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4045 zfs write throttle & i/o scheduler performance work
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>


   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  23  * Use is subject to license terms.
  24  */
  25 
  26 /*
  27  * Copyright (c) 2012 by Delphix. All rights reserved.
  28  */
  29 
  30 #include <sys/zfs_context.h>
  31 #include <sys/vdev_impl.h>
  32 #include <sys/spa_impl.h>
  33 #include <sys/zio.h>
  34 #include <sys/avl.h>

  35 
  36 /*
  37  * These tunables are for performance analysis.










































































  38  */
  39 
  40 /* The maximum number of I/Os concurrently pending to each device. */
  41 int zfs_vdev_max_pending = 10;




  42 
  43 /*
  44  * The initial number of I/Os pending to each device, before it starts ramping
  45  * up to zfs_vdev_max_pending.












  46  */
  47 int zfs_vdev_min_pending = 4;









  48 
  49 /*
  50  * The deadlines are grouped into buckets based on zfs_vdev_time_shift:
  51  * deadline = pri + gethrtime() >> time_shift)



  52  */
  53 int zfs_vdev_time_shift = 29; /* each bucket is 0.537 seconds */

  54 
  55 /* exponential I/O issue ramp-up rate */
  56 int zfs_vdev_ramp_rate = 2;
  57 
  58 /*
  59  * To reduce IOPs, we aggregate small adjacent I/Os into one large I/O.
  60  * For read I/Os, we also aggregate across small adjacency gaps; for writes
  61  * we include spans of optional I/Os to aid aggregation at the disk even when
  62  * they aren't able to help us aggregate at this level.
  63  */
  64 int zfs_vdev_aggregation_limit = SPA_MAXBLOCKSIZE;
  65 int zfs_vdev_read_gap_limit = 32 << 10;
  66 int zfs_vdev_write_gap_limit = 4 << 10;
  67 
  68 /*
  69  * Virtual device vector for disk I/O scheduling.
  70  */
  71 int
  72 vdev_queue_deadline_compare(const void *x1, const void *x2)
  73 {
  74         const zio_t *z1 = x1;
  75         const zio_t *z2 = x2;
  76 
  77         if (z1->io_deadline < z2->io_deadline)
  78                 return (-1);
  79         if (z1->io_deadline > z2->io_deadline)
  80                 return (1);
  81 
  82         if (z1->io_offset < z2->io_offset)
  83                 return (-1);
  84         if (z1->io_offset > z2->io_offset)
  85                 return (1);
  86 
  87         if (z1 < z2)
  88                 return (-1);
  89         if (z1 > z2)
  90                 return (1);
  91 
  92         return (0);
  93 }
  94 
  95 int
  96 vdev_queue_offset_compare(const void *x1, const void *x2)
  97 {
  98         const zio_t *z1 = x1;
  99         const zio_t *z2 = x2;
 100 
 101         if (z1->io_offset < z2->io_offset)
 102                 return (-1);
 103         if (z1->io_offset > z2->io_offset)
 104                 return (1);
 105 
 106         if (z1 < z2)
 107                 return (-1);
 108         if (z1 > z2)
 109                 return (1);
 110 
 111         return (0);
 112 }
 113 
 114 void
 115 vdev_queue_init(vdev_t *vd)
 116 {
 117         vdev_queue_t *vq = &vd->vdev_queue;
 118 
 119         mutex_init(&vq->vq_lock, NULL, MUTEX_DEFAULT, NULL);

 120 
 121         avl_create(&vq->vq_deadline_tree, vdev_queue_deadline_compare,
 122             sizeof (zio_t), offsetof(struct zio, io_deadline_node));
 123 
 124         avl_create(&vq->vq_read_tree, vdev_queue_offset_compare,
 125             sizeof (zio_t), offsetof(struct zio, io_offset_node));
 126 
 127         avl_create(&vq->vq_write_tree, vdev_queue_offset_compare,
 128             sizeof (zio_t), offsetof(struct zio, io_offset_node));
 129 
 130         avl_create(&vq->vq_pending_tree, vdev_queue_offset_compare,
 131             sizeof (zio_t), offsetof(struct zio, io_offset_node));






 132 }
 133 
 134 void
 135 vdev_queue_fini(vdev_t *vd)
 136 {
 137         vdev_queue_t *vq = &vd->vdev_queue;
 138 
 139         avl_destroy(&vq->vq_deadline_tree);
 140         avl_destroy(&vq->vq_read_tree);
 141         avl_destroy(&vq->vq_write_tree);
 142         avl_destroy(&vq->vq_pending_tree);
 143 
 144         mutex_destroy(&vq->vq_lock);
 145 }
 146 
 147 static void
 148 vdev_queue_io_add(vdev_queue_t *vq, zio_t *zio)
 149 {
 150         spa_t *spa = zio->io_spa;
 151         avl_add(&vq->vq_deadline_tree, zio);
 152         avl_add(zio->io_vdev_tree, zio);
 153 
 154         if (spa->spa_iokstat != NULL) {
 155                 mutex_enter(&spa->spa_iokstat_lock);


 156                 kstat_waitq_enter(spa->spa_iokstat->ks_data);
 157                 mutex_exit(&spa->spa_iokstat_lock);
 158         }
 159 }
 160 
 161 static void
 162 vdev_queue_io_remove(vdev_queue_t *vq, zio_t *zio)
 163 {
 164         spa_t *spa = zio->io_spa;
 165         avl_remove(&vq->vq_deadline_tree, zio);
 166         avl_remove(zio->io_vdev_tree, zio);
 167 
 168         if (spa->spa_iokstat != NULL) {
 169                 mutex_enter(&spa->spa_iokstat_lock);



 170                 kstat_waitq_exit(spa->spa_iokstat->ks_data);
 171                 mutex_exit(&spa->spa_iokstat_lock);
 172         }
 173 }
 174 
 175 static void
 176 vdev_queue_pending_add(vdev_queue_t *vq, zio_t *zio)
 177 {
 178         spa_t *spa = zio->io_spa;
 179         avl_add(&vq->vq_pending_tree, zio);
 180         if (spa->spa_iokstat != NULL) {



 181                 mutex_enter(&spa->spa_iokstat_lock);


