new_cfqq);
  
          rcu_read_unlock();
          return cfqq;
  }
  
  static struct cfq_queue **
  cfq_async_queue_prio(struct cfq_data *cfqd, int ioprio_class, int ioprio)
  {
          switch (ioprio_class) {
          case IOPRIO_CLASS_RT:
                  return &cfqd->async_cfqq[0][ioprio];
          case IOPRIO_CLASS_NONE:
                  ioprio = IOPRIO_NORM;
                  /* fall through */
          case IOPRIO_CLASS_BE:
                  return &cfqd->async_cfqq[1][ioprio];
          case IOPRIO_CLASS_IDLE:
                  return &cfqd->async_idle_cfqq;
          default:
                  BUG();
          }
  }
  
  static struct cfq_queue *
  cfq_get_queue(struct cfq_data *cfqd, bool is_sync, struct cfq_io_cq *cic,
                struct bio *bio, gfp_t gfp_mask)
  {
          const int ioprio_class = IOPRIO_PRIO_CLASS(cic->ioprio);
          const int ioprio = IOPRIO_PRIO_DATA(cic->ioprio);
          struct cfq_queue **async_cfqq = NULL;
          struct cfq_queue *cfqq = NULL;
  
          if (!is_sync) {
                  async_cfqq = cfq_async_queue_prio(cfqd, ioprio_class, ioprio);
                  cfqq = *async_cfqq;
          }
  
          if (!cfqq)
                  cfqq = cfq_find_alloc_queue(cfqd, is_sync, cic, bio, gfp_mask);
  
          /*
           * pin the queue now that it's allocated, scheduler exit will prune it
           */
          if (!is_sync && !(*async_cfqq)) {
                  cfqq->ref++;
                  *async_cfqq = cfqq;
          }
  
          cfqq->ref++;
          return cfqq;
  }
  
  static void
  __cfq_update_io_thinktime(struct cfq_ttime *ttime, unsigned long slice_idle)
  {
          unsigned long elapsed = jiffies - ttime->last_end_request;
          elapsed = min(elapsed, 2UL * slice_idle);
  
          ttime->ttime_samples = (7*ttime->ttime_samples + 256) / 8;
          ttime->ttime_total = (7*ttime->ttime_total + 256*elapsed) / 8;
          ttime->ttime_mean = (ttime->ttime_total + 128) / ttime->ttime_samples;
  }
  
  static void
  cfq_update_io_thinktime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                          struct cfq_io_cq *cic)
  {
          if (cfq_cfqq_sync(cfqq)) {
                  __cfq_update_io_thinktime(&cic->ttime, cfqd->cfq_slice_idle);
                  __cfq_update_io_thinktime(&cfqq->service_tree->ttime,
                          cfqd->cfq_slice_idle);
          }
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
          __cfq_update_io_thinktime(&cfqq->cfqg->ttime, cfqd->cfq_group_idle);
  #endif
  }
  
  static void
  cfq_update_io_seektime(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                         struct request *rq)
  {
          sector_t sdist = 0;
          sector_t n_sec = blk_rq_sectors(rq);
          if (cfqq->last_request_pos) {
                  if (cfqq->last_request_pos < blk_rq_pos(rq))
                          sdist = blk_rq_pos(rq) - cfqq->last_request_pos;
                  else
                          sdist = cfqq->last_request_pos - blk_rq_pos(rq);
          }
  
          cfqq->seek_history <<= 1;
          if (blk_queue_nonrot(cfqd->queue))
                  cfqq->seek_history |= (n_sec < CFQQ_SECT_THR_NONROT);
          else
                  cfqq->seek_history |= (sdist > CFQQ_SEEK_THR);
  }
  
  /*
   * Disable idle window if the process thinks too long or seeks so much that
   * it doesn't matter
   */
  static void
  cfq_update_idle_window(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                         struct cfq_io_cq *cic)
  {
          int old_idle, enable_idle;
  
          /*
           * Don't idle for async or idle io prio class
           */
          if (!cfq_cfqq_sync(cfqq) || cfq_class_idle(cfqq))
                  return;
  
          enable_idle = old_idle = cfq_cfqq_idle_window(cfqq);
  
          if (cfqq->queued[0] + cfqq->queued[1] >= 4)
                  cfq_mark_cfqq_deep(cfqq);
  
          if (cfqq->next_rq && (cfqq->next_rq->cmd_flags & REQ_NOIDLE))
                  enable_idle = 0;
          else if (!atomic_read(&cic->icq.ioc->active_ref) ||
                   !cfqd->cfq_slice_idle ||
                   (!cfq_cfqq_deep(cfqq) && CFQQ_SEEKY(cfqq)))
                  enable_idle = 0;
          else if (sample_valid(cic->ttime.ttime_samples)) {
                  if (cic->ttime.ttime_mean > cfqd->cfq_slice_idle)
                          enable_idle = 0;
                  else
                          enable_idle = 1;
          }
  
          if (old_idle != enable_idle) {
                  cfq_log_cfqq(cfqd, cfqq, "idle=%d", enable_idle);
                  if (enable_idle)
                          cfq_mark_cfqq_idle_window(cfqq);
                  else
                          cfq_clear_cfqq_idle_window(cfqq);
          }
  }
  
