module/zfs/vdev_queue.c

   1 /*
   2  * CDDL HEADER START
   3  *
   4  * The contents of this file are subject to the terms of the
   5  * Common Development and Distribution License (the "License").
   6  * You may not use this file except in compliance with the License.
   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 #include <sys/zfs_context.h>
  27 #include <sys/vdev_impl.h>
  28 #include <sys/zio.h>
  29 #include <sys/avl.h>
  30
  31 /*
  32  * These tunables are for performance analysis.
  33  */
  34 /*
  35  * zfs_vdev_max_pending is the maximum number of i/os concurrently
  36  * pending to each device.  zfs_vdev_min_pending is the initial number
  37  * of i/os pending to each device (before it starts ramping up to
  38  * max_pending).
  39  */
  40 int zfs_vdev_max_pending = 10;
  41 int zfs_vdev_min_pending = 4;
  42
  43 /* deadline = pri + ddi_get_lbolt64() >> time_shift) */
  44 int zfs_vdev_time_shift = 6;
  45
  46 /* exponential I/O issue ramp-up rate */
  47 int zfs_vdev_ramp_rate = 2;
  48
  49 /*
  50  * To reduce IOPs, we aggregate small adjacent I/Os into one large I/O.
  51  * For read I/Os, we also aggregate across small adjacency gaps; for writes
  52  * we include spans of optional I/Os to aid aggregation at the disk even when
  53  * they aren't able to help us aggregate at this level.
  54  */
  55 int zfs_vdev_aggregation_limit = SPA_MAXBLOCKSIZE;
  56 int zfs_vdev_read_gap_limit = 32 << 10;
  57 int zfs_vdev_write_gap_limit = 4 << 10;
  58
  59 /*
  60  * Virtual device vector for disk I/O scheduling.
  61  */
  62 int
  63 vdev_queue_deadline_compare(const void *x1, const void *x2)
  64 {
  65         const zio_t *z1 = x1;
  66         const zio_t *z2 = x2;
  67
  68         if (z1->io_deadline < z2->io_deadline)
  69                 return (-1);
  70         if (z1->io_deadline > z2->io_deadline)
  71                 return (1);
  72
  73         if (z1->io_offset < z2->io_offset)
  74                 return (-1);
  75         if (z1->io_offset > z2->io_offset)
  76                 return (1);
  77
  78         if (z1 < z2)
  79                 return (-1);
  80         if (z1 > z2)
  81                 return (1);
  82
  83         return (0);
  84 }
  85
  86 int
  87 vdev_queue_offset_compare(const void *x1, const void *x2)
  88 {
  89         const zio_t *z1 = x1;
  90         const zio_t *z2 = x2;
  91
  92         if (z1->io_offset < z2->io_offset)
  93                 return (-1);
  94         if (z1->io_offset > z2->io_offset)
  95                 return (1);
  96
  97         if (z1 < z2)
  98                 return (-1);
  99         if (z1 > z2)
 100                 return (1);
 101
 102         return (0);
 103 }
 104
 105 void
 106 vdev_queue_init(vdev_t *vd)
 107 {
 108         vdev_queue_t *vq = &vd->vdev_queue;
 109         int i;
 110
 111         mutex_init(&vq->vq_lock, NULL, MUTEX_DEFAULT, NULL);
 112
 113         avl_create(&vq->vq_deadline_tree, vdev_queue_deadline_compare,
 114             sizeof (zio_t), offsetof(struct zio, io_deadline_node));
 115
 116         avl_create(&vq->vq_read_tree, vdev_queue_offset_compare,
 117             sizeof (zio_t), offsetof(struct zio, io_offset_node));
 118
 119         avl_create(&vq->vq_write_tree, vdev_queue_offset_compare,
 120             sizeof (zio_t), offsetof(struct zio, io_offset_node));
 121
 122         avl_create(&vq->vq_pending_tree, vdev_queue_offset_compare,
 123             sizeof (zio_t), offsetof(struct zio, io_offset_node));
 124
 125         /*
 126          * A list of buffers which can be used for aggregate I/O, this
 127          * avoids the need to allocate them on demand when memory is low.
