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 unsigned int starved; /* times reads have starved writes */
43
44 /*
45 * settings that change how the i/o scheduler behaves
46 */
47 int fifo_expire[2];
48 int fifo_batch;
49 int writes_starved;
50 int front_merges;
51 };
52
53 static inline struct rb_root *
54 deadline_rb_root(struct deadline_data *dd, struct request *rq)
55 {
56 return &dd->sort_list[rq_data_dir(rq)];
57 }
58
59 /*
60 * get the request after `rq' in sector-sorted order
61 */
62 static inline struct request *
63 deadline_latter_request(struct request *rq)
64 {
65 struct rb_node *node = rb_next(&rq->rb_node);
66
67 if (node)
68 return rb_entry_rq(node);
69
70 return NULL;
71 }
72
73 static void
74 deadline_add_rq_rb(struct deadline_data *dd, struct request *rq)
75 {
76 struct rb_root *root = deadline_rb_root(dd, rq);
77
78 elv_rb_add(root, rq);
79 }
80
81 static inline void
82 deadline_del_rq_rb(struct deadline_data *dd, struct request *rq)
83 {
84 const int data_dir = rq_data_dir(rq);
85
86 if (dd->next_rq[data_dir] == rq)
87 dd->next_rq[data_dir] = deadline_latter_request(rq);
88
89 elv_rb_del(deadline_rb_root(dd, rq), rq);
90 }
91
92 /*
93 * add rq to rbtree and fifo
94 */
95 static void
96 deadline_add_request(struct request_queue *q, struct request *rq)
97 {
98 struct deadline_data *dd = q->elevator->elevator_data;
99 const int data_dir = rq_data_dir(rq);
100
101 /*
102 * This may be a requeue of a write request that has locked its
103 * target zone. If it is the case, this releases the zone lock.
104 */
105 blk_req_zone_write_unlock(rq);
106
107 deadline_add_rq_rb(dd, rq);
108
109 /*
110 * set expire time and add to fifo list
111 */
112 rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
113 list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
114 }
115
116 /*
117 * remove rq from rbtree and fifo.
118 */
119 static void deadline_remove_request(struct request_queue *q, struct request *rq)
120 {
121 struct deadline_data *dd = q->elevator->elevator_data;
122
123 rq_fifo_clear(rq);
124 deadline_del_rq_rb(dd, rq);
125 }
126
127 static enum elv_merge
128 deadline_merge(struct request_queue *q, struct request **req, struct bio *bio)
129 {
130 struct deadline_data *dd = q->elevator->elevator_data;
131 struct request *__rq;
132
133 /*
134 * check for front merge
135 */
136 if (dd->front_merges) {
137 sector_t sector = bio_end_sector(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_bio_merge_ok(__rq, bio)) {
144 *req = __rq;
145 return ELEVATOR_FRONT_MERGE;
146 }
147 }
148 }
149
150 return ELEVATOR_NO_MERGE;
151 }
152
153 static void deadline_merged_request(struct request_queue *q,
154 struct request *req, enum elv_merge type)
155 {
156 struct deadline_data *dd = q->elevator->elevator_data;
157
158 /*
159 * if the merge was a front merge, we need to reposition request
160 */
161 if (type == ELEVATOR_FRONT_MERGE) {
162 elv_rb_del(deadline_rb_root(dd, req), req);
163 deadline_add_rq_rb(dd, req);
164 }
165 }
166
167 static void
168 deadline_merged_requests(struct request_queue *q, struct request *req,
169 struct request *next)
170 {
171 /*
172 * if next expires before rq, assign its expire time to rq
173 * and move into next position (next will be deleted) in fifo
174 */
175 if (!list_empty(&req->queuelist) && !list_empty(&next->queuelist)) {
176 if (time_before((unsigned long)next->fifo_time,
177 (unsigned long)req->fifo_time)) {
178 list_move(&req->queuelist, &next->queuelist);
179 req->fifo_time = next->fifo_time;
180 }
181 }
182
183 /*
184 * kill knowledge of next, this one is a goner
185 */
186 deadline_remove_request(q, next);
187 }
188
189 /*
190 * move request from sort list to dispatch queue.
191 */
192 static inline void
193 deadline_move_to_dispatch(struct deadline_data *dd, struct request *rq)
194 {
195 struct request_queue *q = rq->q;
196
197 /*
198 * For a zoned block device, write requests must write lock their
199 * target zone.
200 */
201 blk_req_zone_write_lock(rq);
202
203 deadline_remove_request(q, rq);
204 elv_dispatch_add_tail(q, rq);
205 }
206
207 /*
208 * move an entry to dispatch queue
209 */
210 static void
211 deadline_move_request(struct deadline_data *dd, struct request *rq)
212 {
213 const int data_dir = rq_data_dir(rq);
214
215 dd->next_rq[READ] = NULL;
216 dd->next_rq[WRITE] = NULL;
217 dd->next_rq[data_dir] = deadline_latter_request(rq);
218
219 /*
220 * take it off the sort and fifo list, move
221 * to dispatch queue
222 */
223 deadline_move_to_dispatch(dd, rq);
224 }
225
226 /*
227 * deadline_check_fifo returns 0 if there are no expired requests on the fifo,
228 * 1 otherwise. Requires !list_empty(&dd->fifo_list[data_dir])
229 */
230 static inline int deadline_check_fifo(struct deadline_data *dd, int ddir)
231 {
232 struct request *rq = rq_entry_fifo(dd->fifo_list[ddir].next);
233
234 /*
235 * rq is expired!