  /*
   * Check if new_cfqq should preempt the currently active queue. Return 0 for
   * no or if we aren't sure, a 1 will cause a preempt.
   */
  static bool
  cfq_should_preempt(struct cfq_data *cfqd, struct cfq_queue *new_cfqq,
                     struct request *rq)
  {
          struct cfq_queue *cfqq;
  
          cfqq = cfqd->active_queue;
          if (!cfqq)
                  return false;
  
          if (cfq_class_idle(new_cfqq))
                  return false;
  
          if (cfq_class_idle(cfqq))
                  return true;
  
          /*
           * Don't allow a non-RT request to preempt an ongoing RT cfqq timeslice.
           */
          if (cfq_class_rt(cfqq) && !cfq_class_rt(new_cfqq))
                  return false;
  
          /*
           * if the new request is sync, but the currently running queue is
           * not, let the sync request have priority.
           */
          if (rq_is_sync(rq) && !cfq_cfqq_sync(cfqq))
                  return true;
  
          if (new_cfqq->cfqg != cfqq->cfqg)
                  return false;
  
          if (cfq_slice_used(cfqq))
                  return true;
  
          /* Allow preemption only if we are idling on sync-noidle tree */
          if (cfqd->serving_type == SYNC_NOIDLE_WORKLOAD &&
              cfqq_type(new_cfqq) == SYNC_NOIDLE_WORKLOAD &&
              new_cfqq->service_tree->count == 2 &&
              RB_EMPTY_ROOT(&cfqq->sort_list))
                  return true;
  
          /*
           * So both queues are sync. Let the new request get disk time if
           * it's a metadata request and the current queue is doing regular IO.
           */
          if ((rq->cmd_flags & REQ_PRIO) && !cfqq->prio_pending)
                  return true;
  
          /*
           * Allow an RT request to pre-empt an ongoing non-RT cfqq timeslice.
           */
          if (cfq_class_rt(new_cfqq) && !cfq_class_rt(cfqq))
                  return true;
  
          /* An idle queue should not be idle now for some reason */
          if (RB_EMPTY_ROOT(&cfqq->sort_list) && !cfq_should_idle(cfqd, cfqq))
                  return true;
  
          if (!cfqd->active_cic || !cfq_cfqq_wait_request(cfqq))
                  return false;
  
          /*
           * if this request is as-good as one we would expect from the
           * current cfqq, let it preempt
           */
          if (cfq_rq_close(cfqd, cfqq, rq))
                  return true;
  
          return false;
  }
  
  /*
   * cfqq preempts the active queue. if we allowed preempt with no slice left,
   * let it have half of its nominal slice.
   */
  static void cfq_preempt_queue(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          enum wl_type_t old_type = cfqq_type(cfqd->active_queue);
  
          cfq_log_cfqq(cfqd, cfqq, "preempt");
          cfq_slice_expired(cfqd, 1);
  
          /*
           * workload type is changed, don't save slice, otherwise preempt
           * doesn't happen
           */
          if (old_type != cfqq_type(cfqq))
                  cfqq->cfqg->saved_workload_slice = 0;
  
          /*
           * Put the new queue at the front of the of the current list,
           * so we know that it will be selected next.
           */
          BUG_ON(!cfq_cfqq_on_rr(cfqq));
  
          cfq_service_tree_add(cfqd, cfqq, 1);
  
          cfqq->slice_end = 0;
          cfq_mark_cfqq_slice_new(cfqq);
  }
  
  /*
   * Called when a new fs request (rq) is added (to cfqq). Check if there's
   * something we should do about it
   */
  static void
  cfq_rq_enqueued(struct cfq_data *cfqd, struct cfq_queue *cfqq,
                  struct request *rq)
  {
          struct cfq_io_cq *cic = RQ_CIC(rq);
  
          cfqd->rq_queued++;
          if (rq->cmd_flags & REQ_PRIO)
                  cfqq->prio_pending++;
  
          cfq_update_io_thinktime(cfqd, cfqq, cic);
          cfq_update_io_seektime(cfqd, cfqq, rq);
          cfq_update_idle_window(cfqd, cfqq, cic);
  
          cfqq->last_request_pos = blk_rq_pos(rq) + blk_rq_sectors(rq);
  