 182                 kstat_runq_enter(spa->spa_iokstat->ks_data);
 183                 mutex_exit(&spa->spa_iokstat_lock);
 184         }
 185 }
 186 
 187 static void
 188 vdev_queue_pending_remove(vdev_queue_t *vq, zio_t *zio)
 189 {
 190         spa_t *spa = zio->io_spa;
 191         avl_remove(&vq->vq_pending_tree, zio);







 192         if (spa->spa_iokstat != NULL) {
 193                 kstat_io_t *ksio = spa->spa_iokstat->ks_data;
 194 
 195                 mutex_enter(&spa->spa_iokstat_lock);
 196                 kstat_runq_exit(spa->spa_iokstat->ks_data);
 197                 if (zio->io_type == ZIO_TYPE_READ) {
 198                         ksio->reads++;
 199                         ksio->nread += zio->io_size;
 200                 } else if (zio->io_type == ZIO_TYPE_WRITE) {
 201                         ksio->writes++;
 202                         ksio->nwritten += zio->io_size;
 203                 }
 204                 mutex_exit(&spa->spa_iokstat_lock);
 205         }

 206 }
 207 
 208 static void
 209 vdev_queue_agg_io_done(zio_t *aio)
 210 {

 211         zio_t *pio;
 212 
 213         while ((pio = zio_walk_parents(aio)) != NULL)
 214                 if (aio->io_type == ZIO_TYPE_READ)
 215                         bcopy((char *)aio->io_data + (pio->io_offset -
 216                             aio->io_offset), pio->io_data, pio->io_size);


 217 
 218         zio_buf_free(aio->io_data, aio->io_size);
 219 }
 220 







































































 221 /*




































 222  * Compute the range spanned by two i/os, which is the endpoint of the last
 223  * (lio->io_offset + lio->io_size) minus start of the first (fio->io_offset).
 224  * Conveniently, the gap between fio and lio is given by -IO_SPAN(lio, fio);
 225  * thus fio and lio are adjacent if and only if IO_SPAN(lio, fio) == 0.
 226  */
 227 #define IO_SPAN(fio, lio) ((lio)->io_offset + (lio)->io_size - (fio)->io_offset)
 228 #define IO_GAP(fio, lio) (-IO_SPAN(lio, fio))
 229 
 230 static zio_t *
 231 vdev_queue_io_to_issue(vdev_queue_t *vq, uint64_t pending_limit)
 232 {
 233         zio_t *fio, *lio, *aio, *dio, *nio, *mio;
 234         avl_tree_t *t;
 235         int flags;
 236         uint64_t maxspan = zfs_vdev_aggregation_limit;
 237         uint64_t maxgap;
 238         int stretch;

 239 
 240 again:
 241         ASSERT(MUTEX_HELD(&vq->vq_lock));
 242 
 243         if (avl_numnodes(&vq->vq_pending_tree) >= pending_limit ||
 244             avl_numnodes(&vq->vq_deadline_tree) == 0)





 245                 return (NULL);
 246 
 247         fio = lio = avl_first(&vq->vq_deadline_tree);
 248 
 249         t = fio->io_vdev_tree;
 250         flags = fio->io_flags & ZIO_FLAG_AGG_INHERIT;
 251         maxgap = (t == &vq->vq_read_tree) ? zfs_vdev_read_gap_limit : 0;
 252 
 253         if (!(flags & ZIO_FLAG_DONT_AGGREGATE)) {
 254                 /*
 255                  * We can aggregate I/Os that are sufficiently adjacent and of
 256                  * the same flavor, as expressed by the AGG_INHERIT flags.
 257                  * The latter requirement is necessary so that certain
 258                  * attributes of the I/O, such as whether it's a normal I/O
 259                  * or a scrub/resilver, can be preserved in the aggregate.
 260                  * We can include optional I/Os, but don't allow them
 261                  * to begin a range as they add no benefit in that situation.
 262                  */
 263 
 264                 /*
 265                  * We keep track of the last non-optional I/O.
 266                  */
 267                 mio = (fio->io_flags & ZIO_FLAG_OPTIONAL) ? NULL : fio;
 268 
 269                 /*
 270                  * Walk backwards through sufficiently contiguous I/Os
 271                  * recording the last non-option I/O.
 272                  */
 273                 while ((dio = AVL_PREV(t, fio)) != NULL &&
 274                     (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
 275                     IO_SPAN(dio, lio) <= maxspan &&
 276                     IO_GAP(dio, fio) <= maxgap) {
 277                         fio = dio;
 278                         if (mio == NULL && !(fio->io_flags & ZIO_FLAG_OPTIONAL))
 279                                 mio = fio;
 280                 }
 281 
 282                 /*
 283                  * Skip any initial optional I/Os.
 284                  */
 285                 while ((fio->io_flags & ZIO_FLAG_OPTIONAL) && fio != lio) {
 286                         fio = AVL_NEXT(t, fio);
 287                         ASSERT(fio != NULL);
 288                 }
 289 
 290                 /*
 291                  * Walk forward through sufficiently contiguous I/Os.
 292                  */
 293                 while ((dio = AVL_NEXT(t, lio)) != NULL &&
 294                     (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
 295                     IO_SPAN(fio, dio) <= maxspan &&
 296                     IO_GAP(lio, dio) <= maxgap) {
 297                         lio = dio;
 298                         if (!(lio->io_flags & ZIO_FLAG_OPTIONAL))
 299                                 mio = lio;
 300                 }
 301 
 302                 /*
 303                  * Now that we've established the range of the I/O aggregation
 304                  * we must decide what to do with trailing optional I/Os.
 305                  * For reads, there's nothing to do. While we are unable to
 306                  * aggregate further, it's possible that a trailing optional
 307                  * I/O would allow the underlying device to aggregate with
 308                  * subsequent I/Os. We must therefore determine if the next
 309                  * non-optional I/O is close enough to make aggregation
 310                  * worthwhile.
 311                  */
 312                 stretch = B_FALSE;
 313                 if (t != &vq->vq_read_tree && mio != NULL) {
 314                         nio = lio;
 315                         while ((dio = AVL_NEXT(t, nio)) != NULL &&
 316                             IO_GAP(nio, dio) == 0 &&
 317                             IO_GAP(mio, dio) <= zfs_vdev_write_gap_limit) {
 318                                 nio = dio;
 319                                 if (!(nio->io_flags & ZIO_FLAG_OPTIONAL)) {
 320                                         stretch = B_TRUE;
 321                                         break;
 322                                 }
 323                         }
 324                 }
 325 
 326                 if (stretch) {
 327                         /* This may be a no-op. */
 328                         VERIFY((dio = AVL_NEXT(t, lio)) != NULL);
 329                         dio->io_flags &= ~ZIO_FLAG_OPTIONAL;
 330                 } else {
 331                         while (lio != mio && lio != fio) {
 332                                 ASSERT(lio->io_flags & ZIO_FLAG_OPTIONAL);
 333                                 lio = AVL_PREV(t, lio);
 334                                 ASSERT(lio != NULL);
 335                         }
 336                 }
 337         }
 338 
 339         if (fio != lio) {
 340                 uint64_t size = IO_SPAN(fio, lio);
 341                 ASSERT(size <= zfs_vdev_aggregation_limit);
 342 
 343                 aio = zio_vdev_delegated_io(fio->io_vd, fio->io_offset,
 344                     zio_buf_alloc(size), size, fio->io_type, ZIO_PRIORITY_AGG,



