2 * Anticipatory & deadline i/o scheduler.
4 * Copyright (C) 2002 Jens Axboe <axboe@kernel.dk>
5 * Nick Piggin <nickpiggin@yahoo.com.au>
8 #include <linux/kernel.h>
10 #include <linux/blkdev.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/interrupt.h>
24 * See Documentation/block/as-iosched.txt
28 * max time before a read is submitted.
30 #define default_read_expire (HZ / 8)
33 * ditto for writes, these limits are not hard, even
34 * if the disk is capable of satisfying them.
36 #define default_write_expire (HZ / 4)
39 * read_batch_expire describes how long we will allow a stream of reads to
40 * persist before looking to see whether it is time to switch over to writes.
42 #define default_read_batch_expire (HZ / 2)
45 * write_batch_expire describes how long we want a stream of writes to run for.
46 * This is not a hard limit, but a target we set for the auto-tuning thingy.
47 * See, the problem is: we can send a lot of writes to disk cache / TCQ in
48 * a short amount of time...
50 #define default_write_batch_expire (HZ / 8)
53 * max time we may wait to anticipate a read (default around 6ms)
55 #define default_antic_expire ((HZ / 150) ? HZ / 150 : 1)
58 * Keep track of up to 20ms thinktimes. We can go as big as we like here,
59 * however huge values tend to interfere and not decay fast enough. A program
60 * might be in a non-io phase of operation. Waiting on user input for example,
61 * or doing a lengthy computation. A small penalty can be justified there, and
62 * will still catch out those processes that constantly have large thinktimes.
64 #define MAX_THINKTIME (HZ/50UL)
66 /* Bits in as_io_context.state */
68 AS_TASK_RUNNING
=0, /* Process has not exited */
69 AS_TASK_IOSTARTED
, /* Process has started some IO */
70 AS_TASK_IORUNNING
, /* Process has completed some IO */
73 enum anticipation_status
{
74 ANTIC_OFF
=0, /* Not anticipating (normal operation) */
75 ANTIC_WAIT_REQ
, /* The last read has not yet completed */
76 ANTIC_WAIT_NEXT
, /* Currently anticipating a request vs
77 last read (which has completed) */
78 ANTIC_FINISHED
, /* Anticipating but have found a candidate
87 struct request_queue
*q
; /* the "owner" queue */
90 * requests (as_rq s) are present on both sort_list and fifo_list
92 struct rb_root sort_list
[2];
93 struct list_head fifo_list
[2];
95 struct request
*next_rq
[2]; /* next in sort order */
96 sector_t last_sector
[2]; /* last REQ_SYNC & REQ_ASYNC sectors */
98 unsigned long exit_prob
; /* probability a task will exit while
100 unsigned long exit_no_coop
; /* probablility an exited task will
101 not be part of a later cooperating
103 unsigned long new_ttime_total
; /* mean thinktime on new proc */
104 unsigned long new_ttime_mean
;
105 u64 new_seek_total
; /* mean seek on new proc */
106 sector_t new_seek_mean
;
108 unsigned long current_batch_expires
;
109 unsigned long last_check_fifo
[2];
110 int changed_batch
; /* 1: waiting for old batch to end */
111 int new_batch
; /* 1: waiting on first read complete */
112 int batch_data_dir
; /* current batch REQ_SYNC / REQ_ASYNC */
113 int write_batch_count
; /* max # of reqs in a write batch */
114 int current_write_count
; /* how many requests left this batch */
115 int write_batch_idled
; /* has the write batch gone idle? */
117 enum anticipation_status antic_status
;
118 unsigned long antic_start
; /* jiffies: when it started */
119 struct timer_list antic_timer
; /* anticipatory scheduling timer */
120 struct work_struct antic_work
; /* Deferred unplugging */
121 struct io_context
*io_context
; /* Identify the expected process */
122 int ioc_finished
; /* IO associated with io_context is finished */
126 * settings that change how the i/o scheduler behaves
128 unsigned long fifo_expire
[2];
129 unsigned long batch_expire
[2];
130 unsigned long antic_expire
;
137 AS_RQ_NEW
=0, /* New - not referenced and not on any lists */
138 AS_RQ_QUEUED
, /* In the request queue. It belongs to the
140 AS_RQ_DISPATCHED
, /* On the dispatch list. It belongs to the
142 AS_RQ_PRESCHED
, /* Debug poisoning for requests being used */
145 AS_RQ_POSTSCHED
, /* when they shouldn't be */
148 #define RQ_IOC(rq) ((struct io_context *) (rq)->elevator_private)
149 #define RQ_STATE(rq) ((enum arq_state)(rq)->elevator_private2)
150 #define RQ_SET_STATE(rq, state) ((rq)->elevator_private2 = (void *) state)
152 static DEFINE_PER_CPU(unsigned long, ioc_count
);
153 static struct completion
*ioc_gone
;
155 static void as_move_to_dispatch(struct as_data
*ad
, struct request
*rq
);
156 static void as_antic_stop(struct as_data
*ad
);
159 * IO Context helper functions
162 /* Called to deallocate the as_io_context */
163 static void free_as_io_context(struct as_io_context
*aic
)
166 elv_ioc_count_dec(ioc_count
);
167 if (ioc_gone
&& !elv_ioc_count_read(ioc_count
))
171 static void as_trim(struct io_context
*ioc
)
173 spin_lock(&ioc
->lock
);
175 free_as_io_context(ioc
->aic
);
177 spin_unlock(&ioc
->lock
);
180 /* Called when the task exits */
181 static void exit_as_io_context(struct as_io_context
*aic
)
183 WARN_ON(!test_bit(AS_TASK_RUNNING
, &aic
->state
));
184 clear_bit(AS_TASK_RUNNING
, &aic
->state
);
187 static struct as_io_context
*alloc_as_io_context(void)
189 struct as_io_context
*ret
;
191 ret
= kmalloc(sizeof(*ret
), GFP_ATOMIC
);
193 ret
->dtor
= free_as_io_context
;
194 ret
->exit
= exit_as_io_context
;
195 ret
->state
= 1 << AS_TASK_RUNNING
;
196 atomic_set(&ret
->nr_queued
, 0);
197 atomic_set(&ret
->nr_dispatched
, 0);
198 spin_lock_init(&ret
->lock
);
199 ret
->ttime_total
= 0;
200 ret
->ttime_samples
= 0;
203 ret
->seek_samples
= 0;
205 elv_ioc_count_inc(ioc_count
);
212 * If the current task has no AS IO context then create one and initialise it.
