1 /*
2 * linux/drivers/block/elevator.c
3 *
4 * Block device elevator/IO-scheduler.
5 *
6 * Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
7 *
8 * 30042000 Jens Axboe <axboe@suse.de> :
9 *
10 * Split the elevator a bit so that it is possible to choose a different
11 * one or even write a new "plug in". There are three pieces:
12 * - elevator_fn, inserts a new request in the queue list
13 * - elevator_merge_fn, decides whether a new buffer can be merged with
14 * an existing request
15 * - elevator_dequeue_fn, called when a request is taken off the active list
16 *
17 * 20082000 Dave Jones <davej@suse.de> :
18 * Removed tests for max-bomb-segments, which was breaking elvtune
19 * when run without -bN
20 *
21 * Jens:
22 * - Rework again to work with bio instead of buffer_heads
23 * - loose bi_dev comparisons, partition handling is right now
24 * - completely modularize elevator setup and teardown
25 *
26 */
27 #include <linux/kernel.h>
28 #include <linux/fs.h>
29 #include <linux/blkdev.h>
30 #include <linux/elevator.h>
31 #include <linux/bio.h>
32 #include <linux/config.h>
33 #include <linux/module.h>
34 #include <linux/slab.h>
35 #include <linux/init.h>
36 #include <linux/compiler.h>
37
38 #include <asm/uaccess.h>
39
40 static DEFINE_SPINLOCK(elv_list_lock);
41 static LIST_HEAD(elv_list);
42
43 /*
44 * can we safely merge with this request?
45 */
46 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
47 {
48 if (!rq_mergeable(rq))
49 return 0;
50
51 /*
52 * different data direction or already started, don't merge
53 */
54 if (bio_data_dir(bio) != rq_data_dir(rq))
55 return 0;
56
57 /*
58 * same device and no special stuff set, merge is ok
59 */
60 if (rq->rq_disk == bio->bi_bdev->bd_disk &&
61 !rq->waiting && !rq->special)
62 return 1;
63
64 return 0;
65 }
66 EXPORT_SYMBOL(elv_rq_merge_ok);
67
68 inline int elv_try_merge(struct request *__rq, struct bio *bio)
69 {
70 int ret = ELEVATOR_NO_MERGE;
71
72 /*
73 * we can merge and sequence is ok, check if it's possible
74 */
75 if (elv_rq_merge_ok(__rq, bio)) {
76 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
77 ret = ELEVATOR_BACK_MERGE;
78 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
79 ret = ELEVATOR_FRONT_MERGE;
80 }
81
82 return ret;
83 }
84 EXPORT_SYMBOL(elv_try_merge);
85
86 inline int elv_try_last_merge(request_queue_t *q, struct bio *bio)
87 {
88 if (q->last_merge)
89 return elv_try_merge(q->last_merge, bio);
90
91 return ELEVATOR_NO_MERGE;
92 }
93 EXPORT_SYMBOL(elv_try_last_merge);
94
95 struct elevator_type *elevator_find(const char *name)
96 {
97 struct elevator_type *e = NULL;
98 struct list_head *entry;
99
100 spin_lock_irq(&elv_list_lock);
101 list_for_each(entry, &elv_list) {
102 struct elevator_type *__e;
103
104 __e = list_entry(entry, struct elevator_type, list);
105
106 if (!strcmp(__e->elevator_name, name)) {
107 e = __e;
108 break;
109 }
110 }
111 spin_unlock_irq(&elv_list_lock);
112
113 return e;
114 }
115
116 static void elevator_put(struct elevator_type *e)
117 {
118 module_put(e->elevator_owner);
119 }
120
121 static struct elevator_type *elevator_get(const char *name)
122 {
123 struct elevator_type *e = elevator_find(name);
124
125 if (!e)
126 return NULL;
127 if (!try_module_get(e->elevator_owner))
