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   1 /*
   2  *  Deadline i/o scheduler.
   3  *
   4  *  Copyright (C) 2002 Jens Axboe <axboe@suse.de>
   5  */
   6 #include <linux/kernel.h>
   7 #include <linux/fs.h>
   8 #include <linux/blkdev.h>
   9 #include <linux/elevator.h>
  10 #include <linux/bio.h>
  11 #include <linux/module.h>
  12 #include <linux/slab.h>
  13 #include <linux/init.h>
  14 #include <linux/compiler.h>
  15 #include <linux/rbtree.h>
  16
  17 /*
  18  * See Documentation/block/deadline-iosched.txt
  19  */
  20 static const int read_expire = HZ / 2;  /* max time before a read is submitted. */
  21 static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
  22 static const int writes_starved = 2;    /* max times reads can starve a write */
  23 static const int fifo_batch = 16;       /* # of sequential requests treated as one
  24                                      by the above parameters. For throughput. */
  25
  26 struct deadline_data {
  27         /*
  28          * run time data
  29          */
  30
  31         /*
  32          * requests (deadline_rq s) are present on both sort_list and fifo_list
  33          */
  34         struct rb_root sort_list[2];
  35         struct list_head fifo_list[2];
  36
  37         /*
  38          * next in sort order. read, write or both are NULL
  39          */
  40         struct deadline_rq *next_drq[2];
  41         unsigned int batching;          /* number of sequential requests made */
  42         sector_t last_sector;           /* head position */
  43         unsigned int starved;           /* times reads have starved writes */
  44
  45         /*
  46          * settings that change how the i/o scheduler behaves
  47          */
  48         int fifo_expire[2];
  49         int fifo_batch;
  50         int writes_starved;
  51         int front_merges;
  52
  53         mempool_t *drq_pool;
  54 };
  55
  56 /*
  57  * pre-request data.
  58  */
  59 struct deadline_rq {
  60         /*
  61          * rbtree index, key is the starting offset
  62          */
  63         struct rb_node rb_node;
  64         sector_t rb_key;
  65
  66         struct request *request;
  67
  68         /*
  69          * expire fifo
  70          */
  71         struct list_head fifo;
  72         unsigned long expires;
  73 };
  74
  75 static void deadline_move_request(struct deadline_data *dd, struct deadline_rq *drq);
  76
  77 static kmem_cache_t *drq_pool;
  78
  79 #define RQ_DATA(rq)     ((struct deadline_rq *) (rq)->elevator_private)
  80
  81 /*
  82  * rb tree support functions
  83  */
  84 #define rb_entry_drq(node)      rb_entry((node), struct deadline_rq, rb_node)
  85 #define DRQ_RB_ROOT(dd, drq)    (&(dd)->sort_list[rq_data_dir((drq)->request)])
  86 #define rq_rb_key(rq)           (rq)->sector
  87
  88 static struct deadline_rq *
  89 __deadline_add_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
  90 {
  91         struct rb_node **p = &DRQ_RB_ROOT(dd, drq)->rb_node;
  92         struct rb_node *parent = NULL;
  93         struct deadline_rq *__drq;
  94
  95         while (*p) {
  96                 parent = *p;
  97                 __drq = rb_entry_drq(parent);
  98
  99                 if (drq->rb_key < __drq->rb_key)
 100                         p = &(*p)->rb_left;
 101                 else if (drq->rb_key > __drq->rb_key)
 102                         p = &(*p)->rb_right;
 103                 else
 104                         return __drq;
 105         }
 106
 107         rb_link_node(&drq->rb_node, parent, p);
 108         return NULL;
 109 }
 110
 111 static void
 112 deadline_add_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
 113 {
 114         struct deadline_rq *__alias;
 115
 116         drq->rb_key = rq_rb_key(drq->request);
 117
 118 retry:
 119         __alias = __deadline_add_drq_rb(dd, drq);
 120         if (!__alias) {
 121                 rb_insert_color(&drq->rb_node, DRQ_RB_ROOT(dd, drq));
 122                 return;
 123         }
 124
 125         deadline_move_request(dd, __alias);
 126         goto retry;
 127 }
 128
 129 static inline void
 130 deadline_del_drq_rb(struct deadline_data *dd, struct deadline_rq *drq)
 131 {
 132         const int data_dir = rq_data_dir(drq->request);
 133
 134         if (dd->next_drq[data_dir] == drq) {
 135                 struct rb_node *rbnext = rb_next(&drq->rb_node);
 136
 137                 dd->next_drq[data_dir] = NULL;
 138                 if (rbnext)
 139                         dd->next_drq[data_dir] = rb_entry_drq(rbnext);
 140         }
 141
 142         BUG_ON(!RB_EMPTY_NODE(&drq->rb_node));
 143         rb_erase(&drq->rb_node, DRQ_RB_ROOT(dd, drq));
 144         RB_CLEAR_NODE(&drq->rb_node);
 145 }
 146
 147 static struct request *
 148 deadline_find_drq_rb(struct deadline_data *dd, sector_t sector, int data_dir)
 149 {
 150         struct rb_node *n = dd->sort_list[data_dir].rb_node;
 151         struct deadline_rq *drq;
 152
 153         while (n) {
 154                 drq = rb_entry_drq(n);
 155
 156                 if (sector < drq->rb_key)
 157                         n = n->rb_left;
 158                 else if (sector > drq->rb_key)
 159                         n = n->rb_right;
 160                 else
 161                         return drq->request;
 162         }
 163
 164         return NULL;
 165 }
 166
 167 /*
 168  * deadline_find_first_drq finds the first (lowest sector numbered) request
 169  * for the specified data_dir. Used to sweep back to the start of the disk
 170  * (1-way elevator) after we process the last (highest sector) request.
