| 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 | */ |
| 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 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 | |
| 54 | static void deadline_move_request(struct deadline_data *, struct request *); |
| 55 | |
| 56 | static inline struct rb_root * |
| 57 | deadline_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 | */ |
| 65 | static inline struct request * |
| 66 | deadline_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 | |
| 76 | static void |
| 77 | deadline_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 | |
| 86 | static inline void |
| 87 | deadline_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 | */ |
| 100 | static void |
| 101 | deadline_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 | */ |
| 118 | static 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 | |
| 126 | static int |
| 127 | deadline_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 != blk_rq_pos(__rq)); |
| 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; |
| 151 | out: |
| 152 | *req = __rq; |
| 153 | return ret; |
| 154 | } |
| 155 | |
| 156 | static 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 | |
| 170 | static void |
| 171 | deadline_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 | */ |
| 194 | static inline void |
| 195 | deadline_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 | */ |
| 206 | static void |
| 207 | deadline_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 | */ |
| 228 | static 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 | */ |
| 245 | static 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) { |
| 286 | dispatch_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 | |
| 298 | dispatch_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 | |
| 319 | dispatch_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 | |
| 329 | static 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 | |
| 337 | static void deadline_exit_queue(struct elevator_queue *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 | */ |
| 350 | static 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 | |
| 374 | static ssize_t |
| 375 | deadline_var_show(int var, char *page) |
| 376 | { |
| 377 | return sprintf(page, "%d\n", var); |
| 378 | } |
| 379 | |
| 380 | static ssize_t |
| 381 | deadline_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) \ |
| 390 | static ssize_t __FUNC(struct elevator_queue *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 | } |
| 398 | SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1); |
| 399 | SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1); |
| 400 | SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0); |
| 401 | SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0); |
| 402 | SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0); |
| 403 | #undef SHOW_FUNCTION |
| 404 | |
| 405 | #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \ |
| 406 | static ssize_t __FUNC(struct elevator_queue *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 | } |
| 421 | STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1); |
| 422 | STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1); |
| 423 | STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0); |
| 424 | STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0); |
| 425 | STORE_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 | |
| 432 | static 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 | |
| 441 | static 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 | |
| 460 | static int __init deadline_init(void) |
| 461 | { |
| 462 | elv_register(&iosched_deadline); |
| 463 | |
| 464 | return 0; |
| 465 | } |
| 466 | |
| 467 | static void __exit deadline_exit(void) |
| 468 | { |
| 469 | elv_unregister(&iosched_deadline); |
| 470 | } |
| 471 | |
| 472 | module_init(deadline_init); |
| 473 | module_exit(deadline_exit); |
| 474 | |
| 475 | MODULE_AUTHOR("Jens Axboe"); |
| 476 | MODULE_LICENSE("GPL"); |
| 477 | MODULE_DESCRIPTION("deadline IO scheduler"); |