 128          */
 129         list_create(&vq->vq_io_list, sizeof (vdev_io_t),
 130             offsetof(vdev_io_t, vi_node));
 131
 132         for (i = 0; i < zfs_vdev_max_pending; i++)
 133                 list_insert_tail(&vq->vq_io_list, zio_vdev_alloc());
 134 }
 135
 136 void
 137 vdev_queue_fini(vdev_t *vd)
 138 {
 139         vdev_queue_t *vq = &vd->vdev_queue;
 140         vdev_io_t *vi;
 141
 142         avl_destroy(&vq->vq_deadline_tree);
 143         avl_destroy(&vq->vq_read_tree);
 144         avl_destroy(&vq->vq_write_tree);
 145         avl_destroy(&vq->vq_pending_tree);
 146
 147         while ((vi = list_head(&vq->vq_io_list)) != NULL) {
 148                 list_remove(&vq->vq_io_list, vi);
 149                 zio_vdev_free(vi);
 150         }
 151
 152         list_destroy(&vq->vq_io_list);
 153
 154         mutex_destroy(&vq->vq_lock);
 155 }
 156
 157 static void
 158 vdev_queue_io_add(vdev_queue_t *vq, zio_t *zio)
 159 {
 160         avl_add(&vq->vq_deadline_tree, zio);
 161         avl_add(zio->io_vdev_tree, zio);
 162 }
 163
 164 static void
 165 vdev_queue_io_remove(vdev_queue_t *vq, zio_t *zio)
 166 {
 167         avl_remove(&vq->vq_deadline_tree, zio);
 168         avl_remove(zio->io_vdev_tree, zio);
 169 }
 170
 171 static void
 172 vdev_queue_agg_io_done(zio_t *aio)
 173 {
 174         vdev_queue_t *vq = &aio->io_vd->vdev_queue;
 175         vdev_io_t *vi = aio->io_data;
 176         zio_t *pio;
 177
 178         while ((pio = zio_walk_parents(aio)) != NULL)
 179                 if (aio->io_type == ZIO_TYPE_READ)
 180                         bcopy((char *)aio->io_data + (pio->io_offset -
 181                             aio->io_offset), pio->io_data, pio->io_size);
 182
 183         mutex_enter(&vq->vq_lock);
 184         list_insert_tail(&vq->vq_io_list, vi);
 185         mutex_exit(&vq->vq_lock);
 186 }
 187
 188 /*
 189  * Compute the range spanned by two i/os, which is the endpoint of the last
 190  * (lio->io_offset + lio->io_size) minus start of the first (fio->io_offset).
 191  * Conveniently, the gap between fio and lio is given by -IO_SPAN(lio, fio);
 192  * thus fio and lio are adjacent if and only if IO_SPAN(lio, fio) == 0.
 193  */
 194 #define IO_SPAN(fio, lio) ((lio)->io_offset + (lio)->io_size - (fio)->io_offset)
 195 #define IO_GAP(fio, lio) (-IO_SPAN(lio, fio))
 196
 197 static zio_t *
 198 vdev_queue_io_to_issue(vdev_queue_t *vq, uint64_t pending_limit)
 199 {
 200         zio_t *fio, *lio, *aio, *dio, *nio, *mio;
 201         avl_tree_t *t;
 202         vdev_io_t *vi;
 203         int flags;
 204         uint64_t maxspan = MIN(zfs_vdev_aggregation_limit, SPA_MAXBLOCKSIZE);
 205         uint64_t maxgap;
 206         int stretch;
 207
 208 again:
 209         ASSERT(MUTEX_HELD(&vq->vq_lock));
 210
 211         if (avl_numnodes(&vq->vq_pending_tree) >= pending_limit ||
 212             avl_numnodes(&vq->vq_deadline_tree) == 0)
 213                 return (NULL);
 214
 215         fio = lio = avl_first(&vq->vq_deadline_tree);
 216
 217         t = fio->io_vdev_tree;
 218         flags = fio->io_flags & ZIO_FLAG_AGG_INHERIT;
 219         maxgap = (t == &vq->vq_read_tree) ? zfs_vdev_read_gap_limit : 0;
 220
 221         vi = list_head(&vq->vq_io_list);
 222         if (vi == NULL) {
 223                 vi = zio_vdev_alloc();
 224                 list_insert_head(&vq->vq_io_list, vi);
 225         }
 226
 227         if (!(flags & ZIO_FLAG_DONT_AGGREGATE)) {
 228                 /*
 229                  * We can aggregate I/Os that are sufficiently adjacent and of
 230                  * the same flavor, as expressed by the AGG_INHERIT flags.
 231                  * The latter requirement is necessary so that certain
 232                  * attributes of the I/O, such as whether it's a normal I/O
 233                  * or a scrub/resilver, can be preserved in the aggregate.
 234                  * We can include optional I/Os, but don't allow them
 235                  * to begin a range as they add no benefit in that situation.
 236                  */
 237
 238                 /*
 239                  * We keep track of the last non-optional I/O.
 240                  */
 241                 mio = (fio->io_flags & ZIO_FLAG_OPTIONAL) ? NULL : fio;
 242
 243                 /*
 244                  * Walk backwards through sufficiently contiguous I/Os
 245                  * recording the last non-option I/O.
