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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 enum elv_merge 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 struct request *free = NULL;
375 bool ret;
376
377 spin_lock(&dd->lock);
378 ret = blk_mq_sched_try_merge(q, bio, &free);
379 spin_unlock(&dd->lock);
380
381 if (free)
382 blk_mq_free_request(free);
383
384 return ret;
385 }
386
387 /*
388 * add rq to rbtree and fifo
389 */
390 static void dd_insert_request(struct blk_mq_hw_ctx *hctx, struct request *rq,
391 bool at_head)
392 {
393 struct request_queue *q = hctx->queue;
394 struct deadline_data *dd = q->elevator->elevator_data;
395 const int data_dir = rq_data_dir(rq);
396
397 if (blk_mq_sched_try_insert_merge(q, rq))
398 return;
399
400 blk_mq_sched_request_inserted(rq);
401
402 if (at_head || blk_rq_is_passthrough(rq)) {
403 if (at_head)
404 list_add(&rq->queuelist, &dd->dispatch);
405 else
406 list_add_tail(&rq->queuelist, &dd->dispatch);
407 } else {
408 deadline_add_rq_rb(dd, rq);
409
410 if (rq_mergeable(rq)) {
411 elv_rqhash_add(q, rq);
412 if (!q->last_merge)
413 q->last_merge = rq;
414 }
415
416 /*
417 * set expire time and add to fifo list
418 */
419 rq->fifo_time = jiffies + dd->fifo_expire[data_dir];
420 list_add_tail(&rq->queuelist, &dd->fifo_list[data_dir]);
421 }
422 }
423
424 static void dd_insert_requests(struct blk_mq_hw_ctx *hctx,
425 struct list_head *list, bool at_head)
426 {
427 struct request_queue *q = hctx->queue;
428 struct deadline_data *dd = q->elevator->elevator_data;
429
430 spin_lock(&dd->lock);
431 while (!list_empty(list)) {
432 struct request *rq;
433
434 rq = list_first_entry(list, struct request, queuelist);
435 list_del_init(&rq->queuelist);
436 dd_insert_request(hctx, rq, at_head);
437 }
438 spin_unlock(&dd->lock);
439 }
440
441 static bool dd_has_work(struct blk_mq_hw_ctx *hctx)
442 {
443 struct deadline_data *dd = hctx->queue->elevator->elevator_data;
444
445 return !list_empty_careful(&dd->dispatch) ||
446 !list_empty_careful(&dd->fifo_list[0]) ||
447 !list_empty_careful(&dd->fifo_list[1]);
448 }
449
450 /*
451 * sysfs parts below
452 */
453 static ssize_t
454 deadline_var_show(int var, char *page)
455 {
456 return sprintf(page, "%d\n", var);
457 }
458
459 static ssize_t
460 deadline_var_store(int *var, const char *page, size_t count)
461 {
462 char *p = (char *) page;
463
464 *var = simple_strtol(p, &p, 10);
465 return count;
466 }
467
468 #define SHOW_FUNCTION(__FUNC, __VAR, __CONV) \
469 static ssize_t __FUNC(struct elevator_queue *e, char *page) \
470 { \
471 struct deadline_data *dd = e->elevator_data; \
472 int __data = __VAR; \
473 if (__CONV) \
474 __data = jiffies_to_msecs(__data); \
475 return deadline_var_show(__data, (page)); \
476 }
477 SHOW_FUNCTION(deadline_read_expire_show, dd->fifo_expire[READ], 1);
478 SHOW_FUNCTION(deadline_write_expire_show, dd->fifo_expire[WRITE], 1);
479 SHOW_FUNCTION(deadline_writes_starved_show, dd->writes_starved, 0);
480 SHOW_FUNCTION(deadline_front_merges_show, dd->front_merges, 0);
481 SHOW_FUNCTION(deadline_fifo_batch_show, dd->fifo_batch, 0);
482 #undef SHOW_FUNCTION
483
484 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX, __CONV) \
485 static ssize_t __FUNC(struct elevator_queue *e, const char *page, size_t count) \
486 { \
487 struct deadline_data *dd = e->elevator_data; \
488 int __data; \
489 int ret = deadline_var_store(&__data, (page), count); \
490 if (__data < (MIN)) \
491 __data = (MIN); \
492 else if (__data > (MAX)) \
493 __data = (MAX); \
494 if (__CONV) \
495 *(__PTR) = msecs_to_jiffies(__data); \
496 else \
497 *(__PTR) = __data; \
498 return ret; \
499 }
500 STORE_FUNCTION(deadline_read_expire_store, &dd->fifo_expire[READ], 0, INT_MAX, 1);
501 STORE_FUNCTION(deadline_write_expire_store, &dd->fifo_expire[WRITE], 0, INT_MAX, 1);
502 STORE_FUNCTION(deadline_writes_starved_store, &dd->writes_starved, INT_MIN, INT_MAX, 0);
503 STORE_FUNCTION(deadline_front_merges_store, &dd->front_merges, 0, 1, 0);
504 STORE_FUNCTION(deadline_fifo_batch_store, &dd->fifo_batch, 0, INT_MAX, 0);
505 #undef STORE_FUNCTION
506
507 #define DD_ATTR(name) \
508 __ATTR(name, S_IRUGO|S_IWUSR, deadline_##name##_show, \
509 deadline_##name##_store)
510
511 static struct elv_fs_entry deadline_attrs[] = {
512 DD_ATTR(read_expire),
513 DD_ATTR(write_expire),
514 DD_ATTR(writes_starved),
515 DD_ATTR(front_merges),
516 DD_ATTR(fifo_batch),
517 __ATTR_NULL
518 };
519
520 static struct elevator_type mq_deadline = {
521 .ops.mq = {
522 .insert_requests = dd_insert_requests,
523 .dispatch_request = dd_dispatch_request,
524 .next_request = elv_rb_latter_request,
525 .former_request = elv_rb_former_request,
526 .bio_merge = dd_bio_merge,
527 .request_merge = dd_request_merge,
528 .requests_merged = dd_merged_requests,
529 .request_merged = dd_request_merged,
530 .has_work = dd_has_work,
531 .init_sched = dd_init_queue,
532 .exit_sched = dd_exit_queue,
533 },
534
535 .uses_mq = true,
536 .elevator_attrs = deadline_attrs,
537 .elevator_name = "mq-deadline",
538 .elevator_owner = THIS_MODULE,
539 };
540
541 static int __init deadline_init(void)
542 {
543 return elv_register(&mq_deadline);
544 }
545
546 static void __exit deadline_exit(void)
547 {
548 elv_unregister(&mq_deadline);
549 }
550
551 module_init(deadline_init);
552 module_exit(deadline_exit);
553
554 MODULE_AUTHOR("Jens Axboe");
555 MODULE_LICENSE("GPL");
556 MODULE_DESCRIPTION("MQ deadline IO scheduler");