2 * linux/drivers/block/elevator.c
4 * Block device elevator/IO-scheduler.
6 * Copyright (C) 2000 Andrea Arcangeli <andrea@suse.de> SuSE
8 * 30042000 Jens Axboe <axboe@suse.de> :
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
15 * - elevator_dequeue_fn, called when a request is taken off the active list
17 * 20082000 Dave Jones <davej@suse.de> :
18 * Removed tests for max-bomb-segments, which was breaking elvtune
19 * when run without -bN
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
27 #include <linux/kernel.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>
38 #include <asm/uaccess.h>
41 * can we safely merge with this request?
43 inline int elv_rq_merge_ok(struct request *rq, struct bio *bio)
45 if (!rq_mergeable(rq))
49 * different data direction or already started, don't merge
51 if (bio_data_dir(bio) != rq_data_dir(rq))
55 * same device and no special stuff set, merge is ok
57 if (rq->rq_disk == bio->bi_bdev->bd_disk &&
58 !rq->waiting && !rq->special)
64 inline int elv_try_merge(struct request *__rq, struct bio *bio)
66 int ret = ELEVATOR_NO_MERGE;
69 * we can merge and sequence is ok, check if it's possible
71 if (elv_rq_merge_ok(__rq, bio)) {
72 if (__rq->sector + __rq->nr_sectors == bio->bi_sector)
73 ret = ELEVATOR_BACK_MERGE;
74 else if (__rq->sector - bio_sectors(bio) == bio->bi_sector)
75 ret = ELEVATOR_FRONT_MERGE;
81 inline int elv_try_last_merge(request_queue_t *q, struct bio *bio)
84 return elv_try_merge(q->last_merge, bio);
86 return ELEVATOR_NO_MERGE;
90 * general block -> elevator interface starts here
92 int elevator_init(request_queue_t *q, elevator_t *type)
94 elevator_t *e = &q->elevator;
96 memcpy(e, type, sizeof(*e));
98 INIT_LIST_HEAD(&q->queue_head);
101 if (e->elevator_init_fn)
102 return e->elevator_init_fn(q, e);
107 void elevator_exit(request_queue_t *q)
109 elevator_t *e = &q->elevator;
111 if (e->elevator_exit_fn)
112 e->elevator_exit_fn(q, e);
115 int elevator_global_init(void)
120 int elv_merge(request_queue_t *q, struct request **req, struct bio *bio)
122 elevator_t *e = &q->elevator;
124 if (e->elevator_merge_fn)
125 return e->elevator_merge_fn(q, req, bio);
127 return ELEVATOR_NO_MERGE;
130 void elv_merged_request(request_queue_t *q, struct request *rq)
132 elevator_t *e = &q->elevator;
134 if (e->elevator_merged_fn)
135 e->elevator_merged_fn(q, rq);
138 void elv_merge_requests(request_queue_t *q, struct request *rq,
139 struct request *next)
141 elevator_t *e = &q->elevator;
143 if (q->last_merge == next)
144 q->last_merge = NULL;
146 if (e->elevator_merge_req_fn)
147 e->elevator_merge_req_fn(q, rq, next);
150 void elv_requeue_request(request_queue_t *q, struct request *rq)
153 * it already went through dequeue, we need to decrement the
154 * in_flight count again
156 if (blk_account_rq(rq))
160 * if iosched has an explicit requeue hook, then use that. otherwise
161 * just put the request at the front of the queue
163 if (q->elevator.elevator_requeue_req_fn)
164 q->elevator.elevator_requeue_req_fn(q, rq);
166 __elv_add_request(q, rq, ELEVATOR_INSERT_FRONT, 0);
169 void __elv_add_request(request_queue_t *q, struct request *rq, int where,
176 q->elevator.elevator_add_req_fn(q, rq, where);
179 void elv_add_request(request_queue_t *q, struct request *rq, int where,
184 spin_lock_irqsave(q->queue_lock, flags);
185 __elv_add_request(q, rq, where, plug);
186 spin_unlock_irqrestore(q->queue_lock, flags);
189 static inline struct request *__elv_next_request(request_queue_t *q)
191 return q->elevator.elevator_next_req_fn(q);
194 struct request *elv_next_request(request_queue_t *q)
199 while ((rq = __elv_next_request(q))) {
201 * just mark as started even if we don't start it, a request
202 * that has been delayed should not be passed by new incoming
205 rq->flags |= REQ_STARTED;