128 return NULL;
129
130 return e;
131 }
132
133 static int elevator_attach(request_queue_t *q, struct elevator_type *e,
134 struct elevator_queue *eq)
135 {
136 int ret = 0;
137
138 memset(eq, 0, sizeof(*eq));
139 eq->ops = &e->ops;
140 eq->elevator_type = e;
141
142 INIT_LIST_HEAD(&q->queue_head);
143 q->last_merge = NULL;
144 q->elevator = eq;
145
146 if (eq->ops->elevator_init_fn)
147 ret = eq->ops->elevator_init_fn(q, eq);
148
149 return ret;
150 }
151
152 static char chosen_elevator[16];
153
154 static void elevator_setup_default(void)
155 {
156 /*
157 * check if default is set and exists
158 */
159 if (chosen_elevator[0] && elevator_find(chosen_elevator))
160 return;
161
162 #if defined(CONFIG_IOSCHED_AS)
163 strcpy(chosen_elevator, "anticipatory");
164 #elif defined(CONFIG_IOSCHED_DEADLINE)
165 strcpy(chosen_elevator, "deadline");
166 #elif defined(CONFIG_IOSCHED_CFQ)
167 strcpy(chosen_elevator, "cfq");
168 #elif defined(CONFIG_IOSCHED_NOOP)
169 strcpy(chosen_elevator, "noop");
170 #else
171 #error "You must build at least 1 IO scheduler into the kernel"
172 #endif
173 }
174
175 static int __init elevator_setup(char *str)
176 {
177 strncpy(chosen_elevator, str, sizeof(chosen_elevator) - 1);
178 return 0;
179 }
180
181 __setup("elevator=", elevator_setup);
182
183 int elevator_init(request_queue_t *q, char *name)
184 {
185 struct elevator_type *e = NULL;
186 struct elevator_queue *eq;
187 int ret = 0;
188
189 elevator_setup_default();
190
191 if (!name)
192 name = chosen_elevator;
193
194 e = elevator_get(name);
195 if (!e)
196 return -EINVAL;
197
198 eq = kmalloc(sizeof(struct elevator_queue), GFP_KERNEL);
199 if (!eq) {
200 elevator_put(e->elevator_type);
201 return -ENOMEM;
202 }
203
204 ret = elevator_attach(q, e, eq);
205 if (ret) {
206 kfree(eq);
207 elevator_put(e->elevator_type);
208 }
209
210 return ret;
211 }
212
213 void elevator_exit(elevator_t *e)
214 {
215 if (e->ops->elevator_exit_fn)
216 e->ops->elevator_exit_fn(e);
217
218 elevator_put(e->elevator_type);
219 e->elevator_type = NULL;
220 kfree(e);
221 }
222
223 int elevator_global_init(void)
224 {
225 return 0;
226 }
227
228 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
229 {
230 elevator_t *e = q->elevator;
231
232 if (e->ops->elevator_merge_fn)
233 return e->ops->elevator_merge_fn(q, req, bio);
234
235 return ELEVATOR_NO_MERGE;
236 }
237
238 void elv_merged_request(request_queue_t *q, struct request *rq)
239 {
240 elevator_t *e = q->elevator;
241
242 if (e->ops->elevator_merged_fn)
243 e->ops->elevator_merged_fn(q, rq);
244 }
245
246 void elv_merge_requests(request_queue_t *q, struct request *rq,
247 struct request *next)
248 {
249 elevator_t *e = q->elevator;
250
251 if (q->last_merge == next)
252 q->last_merge = NULL;
253
254 if (e->ops->elevator_merge_req_fn)
255 e->ops->elevator_merge_req_fn(q, rq, next);
256 }
257
258 void elv_requeue_request(request_queue_t *q, struct request *rq)
259 {
260 /*
261 * it already went through dequeue, we need to decrement the
262 * in_flight count again
263 */
264 if (blk_account_rq(rq))
265 q->in_flight--;
266
267 /*
268 * if iosched has an explicit requeue hook, then use that. otherwise
269 * just put the request at the front of the queue
270 */