          if (cfqq == cfqd->active_queue) {
                  /*
                   * Remember that we saw a request from this process, but
                   * don't start queuing just yet. Otherwise we risk seeing lots
                   * of tiny requests, because we disrupt the normal plugging
                   * and merging. If the request is already larger than a single
                   * page, let it rip immediately. For that case we assume that
                   * merging is already done. Ditto for a busy system that
                   * has other work pending, don't risk delaying until the
                   * idle timer unplug to continue working.
                   */
                  if (cfq_cfqq_wait_request(cfqq)) {
                          if (blk_rq_bytes(rq) > PAGE_CACHE_SIZE ||
                              cfqd->busy_queues > 1) {
                                  cfq_del_timer(cfqd, cfqq);
                                  cfq_clear_cfqq_wait_request(cfqq);
                                  __blk_run_queue(cfqd->queue);
                          } else {
                                  cfqg_stats_update_idle_time(cfqq->cfqg);
                                  cfq_mark_cfqq_must_dispatch(cfqq);
                          }
                  }
          } else if (cfq_should_preempt(cfqd, cfqq, rq)) {
                  /*
                   * not the active queue - expire current slice if it is
                   * idle and has expired it's mean thinktime or this new queue
                   * has some old slice time left and is of higher priority or
                   * this new queue is RT and the current one is BE
                   */
                  cfq_preempt_queue(cfqd, cfqq);
                  __blk_run_queue(cfqd->queue);
          }
  }
  
  static void cfq_insert_request(struct request_queue *q, struct request *rq)
  {
          struct cfq_data *cfqd = q->elevator->elevator_data;
          struct cfq_queue *cfqq = RQ_CFQQ(rq);
  
          cfq_log_cfqq(cfqd, cfqq, "insert_request");
          cfq_init_prio_data(cfqq, RQ_CIC(rq));
  
          rq_set_fifo_time(rq, jiffies + cfqd->cfq_fifo_expire[rq_is_sync(rq)]);
          list_add_tail(&rq->queuelist, &cfqq->fifo);
          cfq_add_rq_rb(rq);
          cfqg_stats_update_io_add(RQ_CFQG(rq), cfqd->serving_group,
                                   rq->cmd_flags);
          cfq_rq_enqueued(cfqd, cfqq, rq);
  }
  
  /*
   * Update hw_tag based on peak queue depth over 50 samples under
   * sufficient load.
   */
  static void cfq_update_hw_tag(struct cfq_data *cfqd)
  {
          struct cfq_queue *cfqq = cfqd->active_queue;
  
          if (cfqd->rq_in_driver > cfqd->hw_tag_est_depth)
                  cfqd->hw_tag_est_depth = cfqd->rq_in_driver;
  
          if (cfqd->hw_tag == 1)
                  return;
  
          if (cfqd->rq_queued <= CFQ_HW_QUEUE_MIN &&
              cfqd->rq_in_driver <= CFQ_HW_QUEUE_MIN)
                  return;
  
          /*
           * If active queue hasn't enough requests and can idle, cfq might not
           * dispatch sufficient requests to hardware. Don't zero hw_tag in this
           * case
           */
          if (cfqq && cfq_cfqq_idle_window(cfqq) &&
              cfqq->dispatched + cfqq->queued[0] + cfqq->queued[1] <
              CFQ_HW_QUEUE_MIN && cfqd->rq_in_driver < CFQ_HW_QUEUE_MIN)
                  return;
  
          if (cfqd->hw_tag_samples++ < 50)
                  return;
  
          if (cfqd->hw_tag_est_depth >= CFQ_HW_QUEUE_MIN)
                  cfqd->hw_tag = 1;
          else
                  cfqd->hw_tag = 0;
  }
  
  static bool cfq_should_wait_busy(struct cfq_data *cfqd, struct cfq_queue *cfqq)
  {
          struct cfq_io_cq *cic = cfqd->active_cic;
  
          /* If the queue already has requests, don't wait */
          if (!RB_EMPTY_ROOT(&cfqq->sort_list))
                  return false;
  
          /* If there are other queues in the group, don't wait */
          if (cfqq->cfqg->nr_cfqq > 1)
                  return false;
  
          /* the only queue in the group, but think time is big */
          if (cfq_io_thinktime_big(cfqd, &cfqq->cfqg->ttime, true))
                  return false;
  
          if (cfq_slice_used(cfqq))
                  return true;
  
          /* if slice left is less than think time, wait busy */
          if (cic && sample_valid(cic->ttime.ttime_samples)
              && (cfqq->slice_end - jiffies < cic->ttime.ttime_mean))
                  return true;
  
          /*
           * If think times is less than a jiffy than ttime_mean=0 and above
           * will not be true. It might happen that slice has not expired yet
           * but will expire soon (4-5 ns) during select_queue(). To cover the
           * case where think time is less than a jiffy, mark the queue wait
           * busy if only 1 jiffy is left in the slice.
           */
          if (cfqq->slice_end - jiffies == 1)
                  return true;
  
          return false;
  }
  
  static void cfq_completed_request(struct request_queue *q, struct request *rq)
  {
          struct cfq_queue *cfqq = RQ_CFQQ(rq);
          struct cfq_data *cfqd = cfqq->cfqd;
          const int sync = rq_is_sync(rq);
          unsigned long now;
  
          now = jiffies;
          cfq_log_cfqq(cfqd, cfqq, "complete rqnoidle %d",
                       !!(rq->cmd_flags & REQ_NOIDLE));
  
          cfq_update_hw_tag(cfqd);
  
