linux/block/deadline-iosched.c
<<
>>
Prefs
   1/*
   2 *  Deadline i/o scheduler.
   3 *
   4 *  Copyright (C) 2002 Jens Axboe <axboe@kernel.dk>
   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 */
  20static const int read_expire = HZ / 2;  /* max time before a read is submitted. */
  21static const int write_expire = 5 * HZ; /* ditto for writes, these limits are SOFT! */
  22static const int writes_starved = 2;    /* max times reads can starve a write */
  23static const int fifo_batch = 16;       /* # of sequential requests treated as one
  24                                     by the above parameters. For throughput. */
  25
  26struct 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 request *next_rq[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
  54static void deadline_move_request(struct deadline_data *, struct request *);
  55
  56static inline struct rb_root *
  57deadline_rb_root(struct deadline_data *dd, struct request *rq)
  58{
  59        return &dd->sort_list[rq_data_dir(rq)];
  60}
  61
  62/*
  63 * get the request after `rq' in sector-sorted order
  64 */
  65static inline struct request *
  66deadline_latter_request(struct request *rq)
  67{
  68        struct rb_node *node = rb_next(&rq->rb_node);
  69
  70        if (node)
  71                return rb_entry_rq(node);
  72
  73        return NULL;
  74}
  75
  76static void
  77deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
  78{
  79        struct rb_root *root = deadline_rb_root(dd, rq);
  80        struct request *__alias;
  81
  82        while (unlikely(__alias = elv_rb_add(root, rq)))
  83                deadline_move_request(dd, __alias);
  84}
  85
  86static inline void
  87deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
  88{
  89        const int data_dir = rq_data_dir(rq);
  90
  91        if (dd->next_rq[data_dir] == rq)
  92                dd->next_rq[data_dir] = deadline_latter_request(rq);
  93
  94        elv_rb_del(deadline_rb_root(dd, rq), rq);
  95}
  96
  97/*
  98 * add rq to rbtree and fifo
  99 */
 100static void
 101deadline_add_request(struct request_queue *q, struct request *rq)
 102{
 103        struct deadline_data *dd = q->elevator->elevator_data;
 104        const int data_dir = rq_data_dir(rq);
 105
 106        deadline_add_rq_rb(dd, rq);
 107
 108        /*
 109         * set expire time and add to fifo list
 110         */
 111        rq_set_fifo_time(rq, jiffies + dd->fifo_expire[data_dir]);
 112        list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
 113}
 114
 115/*
 116 * remove rq from rbtree and fifo.
 117 */
 118static void deadline_remove_request(struct request_queue *q, struct request *rq)
 119{
 120        struct deadline_data *dd = q->elevator->elevator_data;
 121
 122        rq_fifo_clear(rq);
 123        deadline_del_rq_rb(dd, rq);
 124}
 125
 126static int
 127deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
 128{
 129        struct deadline_data *dd = q->elevator->elevator_data;
 130        struct request *__rq;
 131        int ret;
 132
 133        /*
 134         * check for front merge
 135         */
 136        if (dd->front_merges) {
 137                sector_t sector = bio->bi_sector + bio_sectors(bio);
 138
 139                __rq = elv_rb_find(&dd->sort_list[bio_data_dir(bio)], sector);
 140                if (__rq) {
 141                        BUG_ON(sector != __rq->sector);
 142
 143                        if (elv_rq_merge_ok(__rq, bio)) {
 144                                ret = ELEVATOR_FRONT_MERGE;
 145                                goto out;
 146                        }
 147                }
 148        }
 149
 150        return ELEVATOR_NO_MERGE;
 151out:
 152        *req = __rq;
 153        return ret;
 154}
 155
 156static void deadline_merged_request(struct request_queue *q,
 157                                    struct request *req, int type)
 158{
 159        struct deadline_data *dd = q->elevator->elevator_data;
 160
 161        /*
 162         * if the merge was a front merge, we need to reposition request
 163         */
 164        if (type == ELEVATOR_FRONT_MERGE) {
 165                elv_rb_del(deadline_rb_root(dd, req), req);
 166                deadline_add_rq_rb(dd, req);
 167        }
 168}
 169
 170static void
 171deadline_merged_requests(struct request_queue *q, struct request *req,
 172                         struct request *next)
 173{
 174        /*
 175         * if next expires before rq, assign its expire time to rq
 176         * and move into next position (next will be deleted) in fifo
 177         */
 178        if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
 179                if (time_before(rq_fifo_time(next), rq_fifo_time(req))) {
 180                        list_move(&req->queuelist, &next->queuelist);
 181                        rq_set_fifo_time(req, rq_fifo_time(next));
 182                }
 183        }
 184
 185        /*
 186         * kill knowledge of next, this one is a goner
 187         */
 188        deadline_remove_request(q, next);
 189}
 190
 191/*
 192 * move request from sort list to dispatch queue.
