FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/vdev_queue.c

     /*
      * CDDL HEADER START
      *
      * The contents of this file are subject to the terms of the
      * Common Development and Distribution License (the "License").
      * You may not use this file except in compliance with the License.
      *
      * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
      * or https://opensource.org/licenses/CDDL-1.0.
     * See the License for the specific language governing permissions
     * and limitations under the License.
     *
     * When distributing Covered Code, include this CDDL HEADER in each
     * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     * If applicable, add the following below this CDDL HEADER, with the
     * fields enclosed by brackets "[]" replaced with your own identifying
     * information: Portions Copyright [yyyy] [name of copyright owner]
     *
     * CDDL HEADER END
     */
    /*
     * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
     * Use is subject to license terms.
     */
    
    /*
     * Copyright (c) 2012, 2018 by Delphix. All rights reserved.
     */
    
    #include <sys/zfs_context.h>
    #include <sys/vdev_impl.h>
    #include <sys/spa_impl.h>
    #include <sys/zio.h>
    #include <sys/avl.h>
    #include <sys/dsl_pool.h>
    #include <sys/metaslab_impl.h>
    #include <sys/spa.h>
    #include <sys/abd.h>
    
    /*
     * ZFS I/O Scheduler
     * ---------------
     *
     * ZFS issues I/O operations to leaf vdevs to satisfy and complete zios.  The
     * I/O scheduler determines when and in what order those operations are
     * issued.  The I/O scheduler divides operations into five I/O classes
     * prioritized in the following order: sync read, sync write, async read,
     * async write, and scrub/resilver.  Each queue defines the minimum and
     * maximum number of concurrent operations that may be issued to the device.
     * In addition, the device has an aggregate maximum. Note that the sum of the
     * per-queue minimums must not exceed the aggregate maximum. If the
     * sum of the per-queue maximums exceeds the aggregate maximum, then the
     * number of active i/os may reach zfs_vdev_max_active, in which case no
     * further i/os will be issued regardless of whether all per-queue
     * minimums have been met.
     *
     * For many physical devices, throughput increases with the number of
     * concurrent operations, but latency typically suffers. Further, physical
     * devices typically have a limit at which more concurrent operations have no
     * effect on throughput or can actually cause it to decrease.
     *
     * The scheduler selects the next operation to issue by first looking for an
     * I/O class whose minimum has not been satisfied. Once all are satisfied and
     * the aggregate maximum has not been hit, the scheduler looks for classes
     * whose maximum has not been satisfied. Iteration through the I/O classes is
     * done in the order specified above. No further operations are issued if the
     * aggregate maximum number of concurrent operations has been hit or if there
     * are no operations queued for an I/O class that has not hit its maximum.
     * Every time an i/o is queued or an operation completes, the I/O scheduler
     * looks for new operations to issue.
     *
     * All I/O classes have a fixed maximum number of outstanding operations
     * except for the async write class. Asynchronous writes represent the data
     * that is committed to stable storage during the syncing stage for
     * transaction groups (see txg.c). Transaction groups enter the syncing state
     * periodically so the number of queued async writes will quickly burst up and
     * then bleed down to zero. Rather than servicing them as quickly as possible,
     * the I/O scheduler changes the maximum number of active async write i/os
     * according to the amount of dirty data in the pool (see dsl_pool.c). Since
     * both throughput and latency typically increase with the number of
     * concurrent operations issued to physical devices, reducing the burstiness
     * in the number of concurrent operations also stabilizes the response time of
     * operations from other -- and in particular synchronous -- queues. In broad
     * strokes, the I/O scheduler will issue more concurrent operations from the
     * async write queue as there's more dirty data in the pool.
     *
     * Async Writes
     *
     * The number of concurrent operations issued for the async write I/O class
     * follows a piece-wise linear function defined by a few adjustable points.
     *
     *        |                   o---------| <-- zfs_vdev_async_write_max_active
     *   ^    |                  /^         |
     *   |    |                 / |         |
     * active |                /  |         |
     *  I/O   |               /   |         |
     * count  |              /    |         |
     *        |             /     |         |
     *        |------------o      |         | <-- zfs_vdev_async_write_min_active
    *       0|____________^______|_________|
    *        0%           |      |       100% of zfs_dirty_data_max
    *                     |      |
    *                     |      `-- zfs_vdev_async_write_active_max_dirty_percent
    *                     `--------- zfs_vdev_async_write_active_min_dirty_percent
    *
    * Until the amount of dirty data exceeds a minimum percentage of the dirty
    * data allowed in the pool, the I/O scheduler will limit the number of
    * concurrent operations to the minimum. As that threshold is crossed, the
    * number of concurrent operations issued increases linearly to the maximum at
    * the specified maximum percentage of the dirty data allowed in the pool.
    *
    * Ideally, the amount of dirty data on a busy pool will stay in the sloped
    * part of the function between zfs_vdev_async_write_active_min_dirty_percent
    * and zfs_vdev_async_write_active_max_dirty_percent. If it exceeds the
    * maximum percentage, this indicates that the rate of incoming data is
    * greater than the rate that the backend storage can handle. In this case, we
    * must further throttle incoming writes (see dmu_tx_delay() for details).
    */
   
   /*
    * The maximum number of i/os active to each device.  Ideally, this will be >=
    * the sum of each queue's max_active.
    */
   uint_t zfs_vdev_max_active = 1000;
   