236 */
237 if (time_after_eq(jiffies, (unsigned long)rq->fifo_time))
238 return 1;
239
240 return 0;
241 }
242
243 /*
244 * For the specified data direction, return the next request to dispatch using
245 * arrival ordered lists.
246 */
247 static struct request *
248 deadline_fifo_request(struct deadline_data *dd, int data_dir)
249 {
250 struct request *rq;
251
252 if (WARN_ON_ONCE(data_dir != READ && data_dir != WRITE))
253 return NULL;
254
255 if (list_empty(&dd->fifo_list[data_dir]))
256 return NULL;
257
258 rq = rq_entry_fifo(dd->fifo_list[data_dir].next);
259 if (data_dir == READ || !blk_queue_is_zoned(rq->q))
260 return rq;
261
262 /*
263 * Look for a write request that can be dispatched, that is one with
264 * an unlocked target zone.
265 */
266 list_for_each_entry(rq, &dd->fifo_list[WRITE], queuelist) {
267 if (blk_req_can_dispatch_to_zone(rq))
268 return rq;
269 }
270
271 return NULL;
272 }
273
274 /*
275 * For the specified data direction, return the next request to dispatch using
276 * sector position sorted lists.
277 */
278 static struct request *
279 deadline_next_request(struct deadline_data *dd, int data_dir)
280 {
281 struct request *rq;
282
283 if (WARN_ON_ONCE(data_dir != READ && data_dir != WRITE))
284 return NULL;
285
286 rq = dd->next_rq[data_dir];
287 if (!rq)
288 return NULL;
289
290 if (data_dir == READ || !blk_queue_is_zoned(rq->q))
291 return rq;
292
293 /*
294 * Look for a write request that can be dispatched, that is one with
295 * an unlocked target zone.
296 */
297 while (rq) {
298 if (blk_req_can_dispatch_to_zone(rq))
299 return rq;
300 rq = deadline_latter_request(rq);
301 }
302
303 return NULL;
304 }
305
306 /*
307 * deadline_dispatch_requests selects the best request according to
308 * read/write expire, fifo_batch, etc
309 */
310 static int deadline_dispatch_requests(struct request_queue *q, int force)
311 {
312 struct deadline_data *dd = q->elevator->elevator_data;
313 const int reads = !list_empty(&dd->fifo_list[READ]);
314 const int writes = !list_empty(&dd->fifo_list[WRITE]);
315 struct request *rq, *next_rq;
316 int data_dir;
317
318 /*
319 * batches are currently reads XOR writes
320 */
321 rq = deadline_next_request(dd, WRITE);
322 if (!rq)
323 rq = deadline_next_request(dd, READ);
324
325 if (rq && dd->batching < dd->fifo_batch)
326 /* we have a next request are still entitled to batch */
327 goto dispatch_request;
328
329 /*
330 * at this point we are not running a batch. select the appropriate
331 * data direction (read / write)
332 */
333
334 if (reads) {
335 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[READ]));
336
337 if (deadline_fifo_request(dd, WRITE) &&
338 (dd->starved++ >= dd->writes_starved))
339 goto dispatch_writes;
340
341 data_dir = READ;
342
343 goto dispatch_find_request;
344 }
345
346 /*
347 * there are either no reads or writes have been starved
348 */
349
350 if (writes) {
351 dispatch_writes:
352 BUG_ON(RB_EMPTY_ROOT(&dd->sort_list[WRITE]));
353
354 dd->starved = 0;
355
356 data_dir = WRITE;
357
358 goto dispatch_find_request;
359 }
360
361 return 0;
362
363 dispatch_find_request:
364 /*
365 * we are not running a batch, find best request for selected data_dir
366 */
367 next_rq = deadline_next_request(dd, data_dir);
368 if (deadline_check_fifo(dd, data_dir) || !next_rq) {
369 /*
370 * A deadline has expired, the last request was in the other
371 * direction, or we have run out of higher-sectored requests.
372 * Start again from the request with the earliest expiry time.
373 */
374 rq = deadline_fifo_request(dd, data_dir);
375 } else {
376 /*
377 * The last req was the same dir and we have a next request in
378 * sort order. No expired requests so continue on from here.
379 */
380 rq = next_rq;
381 }
382
383 /*
384 * For a zoned block device, if we only have writes queued and none of
385 * them can be dispatched, rq will be NULL.
386 */
387 if (!rq)
388 return 0;
389
390 dd->batching = 0;
391
392 dispatch_request:
393 /*
394 * rq is the selected appropriate request.