 193 */
 194static inline void
 195deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
 196{
 197        struct request_queue *q = rq->q;
 198
 199        deadline_remove_request(q, rq);
 200        elv_dispatch_add_tail(q, rq);
 201}
 202
 203/*
 204 * move an entry to dispatch queue
 205 */
 206static void
 207deadline_move_request(struct deadline_data *dd, struct request *rq)
 208{
 209        const int data_dir = rq_data_dir(rq);
 210
 211        dd->next_rq[READ] = NULL;
 212        dd->next_rq[WRITE] = NULL;
 213        dd->next_rq[data_dir] = deadline_latter_request(rq);
 214
 215        dd->last_sector = rq_end_sector(rq);
 216
 217        /*
 218         * take it off the sort and fifo list, move
 219         * to dispatch queue
 220         */
 221        deadline_move_to_dispatch(dd, rq);
 222}
 223
 224/*
 225 * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
 226 * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
 227 */
 228static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
 229{
 230        struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
 231
 232        /*
 233         * rq is expired!
 234         */
 235        if (time_after(jiffies, rq_fifo_time(rq)))
 236                return 1;
 237
 238        return 0;
 239}
 240
 241/*
 242 * deadline_dispatch_requests selects the best request according to
 243 * read/write expire, fifo_batch, etc
 244 */
 245static int deadline_dispatch_requests(struct request_queue *q, int force)
 246{
 247        struct deadline_data *dd = q->elevator->elevator_data;
 248        const int reads = !list_empty(&dd->fifo_list[READ]);
 249        const int writes = !list_empty(&dd->fifo_list[WRITE]);
 250        struct request *rq;
 251        int data_dir;
 252
 253        /*
 254         * batches are currently reads XOR writes
 255         */
 256        if (dd->next_rq[WRITE])
 257                rq = dd->next_rq[WRITE];
 258        else
 259                rq = dd->next_rq[READ];
 260
 261        if (rq && dd->batching < dd->fifo_batch)
 262                /* we have a next request are still entitled to batch */
 263                goto dispatch_request;
 264
 265        /*
 266         * at this point we are not running a batch. select the appropriate
 267         * data direction (read / write)
 268         */
 269
 270        if (reads) {
 271                BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
 272
 273                if (writes && (dd->starved++ >= dd->writes_starved))
 274                        goto dispatch_writes;
 275
 276                data_dir = READ;
 277
 278                goto dispatch_find_request;
 279        }
 280
 281        /*
 282         * there are either no reads or writes have been starved
 283         */
 284
 285        if (writes) {
 286dispatch_writes:
 287                BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
 288
 289                dd->starved = 0;
 290
 291                data_dir = WRITE;
 292
 293                goto dispatch_find_request;
 294        }
 295
 296        return 0;
 297
 298dispatch_find_request:
 299        /*
 300         * we are not running a batch, find best request for selected data_dir
 301         */
 302        if (deadline_check_fifo(dd, data_dir) || !dd->next_rq[data_dir]) {
 303                /*
 304                 * A deadline has expired, the last request was in the other
 305                 * direction, or we have run out of higher-sectored requests.
 306                 * Start again from the request with the earliest expiry time.
 307                 */
 308                rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
 309        } else {
 310                /*
 311                 * The last req was the same dir and we have a next request in
 312                 * sort order. No expired requests so continue on from here.
 313                 */
 314                rq = dd->next_rq[data_dir];
 315        }
 316
 317        dd->batching = 0;
 318
 319dispatch_request:
 320        /*
 321         * rq is the selected appropriate request.
 322         */
 323        dd->batching++;
 324        deadline_move_request(dd, rq);
 325
 326        return 1;
 327}
 328
 329static int deadline_queue_empty(struct request_queue *q)
 330{
 331        struct deadline_data *dd = q->elevator->elevator_data;
 332
 333        return list_empty(&dd->fifo_list[WRITE])
 334                && list_empty(&dd->fifo_list[READ]);
 335}
 336
 337static void deadline_exit_queue(elevator_t *e)
 338{
 339        struct deadline_data *dd = e->elevator_data;
 340
 341        BUG_ON(!list_empty(&dd->fifo_list[READ]));
 342        BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
 343
 344        kfree(dd);
 345}
 346
 347/*
 348 * initialize elevator private data (deadline_data).