   /*
    * Per-queue limits on the number of i/os active to each device.  If the
    * number of active i/os is < zfs_vdev_max_active, then the min_active comes
    * into play.  We will send min_active from each queue round-robin, and then
    * send from queues in the order defined by zio_priority_t up to max_active.
    * Some queues have additional mechanisms to limit number of active I/Os in
    * addition to min_active and max_active, see below.
    *
    * In general, smaller max_active's will lead to lower latency of synchronous
    * operations.  Larger max_active's may lead to higher overall throughput,
    * depending on underlying storage.
    *
    * The ratio of the queues' max_actives determines the balance of performance
    * between reads, writes, and scrubs.  E.g., increasing
    * zfs_vdev_scrub_max_active will cause the scrub or resilver to complete
    * more quickly, but reads and writes to have higher latency and lower
    * throughput.
    */
   static uint_t zfs_vdev_sync_read_min_active = 10;
   static uint_t zfs_vdev_sync_read_max_active = 10;
   static uint_t zfs_vdev_sync_write_min_active = 10;
   static uint_t zfs_vdev_sync_write_max_active = 10;
   static uint_t zfs_vdev_async_read_min_active = 1;
   /*  */ uint_t zfs_vdev_async_read_max_active = 3;
   static uint_t zfs_vdev_async_write_min_active = 2;
   /*  */ uint_t zfs_vdev_async_write_max_active = 10;
   static uint_t zfs_vdev_scrub_min_active = 1;
   static uint_t zfs_vdev_scrub_max_active = 3;
   static uint_t zfs_vdev_removal_min_active = 1;
   static uint_t zfs_vdev_removal_max_active = 2;
   static uint_t zfs_vdev_initializing_min_active = 1;
   static uint_t zfs_vdev_initializing_max_active = 1;
   static uint_t zfs_vdev_trim_min_active = 1;
   static uint_t zfs_vdev_trim_max_active = 2;
   static uint_t zfs_vdev_rebuild_min_active = 1;
   static uint_t zfs_vdev_rebuild_max_active = 3;
   
   /*
    * When the pool has less than zfs_vdev_async_write_active_min_dirty_percent
    * dirty data, use zfs_vdev_async_write_min_active.  When it has more than
    * zfs_vdev_async_write_active_max_dirty_percent, use
    * zfs_vdev_async_write_max_active. The value is linearly interpolated
    * between min and max.
    */
   uint_t zfs_vdev_async_write_active_min_dirty_percent = 30;
   uint_t zfs_vdev_async_write_active_max_dirty_percent = 60;
   
   /*
    * For non-interactive I/O (scrub, resilver, removal, initialize and rebuild),
    * the number of concurrently-active I/O's is limited to *_min_active, unless
    * the vdev is "idle".  When there are no interactive I/Os active (sync or
    * async), and zfs_vdev_nia_delay I/Os have completed since the last
    * interactive I/O, then the vdev is considered to be "idle", and the number
    * of concurrently-active non-interactive I/O's is increased to *_max_active.
    */
   static uint_t zfs_vdev_nia_delay = 5;
   
   /*
    * Some HDDs tend to prioritize sequential I/O so high that concurrent
    * random I/O latency reaches several seconds.  On some HDDs it happens
    * even if sequential I/Os are submitted one at a time, and so setting
    * *_max_active to 1 does not help.  To prevent non-interactive I/Os, like
    * scrub, from monopolizing the device no more than zfs_vdev_nia_credit
    * I/Os can be sent while there are outstanding incomplete interactive
    * I/Os.  This enforced wait ensures the HDD services the interactive I/O
    * within a reasonable amount of time.
    */
   static uint_t zfs_vdev_nia_credit = 5;
   
   /*
    * To reduce IOPs, we aggregate small adjacent I/Os into one large I/O.
    * For read I/Os, we also aggregate across small adjacency gaps; for writes
    * we include spans of optional I/Os to aid aggregation at the disk even when
    * they aren't able to help us aggregate at this level.
    */
   static uint_t zfs_vdev_aggregation_limit = 1 << 20;
   static uint_t zfs_vdev_aggregation_limit_non_rotating = SPA_OLD_MAXBLOCKSIZE;
   static uint_t zfs_vdev_read_gap_limit = 32 << 10;
   static uint_t zfs_vdev_write_gap_limit = 4 << 10;
   
   /*
    * Define the queue depth percentage for each top-level. This percentage is
    * used in conjunction with zfs_vdev_async_max_active to determine how many
    * allocations a specific top-level vdev should handle. Once the queue depth
    * reaches zfs_vdev_queue_depth_pct * zfs_vdev_async_write_max_active / 100
    * then allocator will stop allocating blocks on that top-level device.
    * The default kernel setting is 1000% which will yield 100 allocations per
    * device. For userland testing, the default setting is 300% which equates
    * to 30 allocations per device.
    */
   #ifdef _KERNEL
   uint_t zfs_vdev_queue_depth_pct = 1000;
   #else
   uint_t zfs_vdev_queue_depth_pct = 300;
   #endif
   
   /*
    * When performing allocations for a given metaslab, we want to make sure that
    * there are enough IOs to aggregate together to improve throughput. We want to
    * ensure that there are at least 128k worth of IOs that can be aggregated, and
    * we assume that the average allocation size is 4k, so we need the queue depth
    * to be 32 per allocator to get good aggregation of sequential writes.
    */
   uint_t zfs_vdev_def_queue_depth = 32;
   