          WARN_ON(!cfqd->rq_in_driver);
          WARN_ON(!cfqq->dispatched);
          cfqd->rq_in_driver--;
          cfqq->dispatched--;
          (RQ_CFQG(rq))->dispatched--;
          cfqg_stats_update_completion(cfqq->cfqg, rq_start_time_ns(rq),
                                       rq_io_start_time_ns(rq), rq->cmd_flags);
  
          cfqd->rq_in_flight[cfq_cfqq_sync(cfqq)]--;
  
          if (sync) {
                  struct cfq_rb_root *service_tree;
  
                  RQ_CIC(rq)->ttime.last_end_request = now;
  
                  if (cfq_cfqq_on_rr(cfqq))
                          service_tree = cfqq->service_tree;
                  else
                          service_tree = service_tree_for(cfqq->cfqg,
                                  cfqq_prio(cfqq), cfqq_type(cfqq));
                  service_tree->ttime.last_end_request = now;
                  if (!time_after(rq->start_time + cfqd->cfq_fifo_expire[1], now))
                          cfqd->last_delayed_sync = now;
          }
  
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
          cfqq->cfqg->ttime.last_end_request = now;
  #endif
  
          /*
           * If this is the active queue, check if it needs to be expired,
           * or if we want to idle in case it has no pending requests.
           */
          if (cfqd->active_queue == cfqq) {
                  const bool cfqq_empty = RB_EMPTY_ROOT(&cfqq->sort_list);
  
                  if (cfq_cfqq_slice_new(cfqq)) {
                          cfq_set_prio_slice(cfqd, cfqq);
                          cfq_clear_cfqq_slice_new(cfqq);
                  }
  
                  /*
                   * Should we wait for next request to come in before we expire
                   * the queue.
                   */
                  if (cfq_should_wait_busy(cfqd, cfqq)) {
                          unsigned long extend_sl = cfqd->cfq_slice_idle;
                          if (!cfqd->cfq_slice_idle)
                                  extend_sl = cfqd->cfq_group_idle;
                          cfqq->slice_end = jiffies + extend_sl;
                          cfq_mark_cfqq_wait_busy(cfqq);
                          cfq_log_cfqq(cfqd, cfqq, "will busy wait");
                  }
  
                  /*
                   * Idling is not enabled on:
                   * - expired queues
                   * - idle-priority queues
                   * - async queues
                   * - queues with still some requests queued
                   * - when there is a close cooperator
                   */
                  if (cfq_slice_used(cfqq) || cfq_class_idle(cfqq))
                          cfq_slice_expired(cfqd, 1);
                  else if (sync && cfqq_empty &&
                           !cfq_close_cooperator(cfqd, cfqq)) {
                          cfq_arm_slice_timer(cfqd);
                  }
          }
  
          if (!cfqd->rq_in_driver)
                  cfq_schedule_dispatch(cfqd);
  }
  
  static inline int __cfq_may_queue(struct cfq_queue *cfqq)
  {
          if (cfq_cfqq_wait_request(cfqq) && !cfq_cfqq_must_alloc_slice(cfqq)) {
                  cfq_mark_cfqq_must_alloc_slice(cfqq);
                  return ELV_MQUEUE_MUST;
          }
  
          return ELV_MQUEUE_MAY;
  }
  
  static int cfq_may_queue(struct request_queue *q, int rw)
  {
          struct cfq_data *cfqd = q->elevator->elevator_data;
          struct task_struct *tsk = current;
          struct cfq_io_cq *cic;
          struct cfq_queue *cfqq;
  
          /*
           * don't force setup of a queue from here, as a call to may_queue
           * does not necessarily imply that a request actually will be queued.
           * so just lookup a possibly existing queue, or return 'may queue'
           * if that fails
           */
          cic = cfq_cic_lookup(cfqd, tsk->io_context);
          if (!cic)
                  return ELV_MQUEUE_MAY;
  
          cfqq = cic_to_cfqq(cic, rw_is_sync(rw));
          if (cfqq) {
                  cfq_init_prio_data(cfqq, cic);
  
                  return __cfq_may_queue(cfqq);
          }
  
          return ELV_MQUEUE_MAY;
  }
  
  /*
   * queue lock held here
   */
  static void cfq_put_request(struct request *rq)
  {
          struct cfq_queue *cfqq = RQ_CFQQ(rq);
  
          if (cfqq) {
                  const int rw = rq_data_dir(rq);
  
                  BUG_ON(!cfqq->allocated[rw]);
                  cfqq->allocated[rw]--;
  