395 */
396 dd->batching++;
397 deadline_move_request(dd, rq);
398
399 return 1;
400 }
401
402 /*
403 * For zoned block devices, write unlock the target zone of completed
404 * write requests.
405 */
406 static void
407 deadline_completed_request(struct request_queue *q, struct request *rq)
408 {
409 blk_req_zone_write_unlock(rq);
410 }
411
412 static void deadline_exit_queue(struct elevator_queue *e)
413 {
414 struct deadline_data *dd = e->elevator_data;
415
416 BUG_ON(!list_empty(&dd->fifo_list[READ]));
417 BUG_ON(!list_empty(&dd->fifo_list[WRITE]));
418
419 kfree(dd);
420 }
421
422 /*
423 * initialize elevator private data (deadline_data).
424 */
425 static int deadline_init_queue(struct request_queue *q, struct elevator_type *e)
426 {
427 struct deadline_data *dd;
428 struct elevator_queue *eq;
429
430 eq = elevator_alloc(q, e);
431 if (!eq)
432 return -ENOMEM;
433
434 dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
435 if (!dd) {
436 kobject_put(&eq->kobj);
437 return -ENOMEM;
438 }
439 eq->elevator_data = dd;
440
441 INIT_LIST_HEAD(&dd->fifo_list[READ]);
442 INIT_LIST_HEAD(&dd->fifo_list[WRITE]);
443 dd->sort_list[READ] = RB_ROOT;
444 dd->sort_list[WRITE] = RB_ROOT;
445 dd->fifo_expire[READ] = read_expire;
446 dd->fifo_expire[WRITE] = write_expire;
447 dd->writes_starved = writes_starved;
448 dd->front_merges = 1;
449 dd->fifo_batch = fifo_batch;
450
451 spin_lock_irq(q->queue_lock);
452 q->elevator = eq;
453 spin_unlock_irq(q->queue_lock);
454 return 0;
455 }
456
457 /*
458 * sysfs parts below
459 */
460
461 static ssize_t
462 deadline_var_show(int var, char *page)
463 {
464 return sprintf(page, "%d\n", var);
465 }
466
467 static void
468 deadline_var_store(int *var, const char *page)
469 {
470 char *p = (char *) page;
471
472 *var = simple_strtol(p, &p, 10);
473 }
474
475 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
476 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
477 { \
478 struct deadline_data *dd = e->elevator_data; \
479 int __data = __VAR; \
480 if (__CONV) \
481 __data = jiffies_to_msecs(__data); \
482 return deadline_var_show(__data, (page)); \
483 }
484 SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
485 SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
486 SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
487 SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
488 SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
489 #undef SHOW_FUNCTION
490
491 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
492 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
493 { \
494 struct deadline_data *dd = e->elevator_data; \
495 int __data; \
496 deadline_var_store(&__data, (page)); \
497 if (__data < (MIN)) \
498 __data = (MIN); \
499 else if (__data > (MAX)) \
500 __data = (MAX); \
501 if (__CONV) \
502 *(__PTR) = msecs_to_jiffies(__data); \
503 else \
504 *(__PTR) = __data; \
505 return count; \
506 }
507 STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
508 STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
509 STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
510 STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
511 STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
512 #undef STORE_FUNCTION
513
514 #define DD_ATTR(name) \
515 __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
516 deadline_##name##_store)
517
518 static struct elv_fs_entry deadline_attrs[] = {
519 DD_ATTR(read_expire),
520 DD_ATTR(write_expire),
521 DD_ATTR(writes_starved),
522 DD_ATTR(front_merges),
523 DD_ATTR(fifo_batch),
524 __ATTR_NULL
525 };
526
527 static struct elevator_type iosched_deadline = {
528 .ops.sq = {
529 .elevator_merge_fn = deadline_merge,
530 .elevator_merged_fn = deadline_merged_request,
531 .elevator_merge_req_fn = deadline_merged_requests,
532 .elevator_dispatch_fn = deadline_dispatch_requests,
533 .elevator_completed_req_fn = deadline_completed_request,
534 .elevator_add_req_fn = deadline_add_request,
535 .elevator_former_req_fn = elv_rb_former_request,
536 .elevator_latter_req_fn = elv_rb_latter_request,
537 .elevator_init_fn = deadline_init_queue,
538 .elevator_exit_fn = deadline_exit_queue,
539 },
540
541 .elevator_attrs = deadline_attrs,
542 .elevator_name = "deadline",
543 .elevator_owner = THIS_MODULE,
544 };
545
546 static int __init deadline_init(void)
547 {
548 return elv_register(&iosched_deadline);
549 }
550
551 static void __exit deadline_exit(void)
552 {
553 elv_unregister(&iosched_deadline);
554 }
555
556 module_init(deadline_init);
557 module_exit(deadline_exit);
558
559 MODULE_AUTHOR("Jens Axboe");
560 MODULE_LICENSE("GPL");
561 MODULE_DESCRIPTION("deadline IO scheduler");
562
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