 171  */
 172 static struct deadline_rq *
 173 deadline_find_first_drq(struct deadline_data *dd, int data_dir)
 174 {
 175         struct rb_node *n = dd->sort_list[data_dir].rb_node;
 176
 177         for (;;) {
 178                 if (n->rb_left == NULL)
 179                         return rb_entry_drq(n);
 180
 181                 n = n->rb_left;
 182         }
 183 }
 184
 185 /*
 186  * add drq to rbtree and fifo
 187  */
 188 static void
 189 deadline_add_request(struct request_queue *q, struct request *rq)
 190 {
 191         struct deadline_data *dd = q->elevator->elevator_data;
 192         struct deadline_rq *drq = RQ_DATA(rq);
 193         const int data_dir = rq_data_dir(drq->request);
 194
 195         deadline_add_drq_rb(dd, drq);
 196
 197         /*
 198          * set expire time (only used for reads) and add to fifo list
 199          */
 200         drq->expires = jiffies + dd->fifo_expire[data_dir];
 201         list_add_tail(&drq->fifo, &dd->fifo_list[data_dir]);
 202 }
 203
 204 /*
 205  * remove rq from rbtree and fifo.
 206  */
 207 static void deadline_remove_request(request_queue_t *q, struct request *rq)
 208 {
 209         struct deadline_rq *drq = RQ_DATA(rq);
 210         struct deadline_data *dd = q->elevator->elevator_data;
 211
 212         list_del_init(&drq->fifo);
 213         deadline_del_drq_rb(dd, drq);
 214 }
 215
 216 static int
 217 deadline_merge(request_queue_t *q, struct request **req, struct bio *bio)
 218 {
 219         struct deadline_data *dd = q->elevator->elevator_data;
 220         struct request *__rq;
 221         int ret;
 222
 223         /*
 224          * check for front merge
 225          */
 226         if (dd->front_merges) {
 227                 sector_t rb_key = bio->bi_sector + bio_sectors(bio);
 228
 229                 __rq = deadline_find_drq_rb(dd, rb_key, bio_data_dir(bio));
 230                 if (__rq) {
 231                         BUG_ON(rb_key != rq_rb_key(__rq));
 232
 233                         if (elv_rq_merge_ok(__rq, bio)) {
 234                                 ret = ELEVATOR_FRONT_MERGE;
 235                                 goto out;
 236                         }
 237                 }
 238         }
 239
 240         return ELEVATOR_NO_MERGE;
 241 out:
 242         *req = __rq;
 243         return ret;
 244 }
 245
 246 static void deadline_merged_request(request_queue_t *q, struct request *req)
 247 {
 248         struct deadline_data *dd = q->elevator->elevator_data;
 249         struct deadline_rq *drq = RQ_DATA(req);
 250
 251         /*
 252          * if the merge was a front merge, we need to reposition request
 253          */
 254         if (rq_rb_key(req) != drq->rb_key) {
 255                 deadline_del_drq_rb(dd, drq);
 256                 deadline_add_drq_rb(dd, drq);
 257         }
 258 }
 259
 260 static void
 261 deadline_merged_requests(request_queue_t *q, struct request *req,
 262                          struct request *next)
 263 {
 264         struct deadline_data *dd = q->elevator->elevator_data;
 265         struct deadline_rq *drq = RQ_DATA(req);
 266         struct deadline_rq *dnext = RQ_DATA(next);
 267
 268         BUG_ON(!drq);
 269         BUG_ON(!dnext);
 270
 271         if (rq_rb_key(req) != drq->rb_key) {
 272                 deadline_del_drq_rb(dd, drq);
 273                 deadline_add_drq_rb(dd, drq);
 274         }
 275
 276         /*
 277          * if dnext expires before drq, assign its expire time to drq
 278          * and move into dnext position (dnext will be deleted) in fifo
 279          */
 280         if (!list_empty(&drq->fifo) && !list_empty(&dnext->fifo)) {
 281                 if (time_before(dnext->expires, drq->expires)) {
 282                         list_move(&drq->fifo, &dnext->fifo);
 283                         drq->expires = dnext->expires;
 284                 }
 285         }
 286
 287         /*
 288          * kill knowledge of next, this one is a goner
 289          */
 290         deadline_remove_request(q, next);
 291 }
 292
 293 /*
 294  * move request from sort list to dispatch queue.