 345                     flags | ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE,
 346                     vdev_queue_agg_io_done, NULL);
 347                 aio->io_timestamp = fio->io_timestamp;
 348 
 349                 nio = fio;
 350                 do {
 351                         dio = nio;
 352                         nio = AVL_NEXT(t, dio);
 353                         ASSERT(dio->io_type == aio->io_type);
 354                         ASSERT(dio->io_vdev_tree == t);
 355 
 356                         if (dio->io_flags & ZIO_FLAG_NODATA) {
 357                                 ASSERT(dio->io_type == ZIO_TYPE_WRITE);
 358                                 bzero((char *)aio->io_data + (dio->io_offset -
 359                                     aio->io_offset), dio->io_size);
 360                         } else if (dio->io_type == ZIO_TYPE_WRITE) {
 361                                 bcopy(dio->io_data, (char *)aio->io_data +
 362                                     (dio->io_offset - aio->io_offset),
 363                                     dio->io_size);
 364                         }
 365 
 366                         zio_add_child(dio, aio);
 367                         vdev_queue_io_remove(vq, dio);
 368                         zio_vdev_io_bypass(dio);
 369                         zio_execute(dio);
 370                 } while (dio != lio);
 371 
 372                 vdev_queue_pending_add(vq, aio);
 373 
 374                 return (aio);



















 375         }
 376 
 377         ASSERT(fio->io_vdev_tree == t);
 378         vdev_queue_io_remove(vq, fio);












 379 






 380         /*
 381          * If the I/O is or was optional and therefore has no data, we need to
 382          * simply discard it. We need to drop the vdev queue's lock to avoid a
 383          * deadlock that we could encounter since this I/O will complete
 384          * immediately.
 385          */
 386         if (fio->io_flags & ZIO_FLAG_NODATA) {
 387                 mutex_exit(&vq->vq_lock);
 388                 zio_vdev_io_bypass(fio);
 389                 zio_execute(fio);
 390                 mutex_enter(&vq->vq_lock);
 391                 goto again;
 392         }
 393 
 394         vdev_queue_pending_add(vq, fio);

 395 
 396         return (fio);
 397 }
 398 
 399 zio_t *
 400 vdev_queue_io(zio_t *zio)
 401 {
 402         vdev_queue_t *vq = &zio->io_vd->vdev_queue;
 403         zio_t *nio;
 404 
 405         ASSERT(zio->io_type == ZIO_TYPE_READ || zio->io_type == ZIO_TYPE_WRITE);
 406 
 407         if (zio->io_flags & ZIO_FLAG_DONT_QUEUE)
 408                 return (zio);
 409 
















 410         zio->io_flags |= ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE;
 411 
 412         if (zio->io_type == ZIO_TYPE_READ)
 413                 zio->io_vdev_tree = &vq->vq_read_tree;
 414         else
 415                 zio->io_vdev_tree = &vq->vq_write_tree;
 416 
 417         mutex_enter(&vq->vq_lock);
 418 
 419         zio->io_timestamp = gethrtime();
 420         zio->io_deadline = (zio->io_timestamp >> zfs_vdev_time_shift) +
 421             zio->io_priority;
 422 
 423         vdev_queue_io_add(vq, zio);
 424 
 425         nio = vdev_queue_io_to_issue(vq, zfs_vdev_min_pending);
 426 
 427         mutex_exit(&vq->vq_lock);
 428 
 429         if (nio == NULL)
 430                 return (NULL);
 431 
 432         if (nio->io_done == vdev_queue_agg_io_done) {
 433                 zio_nowait(nio);
 434                 return (NULL);
 435         }
 436 
 437         return (nio);
 438 }
 439 
 440 void
 441 vdev_queue_io_done(zio_t *zio)
 442 {
 443         vdev_queue_t *vq = &zio->io_vd->vdev_queue;

 444 
 445         if (zio_injection_enabled)
 446                 delay(SEC_TO_TICK(zio_handle_io_delay(zio)));
 447 
 448         mutex_enter(&vq->vq_lock);
 449 
 450         vdev_queue_pending_remove(vq, zio);
 451 
 452         vq->vq_io_complete_ts = gethrtime();
 453 
 454         for (int i = 0; i < zfs_vdev_ramp_rate; i++) {
 455                 zio_t *nio = vdev_queue_io_to_issue(vq, zfs_vdev_max_pending);
 456                 if (nio == NULL)
 457                         break;
 458                 mutex_exit(&vq->vq_lock);
 459                 if (nio->io_done == vdev_queue_agg_io_done) {
 460                         zio_nowait(nio);
 461                 } else {
 462                         zio_vdev_io_reissue(nio);
 463                         zio_execute(nio);
 464                 }
 465                 mutex_enter(&vq->vq_lock);
 466         }
 467 
 468         mutex_exit(&vq->vq_lock);
 469 }