                  /* Put down rq reference on cfqg */
                  cfqg_put(RQ_CFQG(rq));
                  rq->elv.priv[0] = NULL;
                  rq->elv.priv[1] = NULL;
  
                  cfq_put_queue(cfqq);
          }
  }
  
  static struct cfq_queue *
  cfq_merge_cfqqs(struct cfq_data *cfqd, struct cfq_io_cq *cic,
                  struct cfq_queue *cfqq)
  {
          cfq_log_cfqq(cfqd, cfqq, "merging with queue %p", cfqq->new_cfqq);
          cic_set_cfqq(cic, cfqq->new_cfqq, 1);
          cfq_mark_cfqq_coop(cfqq->new_cfqq);
          cfq_put_queue(cfqq);
          return cic_to_cfqq(cic, 1);
  }
  
  /*
   * Returns NULL if a new cfqq should be allocated, or the old cfqq if this
   * was the last process referring to said cfqq.
   */
  static struct cfq_queue *
  split_cfqq(struct cfq_io_cq *cic, struct cfq_queue *cfqq)
  {
          if (cfqq_process_refs(cfqq) == 1) {
                  cfqq->pid = current->pid;
                  cfq_clear_cfqq_coop(cfqq);
                  cfq_clear_cfqq_split_coop(cfqq);
                  return cfqq;
          }
  
          cic_set_cfqq(cic, NULL, 1);
  
          cfq_put_cooperator(cfqq);
  
          cfq_put_queue(cfqq);
          return NULL;
  }
  /*
   * Allocate cfq data structures associated with this request.
   */
  static int
  cfq_set_request(struct request_queue *q, struct request *rq, struct bio *bio,
                  gfp_t gfp_mask)
  {
          struct cfq_data *cfqd = q->elevator->elevator_data;
          struct cfq_io_cq *cic = icq_to_cic(rq->elv.icq);
          const int rw = rq_data_dir(rq);
          const bool is_sync = rq_is_sync(rq);
          struct cfq_queue *cfqq;
  
          might_sleep_if(gfp_mask & __GFP_WAIT);
  
          spin_lock_irq(q->queue_lock);
  
          check_ioprio_changed(cic, bio);
          check_blkcg_changed(cic, bio);
  new_queue:
          cfqq = cic_to_cfqq(cic, is_sync);
          if (!cfqq || cfqq == &cfqd->oom_cfqq) {
                  cfqq = cfq_get_queue(cfqd, is_sync, cic, bio, gfp_mask);
                  cic_set_cfqq(cic, cfqq, is_sync);
          } else {
                  /*
                   * If the queue was seeky for too long, break it apart.
                   */
                  if (cfq_cfqq_coop(cfqq) && cfq_cfqq_split_coop(cfqq)) {
                          cfq_log_cfqq(cfqd, cfqq, "breaking apart cfqq");
                          cfqq = split_cfqq(cic, cfqq);
                          if (!cfqq)
                                  goto new_queue;
                  }
  
                  /*
                   * Check to see if this queue is scheduled to merge with
                   * another, closely cooperating queue.  The merging of
                   * queues happens here as it must be done in process context.
                   * The reference on new_cfqq was taken in merge_cfqqs.
                   */
                  if (cfqq->new_cfqq)
                          cfqq = cfq_merge_cfqqs(cfqd, cic, cfqq);
          }
  
          cfqq->allocated[rw]++;
  
          cfqq->ref++;
          cfqg_get(cfqq->cfqg);
          rq->elv.priv[0] = cfqq;
          rq->elv.priv[1] = cfqq->cfqg;
          spin_unlock_irq(q->queue_lock);
          return 0;
  }
  
  static void cfq_kick_queue(struct work_struct *work)
  {
          struct cfq_data *cfqd =
                  container_of(work, struct cfq_data, unplug_work);
          struct request_queue *q = cfqd->queue;
  
          spin_lock_irq(q->queue_lock);
          __blk_run_queue(cfqd->queue);
          spin_unlock_irq(q->queue_lock);
  }
  
  /*
   * Timer running if the active_queue is currently idling inside its time slice
   */
  static void cfq_idle_slice_timer(unsigned long data)
  {
          struct cfq_data *cfqd = (struct cfq_data *) data;
          struct cfq_queue *cfqq;
          unsigned long flags;
          int timed_out = 1;
  
          cfq_log(cfqd, "idle timer fired");
  
          spin_lock_irqsave(cfqd->queue->queue_lock, flags);
  
          cfqq = cfqd->active_queue;
          if (cfqq) {
                  timed_out = 0;
  
                  /*
                   * We saw a request before the queue expired, let it through
                   */
                  if (cfq_cfqq_must_dispatch(cfqq))
                          goto out_kick;
  
                  /*
                   * expired
                   */
                  if (cfq_slice_used(cfqq))
                          goto expire;
  
                  /*
                   * only expire and reinvoke request handler, if there are
                   * other queues with pending requests
                   */
                  if (!cfqd->busy_queues)
                          goto out_cont;
  