   /*
    * Allow TRIM I/Os to be aggregated.  This should normally not be needed since
    * TRIM I/O for extents up to zfs_trim_extent_bytes_max (128M) can be submitted
    * by the TRIM code in zfs_trim.c.
    */
   static uint_t zfs_vdev_aggregate_trim = 0;
   
   static int
   vdev_queue_offset_compare(const void *x1, const void *x2)
   {
           const zio_t *z1 = (const zio_t *)x1;
           const zio_t *z2 = (const zio_t *)x2;
   
           int cmp = TREE_CMP(z1->io_offset, z2->io_offset);
   
           if (likely(cmp))
                   return (cmp);
   
           return (TREE_PCMP(z1, z2));
   }
   
   static inline avl_tree_t *
   vdev_queue_class_tree(vdev_queue_t *vq, zio_priority_t p)
   {
           return (&vq->vq_class[p].vqc_queued_tree);
   }
   
   static inline avl_tree_t *
   vdev_queue_type_tree(vdev_queue_t *vq, zio_type_t t)
   {
           ASSERT(t == ZIO_TYPE_READ || t == ZIO_TYPE_WRITE || t == ZIO_TYPE_TRIM);
           if (t == ZIO_TYPE_READ)
                   return (&vq->vq_read_offset_tree);
           else if (t == ZIO_TYPE_WRITE)
                   return (&vq->vq_write_offset_tree);
           else
                   return (&vq->vq_trim_offset_tree);
   }
   
   static int
   vdev_queue_timestamp_compare(const void *x1, const void *x2)
   {
           const zio_t *z1 = (const zio_t *)x1;
           const zio_t *z2 = (const zio_t *)x2;
   
           int cmp = TREE_CMP(z1->io_timestamp, z2->io_timestamp);
   
           if (likely(cmp))
                   return (cmp);
   
           return (TREE_PCMP(z1, z2));
   }
   
   static uint_t
   vdev_queue_class_min_active(vdev_queue_t *vq, zio_priority_t p)
   {
           switch (p) {
           case ZIO_PRIORITY_SYNC_READ:
                   return (zfs_vdev_sync_read_min_active);
           case ZIO_PRIORITY_SYNC_WRITE:
                   return (zfs_vdev_sync_write_min_active);
           case ZIO_PRIORITY_ASYNC_READ:
                   return (zfs_vdev_async_read_min_active);
           case ZIO_PRIORITY_ASYNC_WRITE:
                   return (zfs_vdev_async_write_min_active);
           case ZIO_PRIORITY_SCRUB:
                   return (vq->vq_ia_active == 0 ? zfs_vdev_scrub_min_active :
                       MIN(vq->vq_nia_credit, zfs_vdev_scrub_min_active));
           case ZIO_PRIORITY_REMOVAL:
                   return (vq->vq_ia_active == 0 ? zfs_vdev_removal_min_active :
                       MIN(vq->vq_nia_credit, zfs_vdev_removal_min_active));
           case ZIO_PRIORITY_INITIALIZING:
                   return (vq->vq_ia_active == 0 ?zfs_vdev_initializing_min_active:
                       MIN(vq->vq_nia_credit, zfs_vdev_initializing_min_active));
           case ZIO_PRIORITY_TRIM:
                   return (zfs_vdev_trim_min_active);
           case ZIO_PRIORITY_REBUILD:
                   return (vq->vq_ia_active == 0 ? zfs_vdev_rebuild_min_active :
                       MIN(vq->vq_nia_credit, zfs_vdev_rebuild_min_active));
           default:
                   panic("invalid priority %u", p);
                   return (0);
           }
   }
   
   static uint_t
   vdev_queue_max_async_writes(spa_t *spa)
   {
           uint_t writes;
           uint64_t dirty = 0;
           dsl_pool_t *dp = spa_get_dsl(spa);
           uint64_t min_bytes = zfs_dirty_data_max *
               zfs_vdev_async_write_active_min_dirty_percent / 100;
           uint64_t max_bytes = zfs_dirty_data_max *
               zfs_vdev_async_write_active_max_dirty_percent / 100;
   
           /*
            * Async writes may occur before the assignment of the spa's
            * dsl_pool_t if a self-healing zio is issued prior to the
            * completion of dmu_objset_open_impl().
            */
           if (dp == NULL)
                   return (zfs_vdev_async_write_max_active);
   
           /*
            * Sync tasks correspond to interactive user actions. To reduce the
            * execution time of those actions we push data out as fast as possible.
            */
           dirty = dp->dp_dirty_total;
           if (dirty > max_bytes || spa_has_pending_synctask(spa))
                   return (zfs_vdev_async_write_max_active);
   
           if (dirty < min_bytes)
                   return (zfs_vdev_async_write_min_active);
   
           /*
            * linear interpolation:
            * slope = (max_writes - min_writes) / (max_bytes - min_bytes)
            * move right by min_bytes
            * move up by min_writes
            */
           writes = (dirty - min_bytes) *
               (zfs_vdev_async_write_max_active -
               zfs_vdev_async_write_min_active) /
               (max_bytes - min_bytes) +
               zfs_vdev_async_write_min_active;
           ASSERT3U(writes, >=, zfs_vdev_async_write_min_active);
           ASSERT3U(writes, <=, zfs_vdev_async_write_max_active);
           return (writes);
   }
   
