block/mq-deadline.c

   1 /*
   2  *  MQ Deadline i/o scheduler - adaptation of the legacy deadline scheduler,
   3  *  for the blk-mq scheduling framework
   4  *
   5  *  Copyright (C) 2016 Jens Axboe <axboe@kernel.dk>
   6  */
   7 #include <linux/kernel.h>
   8 #include <linux/fs.h>
   9 #include <linux/blkdev.h>
  10 #include <linux/blk-mq.h>
  11 #include <linux/elevator.h>
  12 #include <linux/bio.h>
  13 #include <linux/module.h>
  14 #include <linux/slab.h>
  15 #include <linux/init.h>
  16 #include <linux/compiler.h>
  17 #include <linux/rbtree.h>
  18 #include <linux/sbitmap.h>
  19
  20 #include "blk.h"
  21 #include "blk-mq.h"
  22 #include "blk-mq-tag.h"
  23 #include "blk-mq-sched.h"
  24
  25 /*
  26  * See Documentation/block/deadline-iosched.txt
  27  */
  28 static const int read_expire = HZ / 2;  /* max time before a read is submitted. */
  29 static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
  30 static const int writes_starved = 2;    /* max times reads can starve a write */
  31 static const int fifo_batch = 16;       /* # of sequential requests treated as one
  32                                      by the above parameters. For throughput. */
  33
  34 struct deadline_data {
  35         /*
  36          * run time data
  37          */
  38
  39         /*
  40          * requests (deadline_rq s) are present on both sort_list and fifo_list
  41          */
  42         struct rb_root sort_list[2];
  43         struct list_head fifo_list[2];
  44
  45         /*
  46          * next in sort order. read, write or both are NULL
  47          */
  48         struct request *next_rq[2];
  49         unsigned int batching;          /* number of sequential requests made */
  50         unsigned int starved;           /* times reads have starved writes */
  51
  52         /*
  53          * settings that change how the i/o scheduler behaves
  54          */
  55         int fifo_expire[2];
  56         int fifo_batch;
  57         int writes_starved;
  58         int front_merges;
  59
  60         spinlock_t lock;
  61         struct list_head dispatch;
  62 };
  63
  64 static inline struct rb_root *
  65 deadline_rb_root(struct deadline_data *dd, struct request *rq)
  66 {
  67         return &dd->sort_list[rq_data_dir(rq)];
  68 }
  69
  70 /*
  71  * get the request after `rq' in sector-sorted order
  72  */
  73 static inline struct request *
  74 deadline_latter_request(struct request *rq)
  75 {
  76         struct rb_node *node = rb_next(&rq->rb_node);
  77
  78         if (node)
  79                 return rb_entry_rq(node);
  80
  81         return NULL;
  82 }
  83
  84 static void
  85 deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
  86 {
  87         struct rb_root *root = deadline_rb_root(dd, rq);
  88
  89         elv_rb_add(root, rq);
  90 }
  91
  92 static inline void
  93 deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
  94 {
  95         const int data_dir = rq_data_dir(rq);
  96
  97         if (dd->next_rq[data_dir] == rq)
  98                 dd->next_rq[data_dir] = deadline_latter_request(rq);
  99
 100         elv_rb_del(deadline_rb_root(dd, rq), rq);
 101 }
 102
 103 /*
 104  * remove rq from rbtree and fifo.
