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
 110         mutex_init(&vq->vq_lock, NULL, MUTEX_DEFAULT, NULL);
 111
 112         avl_create(&vq->vq_deadline_tree, vdev_queue_deadline_compare,
 113             sizeof (zio_t), offsetof(struct zio, io_deadline_node));
 114
 115         avl_create(&vq->vq_read_tree, vdev_queue_offset_compare,
 116             sizeof (zio_t), offsetof(struct zio, io_offset_node));
 117
 118         avl_create(&vq->vq_write_tree, vdev_queue_offset_compare,
 119             sizeof (zio_t), offsetof(struct zio, io_offset_node));
 120
 121         avl_create(&vq->vq_pending_tree, vdev_queue_offset_compare,
 122             sizeof (zio_t), offsetof(struct zio, io_offset_node));
 123 }
 124
 125 void
 126 vdev_queue_fini(vdev_t *vd)
 127 {
 128         vdev_queue_t *vq = &vd->vdev_queue;
 129
 130         avl_destroy(&vq->vq_deadline_tree);
 131         avl_destroy(&vq->vq_read_tree);
 132         avl_destroy(&vq->vq_write_tree);
 133         avl_destroy(&vq->vq_pending_tree);
 134
 135         mutex_destroy(&vq->vq_lock);
 136 }
 137
 138 static void
 139 vdev_queue_io_add(vdev_queue_t *vq, zio_t *zio)
 140 {
 141         avl_add(&vq->vq_deadline_tree, zio);
 142         avl_add(zio->io_vdev_tree, zio);
 143 }
 144
 145 static void
 146 vdev_queue_io_remove(vdev_queue_t *vq, zio_t *zio)
 147 {
 148         avl_remove(&vq->vq_deadline_tree, zio);
 149         avl_remove(zio->io_vdev_tree, zio);
 150 }
 151
 152 static void
 153 vdev_queue_agg_io_done(zio_t *aio)
 154 {
 155         zio_t *pio;
 156
 157         while ((pio = zio_walk_parents(aio)) != NULL)
 158                 if (aio->io_type == ZIO_TYPE_READ)
 159                         bcopy((char *)aio->io_data + (pio->io_offset -
 160                             aio->io_offset), pio->io_data, pio->io_size);
 161
 162         zio_buf_free(aio->io_data, aio->io_size);
 163 }
 164
 165 /*
 166  * Compute the range spanned by two i/os, which is the endpoint of the last
 167  * (lio->io_offset + lio->io_size) minus start of the first (fio->io_offset).
 168  * Conveniently, the gap between fio and lio is given by -IO_SPAN(lio, fio);
 169  * thus fio and lio are adjacent if and only if IO_SPAN(lio, fio) == 0.
 170  */
 171 #define IO_SPAN(fio, lio) ((lio)->io_offset + (lio)->io_size - (fio)->io_offset)
 172 #define IO_GAP(fio, lio) (-IO_SPAN(lio, fio))
 173
 174 static zio_t *
 175 vdev_queue_io_to_issue(vdev_queue_t *vq, uint64_t pending_limit)
 176 {
 177         zio_t *fio, *lio, *aio, *dio, *nio, *mio;
 178         avl_tree_t *t;
 179         int flags;
 180         uint64_t maxspan = zfs_vdev_aggregation_limit;
 181         uint64_t maxgap;
 182         int stretch;
 183
 184 again:
 185         ASSERT(MUTEX_HELD(&vq->vq_lock));
 186
 187         if (avl_numnodes(&vq->vq_pending_tree) >= pending_limit ||
 188             avl_numnodes(&vq->vq_deadline_tree) == 0)
 189                 return (NULL);
 190
 191         fio = lio = avl_first(&vq->vq_deadline_tree);
 192
 193         t = fio->io_vdev_tree;
 194         flags = fio->io_flags & ZIO_FLAG_AGG_INHERIT;
 195         maxgap = (t == &vq->vq_read_tree) ? zfs_vdev_read_gap_limit : 0;
 196
 197         if (!(flags & ZIO_FLAG_DONT_AGGREGATE)) {
 198                 /*
 199                  * We can aggregate I/Os that are sufficiently adjacent and of
 200                  * the same flavor, as expressed by the AGG_INHERIT flags.
 201                  * The latter requirement is necessary so that certain
 202                  * attributes of the I/O, such as whether it's a normal I/O
 203                  * or a scrub/resilver, can be preserved in the aggregate.
 204                  * We can include optional I/Os, but don't allow them
 205                  * to begin a range as they add no benefit in that situation.