   static uint_t
   vdev_queue_class_max_active(spa_t *spa, vdev_queue_t *vq, zio_priority_t p)
   {
           switch (p) {
           case ZIO_PRIORITY_SYNC_READ:
                   return (zfs_vdev_sync_read_max_active);
           case ZIO_PRIORITY_SYNC_WRITE:
                   return (zfs_vdev_sync_write_max_active);
           case ZIO_PRIORITY_ASYNC_READ:
                   return (zfs_vdev_async_read_max_active);
           case ZIO_PRIORITY_ASYNC_WRITE:
                   return (vdev_queue_max_async_writes(spa));
           case ZIO_PRIORITY_SCRUB:
                   if (vq->vq_ia_active > 0) {
                           return (MIN(vq->vq_nia_credit,
                               zfs_vdev_scrub_min_active));
                   } else if (vq->vq_nia_credit < zfs_vdev_nia_delay)
                           return (MAX(1, zfs_vdev_scrub_min_active));
                   return (zfs_vdev_scrub_max_active);
           case ZIO_PRIORITY_REMOVAL:
                   if (vq->vq_ia_active > 0) {
                           return (MIN(vq->vq_nia_credit,
                               zfs_vdev_removal_min_active));
                   } else if (vq->vq_nia_credit < zfs_vdev_nia_delay)
                           return (MAX(1, zfs_vdev_removal_min_active));
                   return (zfs_vdev_removal_max_active);
           case ZIO_PRIORITY_INITIALIZING:
                   if (vq->vq_ia_active > 0) {
                           return (MIN(vq->vq_nia_credit,
                               zfs_vdev_initializing_min_active));
                   } else if (vq->vq_nia_credit < zfs_vdev_nia_delay)
                           return (MAX(1, zfs_vdev_initializing_min_active));
                   return (zfs_vdev_initializing_max_active);
           case ZIO_PRIORITY_TRIM:
                   return (zfs_vdev_trim_max_active);
           case ZIO_PRIORITY_REBUILD:
                   if (vq->vq_ia_active > 0) {
                           return (MIN(vq->vq_nia_credit,
                               zfs_vdev_rebuild_min_active));
                   } else if (vq->vq_nia_credit < zfs_vdev_nia_delay)
                           return (MAX(1, zfs_vdev_rebuild_min_active));
                   return (zfs_vdev_rebuild_max_active);
           default:
                   panic("invalid priority %u", p);
                   return (0);
           }
   }
   
   /*
    * Return the i/o class to issue from, or ZIO_PRIORITY_NUM_QUEUEABLE if
    * there is no eligible class.
    */
   static zio_priority_t
   vdev_queue_class_to_issue(vdev_queue_t *vq)
   {
           spa_t *spa = vq->vq_vdev->vdev_spa;
           zio_priority_t p, n;
   
           if (avl_numnodes(&vq->vq_active_tree) >= zfs_vdev_max_active)
                   return (ZIO_PRIORITY_NUM_QUEUEABLE);
   
           /*
            * Find a queue that has not reached its minimum # outstanding i/os.
            * Do round-robin to reduce starvation due to zfs_vdev_max_active
            * and vq_nia_credit limits.
            */
           for (n = 0; n < ZIO_PRIORITY_NUM_QUEUEABLE; n++) {
                   p = (vq->vq_last_prio + n + 1) % ZIO_PRIORITY_NUM_QUEUEABLE;
                   if (avl_numnodes(vdev_queue_class_tree(vq, p)) > 0 &&
                       vq->vq_class[p].vqc_active <
                       vdev_queue_class_min_active(vq, p)) {
                           vq->vq_last_prio = p;
                           return (p);
                   }
           }
   
           /*
            * If we haven't found a queue, look for one that hasn't reached its
            * maximum # outstanding i/os.
            */
           for (p = 0; p < ZIO_PRIORITY_NUM_QUEUEABLE; p++) {
                   if (avl_numnodes(vdev_queue_class_tree(vq, p)) > 0 &&
                       vq->vq_class[p].vqc_active <
                       vdev_queue_class_max_active(spa, vq, p)) {
                           vq->vq_last_prio = p;
                           return (p);
                   }
           }
   
           /* No eligible queued i/os */
           return (ZIO_PRIORITY_NUM_QUEUEABLE);
   }
   
   void
   vdev_queue_init(vdev_t *vd)
   {
           vdev_queue_t *vq = &vd->vdev_queue;
           zio_priority_t p;
   
           mutex_init(&vq->vq_lock, NULL, MUTEX_DEFAULT, NULL);
           vq->vq_vdev = vd;
           taskq_init_ent(&vd->vdev_queue.vq_io_search.io_tqent);
   
           avl_create(&vq->vq_active_tree, vdev_queue_offset_compare,
               sizeof (zio_t), offsetof(struct zio, io_queue_node));
           avl_create(vdev_queue_type_tree(vq, ZIO_TYPE_READ),
               vdev_queue_offset_compare, sizeof (zio_t),
               offsetof(struct zio, io_offset_node));
           avl_create(vdev_queue_type_tree(vq, ZIO_TYPE_WRITE),
               vdev_queue_offset_compare, sizeof (zio_t),
               offsetof(struct zio, io_offset_node));
           avl_create(vdev_queue_type_tree(vq, ZIO_TYPE_TRIM),
               vdev_queue_offset_compare, sizeof (zio_t),
               offsetof(struct zio, io_offset_node));
   
           for (p = 0; p < ZIO_PRIORITY_NUM_QUEUEABLE; p++) {
                   int (*compfn) (const void *, const void *);
   
                   /*
                    * The synchronous/trim i/o queues are dispatched in FIFO rather
                    * than LBA order. This provides more consistent latency for
                    * these i/os.
                    */
                   if (p == ZIO_PRIORITY_SYNC_READ ||
                       p == ZIO_PRIORITY_SYNC_WRITE ||
                       p == ZIO_PRIORITY_TRIM) {
                           compfn = vdev_queue_timestamp_compare;
                   } else {
                           compfn = vdev_queue_offset_compare;
                   }
                   avl_create(vdev_queue_class_tree(vq, p), compfn,
                       sizeof (zio_t), offsetof(struct zio, io_queue_node));
           }
   
           vq->vq_last_offset = 0;
   }
   
   void
   vdev_queue_fini(vdev_t *vd)
   {
           vdev_queue_t *vq = &vd->vdev_queue;
   
           for (zio_priority_t p = 0; p < ZIO_PRIORITY_NUM_QUEUEABLE; p++)
                   avl_destroy(vdev_queue_class_tree(vq, p));
           avl_destroy(&vq->vq_active_tree);
           avl_destroy(vdev_queue_type_tree(vq, ZIO_TYPE_READ));
           avl_destroy(vdev_queue_type_tree(vq, ZIO_TYPE_WRITE));
           avl_destroy(vdev_queue_type_tree(vq, ZIO_TYPE_TRIM));
   