   7  *
   8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
   9  * or http://www.opensolaris.org/os/licensing.
  10  * See the License for the specific language governing permissions
  11  * and limitations under the License.
  12  *
  13  * When distributing Covered Code, include this CDDL HEADER in each
  14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
  15  * If applicable, add the following below this CDDL HEADER, with the
  16  * fields enclosed by brackets "[]" replaced with your own identifying
  17  * information: Portions Copyright [yyyy] [name of copyright owner]
  18  *
  19  * CDDL HEADER END
  20  */
  21 /*
  22  * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
  23  * Use is subject to license terms.
  24  */
  25 
  26 /*
  27  * Copyright (c) 2013 by Delphix. All rights reserved.
  28  */
  29 
  30 #include <sys/zfs_context.h>
  31 #include <sys/vdev_impl.h>
  32 #include <sys/spa_impl.h>
  33 #include <sys/zio.h>
  34 #include <sys/avl.h>
  35 #include <sys/dsl_pool.h>
  36 
  37 /*
  38  * ZFS I/O Scheduler
  39  * ---------------
  40  *
  41  * ZFS issues I/O operations to leaf vdevs to satisfy and complete zios.  The
  42  * I/O scheduler determines when and in what order those operations are
  43  * issued.  The I/O scheduler divides operations into five I/O classes
  44  * prioritized in the following order: sync read, sync write, async read,
  45  * async write, and scrub/resilver.  Each queue defines the minimum and
  46  * maximum number of concurrent operations that may be issued to the device.
  47  * In addition, the device has an aggregate maximum. Note that the sum of the
  48  * per-queue minimums must not exceed the aggregate maximum, and if the
  49  * aggregate maximum is equal to or greater than the sum of the per-queue
  50  * maximums, the per-queue minimum has no effect.
  51  *
  52  * For many physical devices, throughput increases with the number of
  53  * concurrent operations, but latency typically suffers. Further, physical
  54  * devices typically have a limit at which more concurrent operations have no
  55  * effect on throughput or can actually cause it to decrease.
  56  *
  57  * The scheduler selects the next operation to issue by first looking for an
  58  * I/O class whose minimum has not been satisfied. Once all are satisfied and
  59  * the aggregate maximum has not been hit, the scheduler looks for classes
  60  * whose maximum has not been satisfied. Iteration through the I/O classes is
  61  * done in the order specified above. No further operations are issued if the
  62  * aggregate maximum number of concurrent operations has been hit or if there
  63  * are no operations queued for an I/O class that has not hit its maximum.
  64  * Every time an i/o is queued or an operation completes, the I/O scheduler
  65  * looks for new operations to issue.
  66  *
  67  * All I/O classes have a fixed maximum number of outstanding operations
  68  * except for the async write class. Asynchronous writes represent the data
  69  * that is committed to stable storage during the syncing stage for
  70  * transaction groups (see txg.c). Transaction groups enter the syncing state
  71  * periodically so the number of queued async writes will quickly burst up and
  72  * then bleed down to zero. Rather than servicing them as quickly as possible,
  73  * the I/O scheduler changes the maximum number of active async write i/os
  74  * according to the amount of dirty data in the pool (see dsl_pool.c). Since
  75  * both throughput and latency typically increase with the number of
  76  * concurrent operations issued to physical devices, reducing the burstiness
  77  * in the number of concurrent operations also stabilizes the response time of
  78  * operations from other -- and in particular synchronous -- queues. In broad
  79  * strokes, the I/O scheduler will issue more concurrent operations from the
  80  * async write queue as there's more dirty data in the pool.
  81  *
  82  * Async Writes
  83  *
  84  * The number of concurrent operations issued for the async write I/O class
  85  * follows a piece-wise linear function defined by a few adjustable points.
  86  *
  87  *        |                   o---------| <-- zfs_vdev_async_write_max_active
  88  *   ^    |                  /^         |
  89  *   |    |                 / |         |
  90  * active |                /  |         |
  91  *  I/O   |               /   |         |
  92  * count  |              /    |         |
  93  *        |             /     |         |
  94  *        |------------o      |         | <-- zfs_vdev_async_write_min_active
  95  *       0|____________^______|_________|
  96  *        0%           |      |       100% of zfs_dirty_data_max
  97  *                     |      |
  98  *                     |      `-- zfs_vdev_async_write_active_max_dirty_percent
  99  *                     `--------- zfs_vdev_async_write_active_min_dirty_percent
 100  *
 101  * Until the amount of dirty data exceeds a minimum percentage of the dirty
 102  * data allowed in the pool, the I/O scheduler will limit the number of
 103  * concurrent operations to the minimum. As that threshold is crossed, the
 104  * number of concurrent operations issued increases linearly to the maximum at
 105  * the specified maximum percentage of the dirty data allowed in the pool.
 106  *
 107  * Ideally, the amount of dirty data on a busy pool will stay in the sloped
 108  * part of the function between zfs_vdev_async_write_active_min_dirty_percent
 109  * and zfs_vdev_async_write_active_max_dirty_percent. If it exceeds the
 110  * maximum percentage, this indicates that the rate of incoming data is
 111  * greater than the rate that the backend storage can handle. In this case, we
 112  * must further throttle incoming writes (see dmu_tx_delay() for details).
 113  */
 114 
 115 /*
 116  * The maximum number of i/os active to each device.  Ideally, this will be >=
 117  * the sum of each queue's max_active.  It must be at least the sum of each
 118  * queue's min_active.
 119  */
 120 uint32_t zfs_vdev_max_active = 1000;
 121 
 122 /*
 123  * Per-queue limits on the number of i/os active to each device.  If the
 124  * sum of the queue's max_active is < zfs_vdev_max_active, then the
 125  * min_active comes into play.  We will send min_active from each queue,
 126  * and then select from queues in the order defined by zio_priority_t.
 127  *
 128  * In general, smaller max_active's will lead to lower latency of synchronous
 129  * operations.  Larger max_active's may lead to higher overall throughput,
 130  * depending on underlying storage.
 131  *
 132  * The ratio of the queues' max_actives determines the balance of performance
 133  * between reads, writes, and scrubs.  E.g., increasing
 134  * zfs_vdev_scrub_max_active will cause the scrub or resilver to complete
 135  * more quickly, but reads and writes to have higher latency and lower
 136  * throughput.
 137  */
 138 uint32_t zfs_vdev_sync_read_min_active = 10;
 139 uint32_t zfs_vdev_sync_read_max_active = 10;
 140 uint32_t zfs_vdev_sync_write_min_active = 10;
 141 uint32_t zfs_vdev_sync_write_max_active = 10;
 142 uint32_t zfs_vdev_async_read_min_active = 1;
 143 uint32_t zfs_vdev_async_read_max_active = 3;
 144 uint32_t zfs_vdev_async_write_min_active = 1;
 145 uint32_t zfs_vdev_async_write_max_active = 10;
 146 uint32_t zfs_vdev_scrub_min_active = 1;
 147 uint32_t zfs_vdev_scrub_max_active = 2;
 148 
 149 /*
 150  * When the pool has less than zfs_vdev_async_write_active_min_dirty_percent
 151  * dirty data, use zfs_vdev_async_write_min_active.  When it has more than
 152  * zfs_vdev_async_write_active_max_dirty_percent, use
 153  * zfs_vdev_async_write_max_active. The value is linearly interpolated
 154  * between min and max.
 155  */
 156 int zfs_vdev_async_write_active_min_dirty_percent = 30;
 157 int zfs_vdev_async_write_active_max_dirty_percent = 60;
 158 



