FreeBSD/Linux Kernel Cross Reference
sys/block/blk-iopoll.c

     /*
      * Functions related to interrupt-poll handling in the block layer. This
      * is similar to NAPI for network devices.
      */
     #include <linux/kernel.h>
     #include <linux/module.h>
     #include <linux/init.h>
     #include <linux/bio.h>
     #include <linux/blkdev.h>
    #include <linux/interrupt.h>
    #include <linux/cpu.h>
    #include <linux/blk-iopoll.h>
    #include <linux/delay.h>
    
    #include "blk.h"
    
    int blk_iopoll_enabled = 1;
    EXPORT_SYMBOL(blk_iopoll_enabled);
    
    static unsigned int blk_iopoll_budget __read_mostly = 256;
    
    static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
    
    /**
     * blk_iopoll_sched - Schedule a run of the iopoll handler
     * @iop:      The parent iopoll structure
     *
     * Description:
     *     Add this blk_iopoll structure to the pending poll list and trigger the
     *     raise of the blk iopoll softirq. The driver must already have gotten a
     *     successful return from blk_iopoll_sched_prep() before calling this.
     **/
    void blk_iopoll_sched(struct blk_iopoll *iop)
    {
            unsigned long flags;
    
            local_irq_save(flags);
            list_add_tail(&iop->list, &__get_cpu_var(blk_cpu_iopoll));
            __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
            local_irq_restore(flags);
    }
    EXPORT_SYMBOL(blk_iopoll_sched);
    
    /**
     * __blk_iopoll_complete - Mark this @iop as un-polled again
     * @iop:      The parent iopoll structure
     *
     * Description:
     *     See blk_iopoll_complete(). This function must be called with interrupts
     *     disabled.
     **/
    void __blk_iopoll_complete(struct blk_iopoll *iop)
    {
            list_del(&iop->list);
            smp_mb__before_clear_bit();
            clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
    }
    EXPORT_SYMBOL(__blk_iopoll_complete);
    
    /**
     * blk_iopoll_complete - Mark this @iop as un-polled again
     * @iop:      The parent iopoll structure
     *
     * Description:
     *     If a driver consumes less than the assigned budget in its run of the
     *     iopoll handler, it'll end the polled mode by calling this function. The
     *     iopoll handler will not be invoked again before blk_iopoll_sched_prep()
     *     is called.
     **/
    void blk_iopoll_complete(struct blk_iopoll *iopoll)
    {
            unsigned long flags;
    
            local_irq_save(flags);
            __blk_iopoll_complete(iopoll);
            local_irq_restore(flags);
    }
    EXPORT_SYMBOL(blk_iopoll_complete);
    
    static void blk_iopoll_softirq(struct softirq_action *h)
    {
            struct list_head *list = &__get_cpu_var(blk_cpu_iopoll);
            int rearm = 0, budget = blk_iopoll_budget;
            unsigned long start_time = jiffies;
    
            local_irq_disable();
    
            while (!list_empty(list)) {
                    struct blk_iopoll *iop;
                    int work, weight;
    
                    /*
                     * If softirq window is exhausted then punt.
                     */
                    if (budget <= 0 || time_after(jiffies, start_time)) {
                            rearm = 1;
                            break;
                    }
    
                   local_irq_enable();
   
                   /* Even though interrupts have been re-enabled, this
                    * access is safe because interrupts can only add new
                    * entries to the tail of this list, and only ->poll()
                    * calls can remove this head entry from the list.
                    */
                   iop = list_entry(list->next, struct blk_iopoll, list);
   
                   weight = iop->weight;
                   work = 0;
                   if (test_bit(IOPOLL_F_SCHED, &iop->state))
                           work = iop->poll(iop, weight);
   
                   budget -= work;
   
                   local_irq_disable();
   
                   /*
                    * Drivers must not modify the iopoll state, if they
                    * consume their assigned weight (or more, some drivers can't
                    * easily just stop processing, they have to complete an
                    * entire mask of commands).In such cases this code
                    * still "owns" the iopoll instance and therefore can
                    * move the instance around on the list at-will.
                    */
                   if (work >= weight) {
                           if (blk_iopoll_disable_pending(iop))
                                   __blk_iopoll_complete(iop);
                           else
                                   list_move_tail(&iop->list, list);
                   }
           }
   
           if (rearm)
                   __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
   
           local_irq_enable();
   }
   
   /**
    * blk_iopoll_disable - Disable iopoll on this @iop
    * @iop:      The parent iopoll structure
    *
    * Description:
    *     Disable io polling and wait for any pending callbacks to have completed.
    **/
   void blk_iopoll_disable(struct blk_iopoll *iop)
   {
           set_bit(IOPOLL_F_DISABLE, &iop->state);
           while (test_and_set_bit(IOPOLL_F_SCHED, &iop->state))
                   msleep(1);
           clear_bit(IOPOLL_F_DISABLE, &iop->state);
   }
   EXPORT_SYMBOL(blk_iopoll_disable);
   
   /**
    * blk_iopoll_enable - Enable iopoll on this @iop
    * @iop:      The parent iopoll structure
    *
    * Description:
    *     Enable iopoll on this @iop. Note that the handler run will not be
    *     scheduled, it will only mark it as active.
    **/
   void blk_iopoll_enable(struct blk_iopoll *iop)
   {
           BUG_ON(!test_bit(IOPOLL_F_SCHED, &iop->state));
           smp_mb__before_clear_bit();
           clear_bit_unlock(IOPOLL_F_SCHED, &iop->state);
   }
   EXPORT_SYMBOL(blk_iopoll_enable);
   
   /**
    * blk_iopoll_init - Initialize this @iop
    * @iop:      The parent iopoll structure
    * @weight:   The default weight (or command completion budget)
    * @poll_fn:  The handler to invoke
    *
    * Description:
    *     Initialize this blk_iopoll structure. Before being actively used, the
    *     driver must call blk_iopoll_enable().
    **/
   void blk_iopoll_init(struct blk_iopoll *iop, int weight, blk_iopoll_fn *poll_fn)
   {
           memset(iop, 0, sizeof(*iop));
           INIT_LIST_HEAD(&iop->list);
           iop->weight = weight;
           iop->poll = poll_fn;
           set_bit(IOPOLL_F_SCHED, &iop->state);
   }
   EXPORT_SYMBOL(blk_iopoll_init);
   
   static int __cpuinit blk_iopoll_cpu_notify(struct notifier_block *self,
                                             unsigned long action, void *hcpu)
   {
           /*
            * If a CPU goes away, splice its entries to the current CPU
            * and trigger a run of the softirq
            */
           if (action == CPU_DEAD || action == CPU_DEAD_FROZEN) {
                   int cpu = (unsigned long) hcpu;
   
                   local_irq_disable();
                   list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
                                    &__get_cpu_var(blk_cpu_iopoll));
                   __raise_softirq_irqoff(BLOCK_IOPOLL_SOFTIRQ);
                   local_irq_enable();
           }
   
           return NOTIFY_OK;
   }
   
   static struct notifier_block __cpuinitdata blk_iopoll_cpu_notifier = {
           .notifier_call  = blk_iopoll_cpu_notify,
   };
   
   static __init int blk_iopoll_setup(void)
   {
           int i;
   
           for_each_possible_cpu(i)
                   INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
   
           open_softirq(BLOCK_IOPOLL_SOFTIRQ, blk_iopoll_softirq);
           register_hotcpu_notifier(&blk_iopoll_cpu_notifier);
           return 0;
   }
   subsys_initcall(blk_iopoll_setup);

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