                  /*
                   * not expired and it has a request pending, let it dispatch
                   */
                  if (!RB_EMPTY_ROOT(&cfqq->sort_list))
                          goto out_kick;
  
                  /*
                   * Queue depth flag is reset only when the idle didn't succeed
                   */
                  cfq_clear_cfqq_deep(cfqq);
          }
  expire:
          cfq_slice_expired(cfqd, timed_out);
  out_kick:
          cfq_schedule_dispatch(cfqd);
  out_cont:
          spin_unlock_irqrestore(cfqd->queue->queue_lock, flags);
  }
  
  static void cfq_shutdown_timer_wq(struct cfq_data *cfqd)
  {
          del_timer_sync(&cfqd->idle_slice_timer);
          cancel_work_sync(&cfqd->unplug_work);
  }
  
  static void cfq_put_async_queues(struct cfq_data *cfqd)
  {
          int i;
  
          for (i = 0; i < IOPRIO_BE_NR; i++) {
                  if (cfqd->async_cfqq[0][i])
                          cfq_put_queue(cfqd->async_cfqq[0][i]);
                  if (cfqd->async_cfqq[1][i])
                          cfq_put_queue(cfqd->async_cfqq[1][i]);
          }
  
          if (cfqd->async_idle_cfqq)
                  cfq_put_queue(cfqd->async_idle_cfqq);
  }
  
  static void cfq_exit_queue(struct elevator_queue *e)
  {
          struct cfq_data *cfqd = e->elevator_data;
          struct request_queue *q = cfqd->queue;
  
          cfq_shutdown_timer_wq(cfqd);
  
          spin_lock_irq(q->queue_lock);
  
          if (cfqd->active_queue)
                  __cfq_slice_expired(cfqd, cfqd->active_queue, 0);
  
          cfq_put_async_queues(cfqd);
  
          spin_unlock_irq(q->queue_lock);
  
          cfq_shutdown_timer_wq(cfqd);
  
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
          blkcg_deactivate_policy(q, &blkcg_policy_cfq);
  #else
          kfree(cfqd->root_group);
  #endif
          kfree(cfqd);
  }
  
  static int cfq_init_queue(struct request_queue *q)
  {
          struct cfq_data *cfqd;
          struct blkcg_gq *blkg __maybe_unused;
          int i, ret;
  
          cfqd = kmalloc_node(sizeof(*cfqd), GFP_KERNEL | __GFP_ZERO, q->node);
          if (!cfqd)
                  return -ENOMEM;
  
          cfqd->queue = q;
          q->elevator->elevator_data = cfqd;
  
          /* Init root service tree */
          cfqd->grp_service_tree = CFQ_RB_ROOT;
  
          /* Init root group and prefer root group over other groups by default */
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
          ret = blkcg_activate_policy(q, &blkcg_policy_cfq);
          if (ret)
                  goto out_free;
  
          cfqd->root_group = blkg_to_cfqg(q->root_blkg);
  #else
          ret = -ENOMEM;
          cfqd->root_group = kzalloc_node(sizeof(*cfqd->root_group),
                                          GFP_KERNEL, cfqd->queue->node);
          if (!cfqd->root_group)
                  goto out_free;
  
          cfq_init_cfqg_base(cfqd->root_group);
  #endif
          cfqd->root_group->weight = 2 * CFQ_WEIGHT_DEFAULT;
  
          /*
           * Not strictly needed (since RB_ROOT just clears the node and we
           * zeroed cfqd on alloc), but better be safe in case someone decides
           * to add magic to the rb code
           */
          for (i = 0; i < CFQ_PRIO_LISTS; i++)
                  cfqd->prio_trees[i] = RB_ROOT;
  
          /*
           * Our fallback cfqq if cfq_find_alloc_queue() runs into OOM issues.
           * Grab a permanent reference to it, so that the normal code flow
           * will not attempt to free it.  oom_cfqq is linked to root_group
           * but shouldn't hold a reference as it'll never be unlinked.  Lose
           * the reference from linking right away.
           */
          cfq_init_cfqq(cfqd, &cfqd->oom_cfqq, 1, 0);
          cfqd->oom_cfqq.ref++;
  
          spin_lock_irq(q->queue_lock);
          cfq_link_cfqq_cfqg(&cfqd->oom_cfqq, cfqd->root_group);
          cfqg_put(cfqd->root_group);
          spin_unlock_irq(q->queue_lock);
  
          init_timer(&cfqd->idle_slice_timer);
          cfqd->idle_slice_timer.function = cfq_idle_slice_timer;
          cfqd->idle_slice_timer.data = (unsigned long) cfqd;
  