 159 /*
 160  * To reduce IOPs, we aggregate small adjacent I/Os into one large I/O.
 161  * For read I/Os, we also aggregate across small adjacency gaps; for writes
 162  * we include spans of optional I/Os to aid aggregation at the disk even when
 163  * they aren't able to help us aggregate at this level.
 164  */
 165 int zfs_vdev_aggregation_limit = SPA_MAXBLOCKSIZE;
 166 int zfs_vdev_read_gap_limit = 32 << 10;
 167 int zfs_vdev_write_gap_limit = 4 << 10;
 168 



 169 int
 170 vdev_queue_offset_compare(const void *x1, const void *x2)
 171 {
 172         const zio_t *z1 = x1;
 173         const zio_t *z2 = x2;
 174 





 175         if (z1->io_offset < z2->io_offset)
 176                 return (-1);
 177         if (z1->io_offset > z2->io_offset)
 178                 return (1);
 179 
 180         if (z1 < z2)
 181                 return (-1);
 182         if (z1 > z2)
 183                 return (1);
 184 
 185         return (0);
 186 }
 187 
 188 int
 189 vdev_queue_timestamp_compare(const void *x1, const void *x2)
 190 {
 191         const zio_t *z1 = x1;
 192         const zio_t *z2 = x2;
 193 
 194         if (z1->io_timestamp < z2->io_timestamp)
 195                 return (-1);
 196         if (z1->io_timestamp > z2->io_timestamp)
 197                 return (1);
 198 
 199         if (z1 < z2)
 200                 return (-1);
 201         if (z1 > z2)
 202                 return (1);
 203 
 204         return (0);
 205 }
 206 
 207 void
 208 vdev_queue_init(vdev_t *vd)
 209 {
 210         vdev_queue_t *vq = &vd->vdev_queue;
 211 
 212         mutex_init(&vq->vq_lock, NULL, MUTEX_DEFAULT, NULL);
 213         vq->vq_vdev = vd;
 214 
 215         avl_create(&vq->vq_active_tree, vdev_queue_offset_compare,
 216             sizeof (zio_t), offsetof(struct zio, io_queue_node));
 217 
 218         for (zio_priority_t p = 0; p < ZIO_PRIORITY_NUM_QUEUEABLE; p++) {
 219                 /*
 220                  * The synchronous i/o queues are FIFO rather than LBA ordered.
 221                  * This provides more consistent latency for these i/os, and
 222                  * they tend to not be tightly clustered anyway so there is
 223                  * little to no throughput loss.
 224                  */
 225                 boolean_t fifo = (p == ZIO_PRIORITY_SYNC_READ ||
 226                     p == ZIO_PRIORITY_SYNC_WRITE);
 227                 avl_create(&vq->vq_class[p].vqc_queued_tree,
 228                     fifo ? vdev_queue_timestamp_compare :
 229                     vdev_queue_offset_compare,
 230                     sizeof (zio_t), offsetof(struct zio, io_queue_node));
 231         }
 232 }
 233 
 234 void
 235 vdev_queue_fini(vdev_t *vd)
 236 {
 237         vdev_queue_t *vq = &vd->vdev_queue;
 238 
 239         for (zio_priority_t p = 0; p < ZIO_PRIORITY_NUM_QUEUEABLE; p++)
 240                 avl_destroy(&vq->vq_class[p].vqc_queued_tree);
 241         avl_destroy(&vq->vq_active_tree);

 242 
 243         mutex_destroy(&vq->vq_lock);
 244 }
 245 
 246 static void
 247 vdev_queue_io_add(vdev_queue_t *vq, zio_t *zio)
 248 {
 249         spa_t *spa = zio->io_spa;
 250         ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
 251         avl_add(&vq->vq_class[zio->io_priority].vqc_queued_tree, zio);
 252 

 253         mutex_enter(&spa->spa_iokstat_lock);
 254         spa->spa_queue_stats[zio->io_priority].spa_queued++;
 255         if (spa->spa_iokstat != NULL)
 256                 kstat_waitq_enter(spa->spa_iokstat->ks_data);
 257         mutex_exit(&spa->spa_iokstat_lock);

 258 }
 259 
 260 static void
 261 vdev_queue_io_remove(vdev_queue_t *vq, zio_t *zio)
 262 {
 263         spa_t *spa = zio->io_spa;
 264         ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
 265         avl_remove(&vq->vq_class[zio->io_priority].vqc_queued_tree, zio);
 266 

 267         mutex_enter(&spa->spa_iokstat_lock);
 268         ASSERT3U(spa->spa_queue_stats[zio->io_priority].spa_queued, >, 0);
 269         spa->spa_queue_stats[zio->io_priority].spa_queued--;
 270         if (spa->spa_iokstat != NULL)
 271                 kstat_waitq_exit(spa->spa_iokstat->ks_data);
 272         mutex_exit(&spa->spa_iokstat_lock);

 273 }
 274 
 275 static void
 276 vdev_queue_pending_add(vdev_queue_t *vq, zio_t *zio)
 277 {
 278         spa_t *spa = zio->io_spa;
 279         ASSERT(MUTEX_HELD(&vq->vq_lock));
 280         ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
 281         vq->vq_class[zio->io_priority].vqc_active++;
 282         avl_add(&vq->vq_active_tree, zio);
 283 
 284         mutex_enter(&spa->spa_iokstat_lock);
 285         spa->spa_queue_stats[zio->io_priority].spa_active++;
 286         if (spa->spa_iokstat != NULL)
 287                 kstat_runq_enter(spa->spa_iokstat->ks_data);
 288         mutex_exit(&spa->spa_iokstat_lock);