271 if (q->elevator->ops->elevator_requeue_req_fn)
272 q->elevator->ops->elevator_requeue_req_fn(q, rq);
273 else
274 __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
275 }
276
277 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
278 int plug)
279 {
280 /*
281 * barriers implicitly indicate back insertion
282 */
283 if (rq->flags & (REQ_SOFTBARRIER | REQ_HARDBARRIER) &&
284 where == ELEVATOR_INSERT_SORT)
285 where = ELEVATOR_INSERT_BACK;
286
287 if (plug)
288 blk_plug_device(q);
289
290 rq->q = q;
291
292 if (!test_bit(QUEUE_FLAG_DRAIN, &q->queue_flags)) {
293 q->elevator->ops->elevator_add_req_fn(q, rq, where);
294
295 if (blk_queue_plugged(q)) {
296 int nrq = q->rq.count[READ] + q->rq.count[WRITE]
297 - q->in_flight;
298
299 if (nrq == q->unplug_thresh)
300 __generic_unplug_device(q);
301 }
302 } else
303 /*
304 * if drain is set, store the request "locally". when the drain
305 * is finished, the requests will be handed ordered to the io
306 * scheduler
307 */
308 list_add_tail(&rq->queuelist, &q->drain_list);
309 }
310
311 void elv_add_request(request_queue_t *q, struct request *rq, int where,
312 int plug)
313 {
314 unsigned long flags;
315
316 spin_lock_irqsave(q->queue_lock, flags);
317 __elv_add_request(q, rq, where, plug);
318 spin_unlock_irqrestore(q->queue_lock, flags);
319 }
320
321 static inline struct request *__elv_next_request(request_queue_t *q)
322 {
323 return q->elevator->ops->elevator_next_req_fn(q);
324 }
325
326 struct request *elv_next_request(request_queue_t *q)
327 {
328 struct request *rq;
329 int ret;
330
331 while ((rq = __elv_next_request(q)) != NULL) {
332 /*
333 * just mark as started even if we don't start it, a request
334 * that has been delayed should not be passed by new incoming
335 * requests
336 */
337 rq->flags |= REQ_STARTED;
338
339 if (rq == q->last_merge)
340 q->last_merge = NULL;
341
342 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
343 break;
344
345 ret = q->prep_rq_fn(q, rq);
346 if (ret == BLKPREP_OK) {
347 break;
348 } else if (ret == BLKPREP_DEFER) {
349 rq = NULL;
350 break;
351 } else if (ret == BLKPREP_KILL) {
352 int nr_bytes = rq->hard_nr_sectors << 9;
353
354 if (!nr_bytes)
355 nr_bytes = rq->data_len;
356
357 blkdev_dequeue_request(rq);
358 rq->flags |= REQ_QUIET;
359 end_that_request_chunk(rq, 0, nr_bytes);
360 end_that_request_last(rq);
361 } else {
362 printk(KERN_ERR "%s: bad return=%d\n", __FUNCTION__,
363 ret);
364 break;
365 }
366 }
367
368 return rq;
369 }
370
371 void elv_remove_request(request_queue_t *q, struct request *rq)
372 {
373 elevator_t *e = q->elevator;
374
375 /*
376 * the time frame between a request being removed from the lists
377 * and to it is freed is accounted as io that is in progress at
378 * the driver side. note that we only account requests that the
379 * driver has seen (REQ_STARTED set), to avoid false accounting
380 * for request-request merges
381 */
382 if (blk_account_rq(rq))
383 q->in_flight++;
384
385 /*
386 * the main clearing point for q->last_merge is on retrieval of
387 * request by driver (it calls elv_next_request()), but it _can_
388 * also happen here if a request is added to the queue but later
389 * deleted without ever being given to driver (merged with another
390 * request).