 246                  */
 247                 while ((dio = AVL_PREV(t, fio)) != NULL &&
 248                     (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
 249                     IO_SPAN(dio, lio) <= maxspan &&
 250                     IO_GAP(dio, fio) <= maxgap) {
 251                         fio = dio;
 252                         if (mio == NULL && !(fio->io_flags & ZIO_FLAG_OPTIONAL))
 253                                 mio = fio;
 254                 }
 255
 256                 /*
 257                  * Skip any initial optional I/Os.
 258                  */
 259                 while ((fio->io_flags & ZIO_FLAG_OPTIONAL) && fio != lio) {
 260                         fio = AVL_NEXT(t, fio);
 261                         ASSERT(fio != NULL);
 262                 }
 263
 264                 /*
 265                  * Walk forward through sufficiently contiguous I/Os.
 266                  */
 267                 while ((dio = AVL_NEXT(t, lio)) != NULL &&
 268                     (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
 269                     IO_SPAN(fio, dio) <= maxspan &&
 270                     IO_GAP(lio, dio) <= maxgap) {
 271                         lio = dio;
 272                         if (!(lio->io_flags & ZIO_FLAG_OPTIONAL))
 273                                 mio = lio;
 274                 }
 275
 276                 /*
 277                  * Now that we've established the range of the I/O aggregation
 278                  * we must decide what to do with trailing optional I/Os.
 279                  * For reads, there's nothing to do. While we are unable to
 280                  * aggregate further, it's possible that a trailing optional
 281                  * I/O would allow the underlying device to aggregate with
 282                  * subsequent I/Os. We must therefore determine if the next
 283                  * non-optional I/O is close enough to make aggregation
 284                  * worthwhile.
 285                  */
 286                 stretch = B_FALSE;
 287                 if (t != &vq->vq_read_tree && mio != NULL) {
 288                         nio = lio;
 289                         while ((dio = AVL_NEXT(t, nio)) != NULL &&
 290                             IO_GAP(nio, dio) == 0 &&
 291                             IO_GAP(mio, dio) <= zfs_vdev_write_gap_limit) {
 292                                 nio = dio;
 293                                 if (!(nio->io_flags & ZIO_FLAG_OPTIONAL)) {
 294                                         stretch = B_TRUE;
 295                                         break;
 296                                 }
 297                         }
 298                 }
 299
 300                 if (stretch) {
 301                         /* This may be a no-op. */
 302                         VERIFY((dio = AVL_NEXT(t, lio)) != NULL);
 303                         dio->io_flags &= ~ZIO_FLAG_OPTIONAL;
 304                 } else {
 305                         while (lio != mio && lio != fio) {
 306                                 ASSERT(lio->io_flags & ZIO_FLAG_OPTIONAL);
 307                                 lio = AVL_PREV(t, lio);
 308                                 ASSERT(lio != NULL);
 309                         }
 310                 }
 311         }
 312
 313         if (fio != lio) {
 314                 uint64_t size = IO_SPAN(fio, lio);
 315                 ASSERT(size <= maxspan);
 316                 ASSERT(vi != NULL);
 317
 318                 aio = zio_vdev_delegated_io(fio->io_vd, fio->io_offset,
 319                     vi, size, fio->io_type, ZIO_PRIORITY_AGG,
 320                     flags | ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE,
 321                     vdev_queue_agg_io_done, NULL);
 322
 323                 nio = fio;
 324                 do {
 325                         dio = nio;
 326                         nio = AVL_NEXT(t, dio);
 327                         ASSERT(dio->io_type == aio->io_type);
 328                         ASSERT(dio->io_vdev_tree == t);
 329
 330                         if (dio->io_flags & ZIO_FLAG_NODATA) {
 331                                 ASSERT(dio->io_type == ZIO_TYPE_WRITE);
 332                                 bzero((char *)aio->io_data + (dio->io_offset -
 333                                     aio->io_offset), dio->io_size);
 334                         } else if (dio->io_type == ZIO_TYPE_WRITE) {
 335                                 bcopy(dio->io_data, (char *)aio->io_data +
 336                                     (dio->io_offset - aio->io_offset),
 337                                     dio->io_size);
 338                         }
 339
 340                         zio_add_child(dio, aio);
 341                         vdev_queue_io_remove(vq, dio);
 342                         zio_vdev_io_bypass(dio);
 343                         zio_execute(dio);
 344                 } while (dio != lio);
 345
 346                 avl_add(&vq->vq_pending_tree, aio);
 347                 list_remove(&vq->vq_io_list, vi);
 348
 349                 return (aio);
 350         }
 351
 352         ASSERT(fio->io_vdev_tree == t);
 353         vdev_queue_io_remove(vq, fio);
 354
 355         /*
 356          * If the I/O is or was optional and therefore has no data, we need to
 357          * simply discard it. We need to drop the vdev queue's lock to avoid a
 358          * deadlock that we could encounter since this I/O will complete
 359          * immediately.