          INIT_WORK(&cfqd->unplug_work, cfq_kick_queue);
  
          cfqd->cfq_quantum = cfq_quantum;
          cfqd->cfq_fifo_expire[0] = cfq_fifo_expire[0];
          cfqd->cfq_fifo_expire[1] = cfq_fifo_expire[1];
          cfqd->cfq_back_max = cfq_back_max;
          cfqd->cfq_back_penalty = cfq_back_penalty;
          cfqd->cfq_slice[0] = cfq_slice_async;
          cfqd->cfq_slice[1] = cfq_slice_sync;
          cfqd->cfq_target_latency = cfq_target_latency;
          cfqd->cfq_slice_async_rq = cfq_slice_async_rq;
          cfqd->cfq_slice_idle = cfq_slice_idle;
          cfqd->cfq_group_idle = cfq_group_idle;
          cfqd->cfq_latency = 1;
          cfqd->hw_tag = -1;
          /*
           * we optimistically start assuming sync ops weren't delayed in last
           * second, in order to have larger depth for async operations.
           */
          cfqd->last_delayed_sync = jiffies - HZ;
          return 0;
  
  out_free:
          kfree(cfqd);
          return ret;
  }
  
  /*
   * sysfs parts below -->
   */
  static ssize_t
  cfq_var_show(unsigned int var, char *page)
  {
          return sprintf(page, "%d\n", var);
  }
  
  static ssize_t
  cfq_var_store(unsigned int *var, const char *page, size_t count)
  {
          char *p = (char *) page;
  
          *var = simple_strtoul(p, &p, 10);
          return count;
  }
  
  #define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
  static ssize_t __FUNC(struct elevator_queue *e, char *page)             \
  {                                                                       \
          struct cfq_data *cfqd = e->elevator_data;                       \
          unsigned int __data = __VAR;                                    \
          if (__CONV)                                                     \
                  __data = jiffies_to_msecs(__data);                      \
          return cfq_var_show(__data, (page));                            \
  }
  SHOW_FUNCTION(cfq_quantum_show, cfqd->cfq_quantum, 0);
  SHOW_FUNCTION(cfq_fifo_expire_sync_show, cfqd->cfq_fifo_expire[1], 1);
  SHOW_FUNCTION(cfq_fifo_expire_async_show, cfqd->cfq_fifo_expire[0], 1);
  SHOW_FUNCTION(cfq_back_seek_max_show, cfqd->cfq_back_max, 0);
  SHOW_FUNCTION(cfq_back_seek_penalty_show, cfqd->cfq_back_penalty, 0);
  SHOW_FUNCTION(cfq_slice_idle_show, cfqd->cfq_slice_idle, 1);
  SHOW_FUNCTION(cfq_group_idle_show, cfqd->cfq_group_idle, 1);
  SHOW_FUNCTION(cfq_slice_sync_show, cfqd->cfq_slice[1], 1);
  SHOW_FUNCTION(cfq_slice_async_show, cfqd->cfq_slice[0], 1);
  SHOW_FUNCTION(cfq_slice_async_rq_show, cfqd->cfq_slice_async_rq, 0);
  SHOW_FUNCTION(cfq_low_latency_show, cfqd->cfq_latency, 0);
  SHOW_FUNCTION(cfq_target_latency_show, cfqd->cfq_target_latency, 1);
  #undef SHOW_FUNCTION
  
  #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
  static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
  {                                                                       \
          struct cfq_data *cfqd = e->elevator_data;                       \
          unsigned int __data;                                            \
          int ret = cfq_var_store(&__data, (page), count);                \
          if (__data < (MIN))                                             \
                  __data = (MIN);                                         \
          else if (__data > (MAX))                                        \
                  __data = (MAX);                                         \
          if (__CONV)                                                     \
                  *(__PTR) = msecs_to_jiffies(__data);                    \
          else                                                            \
                  *(__PTR) = __data;                                      \
          return ret;                                                     \
  }
  STORE_FUNCTION(cfq_quantum_store, &cfqd->cfq_quantum, 1, UINT_MAX, 0);
  STORE_FUNCTION(cfq_fifo_expire_sync_store, &cfqd->cfq_fifo_expire[1], 1,
                  UINT_MAX, 1);
  STORE_FUNCTION(cfq_fifo_expire_async_store, &cfqd->cfq_fifo_expire[0], 1,
                  UINT_MAX, 1);
  STORE_FUNCTION(cfq_back_seek_max_store, &cfqd->cfq_back_max, 0, UINT_MAX, 0);
  STORE_FUNCTION(cfq_back_seek_penalty_store, &cfqd->cfq_back_penalty, 1,
                  UINT_MAX, 0);
  STORE_FUNCTION(cfq_slice_idle_store, &cfqd->cfq_slice_idle, 0, UINT_MAX, 1);
  STORE_FUNCTION(cfq_group_idle_store, &cfqd->cfq_group_idle, 0, UINT_MAX, 1);
  STORE_FUNCTION(cfq_slice_sync_store, &cfqd->cfq_slice[1], 1, UINT_MAX, 1);
  STORE_FUNCTION(cfq_slice_async_store, &cfqd->cfq_slice[0], 1, UINT_MAX, 1);
  STORE_FUNCTION(cfq_slice_async_rq_store, &cfqd->cfq_slice_async_rq, 1,
                  UINT_MAX, 0);
  STORE_FUNCTION(cfq_low_latency_store, &cfqd->cfq_latency, 0, 1, 0);
  STORE_FUNCTION(cfq_target_latency_store, &cfqd->cfq_target_latency, 1, UINT_MAX, 1);
  #undef STORE_FUNCTION
  