391 */
392 if (rq == q->last_merge)
393 q->last_merge = NULL;
394
395 if (e->ops->elevator_remove_req_fn)
396 e->ops->elevator_remove_req_fn(q, rq);
397 }
398
399 int elv_queue_empty(request_queue_t *q)
400 {
401 elevator_t *e = q->elevator;
402
403 if (e->ops->elevator_queue_empty_fn)
404 return e->ops->elevator_queue_empty_fn(q);
405
406 return list_empty(&q->queue_head);
407 }
408
409 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
410 {
411 struct list_head *next;
412
413 elevator_t *e = q->elevator;
414
415 if (e->ops->elevator_latter_req_fn)
416 return e->ops->elevator_latter_req_fn(q, rq);
417
418 next = rq->queuelist.next;
419 if (next != &q->queue_head && next != &rq->queuelist)
420 return list_entry_rq(next);
421
422 return NULL;
423 }
424
425 struct request *elv_former_request(request_queue_t *q, struct request *rq)
426 {
427 struct list_head *prev;
428
429 elevator_t *e = q->elevator;
430
431 if (e->ops->elevator_former_req_fn)
432 return e->ops->elevator_former_req_fn(q, rq);
433
434 prev = rq->queuelist.prev;
435 if (prev != &q->queue_head && prev != &rq->queuelist)
436 return list_entry_rq(prev);
437
438 return NULL;
439 }
440
441 int elv_set_request(request_queue_t *q, struct request *rq, int gfp_mask)
442 {
443 elevator_t *e = q->elevator;
444
445 if (e->ops->elevator_set_req_fn)
446 return e->ops->elevator_set_req_fn(q, rq, gfp_mask);
447
448 rq->elevator_private = NULL;
449 return 0;
450 }
451
452 void elv_put_request(request_queue_t *q, struct request *rq)
453 {
454 elevator_t *e = q->elevator;
455
456 if (e->ops->elevator_put_req_fn)
457 e->ops->elevator_put_req_fn(q, rq);
458 }
459
460 int elv_may_queue(request_queue_t *q, int rw)
461 {
462 elevator_t *e = q->elevator;
463
464 if (e->ops->elevator_may_queue_fn)
465 return e->ops->elevator_may_queue_fn(q, rw);
466
467 return ELV_MQUEUE_MAY;
468 }
469
470 void elv_completed_request(request_queue_t *q, struct request *rq)
471 {
472 elevator_t *e = q->elevator;
473
474 /*
475 * request is released from the driver, io must be done
476 */
477 if (blk_account_rq(rq))
478 q->in_flight--;
479
480 if (e->ops->elevator_completed_req_fn)
481 e->ops->elevator_completed_req_fn(q, rq);
482 }
483
484 int elv_register_queue(struct request_queue *q)
485 {
486 elevator_t *e = q->elevator;
487
488 e->kobj.parent = kobject_get(&q->kobj);
489 if (!e->kobj.parent)
490 return -EBUSY;
491
492 snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
493 e->kobj.ktype = e->elevator_type->elevator_ktype;
494
495 return kobject_register(&e->kobj);
496 }
497
498 void elv_unregister_queue(struct request_queue *q)
499 {
500 if (q) {
501 elevator_t *e = q->elevator;
502 kobject_unregister(&e->kobj);
503 kobject_put(&q->kobj);
504 }
505 }
506
507 int elv_register(struct elevator_type *e)
508 {
509 if (elevator_find(e->elevator_name))
510 BUG();
511
512 spin_lock_irq(&elv_list_lock);
513 list_add_tail(&e->list, &elv_list);
514 spin_unlock_irq(&elv_list_lock);
515
516 printk(KERN_INFO "io scheduler %s registered", e->elevator_name);
517 if (!strcmp(e->elevator_name, chosen_elevator))
518 printk(" (default)");
519 printk("\n");
520 return 0;
521 }
522 EXPORT_SYMBOL_GPL(elv_register);
523
524 void elv_unregister(struct elevator_type *e)
525 {
526 spin_lock_irq(&elv_list_lock);
527 list_del_init(&e->list);
528 spin_unlock_irq(&elv_list_lock);
529 }
530 EXPORT_SYMBOL_GPL(elv_unregister);
531
532 /*
533 * switch to new_e io scheduler. be careful not to introduce deadlocks -
534 * we don't free the old io scheduler, before we have allocated what we
535 * need for the new one. this way we have a chance of going back to the old
536 * one, if the new one fails init for some reason. we also do an intermediate
537 * switch to noop to ensure safety with stack-allocated requests, since they
538 * don't originate from the block layer allocator. noop is safe here, because
539 * it never needs to touch the elevator itself for completion events. DRAIN
540 * flags will make sure we don't touch it for additions either.