 295  */
 296 static inline void
 297 deadline_move_to_dispatch(struct deadline_data *dd, struct deadline_rq *drq)
 298 {
 299         request_queue_t *q = drq->request->q;
 300
 301         deadline_remove_request(q, drq->request);
 302         elv_dispatch_add_tail(q, drq->request);
 303 }
 304
 305 /*
 306  * move an entry to dispatch queue
 307  */
 308 static void
 309 deadline_move_request(struct deadline_data *dd, struct deadline_rq *drq)
 310 {
 311         const int data_dir = rq_data_dir(drq->request);
 312         struct rb_node *rbnext = rb_next(&drq->rb_node);
 313
 314         dd->next_drq[READ] = NULL;
 315         dd->next_drq[WRITE] = NULL;
 316
 317         if (rbnext)
 318                 dd->next_drq[data_dir] = rb_entry_drq(rbnext);
 319
 320         dd->last_sector = drq->request->sector + drq->request->nr_sectors;
 321
 322         /*
 323          * take it off the sort and fifo list, move
 324          * to dispatch queue
 325          */
 326         deadline_move_to_dispatch(dd, drq);
 327 }
 328
 329 #define list_entry_fifo(ptr)    list_entry((ptr), struct deadline_rq, fifo)
 330
 331 /*
 332  * deadline_check_fifo returns 0 if there are no expired reads on the fifo,
 333  * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
 334  */
 335 static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
 336 {
 337         struct deadline_rq *drq = list_entry_fifo(dd->fifo_list[ddir].next);
 338
 339         /*
 340          * drq is expired!
 341          */
 342         if (time_after(jiffies, drq->expires))
 343                 return 1;
 344
 345         return 0;
 346 }
 347
 348 /*
 349  * deadline_dispatch_requests selects the best request according to
 350  * read/write expire, fifo_batch, etc
 351  */
 352 static int deadline_dispatch_requests(request_queue_t *q, int force)
 353 {
 354         struct deadline_data *dd = q->elevator->elevator_data;
 355         const int reads = !list_empty(&dd->fifo_list[READ]);
 356         const int writes = !list_empty(&dd->fifo_list[WRITE]);
 357         struct deadline_rq *drq;
 358         int data_dir;
 359
 360         /*
 361          * batches are currently reads XOR writes
 362          */
 363         if (dd->next_drq[WRITE])
 364                 drq = dd->next_drq[WRITE];
 365         else
 366                 drq = dd->next_drq[READ];
 367
 368         if (drq) {
 369                 /* we have a "next request" */
 370
 371                 if (dd->last_sector != drq->request->sector)
 372                         /* end the batch on a non sequential request */
 373                         dd->batching += dd->fifo_batch;
 374
 375                 if (dd->batching < dd->fifo_batch)
 376                         /* we are still entitled to batch */
 377                         goto dispatch_request;
 378         }
 379
 380         /*
 381          * at this point we are not running a batch. select the appropriate
 382          * data direction (read / write)
 383          */
 384
 385         if (reads) {
 386                 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
 387
 388                 if (writes && (dd->starved++ >= dd->writes_starved))
 389                         goto dispatch_writes;
 390
 391                 data_dir = READ;
 392
 393                 goto dispatch_find_request;
 394         }
 395
 396         /*
 397          * there are either no reads or writes have been starved
 398          */
 399
 400         if (writes) {
 401 dispatch_writes:
 402                 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
 403
 404                 dd->starved = 0;
 405
 406                 data_dir = WRITE;
 407
 408                 goto dispatch_find_request;
 409         }
 410
 411         return 0;
 412
 413 dispatch_find_request:
 414         /*
 415          * we are not running a batch, find best request for selected data_dir
 416          */
 417         if (deadline_check_fifo(dd, data_dir)) {
 418                 /* An expired request exists - satisfy it */
 419                 dd->batching = 0;
 420                 drq = list_entry_fifo(dd->fifo_list[data_dir].next);
 421
 422         } else if (dd->next_drq[data_dir]) {
 423                 /*
 424                  * The last req was the same dir and we have a next request in
 425                  * sort order. No expired requests so continue on from here.