 349 */
 350static void *deadline_init_queue(struct request_queue *q)
 351{
 352        struct deadline_data *dd;
 353
 354        dd = kmalloc_node(sizeof(*dd), GFP_KERNEL | __GFP_ZERO, q->node);
 355        if (!dd)
 356                return NULL;
 357
 358        INIT_LIST_HEAD(&dd->fifo_list[READ]);
 359        INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
 360        dd->sort_list[READ] = RB_ROOT;
 361        dd->sort_list[WRITE] = RB_ROOT;
 362        dd->fifo_expire[READ] = read_expire;
 363        dd->fifo_expire[WRITE] = write_expire;
 364        dd->writes_starved = writes_starved;
 365        dd->front_merges = 1;
 366        dd->fifo_batch = fifo_batch;
 367        return dd;
 368}
 369
 370/*
 371 * sysfs parts below
 372 */
 373
 374static ssize_t
 375deadline_var_show(int var, char *page)
 376{
 377        return sprintf(page, "%d\n", var);
 378}
 379
 380static ssize_t
 381deadline_var_store(int *var, const char *page, size_t count)
 382{
 383        char *p = (char *) page;
 384
 385        *var = simple_strtol(p, &p, 10);
 386        return count;
 387}
 388
 389#define SHOW_FUNCTION(__FUNC, __VAR, __CONV)                            \
 390static ssize_t __FUNC(elevator_t *e, char *page)                        \
 391{                                                                       \
 392        struct deadline_data *dd = e->elevator_data;                    \
 393        int __data = __VAR;                                             \
 394        if (__CONV)                                                     \
 395                __data = jiffies_to_msecs(__data);                      \
 396        return deadline_var_show(__data, (page));                       \
 397}
 398SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
 399SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
 400SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
 401SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
 402SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
 403#undef SHOW_FUNCTION
 404
 405#define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV)                 \
 406static ssize_t __FUNC(elevator_t *e, const char *page, size_t count)    \
 407{                                                                       \
 408        struct deadline_data *dd = e->elevator_data;                    \
 409        int __data;                                                     \
 410        int ret = deadline_var_store(&__data, (page), count);           \
 411        if (__data < (MIN))                                             \
 412                __data = (MIN);                                         \
 413        else if (__data > (MAX))                                        \
 414                __data = (MAX);                                         \
 415        if (__CONV)                                                     \
 416                *(__PTR) = msecs_to_jiffies(__data);                    \
 417        else                                                            \
 418                *(__PTR) = __data;                                      \
 419        return ret;                                                     \
 420}
 421STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
 422STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
 423STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
 424STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
 425STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
 426#undef STORE_FUNCTION
 427
 428#define DD_ATTR(name) \
 429        __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
 430                                      deadline_##name##_store)
 431
 432static struct elv_fs_entry deadline_attrs[] = {
 433        DD_ATTR(read_expire),
 434        DD_ATTR(write_expire),
 435        DD_ATTR(writes_starved),
 436        DD_ATTR(front_merges),
 437        DD_ATTR(fifo_batch),
 438        __ATTR_NULL
 439};
 440
 441static struct elevator_type iosched_deadline = {
 442        .ops = {
 443                .elevator_merge_fn =            deadline_merge,
 444                .elevator_merged_fn =           deadline_merged_request,
 445                .elevator_merge_req_fn =        deadline_merged_requests,
 446                .elevator_dispatch_fn =         deadline_dispatch_requests,
 447                .elevator_add_req_fn =          deadline_add_request,
 448                .elevator_queue_empty_fn =      deadline_queue_empty,
 449                .elevator_former_req_fn =       elv_rb_former_request,
 450                .elevator_latter_req_fn =       elv_rb_latter_request,
 451                .elevator_init_fn =             deadline_init_queue,
 452                .elevator_exit_fn =             deadline_exit_queue,
 453        },
 454
 455        .elevator_attrs = deadline_attrs,
 456        .elevator_name = "deadline",
 457        .elevator_owner = THIS_MODULE,
 458};
 459
 460static int __init deadline_init(void)
 461{
 462        elv_register(&iosched_deadline);
 463
 464        return 0;
 465}
 466
 467static void __exit deadline_exit(void)
 468{
 469        elv_unregister(&iosched_deadline);
 470}
 471
 472module_init(deadline_init);
 473module_exit(deadline_exit);
 474
 475MODULE_AUTHOR("Jens Axboe");
 476MODULE_LICENSE("GPL");
 477MODULE_DESCRIPTION("deadline IO scheduler");
 478