541 */
542 static void elevator_switch(request_queue_t *q, struct elevator_type *new_e)
543 {
544 elevator_t *e = kmalloc(sizeof(elevator_t), GFP_KERNEL);
545 struct elevator_type *noop_elevator = NULL;
546 elevator_t *old_elevator;
547
548 if (!e)
549 goto error;
550
551 /*
552 * first step, drain requests from the block freelist
553 */
554 blk_wait_queue_drained(q, 0);
555
556 /*
557 * unregister old elevator data
558 */
559 elv_unregister_queue(q);
560 old_elevator = q->elevator;
561
562 /*
563 * next step, switch to noop since it uses no private rq structures
564 * and doesn't allocate any memory for anything. then wait for any
565 * non-fs requests in-flight
566 */
567 noop_elevator = elevator_get("noop");
568 spin_lock_irq(q->queue_lock);
569 elevator_attach(q, noop_elevator, e);
570 spin_unlock_irq(q->queue_lock);
571
572 blk_wait_queue_drained(q, 1);
573
574 /*
575 * attach and start new elevator
576 */
577 if (elevator_attach(q, new_e, e))
578 goto fail;
579
580 if (elv_register_queue(q))
581 goto fail_register;
582
583 /*
584 * finally exit old elevator and start queue again
585 */
586 elevator_exit(old_elevator);
587 blk_finish_queue_drain(q);
588 elevator_put(noop_elevator);
589 return;
590
591 fail_register:
592 /*
593 * switch failed, exit the new io scheduler and reattach the old
594 * one again (along with re-adding the sysfs dir)
595 */
596 elevator_exit(e);
597 fail:
598 q->elevator = old_elevator;
599 elv_register_queue(q);
600 blk_finish_queue_drain(q);
601 error:
602 if (noop_elevator)
603 elevator_put(noop_elevator);
604 elevator_put(new_e);
605 printk(KERN_ERR "elevator: switch to %s failed\n",new_e->elevator_name);
606 }
607
608 ssize_t elv_iosched_store(request_queue_t *q, const char *name, size_t count)
609 {
610 char elevator_name[ELV_NAME_MAX];
611 struct elevator_type *e;
612
613 memset(elevator_name, 0, sizeof(elevator_name));
614 strncpy(elevator_name, name, sizeof(elevator_name));
615
616 if (elevator_name[strlen(elevator_name) - 1] == '\n')
617 elevator_name[strlen(elevator_name) - 1] = '\0';
618
619 e = elevator_get(elevator_name);
620 if (!e) {
621 printk(KERN_ERR "elevator: type %s not found\n", elevator_name);
622 return -EINVAL;
623 }
624
625 if (!strcmp(elevator_name, q->elevator->elevator_type->elevator_name))
626 return count;
627
628 elevator_switch(q, e);
629 return count;
630 }
631
632 ssize_t elv_iosched_show(request_queue_t *q, char *name)
633 {
634 elevator_t *e = q->elevator;
635 struct elevator_type *elv = e->elevator_type;
636 struct list_head *entry;
637 int len = 0;
638
639 spin_lock_irq(q->queue_lock);
640 list_for_each(entry, &elv_list) {
641 struct elevator_type *__e;
642
643 __e = list_entry(entry, struct elevator_type, list);
644 if (!strcmp(elv->elevator_name, __e->elevator_name))
645 len += sprintf(name+len, "[%s] ", elv->elevator_name);
646 else
647 len += sprintf(name+len, "%s ", __e->elevator_name);
648 }
649 spin_unlock_irq(q->queue_lock);
650
651 len += sprintf(len+name, "\n");
652 return len;
653 }
654
655 module_init(elevator_global_init);
656
657 EXPORT_SYMBOL(elv_add_request);
658 EXPORT_SYMBOL(__elv_add_request);
659 EXPORT_SYMBOL(elv_requeue_request);
660 EXPORT_SYMBOL(elv_next_request);
661 EXPORT_SYMBOL(elv_remove_request);
662 EXPORT_SYMBOL(elv_queue_empty);
663 EXPORT_SYMBOL(elv_completed_request);
664 EXPORT_SYMBOL(elevator_exit);
665 EXPORT_SYMBOL(elevator_init);
666
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