  #define CFQ_ATTR(name) \
          __ATTR(name, S_IRUGO|S_IWUSR, cfq_##name##_show, cfq_##name##_store)
  
  static struct elv_fs_entry cfq_attrs[] = {
          CFQ_ATTR(quantum),
          CFQ_ATTR(fifo_expire_sync),
          CFQ_ATTR(fifo_expire_async),
          CFQ_ATTR(back_seek_max),
          CFQ_ATTR(back_seek_penalty),
          CFQ_ATTR(slice_sync),
          CFQ_ATTR(slice_async),
          CFQ_ATTR(slice_async_rq),
          CFQ_ATTR(slice_idle),
          CFQ_ATTR(group_idle),
          CFQ_ATTR(low_latency),
          CFQ_ATTR(target_latency),
          __ATTR_NULL
  };
  
  static struct elevator_type iosched_cfq = {
          .ops = {
                  .elevator_merge_fn =            cfq_merge,
                  .elevator_merged_fn =           cfq_merged_request,
                  .elevator_merge_req_fn =        cfq_merged_requests,
                  .elevator_allow_merge_fn =      cfq_allow_merge,
                  .elevator_bio_merged_fn =       cfq_bio_merged,
                  .elevator_dispatch_fn =         cfq_dispatch_requests,
                  .elevator_add_req_fn =          cfq_insert_request,
                  .elevator_activate_req_fn =     cfq_activate_request,
                  .elevator_deactivate_req_fn =   cfq_deactivate_request,
                  .elevator_completed_req_fn =    cfq_completed_request,
                  .elevator_former_req_fn =       elv_rb_former_request,
                  .elevator_latter_req_fn =       elv_rb_latter_request,
                  .elevator_init_icq_fn =         cfq_init_icq,
                  .elevator_exit_icq_fn =         cfq_exit_icq,
                  .elevator_set_req_fn =          cfq_set_request,
                  .elevator_put_req_fn =          cfq_put_request,
                  .elevator_may_queue_fn =        cfq_may_queue,
                  .elevator_init_fn =             cfq_init_queue,
                  .elevator_exit_fn =             cfq_exit_queue,
          },
          .icq_size       =       sizeof(struct cfq_io_cq),
          .icq_align      =       __alignof__(struct cfq_io_cq),
          .elevator_attrs =       cfq_attrs,
          .elevator_name  =       "cfq",
          .elevator_owner =       THIS_MODULE,
  };
  
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
  static struct blkcg_policy blkcg_policy_cfq = {
          .pd_size                = sizeof(struct cfq_group),
          .cftypes                = cfq_blkcg_files,
  
          .pd_init_fn             = cfq_pd_init,
          .pd_reset_stats_fn      = cfq_pd_reset_stats,
  };
  #endif
  
  static int __init cfq_init(void)
  {
          int ret;
  
          /*
           * could be 0 on HZ < 1000 setups
           */
          if (!cfq_slice_async)
                  cfq_slice_async = 1;
          if (!cfq_slice_idle)
                  cfq_slice_idle = 1;
  
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
          if (!cfq_group_idle)
                  cfq_group_idle = 1;
  
          ret = blkcg_policy_register(&blkcg_policy_cfq);
          if (ret)
                  return ret;
  #else
          cfq_group_idle = 0;
  #endif
  
          ret = -ENOMEM;
          cfq_pool = KMEM_CACHE(cfq_queue, 0);
          if (!cfq_pool)
                  goto err_pol_unreg;
  
          ret = elv_register(&iosched_cfq);
          if (ret)
                  goto err_free_pool;
  
          return 0;
  
  err_free_pool:
          kmem_cache_destroy(cfq_pool);
  err_pol_unreg:
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
          blkcg_policy_unregister(&blkcg_policy_cfq);
  #endif
          return ret;
  }
  
  static void __exit cfq_exit(void)
  {
  #ifdef CONFIG_CFQ_GROUP_IOSCHED
          blkcg_policy_unregister(&blkcg_policy_cfq);
  #endif
          elv_unregister(&iosched_cfq);
          kmem_cache_destroy(cfq_pool);
  }
  
  module_init(cfq_init);
  module_exit(cfq_exit);
  
  MODULE_AUTHOR("Jens Axboe");
  MODULE_LICENSE("GPL");
  MODULE_DESCRIPTION("Completely Fair Queueing IO scheduler");