 206                  */
 207
 208                 /*
 209                  * We keep track of the last non-optional I/O.
 210                  */
 211                 mio = (fio->io_flags & ZIO_FLAG_OPTIONAL) ? NULL : fio;
 212
 213                 /*
 214                  * Walk backwards through sufficiently contiguous I/Os
 215                  * recording the last non-option I/O.
 216                  */
 217                 while ((dio = AVL_PREV(t, fio)) != NULL &&
 218                     (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
 219                     IO_SPAN(dio, lio) <= maxspan &&
 220                     IO_GAP(dio, fio) <= maxgap) {
 221                         fio = dio;
 222                         if (mio == NULL && !(fio->io_flags & ZIO_FLAG_OPTIONAL))
 223                                 mio = fio;
 224                 }
 225
 226                 /*
 227                  * Skip any initial optional I/Os.
 228                  */
 229                 while ((fio->io_flags & ZIO_FLAG_OPTIONAL) && fio != lio) {
 230                         fio = AVL_NEXT(t, fio);
 231                         ASSERT(fio != NULL);
 232                 }
 233
 234                 /*
 235                  * Walk forward through sufficiently contiguous I/Os.
 236                  */
 237                 while ((dio = AVL_NEXT(t, lio)) != NULL &&
 238                     (dio->io_flags & ZIO_FLAG_AGG_INHERIT) == flags &&
 239                     IO_SPAN(fio, dio) <= maxspan &&
 240                     IO_GAP(lio, dio) <= maxgap) {
 241                         lio = dio;
 242                         if (!(lio->io_flags & ZIO_FLAG_OPTIONAL))
 243                                 mio = lio;
 244                 }
 245
 246                 /*
 247                  * Now that we've established the range of the I/O aggregation
 248                  * we must decide what to do with trailing optional I/Os.
 249                  * For reads, there's nothing to do. While we are unable to
 250                  * aggregate further, it's possible that a trailing optional
 251                  * I/O would allow the underlying device to aggregate with
 252                  * subsequent I/Os. We must therefore determine if the next
 253                  * non-optional I/O is close enough to make aggregation
 254                  * worthwhile.
 255                  */
 256                 stretch = B_FALSE;
 257                 if (t != &vq->vq_read_tree && mio != NULL) {
 258                         nio = lio;
 259                         while ((dio = AVL_NEXT(t, nio)) != NULL &&
 260                             IO_GAP(nio, dio) == 0 &&
 261                             IO_GAP(mio, dio) <= zfs_vdev_write_gap_limit) {
 262                                 nio = dio;
 263                                 if (!(nio->io_flags & ZIO_FLAG_OPTIONAL)) {
 264                                         stretch = B_TRUE;
 265                                         break;
 266                                 }
 267                         }
 268                 }
 269
 270                 if (stretch) {
 271                         /* This may be a no-op. */
 272                         VERIFY((dio = AVL_NEXT(t, lio)) != NULL);
 273                         dio->io_flags &= ~ZIO_FLAG_OPTIONAL;
 274                 } else {
 275                         while (lio != mio && lio != fio) {
 276                                 ASSERT(lio->io_flags & ZIO_FLAG_OPTIONAL);
 277                                 lio = AVL_PREV(t, lio);
 278                                 ASSERT(lio != NULL);
 279                         }
 280                 }
 281         }
 282
 283         if (fio != lio) {
 284                 uint64_t size = IO_SPAN(fio, lio);
 285                 ASSERT(size <= zfs_vdev_aggregation_limit);
 286
 287                 aio = zio_vdev_delegated_io(fio->io_vd, fio->io_offset,
 288                     zio_buf_alloc(size), size, fio->io_type, ZIO_PRIORITY_AGG,
 289                     flags | ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE,
 290                     vdev_queue_agg_io_done, NULL);
 291
 292                 nio = fio;
 293                 do {
 294                         dio = nio;
 295                         nio = AVL_NEXT(t, dio);
 296                         ASSERT(dio->io_type == aio->io_type);
 297                         ASSERT(dio->io_vdev_tree == t);
 298
 299                         if (dio->io_flags & ZIO_FLAG_NODATA) {
 300                                 ASSERT(dio->io_type == ZIO_TYPE_WRITE);
 301                                 bzero((char *)aio->io_data + (dio->io_offset -
 302                                     aio->io_offset), dio->io_size);
 303                         } else if (dio->io_type == ZIO_TYPE_WRITE) {
 304                                 bcopy(dio->io_data, (char *)aio->io_data +
 305                                     (dio->io_offset - aio->io_offset),
 306                                     dio->io_size);
 307                         }
 308
 309                         zio_add_child(dio, aio);
 310                         vdev_queue_io_remove(vq, dio);
 311                         zio_vdev_io_bypass(dio);
 312                         zio_execute(dio);
 313                 } while (dio != lio);
 314
 315                 avl_add(&vq->vq_pending_tree, aio);
 316
 317                 return (aio);
 318         }
 319
 320         ASSERT(fio->io_vdev_tree == t);
 321         vdev_queue_io_remove(vq, fio);
 322
 323         /*
 324          * If the I/O is or was optional and therefore has no data, we need to
 325          * simply discard it. We need to drop the vdev queue's lock to avoid a
 326          * deadlock that we could encounter since this I/O will complete
 327          * immediately.