 105  */
 106 static void deadline_remove_request(struct request_queue *q, struct request *rq)
 107 {
 108         struct deadline_data *dd = q->elevator->elevator_data;
 109
 110         list_del_init(&rq->queuelist);
 111
 112         /*
 113          * We might not be on the rbtree, if we are doing an insert merge
 114          */
 115         if (!RB_EMPTY_NODE(&rq->rb_node))
 116                 deadline_del_rq_rb(dd, rq);
 117
 118         elv_rqhash_del(q, rq);
 119         if (q->last_merge == rq)
 120                 q->last_merge = NULL;
 121 }
 122
 123 static void dd_request_merged(struct request_queue *q, struct request *req,
 124                               int type)
 125 {
 126         struct deadline_data *dd = q->elevator->elevator_data;
 127
 128         /*
 129          * if the merge was a front merge, we need to reposition request
 130          */
 131         if (type == ELEVATOR_FRONT_MERGE) {
 132                 elv_rb_del(deadline_rb_root(dd, req), req);
 133                 deadline_add_rq_rb(dd, req);
 134         }
 135 }
 136
 137 static void dd_merged_requests(struct request_queue *q, struct request *req,
 138                                struct request *next)
 139 {
 140         /*
 141          * if next expires before rq, assign its expire time to rq
 142          * and move into next position (next will be deleted) in fifo
 143          */
 144         if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
 145                 if (time_before((unsigned long)next->fifo_time,
 146                                 (unsigned long)req->fifo_time)) {
 147                         list_move(&req->queuelist, &next->queuelist);
 148                         req->fifo_time = next->fifo_time;
 149                 }
 150         }
 151
 152         /*
 153          * kill knowledge of next, this one is a goner
 154          */
 155         deadline_remove_request(q, next);
 156 }
 157
 158 /*
 159  * move an entry to dispatch queue
 160  */
 161 static void
 162 deadline_move_request(struct deadline_data *dd, struct request *rq)
 163 {
 164         const int data_dir = rq_data_dir(rq);
 165
 166         dd->next_rq[READ] = NULL;
 167         dd->next_rq[WRITE] = NULL;
 168         dd->next_rq[data_dir] = deadline_latter_request(rq);
 169
 170         /*
 171          * take it off the sort and fifo list
 172          */
 173         deadline_remove_request(rq->q, rq);
 174 }
 175
 176 /*
 177  * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
 178  * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
 179  */
 180 static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
 181 {
 182         struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
 183
 184         /*
 185          * rq is expired!
 186          */
 187         if (time_after_eq(jiffies, (unsigned long)rq->fifo_time))
 188                 return 1;
 189
 190         return 0;
 191 }
 192
 193 /*
 194  * deadline_dispatch_requests selects the best request according to
 195  * read/write expire, fifo_batch, etc
 196  */
 197 static struct request *__dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
 198 {
 199         struct deadline_data *dd = hctx->queue->elevator->elevator_data;
 200         struct request *rq;
 201         bool reads, writes;
 202         int data_dir;
 203
 204         if (!list_empty(&dd->dispatch)) {
 205                 rq = list_first_entry(&dd->dispatch, struct request, queuelist);
 206                 list_del_init(&rq->queuelist);
 207                 goto done;
 208         }
 209
 210         reads = !list_empty(&dd->fifo_list[READ]);
 211         writes = !list_empty(&dd->fifo_list[WRITE]);
 212
 213         /*
 214          * batches are currently reads XOR writes
 215          */
 216         if (dd->next_rq[WRITE])
 217                 rq = dd->next_rq[WRITE];
 218         else
 219                 rq = dd->next_rq[READ];
 220
 221         if (rq && dd->batching < dd->fifo_batch)
 222                 /* we have a next request are still entitled to batch */
 223                 goto dispatch_request;
 224
 225         /*
 226          * at this point we are not running a batch. select the appropriate
 227          * data direction (read / write)
 228          */
 229
 230         if (reads) {
 231                 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
 232
 233                 if (writes && (dd->starved++ >= dd->writes_starved))
 234                         goto dispatch_writes;
 235
 236                 data_dir = READ;
 237
 238                 goto dispatch_find_request;
 239         }
 240
 241         /*
 242          * there are either no reads or writes have been starved
 243          */
 244
 245         if (writes) {
 246 dispatch_writes:
 247                 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
 248
 249                 dd->starved = 0;
 250
 251                 data_dir = WRITE;
 252
 253                 goto dispatch_find_request;
 254         }
 255
 256         return NULL;
 257
 258 dispatch_find_request:
 259         /*
 260          * we are not running a batch, find best request for selected data_dir
 261          */
 262         if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
 263                 /*
 264                  * A deadline has expired, the last request was in the other
 265                  * direction, or we have run out of higher-sectored requests.
 266                  * Start again from the request with the earliest expiry time.
 267                  */
 268                 rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
 269         } else {
 270                 /*
 271                  * The last req was the same dir and we have a next request in
 272                  * sort order. No expired requests so continue on from here.
 273                  */
 274                 rq = dd->next_rq[data_dir];
 275         }
 276
 277         dd->batching = 0;
 278
 279 dispatch_request:
 280         /*
 281          * rq is the selected appropriate request.