 289 }
 290 
 291 static void
 292 vdev_queue_pending_remove(vdev_queue_t *vq, zio_t *zio)
 293 {
 294         spa_t *spa = zio->io_spa;
 295         ASSERT(MUTEX_HELD(&vq->vq_lock));
 296         ASSERT3U(zio->io_priority, <, ZIO_PRIORITY_NUM_QUEUEABLE);
 297         vq->vq_class[zio->io_priority].vqc_active--;
 298         avl_remove(&vq->vq_active_tree, zio);
 299 
 300         mutex_enter(&spa->spa_iokstat_lock);
 301         ASSERT3U(spa->spa_queue_stats[zio->io_priority].spa_active, >, 0);
 302         spa->spa_queue_stats[zio->io_priority].spa_active--;
 303         if (spa->spa_iokstat != NULL) {
 304                 kstat_io_t *ksio = spa->spa_iokstat->ks_data;
 305 

 306                 kstat_runq_exit(spa->spa_iokstat->ks_data);
 307                 if (zio->io_type == ZIO_TYPE_READ) {
 308                         ksio->reads++;
 309                         ksio->nread += zio->io_size;
 310                 } else if (zio->io_type == ZIO_TYPE_WRITE) {
 311                         ksio->writes++;
 312                         ksio->nwritten += zio->io_size;
 313                 }

 314         }
 315         mutex_exit(&spa->spa_iokstat_lock);
 316 }
 317 
 318 static void
 319 vdev_queue_agg_io_done(zio_t *aio)
 320 {
 321         if (aio->io_type == ZIO_TYPE_READ) {
 322                 zio_t *pio;
 323                 while ((pio = zio_walk_parents(aio)) != NULL) {


 324                         bcopy((char *)aio->io_data + (pio->io_offset -
 325                             aio->io_offset), pio->io_data, pio->io_size);
 326                 }
 327         }
 328 
 329         zio_buf_free(aio->io_data, aio->io_size);
 330 }
 331 
 332 static int
 333 vdev_queue_class_min_active(zio_priority_t p)
 334 {
 335         switch (p) {
 336         case ZIO_PRIORITY_SYNC_READ:
 337                 return (zfs_vdev_sync_read_min_active);
 338         case ZIO_PRIORITY_SYNC_WRITE:
 339                 return (zfs_vdev_sync_write_min_active);
 340         case ZIO_PRIORITY_ASYNC_READ:
 341                 return (zfs_vdev_async_read_min_active);
 342         case ZIO_PRIORITY_ASYNC_WRITE:
 343                 return (zfs_vdev_async_write_min_active);
 344         case ZIO_PRIORITY_SCRUB:
 345                 return (zfs_vdev_scrub_min_active);
 346         default:
 347                 panic("invalid priority %u", p);
 348                 return (0);
 349         }
 350 }
 351 
 352 static int
 353 vdev_queue_max_async_writes(uint64_t dirty)
 354 {
 355         int writes;
 356         uint64_t min_bytes = zfs_dirty_data_max *
 357             zfs_vdev_async_write_active_min_dirty_percent / 100;
 358         uint64_t max_bytes = zfs_dirty_data_max *
 359             zfs_vdev_async_write_active_max_dirty_percent / 100;
 360 
 361         if (dirty < min_bytes)
 362                 return (zfs_vdev_async_write_min_active);
 363         if (dirty > max_bytes)
 364                 return (zfs_vdev_async_write_max_active);
 365 
 366         /*
 367          * linear interpolation:
 368          * slope = (max_writes - min_writes) / (max_bytes - min_bytes)
 369          * move right by min_bytes
 370          * move up by min_writes
 371          */
 372         writes = (dirty - min_bytes) *
 373             (zfs_vdev_async_write_max_active -
 374             zfs_vdev_async_write_min_active) /
 375             (max_bytes - min_bytes) +
 376             zfs_vdev_async_write_min_active;
 377         ASSERT3U(writes, >=, zfs_vdev_async_write_min_active);
 378         ASSERT3U(writes, <=, zfs_vdev_async_write_max_active);
 379         return (writes);
 380 }
 381 
 382 static int
 383 vdev_queue_class_max_active(spa_t *spa, zio_priority_t p)
 384 {
 385         switch (p) {
 386         case ZIO_PRIORITY_SYNC_READ:
 387                 return (zfs_vdev_sync_read_max_active);
 388         case ZIO_PRIORITY_SYNC_WRITE:
 389                 return (zfs_vdev_sync_write_max_active);
 390         case ZIO_PRIORITY_ASYNC_READ:
 391                 return (zfs_vdev_async_read_max_active);
 392         case ZIO_PRIORITY_ASYNC_WRITE:
 393                 return (vdev_queue_max_async_writes(
 394                     spa->spa_dsl_pool->dp_dirty_total));
 395         case ZIO_PRIORITY_SCRUB:
 396                 return (zfs_vdev_scrub_max_active);
 397         default:
 398                 panic("invalid priority %u", p);
 399                 return (0);
 400         }
 401 }
 402 
 403 /*
 404  * Return the i/o class to issue from, or ZIO_PRIORITY_MAX_QUEUEABLE if
 405  * there is no eligible class.
 406  */
 407 static zio_priority_t
 408 vdev_queue_class_to_issue(vdev_queue_t *vq)
 409 {
 410         spa_t *spa = vq->vq_vdev->vdev_spa;
 411         zio_priority_t p;
 412 
 413         if (avl_numnodes(&vq->vq_active_tree) >= zfs_vdev_max_active)
 414                 return (ZIO_PRIORITY_NUM_QUEUEABLE);
 415 
 416         /* find a queue that has not reached its minimum # outstanding i/os */
 417         for (p = 0; p < ZIO_PRIORITY_NUM_QUEUEABLE; p++) {
 418                 if (avl_numnodes(&vq->vq_class[p].vqc_queued_tree) > 0 &&
 419                     vq->vq_class[p].vqc_active <
 420                     vdev_queue_class_min_active(p))
 421                         return (p);
 422         }
 423 
 424         /*
 425          * If we haven't found a queue, look for one that hasn't reached its
 426          * maximum # outstanding i/os.
 427          */
 428         for (p = 0; p < ZIO_PRIORITY_NUM_QUEUEABLE; p++) {
 429                 if (avl_numnodes(&vq->vq_class[p].vqc_queued_tree) > 0 &&
 430                     vq->vq_class[p].vqc_active <
 431                     vdev_queue_class_max_active(spa, p))
 432                         return (p);
 433         }
 434 
 435         /* No eligible queued i/os */
 436         return (ZIO_PRIORITY_NUM_QUEUEABLE);
 437 }
 438 
 439 /*
 440  * Compute the range spanned by two i/os, which is the endpoint of the last
 441  * (lio->io_offset + lio->io_size) minus start of the first (fio->io_offset).
 442  * Conveniently, the gap between fio and lio is given by -IO_SPAN(lio, fio);
 443  * thus fio and lio are adjacent if and only if IO_SPAN(lio, fio) == 0.
 444  */
 445 #define IO_SPAN(fio, lio) ((lio)->io_offset + (lio)->io_size - (fio)->io_offset)
 446 #define IO_GAP(fio, lio) (-IO_SPAN(lio, fio))
 447 
 448 static zio_t *
 449 vdev_queue_aggregate(vdev_queue_t *vq, zio_t *zio)
 450 {
 451         zio_t *first, *last, *aio, *dio, *mandatory, *nio;
 452         uint64_t maxgap = 0;
 453         uint64_t size;
 454         boolean_t stretch = B_FALSE;
 455         vdev_queue_class_t *vqc = &vq->vq_class[zio->io_priority];
 456         avl_tree_t *t = &vqc->vqc_queued_tree;
 457         enum zio_flag flags = zio->io_flags & ZIO_FLAG_AGG_INHERIT;
 458 
 459         if (zio->io_flags & ZIO_FLAG_DONT_AGGREGATE)
 460                 return (NULL);
 461 
 462         /*
 463          * The synchronous i/o queues are not sorted by LBA, so we can't
 464          * find adjacent i/os.  These i/os tend to not be tightly clustered,
 465          * or too large to aggregate, so this has little impact on performance.
 466          */
 467         if (zio->io_priority == ZIO_PRIORITY_SYNC_READ ||
 468             zio->io_priority == ZIO_PRIORITY_SYNC_WRITE)
 469                 return (NULL);
 470 
 471         first = last = zio;
 472 
 473         if (zio->io_type == ZIO_TYPE_READ)
 474                 maxgap = zfs_vdev_read_gap_limit;