207 if (rq == q->last_merge)
208 q->last_merge = NULL;
210 if ((rq->flags & REQ_DONTPREP) || !q->prep_rq_fn)
213 ret = q->prep_rq_fn(q, rq);
214 if (ret == BLKPREP_OK) {
216 } else if (ret == BLKPREP_DEFER) {
219 } else if (ret == BLKPREP_KILL) {
220 int nr_bytes = rq->hard_nr_sectors << 9;
223 nr_bytes = rq->data_len;
225 blkdev_dequeue_request(rq);
226 rq->flags |= REQ_QUIET;
227 end_that_request_chunk(rq, 0, nr_bytes);
228 end_that_request_last(rq);
230 printk("%s: bad return=%d\n", __FUNCTION__, ret);
238 void elv_remove_request(request_queue_t *q, struct request *rq)
240 elevator_t *e = &q->elevator;
243 * the time frame between a request being removed from the lists
244 * and to it is freed is accounted as io that is in progress at
245 * the driver side. note that we only account requests that the
246 * driver has seen (REQ_STARTED set), to avoid false accounting
247 * for request-request merges
249 if (blk_account_rq(rq))
253 * the main clearing point for q->last_merge is on retrieval of
254 * request by driver (it calls elv_next_request()), but it _can_
255 * also happen here if a request is added to the queue but later
256 * deleted without ever being given to driver (merged with another
259 if (rq == q->last_merge)
260 q->last_merge = NULL;
262 if (e->elevator_remove_req_fn)
263 e->elevator_remove_req_fn(q, rq);
266 int elv_queue_empty(request_queue_t *q)
268 elevator_t *e = &q->elevator;
270 if (e->elevator_queue_empty_fn)
271 return e->elevator_queue_empty_fn(q);
273 return list_empty(&q->queue_head);
276 struct request *elv_latter_request(request_queue_t *q, struct request *rq)
278 struct list_head *next;
280 elevator_t *e = &q->elevator;
282 if (e->elevator_latter_req_fn)
283 return e->elevator_latter_req_fn(q, rq);
285 next = rq->queuelist.next;
286 if (next != &q->queue_head && next != &rq->queuelist)
287 return list_entry_rq(next);
292 struct request *elv_former_request(request_queue_t *q, struct request *rq)
294 struct list_head *prev;
296 elevator_t *e = &q->elevator;
298 if (e->elevator_former_req_fn)
299 return e->elevator_former_req_fn(q, rq);
301 prev = rq->queuelist.prev;
302 if (prev != &q->queue_head && prev != &rq->queuelist)
303 return list_entry_rq(prev);
308 int elv_set_request(request_queue_t *q, struct request *rq, int gfp_mask)
310 elevator_t *e = &q->elevator;
312 if (e->elevator_set_req_fn)
313 return e->elevator_set_req_fn(q, rq, gfp_mask);
315 rq->elevator_private = NULL;
319 void elv_put_request(request_queue_t *q, struct request *rq)
321 elevator_t *e = &q->elevator;
323 if (e->elevator_put_req_fn)
324 e->elevator_put_req_fn(q, rq);
327 int elv_may_queue(request_queue_t *q, int rw)
329 elevator_t *e = &q->elevator;
331 if (e->elevator_may_queue_fn)
332 return e->elevator_may_queue_fn(q, rw);
337 void elv_completed_request(request_queue_t *q, struct request *rq)
339 elevator_t *e = &q->elevator;
342 * request is released from the driver, io must be done
344 if (blk_account_rq(rq))
347 if (e->elevator_completed_req_fn)
348 e->elevator_completed_req_fn(q, rq);
351 int elv_register_queue(struct request_queue *q)
357 e->kobj.parent = kobject_get(&q->kobj);
361 snprintf(e->kobj.name, KOBJ_NAME_LEN, "%s", "iosched");
362 e->kobj.ktype = e->elevator_ktype;
364 return kobject_register(&e->kobj);
367 void elv_unregister_queue(struct request_queue *q)
370 elevator_t * e = &q->elevator;
371 kobject_unregister(&e->kobj);
372 kobject_put(&q->kobj);
376 module_init(elevator_global_init);
378 EXPORT_SYMBOL(elv_add_request);
379 EXPORT_SYMBOL(__elv_add_request);
380 EXPORT_SYMBOL(elv_requeue_request);
381 EXPORT_SYMBOL(elv_next_request);
382 EXPORT_SYMBOL(elv_remove_request);
383 EXPORT_SYMBOL(elv_queue_empty);
384 EXPORT_SYMBOL(elv_completed_request);
385 EXPORT_SYMBOL(elevator_exit);
386 EXPORT_SYMBOL(elevator_init);