 282          */
 283         dd->batching++;
 284         deadline_move_request(dd, rq);
 285 done:
 286         rq->rq_flags |= RQF_STARTED;
 287         return rq;
 288 }
 289
 290 static struct request *dd_dispatch_request(struct blk_mq_hw_ctx *hctx)
 291 {
 292         struct deadline_data *dd = hctx->queue->elevator->elevator_data;
 293         struct request *rq;
 294
 295         spin_lock(&dd->lock);
 296         rq = __dd_dispatch_request(hctx);
 297         spin_unlock(&dd->lock);
 298
 299         return rq;
 300 }
 301
 302 static void dd_exit_queue(struct elevator_queue *e)
 303 {
 304         struct deadline_data *dd = e->elevator_data;
 305
 306         BUG_ON(!list_empty(&dd->fifo_list[READ]));
 307         BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
 308
 309         kfree(dd);
 310 }
 311
 312 /*
 313  * initialize elevator private data (deadline_data).
 314  */
 315 static int dd_init_queue(struct request_queue *q, struct elevator_type *e)
 316 {
 317         struct deadline_data *dd;
 318         struct elevator_queue *eq;
 319
 320         eq = elevator_alloc(q, e);
 321         if (!eq)
 322                 return -ENOMEM;
 323
 324         dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
 325         if (!dd) {
 326                 kobject_put(&eq->kobj);
 327                 return -ENOMEM;
 328         }
 329         eq->elevator_data = dd;
 330
 331         INIT_LIST_HEAD(&dd->fifo_list[READ]);
 332         INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
 333         dd->sort_list[READ] = RB_ROOT;
 334         dd->sort_list[WRITE] = RB_ROOT;
 335         dd->fifo_expire[READ] = read_expire;
 336         dd->fifo_expire[WRITE] = write_expire;
 337         dd->writes_starved = writes_starved;
 338         dd->front_merges = 1;
 339         dd->fifo_batch = fifo_batch;
 340         spin_lock_init(&dd->lock);
 341         INIT_LIST_HEAD(&dd->dispatch);
 342
 343         q->elevator = eq;
 344         return 0;
 345 }
 346
 347 static int dd_request_merge(struct request_queue *q, struct request **rq,
 348                             struct bio *bio)
 349 {
 350         struct deadline_data *dd = q->elevator->elevator_data;
 351         sector_t sector = bio_end_sector(bio);
 352         struct request *__rq;
 353
 354         if (!dd->front_merges)
 355                 return ELEVATOR_NO_MERGE;
 356
 357         __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
 358         if (__rq) {
 359                 BUG_ON(sector != blk_rq_pos(__rq));
 360
 361                 if (elv_bio_merge_ok(__rq, bio)) {
 362                         *rq = __rq;
 363                         return ELEVATOR_FRONT_MERGE;
 364                 }
 365         }
 366
 367         return ELEVATOR_NO_MERGE;
 368 }
 369
 370 static bool dd_bio_merge(struct blk_mq_hw_ctx *hctx, struct bio *bio)
 371 {
 372         struct request_queue *q = hctx->queue;
 373         struct deadline_data *dd = q->elevator->elevator_data;
 374         int ret;
 375
 376         spin_lock(&dd->lock);
 377         ret = blk_mq_sched_try_merge(q, bio);
 378         spin_unlock(&dd->lock);
 379
 380         return ret;
 381 }
 382
 383 /*
 384  * add rq to rbtree and fifo
 385  */
 386 static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
 387                               bool at_head)
 388 {
 389         struct request_queue *q = hctx->queue;
 390         struct deadline_data *dd = q->elevator->elevator_data;
 391         const int data_dir = rq_data_dir(rq);
 392
 393         if (blk_mq_sched_try_insert_merge(q, rq))
 394                 return;
 395
 396         blk_mq_sched_request_inserted(rq);
 397
 398         if (blk_mq_sched_bypass_insert(hctx, rq))
 399                 return;
 400
 401         if (at_head || blk_rq_is_passthrough(rq)) {
 402                 if (at_head)
 403                         list_add(&rq->queuelist, &dd->dispatch);
 404                 else
 405                         list_add_tail(&rq->queuelist, &dd->dispatch);
 406         } else {
 407                 deadline_add_rq_rb(dd, rq);
 408
 409                 if (rq_mergeable(rq)) {
 410                         elv_rqhash_add(q, rq);
 411                         if (!q->last_merge)
 412                                 q->last_merge = rq;
 413                 }
 414
 415                 /*
 416                  * set expire time and add to fifo list
 417                  */
 418                 rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
 419                 list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
 420         }
 421 }
 422
 423 static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
 424                                struct list_head *list, bool at_head)
 425 {
 426         struct request_queue *q = hctx->queue;
 427         struct deadline_data *dd = q->elevator->elevator_data;
 428
 429         spin_lock(&dd->lock);
 430         while (!list_empty(list)) {
 431                 struct request *rq;
 432
 433                 rq = list_first_entry(list, struct request, queuelist);
 434                 list_del_init(&rq->queuelist);