 328          */
 329         if (fio->io_flags & ZIO_FLAG_NODATA) {
 330                 mutex_exit(&vq->vq_lock);
 331                 zio_vdev_io_bypass(fio);
 332                 zio_execute(fio);
 333                 mutex_enter(&vq->vq_lock);
 334                 goto again;
 335         }
 336
 337         avl_add(&vq->vq_pending_tree, fio);
 338
 339         return (fio);
 340 }
 341
 342 zio_t *
 343 vdev_queue_io(zio_t *zio)
 344 {
 345         vdev_queue_t *vq = &zio->io_vd->vdev_queue;
 346         zio_t *nio;
 347
 348         ASSERT(zio->io_type == ZIO_TYPE_READ || zio->io_type == ZIO_TYPE_WRITE);
 349
 350         if (zio->io_flags & ZIO_FLAG_DONT_QUEUE)
 351                 return (zio);
 352
 353         zio->io_flags |= ZIO_FLAG_DONT_CACHE | ZIO_FLAG_DONT_QUEUE;
 354
 355         if (zio->io_type == ZIO_TYPE_READ)
 356                 zio->io_vdev_tree = &vq->vq_read_tree;
 357         else
 358                 zio->io_vdev_tree = &vq->vq_write_tree;
 359
 360         mutex_enter(&vq->vq_lock);
 361
 362         zio->io_deadline = (ddi_get_lbolt64() >> zfs_vdev_time_shift) +
 363             zio->io_priority;
 364
 365         vdev_queue_io_add(vq, zio);
 366
 367         nio = vdev_queue_io_to_issue(vq, zfs_vdev_min_pending);
 368
 369         mutex_exit(&vq->vq_lock);
 370
 371         if (nio == NULL)
 372                 return (NULL);
 373
 374         if (nio->io_done == vdev_queue_agg_io_done) {
 375                 zio_nowait(nio);
 376                 return (NULL);
 377         }
 378
 379         return (nio);
 380 }
 381
 382 void
 383 vdev_queue_io_done(zio_t *zio)
 384 {
 385         vdev_queue_t *vq = &zio->io_vd->vdev_queue;
 386         int i;
 387
 388         mutex_enter(&vq->vq_lock);
 389
 390         avl_remove(&vq->vq_pending_tree, zio);
 391
 392         for (i = 0; i < zfs_vdev_ramp_rate; i++) {
 393                 zio_t *nio = vdev_queue_io_to_issue(vq, zfs_vdev_max_pending);
 394                 if (nio == NULL)
 395                         break;
 396                 mutex_exit(&vq->vq_lock);
 397                 if (nio->io_done == vdev_queue_agg_io_done) {
 398                         zio_nowait(nio);
 399                 } else {
 400                         zio_vdev_io_reissue(nio);
 401                         zio_execute(nio);
 402                 }
 403                 mutex_enter(&vq->vq_lock);
 404         }
 405
 406         mutex_exit(&vq->vq_lock);
 407 }
 408
 409 #if defined(_KERNEL) && defined(HAVE_SPL)
 410 module_param(zfs_vdev_max_pending, int, 0644);
 411 MODULE_PARM_DESC(zfs_vdev_max_pending, "Maximum pending VDEV IO");
 412
 413 module_param(zfs_vdev_min_pending, int, 0644);
 414 MODULE_PARM_DESC(zfs_vdev_min_pending, "Minimum pending VDEV IO");
 415
 416 module_param(zfs_vdev_aggregation_limit, int, 0644);
 417 MODULE_PARM_DESC(zfs_vdev_aggregation_limit, "Maximum VDEV IO aggregation");
 418 #endif