           mutex_destroy(&vq->vq_lock);
   }
   
   static void
   vdev_queue_io_add(vdev_queue_t *vq, zio_t *zio)
   {
           ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
           avl_add(vdev_queue_class_tree(vq, zio->io_priority), zio);
           avl_add(vdev_queue_type_tree(vq, zio->io_type), zio);
   }
   
   static void
   vdev_queue_io_remove(vdev_queue_t *vq, zio_t *zio)
   {
           ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
           avl_remove(vdev_queue_class_tree(vq, zio->io_priority), zio);
           avl_remove(vdev_queue_type_tree(vq, zio->io_type), zio);
   }
   
   static boolean_t
   vdev_queue_is_interactive(zio_priority_t p)
   {
           switch (p) {
           case ZIO_PRIORITY_SCRUB:
           case ZIO_PRIORITY_REMOVAL:
           case ZIO_PRIORITY_INITIALIZING:
           case ZIO_PRIORITY_REBUILD:
                   return (B_FALSE);
           default:
                   return (B_TRUE);
           }
   }
   
   static void
   vdev_queue_pending_add(vdev_queue_t *vq, zio_t *zio)
   {
           ASSERT(MUTEX_HELD(&vq->vq_lock));
           ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
           vq->vq_class[zio->io_priority].vqc_active++;
           if (vdev_queue_is_interactive(zio->io_priority)) {
                   if (++vq->vq_ia_active == 1)
                           vq->vq_nia_credit = 1;
           } else if (vq->vq_ia_active > 0) {
                   vq->vq_nia_credit--;
           }
           avl_add(&vq->vq_active_tree, zio);
   }
   
   static void
   vdev_queue_pending_remove(vdev_queue_t *vq, zio_t *zio)
   {
           ASSERT(MUTEX_HELD(&vq->vq_lock));
           ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
           vq->vq_class[zio->io_priority].vqc_active--;
           if (vdev_queue_is_interactive(zio->io_priority)) {
                   if (--vq->vq_ia_active == 0)
                           vq->vq_nia_credit = 0;
                   else
                           vq->vq_nia_credit = zfs_vdev_nia_credit;
           } else if (vq->vq_ia_active == 0)
                   vq->vq_nia_credit++;
           avl_remove(&vq->vq_active_tree, zio);
   }
   
   static void
   vdev_queue_agg_io_done(zio_t *aio)
   {
           abd_free(aio->io_abd);
   }
   
   /*
    * Compute the range spanned by two i/os, which is the endpoint of the last
    * (lio->io_offset + lio->io_size) minus start of the first (fio->io_offset).
    * Conveniently, the gap between fio and lio is given by -IO_SPAN(lio, fio);
    * thus fio and lio are adjacent if and only if IO_SPAN(lio, fio) == 0.
    */
   #define IO_SPAN(fio, lio) ((lio)->io_offset + (lio)->io_size - (fio)->io_offset)
   #define IO_GAP(fio, lio) (-IO_SPAN(lio, fio))
   
   /*
    * Sufficiently adjacent io_offset's in ZIOs will be aggregated. We do this
    * by creating a gang ABD from the adjacent ZIOs io_abd's. By using
    * a gang ABD we avoid doing memory copies to and from the parent,
    * child ZIOs. The gang ABD also accounts for gaps between adjacent
    * io_offsets by simply getting the zero ABD for writes or allocating
    * a new ABD for reads and placing them in the gang ABD as well.
    */
   static zio_t *
   vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
   {
           zio_t *first, *last, *aio, *dio, *mandatory, *nio;
           uint64_t maxgap = 0;
           uint64_t size;
           uint64_t limit;
           int maxblocksize;
           boolean_t stretch = B_FALSE;
           avl_tree_t *t = vdev_queue_type_tree(vq, zio->io_type);
           zio_flag_t flags = zio->io_flags & ZIO_FLAG_AGG_INHERIT;
           uint64_t next_offset;
           abd_t *abd;
   
           maxblocksize = spa_maxblocksize(vq->vq_vdev->vdev_spa);
           if (vq->vq_vdev->vdev_nonrot)
                   limit = zfs_vdev_aggregation_limit_non_rotating;
           else
                   limit = zfs_vdev_aggregation_limit;
           limit = MIN(limit, maxblocksize);
   
           if (zio->io_flags & ZIO_FLAG_DONT_AGGREGATE || limit == 0)
                   return (NULL);
   
           /*
            * While TRIM commands could be aggregated based on offset this
            * behavior is disabled until it's determined to be beneficial.
            */
           if (zio->io_type == ZIO_TYPE_TRIM && !zfs_vdev_aggregate_trim)
                   return (NULL);
   
           /*
            * I/Os to distributed spares are directly dispatched to the dRAID
            * leaf vdevs for aggregation.  See the comment at the end of the
            * zio_vdev_io_start() function.
            */
           ASSERT(vq->vq_vdev->vdev_ops != &vdev_draid_spare_ops);
   
           first = last = zio;
   
           if (zio->io_type == ZIO_TYPE_READ)
                   maxgap = zfs_vdev_read_gap_limit;
   
           /*
            * We can aggregate I/Os that are sufficiently adjacent and of
            * the same flavor, as expressed by the AGG_INHERIT flags.
            * The latter requirement is necessary so that certain
            * attributes of the I/O, such as whether it's a normal I/O
            * or a scrub/resilver, can be preserved in the aggregate.
            * We can include optional I/Os, but don't allow them
            * to begin a range as they add no benefit in that situation.
            */
   
           /*
            * We keep track of the last non-optional I/O.
            */
           mandatory = (first->io_flags & ZIO_FLAG_OPTIONAL) ? NULL : first;
   