 475 

 476         /*
 477          * We can aggregate I/Os that are sufficiently adjacent and of
 478          * the same flavor, as expressed by the AGG_INHERIT flags.
 479          * The latter requirement is necessary so that certain
 480          * attributes of the I/O, such as whether it's a normal I/O
 481          * or a scrub/resilver, can be preserved in the aggregate.
 482          * We can include optional I/Os, but don't allow them
 483          * to begin a range as they add no benefit in that situation.
 484          */
 485 
 486         /*
 487          * We keep track of the last non-optional I/O.
 488          */
 489         mandatory = (first->io_flags & ZIO_FLAG_OPTIONAL) ? NULL : first;
 490 
 491         /*
 492          * Walk backwards through sufficiently contiguous I/Os
 493          * recording the last non-option I/O.
 494          */
 495         while ((dio = AVL_PREV(t, first)) != NULL &&
 496             (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
 497             IO_SPAN(dio, last) <= zfs_vdev_aggregation_limit &&
 498             IO_GAP(dio, first) <= maxgap) {
 499                 first = dio;
 500                 if (mandatory == NULL && !(first->io_flags & ZIO_FLAG_OPTIONAL))
 501                         mandatory = first;
 502         }
 503 
 504         /*
 505          * Skip any initial optional I/Os.
 506          */
 507         while ((first->io_flags & ZIO_FLAG_OPTIONAL) && first != last) {
 508                 first = AVL_NEXT(t, first);
 509                 ASSERT(first != NULL);
 510         }
 511 
 512         /*
 513          * Walk forward through sufficiently contiguous I/Os.
 514          */
 515         while ((dio = AVL_NEXT(t, last)) != NULL &&
 516             (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
 517             IO_SPAN(first, dio) <= zfs_vdev_aggregation_limit &&
 518             IO_GAP(last, dio) <= maxgap) {
 519                 last = dio;
 520                 if (!(last->io_flags & ZIO_FLAG_OPTIONAL))
 521                         mandatory = last;
 522         }
 523 
 524         /*
 525          * Now that we've established the range of the I/O aggregation
 526          * we must decide what to do with trailing optional I/Os.
 527          * For reads, there's nothing to do. While we are unable to
 528          * aggregate further, it's possible that a trailing optional
 529          * I/O would allow the underlying device to aggregate with
 530          * subsequent I/Os. We must therefore determine if the next
 531          * non-optional I/O is close enough to make aggregation
 532          * worthwhile.
 533          */
 534         if (zio->io_type == ZIO_TYPE_WRITE && mandatory != NULL) {
 535                 zio_t *nio = last;

 536                 while ((dio = AVL_NEXT(t, nio)) != NULL &&
 537                     IO_GAP(nio, dio) == 0 &&
 538                     IO_GAP(mandatory, dio) <= zfs_vdev_write_gap_limit) {
 539                         nio = dio;
 540                         if (!(nio->io_flags & ZIO_FLAG_OPTIONAL)) {
 541                                 stretch = B_TRUE;
 542                                 break;
 543                         }
 544                 }
 545         }
 546 
 547         if (stretch) {
 548                 /* This may be a no-op. */
 549                 dio = AVL_NEXT(t, last);
 550                 dio->io_flags &= ~ZIO_FLAG_OPTIONAL;
 551         } else {
 552                 while (last != mandatory && last != first) {
 553                         ASSERT(last->io_flags & ZIO_FLAG_OPTIONAL);
 554                         last = AVL_PREV(t, last);
 555                         ASSERT(last != NULL);
 556                 }
 557         }

 558 
 559         if (first == last)
 560                 return (NULL);

 561 
 562         size = IO_SPAN(first, last);
 563         ASSERT3U(size, <=, zfs_vdev_aggregation_limit);
 564 
 565         aio = zio_vdev_delegated_io(first->io_vd, first->io_offset,
 566             zio_buf_alloc(size), size, first->io_type, zio->io_priority,
 567             flags | ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE,
 568             vdev_queue_agg_io_done, NULL);
 569         aio->io_timestamp = first->io_timestamp;
 570 
 571         nio = first;
 572         do {
 573                 dio = nio;
 574                 nio = AVL_NEXT(t, dio);
 575                 ASSERT3U(dio->io_type, ==, aio->io_type);