 426                  */
 427                 drq = dd->next_drq[data_dir];
 428         } else {
 429                 /*
 430                  * The last req was the other direction or we have run out of
 431                  * higher-sectored requests. Go back to the lowest sectored
 432                  * request (1 way elevator) and start a new batch.
 433                  */
 434                 dd->batching = 0;
 435                 drq = deadline_find_first_drq(dd, data_dir);
 436         }
 437
 438 dispatch_request:
 439         /*
 440          * drq is the selected appropriate request.
 441          */
 442         dd->batching++;
 443         deadline_move_request(dd, drq);
 444
 445         return 1;
 446 }
 447
 448 static int deadline_queue_empty(request_queue_t *q)
 449 {
 450         struct deadline_data *dd = q->elevator->elevator_data;
 451
 452         return list_empty(&dd->fifo_list[WRITE])
 453                 && list_empty(&dd->fifo_list[READ]);
 454 }
 455
 456 static struct request *
 457 deadline_former_request(request_queue_t *q, struct request *rq)
 458 {
 459         struct deadline_rq *drq = RQ_DATA(rq);
 460         struct rb_node *rbprev = rb_prev(&drq->rb_node);
 461
 462         if (rbprev)
 463                 return rb_entry_drq(rbprev)->request;
 464
 465         return NULL;
 466 }
 467
 468 static struct request *
 469 deadline_latter_request(request_queue_t *q, struct request *rq)
 470 {
 471         struct deadline_rq *drq = RQ_DATA(rq);
 472         struct rb_node *rbnext = rb_next(&drq->rb_node);
 473
 474         if (rbnext)
 475                 return rb_entry_drq(rbnext)->request;
 476
 477         return NULL;
 478 }
 479
 480 static void deadline_exit_queue(elevator_t *e)
 481 {
 482         struct deadline_data *dd = e->elevator_data;
 483
 484         BUG_ON(!list_empty(&dd->fifo_list[READ]));
 485         BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
 486
 487         mempool_destroy(dd->drq_pool);
 488         kfree(dd);
 489 }
 490
 491 /*
 492  * initialize elevator private data (deadline_data), and alloc a drq for
 493  * each request on the free lists
 494  */
 495 static void *deadline_init_queue(request_queue_t *q, elevator_t *e)
 496 {
 497         struct deadline_data *dd;
 498
 499         if (!drq_pool)
 500                 return NULL;
 501
 502         dd = kmalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
 503         if (!dd)
 504                 return NULL;
 505         memset(dd, 0, sizeof(*dd));
 506
 507         dd->drq_pool = mempool_create_node(BLKDEV_MIN_RQ, mempool_alloc_slab,
 508                                         mempool_free_slab, drq_pool, q->node);
 509         if (!dd->drq_pool) {
 510                 kfree(dd);
 511                 return NULL;
 512         }
 513
 514         INIT_LIST_HEAD(&dd->fifo_list[READ]);
 515         INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
 516         dd->sort_list[READ] = RB_ROOT;
 517         dd->sort_list[WRITE] = RB_ROOT;
 518         dd->fifo_expire[READ] = read_expire;
 519         dd->fifo_expire[WRITE] = write_expire;
 520         dd->writes_starved = writes_starved;
 521         dd->front_merges = 1;
 522         dd->fifo_batch = fifo_batch;
 523         return dd;
 524 }
 525
 526 static void deadline_put_request(request_queue_t *q, struct request *rq)
 527 {
 528         struct deadline_data *dd = q->elevator->elevator_data;
 529         struct deadline_rq *drq = RQ_DATA(rq);
 530
 531         mempool_free(drq, dd->drq_pool);
 532         rq->elevator_private = NULL;
 533 }
 534
 535 static int
 536 deadline_set_request(request_queue_t *q, struct request *rq, struct bio *bio,
 537                      gfp_t gfp_mask)
 538 {
 539         struct deadline_data *dd = q->elevator->elevator_data;
 540         struct deadline_rq *drq;
 541
 542         drq = mempool_alloc(dd->drq_pool, gfp_mask);
 543         if (drq) {
 544                 memset(drq, 0, sizeof(*drq));
 545                 RB_CLEAR_NODE(&drq->rb_node);
 546                 drq->request = rq;
 547
 548                 INIT_LIST_HEAD(&drq->fifo);
 549
 550                 rq->elevator_private = drq;
 551                 return 0;
 552         }
 553
 554         return 1;
 555 }
 556
 557 /*
 558  * sysfs parts below
 559  */
 560
 561 static ssize_t
 562 deadline_var_show(int var, char *page)
 563 {
 564         return sprintf(page, "%d\n", var);
 565 }
 566
 567 static ssize_t
 568 deadline_var_store(int *var, const char *page, size_t count)
 569 {
 570         char *p = (char *) page;
 571
 572         *var = simple_strtol(p, &p, 10);
 573         return count;
 574 }
 575
 576 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