           /*
            * Walk backwards through sufficiently contiguous I/Os
            * recording the last non-optional I/O.
            */
           while ((dio = AVL_PREV(t, first)) != NULL &&
               (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
               IO_SPAN(dio, last) <= limit &&
               IO_GAP(dio, first) <= maxgap &&
               dio->io_type == zio->io_type) {
                   first = dio;
                   if (mandatory == NULL && !(first->io_flags & ZIO_FLAG_OPTIONAL))
                           mandatory = first;
           }
   
           /*
            * Skip any initial optional I/Os.
            */
           while ((first->io_flags & ZIO_FLAG_OPTIONAL) && first != last) {
                   first = AVL_NEXT(t, first);
                   ASSERT(first != NULL);
           }
   
   
           /*
            * Walk forward through sufficiently contiguous I/Os.
            * The aggregation limit does not apply to optional i/os, so that
            * we can issue contiguous writes even if they are larger than the
            * aggregation limit.
            */
           while ((dio = AVL_NEXT(t, last)) != NULL &&
               (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
               (IO_SPAN(first, dio) <= limit ||
               (dio->io_flags & ZIO_FLAG_OPTIONAL)) &&
               IO_SPAN(first, dio) <= maxblocksize &&
               IO_GAP(last, dio) <= maxgap &&
               dio->io_type == zio->io_type) {
                   last = dio;
                   if (!(last->io_flags & ZIO_FLAG_OPTIONAL))
                           mandatory = last;
           }
   
           /*
            * Now that we've established the range of the I/O aggregation
            * we must decide what to do with trailing optional I/Os.
            * For reads, there's nothing to do. While we are unable to
            * aggregate further, it's possible that a trailing optional
            * I/O would allow the underlying device to aggregate with
            * subsequent I/Os. We must therefore determine if the next
            * non-optional I/O is close enough to make aggregation
            * worthwhile.
            */
           if (zio->io_type == ZIO_TYPE_WRITE && mandatory != NULL) {
                   zio_t *nio = last;
                   while ((dio = AVL_NEXT(t, nio)) != NULL &&
                       IO_GAP(nio, dio) == 0 &&
                       IO_GAP(mandatory, dio) <= zfs_vdev_write_gap_limit) {
                           nio = dio;
                           if (!(nio->io_flags & ZIO_FLAG_OPTIONAL)) {
                                   stretch = B_TRUE;
                                   break;
                           }
                   }
           }
   
           if (stretch) {
                   /*
                    * We are going to include an optional io in our aggregated
                    * span, thus closing the write gap.  Only mandatory i/os can
                    * start aggregated spans, so make sure that the next i/o
                    * after our span is mandatory.
                    */
                   dio = AVL_NEXT(t, last);
                   ASSERT3P(dio, !=, NULL);
                   dio->io_flags &= ~ZIO_FLAG_OPTIONAL;
           } else {
                   /* do not include the optional i/o */
                   while (last != mandatory && last != first) {
                           ASSERT(last->io_flags & ZIO_FLAG_OPTIONAL);
                           last = AVL_PREV(t, last);
                           ASSERT(last != NULL);
                   }
           }
   
           if (first == last)
                   return (NULL);
   
           size = IO_SPAN(first, last);
           ASSERT3U(size, <=, maxblocksize);
   
           abd = abd_alloc_gang();
           if (abd == NULL)
                   return (NULL);
   
           aio = zio_vdev_delegated_io(first->io_vd, first->io_offset,
               abd, size, first->io_type, zio->io_priority,
               flags | ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE,
               vdev_queue_agg_io_done, NULL);
           aio->io_timestamp = first->io_timestamp;
   
           nio = first;
           next_offset = first->io_offset;
           do {
                   dio = nio;
                   nio = AVL_NEXT(t, dio);
                   ASSERT3P(dio, !=, NULL);
                   zio_add_child(dio, aio);
                   vdev_queue_io_remove(vq, dio);
   
                   if (dio->io_offset != next_offset) {
                           /* allocate a buffer for a read gap */
                           ASSERT3U(dio->io_type, ==, ZIO_TYPE_READ);
                           ASSERT3U(dio->io_offset, >, next_offset);
                           abd = abd_alloc_for_io(
                               dio->io_offset - next_offset, B_TRUE);
                           abd_gang_add(aio->io_abd, abd, B_TRUE);
                   }
                   if (dio->io_abd &&
                       (dio->io_size != abd_get_size(dio->io_abd))) {
                           /* abd size not the same as IO size */
                           ASSERT3U(abd_get_size(dio->io_abd), >, dio->io_size);
                           abd = abd_get_offset_size(dio->io_abd, 0, dio->io_size);
                           abd_gang_add(aio->io_abd, abd, B_TRUE);
                   } else {
                           if (dio->io_flags & ZIO_FLAG_NODATA) {
                                   /* allocate a buffer for a write gap */
                                   ASSERT3U(dio->io_type, ==, ZIO_TYPE_WRITE);
                                   ASSERT3P(dio->io_abd, ==, NULL);
                                   abd_gang_add(aio->io_abd,
                                       abd_get_zeros(dio->io_size), B_TRUE);
                           } else {
                                   /*
                                    * We pass B_FALSE to abd_gang_add()
                                    * because we did not allocate a new
                                    * ABD, so it is assumed the caller
                                    * will free this ABD.
                                    */
                                   abd_gang_add(aio->io_abd, dio->io_abd,
                                       B_FALSE);
                           }
                   }
                   next_offset = dio->io_offset + dio->io_size;
           } while (dio != last);
           ASSERT3U(abd_get_size(aio->io_abd), ==, aio->io_size);
   