 576 
 577                 if (dio->io_flags & ZIO_FLAG_NODATA) {
 578                         ASSERT3U(dio->io_type, ==, ZIO_TYPE_WRITE);
 579                         bzero((char *)aio->io_data + (dio->io_offset -
 580                             aio->io_offset), dio->io_size);
 581                 } else if (dio->io_type == ZIO_TYPE_WRITE) {
 582                         bcopy(dio->io_data, (char *)aio->io_data +
 583                             (dio->io_offset - aio->io_offset),
 584                             dio->io_size);
 585                 }
 586 
 587                 zio_add_child(dio, aio);
 588                 vdev_queue_io_remove(vq, dio);
 589                 zio_vdev_io_bypass(dio);
 590                 zio_execute(dio);
 591         } while (dio != last);
 592 


 593         return (aio);
 594 }
 595 
 596 static zio_t *
 597 vdev_queue_io_to_issue(vdev_queue_t *vq)
 598 {
 599         zio_t *zio, *aio;
 600         zio_priority_t p;
 601         avl_index_t idx;
 602         vdev_queue_class_t *vqc;
 603         zio_t search;
 604 
 605 again:
 606         ASSERT(MUTEX_HELD(&vq->vq_lock));
 607 
 608         p = vdev_queue_class_to_issue(vq);
 609 
 610         if (p == ZIO_PRIORITY_NUM_QUEUEABLE) {
 611                 /* No eligible queued i/os */
 612                 return (NULL);
 613         }
 614 
 615         /*
 616          * For LBA-ordered queues (async / scrub), issue the i/o which follows
 617          * the most recently issued i/o in LBA (offset) order.
 618          *
 619          * For FIFO queues (sync), issue the i/o with the lowest timestamp.
 620          */
 621         vqc = &vq->vq_class[p];
 622         search.io_timestamp = 0;
 623         search.io_offset = vq->vq_last_offset + 1;
 624         VERIFY3P(avl_find(&vqc->vqc_queued_tree, &search, &idx), ==, NULL);
 625         zio = avl_nearest(&vqc->vqc_queued_tree, idx, AVL_AFTER);
 626         if (zio == NULL)
 627                 zio = avl_first(&vqc->vqc_queued_tree);
 628         ASSERT3U(zio->io_priority, ==, p);
 629 
 630         aio = vdev_queue_aggregate(vq, zio);
 631         if (aio != NULL)
 632                 zio = aio;
 633         else
 634                 vdev_queue_io_remove(vq, zio);
 635 
 636         /*
 637          * If the I/O is or was optional and therefore has no data, we need to
 638          * simply discard it. We need to drop the vdev queue's lock to avoid a
 639          * deadlock that we could encounter since this I/O will complete
 640          * immediately.
 641          */
 642         if (zio->io_flags & ZIO_FLAG_NODATA) {
 643                 mutex_exit(&vq->vq_lock);
 644                 zio_vdev_io_bypass(zio);
 645                 zio_execute(zio);
 646                 mutex_enter(&vq->vq_lock);
 647                 goto again;
 648         }
 649 
 650         vdev_queue_pending_add(vq, zio);
 651         vq->vq_last_offset = zio->io_offset;
 652 
 653         return (zio);
 654 }
 655 
 656 zio_t *
 657 vdev_queue_io(zio_t *zio)
 658 {
 659         vdev_queue_t *vq = &zio->io_vd->vdev_queue;
 660         zio_t *nio;
 661 


 662         if (zio->io_flags & ZIO_FLAG_DONT_QUEUE)
 663                 return (zio);
 664 
 665         /*
 666          * Children i/os inherent their parent's priority, which might
 667          * not match the child's i/o type.  Fix it up here.
 668          */
 669         if (zio->io_type == ZIO_TYPE_READ) {
 670                 if (zio->io_priority != ZIO_PRIORITY_SYNC_READ &&
 671                     zio->io_priority != ZIO_PRIORITY_ASYNC_READ &&
 672                     zio->io_priority != ZIO_PRIORITY_SCRUB)
 673                         zio->io_priority = ZIO_PRIORITY_ASYNC_READ;
 674         } else {
 675                 ASSERT(zio->io_type == ZIO_TYPE_WRITE);
 676                 if (zio->io_priority != ZIO_PRIORITY_SYNC_WRITE &&
 677                     zio->io_priority != ZIO_PRIORITY_ASYNC_WRITE)
 678                         zio->io_priority = ZIO_PRIORITY_ASYNC_WRITE;
 679         }
 680 
 681         zio->io_flags |= ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE;
 682 





 683         mutex_enter(&vq->vq_lock);

 684         zio->io_timestamp = gethrtime();



 685         vdev_queue_io_add(vq, zio);
 686         nio = vdev_queue_io_to_issue(vq);


 687         mutex_exit(&vq->vq_lock);
 688 
 689         if (nio == NULL)
 690                 return (NULL);
 691 
 692         if (nio->io_done == vdev_queue_agg_io_done) {
 693                 zio_nowait(nio);
 694                 return (NULL);
 695         }
 696 
 697         return (nio);
 698 }
 699 
 700 void
 701 vdev_queue_io_done(zio_t *zio)
 702 {
 703         vdev_queue_t *vq = &zio->io_vd->vdev_queue;
 704         zio_t *nio;
 705 
 706         if (zio_injection_enabled)
 707                 delay(SEC_TO_TICK(zio_handle_io_delay(zio)));
 708 
 709         mutex_enter(&vq->vq_lock);
 710 
 711         vdev_queue_pending_remove(vq, zio);
 712 
 713         vq->vq_io_complete_ts = gethrtime();
 714 
 715         while ((nio = vdev_queue_io_to_issue(vq)) != NULL) {



 716                 mutex_exit(&vq->vq_lock);
 717                 if (nio->io_done == vdev_queue_agg_io_done) {
 718                         zio_nowait(nio);
 719                 } else {
 720                         zio_vdev_io_reissue(nio);
 721                         zio_execute(nio);
 722                 }
 723                 mutex_enter(&vq->vq_lock);
 724         }
 725 
 726         mutex_exit(&vq->vq_lock);
 727 }