 360          */
 361         if (fio->io_flags & ZIO_FLAG_NODATA) {
 362                 mutex_exit(&vq->vq_lock);
 363                 zio_vdev_io_bypass(fio);
 364                 zio_execute(fio);
 365                 mutex_enter(&vq->vq_lock);
 366                 goto again;
 367         }
 368
 369         avl_add(&vq->vq_pending_tree, fio);
 370
 371         return (fio);
 372 }
 373
 374 zio_t *
 375 vdev_queue_io(zio_t *zio)
 376 {
 377         vdev_queue_t *vq = &zio->io_vd->vdev_queue;
 378         zio_t *nio;
 379
 380         ASSERT(zio->io_type == ZIO_TYPE_READ || zio->io_type == ZIO_TYPE_WRITE);
 381
 382         if (zio->io_flags & ZIO_FLAG_DONT_QUEUE)
 383                 return (zio);
 384
 385         zio->io_flags |= ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE;
 386
 387         if (zio->io_type == ZIO_TYPE_READ)
 388                 zio->io_vdev_tree = &vq->vq_read_tree;
 389         else
 390                 zio->io_vdev_tree = &vq->vq_write_tree;
 391
 392         mutex_enter(&vq->vq_lock);
 393
 394         zio->io_deadline = (ddi_get_lbolt64() >> zfs_vdev_time_shift) +
 395             zio->io_priority;
 396
 397         vdev_queue_io_add(vq, zio);
 398
 399         nio = vdev_queue_io_to_issue(vq, zfs_vdev_min_pending);
 400
 401         mutex_exit(&vq->vq_lock);
 402
 403         if (nio == NULL)
 404                 return (NULL);
 405
 406         if (nio->io_done == vdev_queue_agg_io_done) {
 407                 zio_nowait(nio);
 408                 return (NULL);
 409         }
 410
 411         return (nio);
 412 }
 413
 414 void
 415 vdev_queue_io_done(zio_t *zio)
 416 {
 417         vdev_queue_t *vq = &zio->io_vd->vdev_queue;
 418         int i;
 419
 420         mutex_enter(&vq->vq_lock);
 421
 422         avl_remove(&vq->vq_pending_tree, zio);
 423
 424         for (i = 0; i < zfs_vdev_ramp_rate; i++) {
 425                 zio_t *nio = vdev_queue_io_to_issue(vq, zfs_vdev_max_pending);
 426                 if (nio == NULL)
 427                         break;
 428                 mutex_exit(&vq->vq_lock);
 429                 if (nio->io_done == vdev_queue_agg_io_done) {
 430                         zio_nowait(nio);
 431                 } else {
 432                         zio_vdev_io_reissue(nio);
 433                         zio_execute(nio);
 434                 }
 435                 mutex_enter(&vq->vq_lock);
 436         }
 437
 438         mutex_exit(&vq->vq_lock);
 439 }
 440
 441 #if defined(_KERNEL) && defined(HAVE_SPL)
 442 module_param(zfs_vdev_max_pending, int, 0644);
 443 MODULE_PARM_DESC(zfs_vdev_max_pending, "Max pending per-vdev I/Os");
 444
 445 module_param(zfs_vdev_min_pending, int, 0644);
 446 MODULE_PARM_DESC(zfs_vdev_min_pending, "Min pending per-vdev I/Os");
 447
 448 module_param(zfs_vdev_aggregation_limit, int, 0644);
 449 MODULE_PARM_DESC(zfs_vdev_aggregation_limit, "Max vdev I/O aggregation size");
 450
 451 module_param(zfs_vdev_time_shift, int, 0644);
 452 MODULE_PARM_DESC(zfs_vdev_time_shift, "Deadline time shift for vdev I/O");
 453
 454 module_param(zfs_vdev_ramp_rate, int, 0644);
 455 MODULE_PARM_DESC(zfs_vdev_ramp_rate, "Exponential I/O issue ramp-up rate");
 456
 457 module_param(zfs_vdev_read_gap_limit, int, 0644);
 458 MODULE_PARM_DESC(zfs_vdev_read_gap_limit, "Aggregate read I/O over gap");
 459
 460 module_param(zfs_vdev_write_gap_limit, int, 0644);
 461 MODULE_PARM_DESC(zfs_vdev_write_gap_limit, "Aggregate write I/O over gap");
 462 #endif