           /*
            * Callers must call zio_vdev_io_bypass() and zio_execute() for
            * aggregated (parent) I/Os so that we could avoid dropping the
            * queue's lock here to avoid a deadlock that we could encounter
            * due to lock order reversal between vq_lock and io_lock in
            * zio_change_priority().
            */
           return (aio);
   }
   
   static zio_t *
   vdev_queue_io_to_issue(vdev_queue_t *vq)
   {
           zio_t *zio, *aio;
           zio_priority_t p;
           avl_index_t idx;
           avl_tree_t *tree;
   
   again:
           ASSERT(MUTEX_HELD(&vq->vq_lock));
   
           p = vdev_queue_class_to_issue(vq);
   
           if (p == ZIO_PRIORITY_NUM_QUEUEABLE) {
                   /* No eligible queued i/os */
                   return (NULL);
           }
   
           /*
            * For LBA-ordered queues (async / scrub / initializing), issue the
            * i/o which follows the most recently issued i/o in LBA (offset) order.
            *
            * For FIFO queues (sync/trim), issue the i/o with the lowest timestamp.
            */
           tree = vdev_queue_class_tree(vq, p);
           vq->vq_io_search.io_timestamp = 0;
           vq->vq_io_search.io_offset = vq->vq_last_offset - 1;
           VERIFY3P(avl_find(tree, &vq->vq_io_search, &idx), ==, NULL);
           zio = avl_nearest(tree, idx, AVL_AFTER);
           if (zio == NULL)
                   zio = avl_first(tree);
           ASSERT3U(zio->io_priority, ==, p);
   
           aio = vdev_queue_aggregate(vq, zio);
           if (aio != NULL) {
                   zio = aio;
           } else {
                   vdev_queue_io_remove(vq, zio);
   
                   /*
                    * If the I/O is or was optional and therefore has no data, we
                    * need to simply discard it. We need to drop the vdev queue's
                    * lock to avoid a deadlock that we could encounter since this
                    * I/O will complete immediately.
                    */
                   if (zio->io_flags & ZIO_FLAG_NODATA) {
                           mutex_exit(&vq->vq_lock);
                           zio_vdev_io_bypass(zio);
                           zio_execute(zio);
                           mutex_enter(&vq->vq_lock);
                           goto again;
                   }
           }
   
           vdev_queue_pending_add(vq, zio);
           vq->vq_last_offset = zio->io_offset + zio->io_size;
   
           return (zio);
   }
   
   zio_t *
   vdev_queue_io(zio_t *zio)
   {
           vdev_queue_t *vq = &zio->io_vd->vdev_queue;
           zio_t *dio, *nio;
           zio_link_t *zl = NULL;
   
           if (zio->io_flags & ZIO_FLAG_DONT_QUEUE)
                   return (zio);
   
           /*
            * Children i/os inherent their parent's priority, which might
            * not match the child's i/o type.  Fix it up here.
            */
           if (zio->io_type == ZIO_TYPE_READ) {
                   ASSERT(zio->io_priority != ZIO_PRIORITY_TRIM);
   
                   if (zio->io_priority != ZIO_PRIORITY_SYNC_READ &&
                       zio->io_priority != ZIO_PRIORITY_ASYNC_READ &&
                       zio->io_priority != ZIO_PRIORITY_SCRUB &&
                       zio->io_priority != ZIO_PRIORITY_REMOVAL &&
                       zio->io_priority != ZIO_PRIORITY_INITIALIZING &&
                       zio->io_priority != ZIO_PRIORITY_REBUILD) {
                           zio->io_priority = ZIO_PRIORITY_ASYNC_READ;
                   }
           } else if (zio->io_type == ZIO_TYPE_WRITE) {
                   ASSERT(zio->io_priority != ZIO_PRIORITY_TRIM);
   
                   if (zio->io_priority != ZIO_PRIORITY_SYNC_WRITE &&
                       zio->io_priority != ZIO_PRIORITY_ASYNC_WRITE &&
                       zio->io_priority != ZIO_PRIORITY_REMOVAL &&
                       zio->io_priority != ZIO_PRIORITY_INITIALIZING &&
                       zio->io_priority != ZIO_PRIORITY_REBUILD) {
                           zio->io_priority = ZIO_PRIORITY_ASYNC_WRITE;
                   }
           } else {
                   ASSERT(zio->io_type == ZIO_TYPE_TRIM);
                   ASSERT(zio->io_priority == ZIO_PRIORITY_TRIM);
           }
   
           zio->io_flags |= ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE;
           zio->io_timestamp = gethrtime();
   
           mutex_enter(&vq->vq_lock);
           vdev_queue_io_add(vq, zio);
           nio = vdev_queue_io_to_issue(vq);
           mutex_exit(&vq->vq_lock);
   
           if (nio == NULL)
                   return (NULL);
   
           if (nio->io_done == vdev_queue_agg_io_done) {
                   while ((dio = zio_walk_parents(nio, &zl)) != NULL) {
                           ASSERT3U(dio->io_type, ==, nio->io_type);
                           zio_vdev_io_bypass(dio);
                           zio_execute(dio);
                   }
                   zio_nowait(nio);
                   return (NULL);
           }
   
           return (nio);
   }
   
   void
   vdev_queue_io_done(zio_t *zio)
   {
           vdev_queue_t *vq = &zio->io_vd->vdev_queue;
           zio_t *dio, *nio;
           zio_link_t *zl = NULL;
   
           hrtime_t now = gethrtime();
           vq->vq_io_complete_ts = now;
           vq->vq_io_delta_ts = zio->io_delta = now - zio->io_timestamp;
   
           mutex_enter(&vq->vq_lock);
           vdev_queue_pending_remove(vq, zio);
   
           while ((nio = vdev_queue_io_to_issue(vq)) != NULL) {
                   mutex_exit(&vq->vq_lock);
                   if (nio->io_done == vdev_queue_agg_io_done) {
                           while ((dio = zio_walk_parents(nio, &zl)) != NULL) {
                                   ASSERT3U(dio->io_type, ==, nio->io_type);
                                   zio_vdev_io_bypass(dio);
                                   zio_execute(dio);
                           }
                           zio_nowait(nio);
                   } else {
                           zio_vdev_io_reissue(nio);
                           zio_execute(nio);
                   }
                   mutex_enter(&vq->vq_lock);
           }
   
           mutex_exit(&vq->vq_lock);
   }
   
   void
   vdev_queue_change_io_priority(zio_t *zio, zio_priority_t priority)
   {
           vdev_queue_t *vq = &zio->io_vd->vdev_queue;
           avl_tree_t *tree;
   