 577 static ssize_t __FUNC(elevator_t *e, char *page)                        \
 578 {                                                                       \
 579         struct deadline_data *dd = e->elevator_data;                    \
 580         int __data = __VAR;                                             \
 581         if (__CONV)                                                     \
 582                 __data = jiffies_to_msecs(__data);                      \
 583         return deadline_var_show(__data, (page));                       \
 584 }
 585 SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
 586 SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
 587 SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
 588 SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
 589 SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
 590 #undef SHOW_FUNCTION
 591
 592 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
 593 static ssize_t __FUNC(elevator_t *e, const char *page, size_t count)    \
 594 {                                                                       \
 595         struct deadline_data *dd = e->elevator_data;                    \
 596         int __data;                                                     \
 597         int ret = deadline_var_store(&__data, (page), count);           \
 598         if (__data < (MIN))                                             \
 599                 __data = (MIN);                                         \
 600         else if (__data > (MAX))                                        \
 601                 __data = (MAX);                                         \
 602         if (__CONV)                                                     \
 603                 *(__PTR) = msecs_to_jiffies(__data);                    \
 604         else                                                            \
 605                 *(__PTR) = __data;                                      \
 606         return ret;                                                     \
 607 }
 608 STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
 609 STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
 610 STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
 611 STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
 612 STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
 613 #undef STORE_FUNCTION
 614
 615 #define DD_ATTR(name) \
 616         __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
 617                                       deadline_##name##_store)
 618
 619 static struct elv_fs_entry deadline_attrs[] = {
 620         DD_ATTR(read_expire),
 621         DD_ATTR(write_expire),
 622         DD_ATTR(writes_starved),
 623         DD_ATTR(front_merges),
 624         DD_ATTR(fifo_batch),
 625         __ATTR_NULL
 626 };
 627
 628 static struct elevator_type iosched_deadline = {
 629         .ops = {
 630                 .elevator_merge_fn =            deadline_merge,
 631                 .elevator_merged_fn =           deadline_merged_request,
 632                 .elevator_merge_req_fn =        deadline_merged_requests,
 633                 .elevator_dispatch_fn =         deadline_dispatch_requests,
 634                 .elevator_add_req_fn =          deadline_add_request,
 635                 .elevator_queue_empty_fn =      deadline_queue_empty,
 636                 .elevator_former_req_fn =       deadline_former_request,
 637                 .elevator_latter_req_fn =       deadline_latter_request,
 638                 .elevator_set_req_fn =          deadline_set_request,
 639                 .elevator_put_req_fn =          deadline_put_request,
 640                 .elevator_init_fn =             deadline_init_queue,
 641                 .elevator_exit_fn =             deadline_exit_queue,
 642         },
 643
 644         .elevator_attrs = deadline_attrs,
 645         .elevator_name = "deadline",
 646         .elevator_owner = THIS_MODULE,
 647 };
 648
 649 static int __init deadline_init(void)
 650 {
 651         int ret;
 652
 653         drq_pool = kmem_cache_create("deadline_drq", sizeof(struct deadline_rq),
 654                                      0, 0, NULL, NULL);
 655
 656         if (!drq_pool)
 657                 return -ENOMEM;
 658
 659         ret = elv_register(&iosched_deadline);
 660         if (ret)
 661                 kmem_cache_destroy(drq_pool);
 662
 663         return ret;
 664 }
 665
 666 static void __exit deadline_exit(void)
 667 {
 668         kmem_cache_destroy(drq_pool);
 669         elv_unregister(&iosched_deadline);
 670 }
 671
 672 module_init(deadline_init);
 673 module_exit(deadline_exit);
 674
 675 MODULE_AUTHOR("Jens Axboe");
 676 MODULE_LICENSE("GPL");
 677 MODULE_DESCRIPTION("deadline IO scheduler");