 435                 dd_insert_request(hctx, rq, at_head);
 436         }
 437         spin_unlock(&dd->lock);
 438 }
 439
 440 static bool dd_has_work(struct blk_mq_hw_ctx *hctx)
 441 {
 442         struct deadline_data *dd = hctx->queue->elevator->elevator_data;
 443
 444         return !list_empty_careful(&dd->dispatch) ||
 445                 !list_empty_careful(&dd->fifo_list[0]) ||
 446                 !list_empty_careful(&dd->fifo_list[1]);
 447 }
 448
 449 /*
 450  * sysfs parts below
 451  */
 452 static ssize_t
 453 deadline_var_show(int var, char *page)
 454 {
 455         return sprintf(page, "%d\n", var);
 456 }
 457
 458 static ssize_t
 459 deadline_var_store(int *var, const char *page, size_t count)
 460 {
 461         char *p = (char *) page;
 462
 463         *var = simple_strtol(p, &p, 10);
 464         return count;
 465 }
 466
 467 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
 468 static ssize_t __FUNC(struct elevator_queue *e, char *page)             \
 469 {                                                                       \
 470         struct deadline_data *dd = e->elevator_data;                    \
 471         int __data = __VAR;                                             \
 472         if (__CONV)                                                     \
 473                 __data = jiffies_to_msecs(__data);                      \
 474         return deadline_var_show(__data, (page));                       \
 475 }
 476 SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
 477 SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
 478 SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
 479 SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
 480 SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
 481 #undef SHOW_FUNCTION
 482
 483 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
 484 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
 485 {                                                                       \
 486         struct deadline_data *dd = e->elevator_data;                    \
 487         int __data;                                                     \
 488         int ret = deadline_var_store(&__data, (page), count);           \
 489         if (__data < (MIN))                                             \
 490                 __data = (MIN);                                         \
 491         else if (__data > (MAX))                                        \
 492                 __data = (MAX);                                         \
 493         if (__CONV)                                                     \
 494                 *(__PTR) = msecs_to_jiffies(__data);                    \
 495         else                                                            \
 496                 *(__PTR) = __data;                                      \
 497         return ret;                                                     \
 498 }
 499 STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
 500 STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
 501 STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
 502 STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
 503 STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
 504 #undef STORE_FUNCTION
 505
 506 #define DD_ATTR(name) \
 507         __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
 508                                       deadline_##name##_store)
 509
 510 static struct elv_fs_entry deadline_attrs[] = {
 511         DD_ATTR(read_expire),
 512         DD_ATTR(write_expire),
 513         DD_ATTR(writes_starved),
 514         DD_ATTR(front_merges),
 515         DD_ATTR(fifo_batch),
 516         __ATTR_NULL
 517 };
 518
 519 static struct elevator_type mq_deadline = {
 520         .ops.mq = {
 521                 .insert_requests        = dd_insert_requests,
 522                 .dispatch_request       = dd_dispatch_request,
 523                 .next_request           = elv_rb_latter_request,
 524                 .former_request         = elv_rb_former_request,
 525                 .bio_merge              = dd_bio_merge,
 526                 .request_merge          = dd_request_merge,
 527                 .requests_merged        = dd_merged_requests,
 528                 .request_merged         = dd_request_merged,
 529                 .has_work               = dd_has_work,
 530                 .init_sched             = dd_init_queue,
 531                 .exit_sched             = dd_exit_queue,
 532         },
 533
 534         .uses_mq        = true,
 535         .elevator_attrs = deadline_attrs,
 536         .elevator_name = "mq-deadline",
 537         .elevator_owner = THIS_MODULE,
 538 };
 539
 540 static int __init deadline_init(void)
 541 {
 542         return elv_register(&mq_deadline);
 543 }
 544
 545 static void __exit deadline_exit(void)
 546 {
 547         elv_unregister(&mq_deadline);
 548 }
 549
 550 module_init(deadline_init);
 551 module_exit(deadline_exit);
 552
 553 MODULE_AUTHOR("Jens Axboe");
 554 MODULE_LICENSE("GPL");
 555 MODULE_DESCRIPTION("MQ deadline IO scheduler");