           /*
            * ZIO_PRIORITY_NOW is used by the vdev cache code and the aggregate zio
            * code to issue IOs without adding them to the vdev queue. In this
            * case, the zio is already going to be issued as quickly as possible
            * and so it doesn't need any reprioritization to help.
            */
           if (zio->io_priority == ZIO_PRIORITY_NOW)
                   return;
   
           ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
           ASSERT3U(priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
   
           if (zio->io_type == ZIO_TYPE_READ) {
                   if (priority != ZIO_PRIORITY_SYNC_READ &&
                       priority != ZIO_PRIORITY_ASYNC_READ &&
                       priority != ZIO_PRIORITY_SCRUB)
                           priority = ZIO_PRIORITY_ASYNC_READ;
           } else {
                   ASSERT(zio->io_type == ZIO_TYPE_WRITE);
                   if (priority != ZIO_PRIORITY_SYNC_WRITE &&
                       priority != ZIO_PRIORITY_ASYNC_WRITE)
                           priority = ZIO_PRIORITY_ASYNC_WRITE;
           }
   
           mutex_enter(&vq->vq_lock);
   
           /*
           * If the zio is in none of the queues we can simply change
           * the priority. If the zio is waiting to be submitted we must
           * remove it from the queue and re-insert it with the new priority.
           * Otherwise, the zio is currently active and we cannot change its
           * priority.
           */
          tree = vdev_queue_class_tree(vq, zio->io_priority);
          if (avl_find(tree, zio, NULL) == zio) {
                  avl_remove(vdev_queue_class_tree(vq, zio->io_priority), zio);
                  zio->io_priority = priority;
                  avl_add(vdev_queue_class_tree(vq, zio->io_priority), zio);
          } else if (avl_find(&vq->vq_active_tree, zio, NULL) != zio) {
                  zio->io_priority = priority;
          }
  
          mutex_exit(&vq->vq_lock);
  }
  
  /*
   * As these two methods are only used for load calculations we're not
   * concerned if we get an incorrect value on 32bit platforms due to lack of
   * vq_lock mutex use here, instead we prefer to keep it lock free for
   * performance.
   */
  int
  vdev_queue_length(vdev_t *vd)
  {
          return (avl_numnodes(&vd->vdev_queue.vq_active_tree));
  }
  
  uint64_t
  vdev_queue_last_offset(vdev_t *vd)
  {
          return (vd->vdev_queue.vq_last_offset);
  }
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, aggregation_limit, UINT, ZMOD_RW,
          "Max vdev I/O aggregation size");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, aggregation_limit_non_rotating, UINT,
          ZMOD_RW, "Max vdev I/O aggregation size for non-rotating media");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, aggregate_trim, UINT, ZMOD_RW,
          "Allow TRIM I/O to be aggregated");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, read_gap_limit, UINT, ZMOD_RW,
          "Aggregate read I/O over gap");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, write_gap_limit, UINT, ZMOD_RW,
          "Aggregate write I/O over gap");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, max_active, UINT, ZMOD_RW,
          "Maximum number of active I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, async_write_active_max_dirty_percent,
          UINT, ZMOD_RW, "Async write concurrency max threshold");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, async_write_active_min_dirty_percent,
          UINT, ZMOD_RW, "Async write concurrency min threshold");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, async_read_max_active, UINT, ZMOD_RW,
          "Max active async read I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, async_read_min_active, UINT, ZMOD_RW,
          "Min active async read I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, async_write_max_active, UINT, ZMOD_RW,
          "Max active async write I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, async_write_min_active, UINT, ZMOD_RW,
          "Min active async write I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, initializing_max_active, UINT, ZMOD_RW,
          "Max active initializing I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, initializing_min_active, UINT, ZMOD_RW,
          "Min active initializing I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, removal_max_active, UINT, ZMOD_RW,
          "Max active removal I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, removal_min_active, UINT, ZMOD_RW,
          "Min active removal I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, scrub_max_active, UINT, ZMOD_RW,
          "Max active scrub I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, scrub_min_active, UINT, ZMOD_RW,
          "Min active scrub I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, sync_read_max_active, UINT, ZMOD_RW,
          "Max active sync read I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, sync_read_min_active, UINT, ZMOD_RW,
          "Min active sync read I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, sync_write_max_active, UINT, ZMOD_RW,
          "Max active sync write I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, sync_write_min_active, UINT, ZMOD_RW,
          "Min active sync write I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, trim_max_active, UINT, ZMOD_RW,
          "Max active trim/discard I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, trim_min_active, UINT, ZMOD_RW,
          "Min active trim/discard I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, rebuild_max_active, UINT, ZMOD_RW,
          "Max active rebuild I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, rebuild_min_active, UINT, ZMOD_RW,
          "Min active rebuild I/Os per vdev");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, nia_credit, UINT, ZMOD_RW,
          "Number of non-interactive I/Os to allow in sequence");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, nia_delay, UINT, ZMOD_RW,
          "Number of non-interactive I/Os before _max_active");
  
  ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, queue_depth_pct, UINT, ZMOD_RW,
          "Queue depth percentage for each top-level vdev");

Cache object: b3cb79601cb2dd3c83c8676d532e95c6