213 * Then take a ref on the task's io context and return it.
215 static struct io_context
*as_get_io_context(int node
)
217 struct io_context
*ioc
= get_io_context(GFP_ATOMIC
, node
);
218 if (ioc
&& !ioc
->aic
) {
219 ioc
->aic
= alloc_as_io_context();
228 static void as_put_io_context(struct request
*rq
)
230 struct as_io_context
*aic
;
232 if (unlikely(!RQ_IOC(rq
)))
235 aic
= RQ_IOC(rq
)->aic
;
237 if (rq_is_sync(rq
) && aic
) {
238 spin_lock(&aic
->lock
);
239 set_bit(AS_TASK_IORUNNING
, &aic
->state
);
240 aic
->last_end_request
= jiffies
;
241 spin_unlock(&aic
->lock
);
244 put_io_context(RQ_IOC(rq
));
248 * rb tree support functions
250 #define RQ_RB_ROOT(ad, rq) (&(ad)->sort_list[rq_is_sync((rq))])
252 static void as_add_rq_rb(struct as_data
*ad
, struct request
*rq
)
254 struct request
*alias
;
256 while ((unlikely(alias
= elv_rb_add(RQ_RB_ROOT(ad
, rq
), rq
)))) {
257 as_move_to_dispatch(ad
, alias
);
262 static inline void as_del_rq_rb(struct as_data
*ad
, struct request
*rq
)
264 elv_rb_del(RQ_RB_ROOT(ad
, rq
), rq
);
268 * IO Scheduler proper
271 #define MAXBACK (1024 * 1024) /*
272 * Maximum distance the disk will go backward
276 #define BACK_PENALTY 2
279 * as_choose_req selects the preferred one of two requests of the same data_dir
280 * ignoring time - eg. timeouts, which is the job of as_dispatch_request
282 static struct request
*
283 as_choose_req(struct as_data
*ad
, struct request
*rq1
, struct request
*rq2
)
286 sector_t last
, s1
, s2
, d1
, d2
;
287 int r1_wrap
=0, r2_wrap
=0; /* requests are behind the disk head */
288 const sector_t maxback
= MAXBACK
;
290 if (rq1
== NULL
|| rq1
== rq2
)
295 data_dir
= rq_is_sync(rq1
);
297 last
= ad
->last_sector
[data_dir
];
301 BUG_ON(data_dir
!= rq_is_sync(rq2
));
304 * Strict one way elevator _except_ in the case where we allow
305 * short backward seeks which are biased as twice the cost of a
306 * similar forward seek.
310 else if (s1
+maxback
>= last
)
311 d1
= (last
- s1
)*BACK_PENALTY
;
314 d1
= 0; /* shut up, gcc */
319 else if (s2
+maxback
>= last
)
320 d2
= (last
- s2
)*BACK_PENALTY
;
326 /* Found required data */
327 if (!r1_wrap
&& r2_wrap
)
329 else if (!r2_wrap
&& r1_wrap
)
331 else if (r1_wrap
&& r2_wrap
) {
332 /* both behind the head */
339 /* Both requests in front of the head */
353 * as_find_next_rq finds the next request after @prev in elevator order.
354 * this with as_choose_req form the basis for how the scheduler chooses
355 * what request to process next. Anticipation works on top of this.
357 static struct request
*
358 as_find_next_rq(struct as_data
*ad
, struct request
*last
)
360 struct rb_node
*rbnext
= rb_next(&last
->rb_node
);
361 struct rb_node
*rbprev
= rb_prev(&last
->rb_node
);
362 struct request
*next
= NULL
, *prev
= NULL
;
364 BUG_ON(RB_EMPTY_NODE(&last
->rb_node
));
367 prev
= rb_entry_rq(rbprev
);
370 next
= rb_entry_rq(rbnext
);
372 const int data_dir
= rq_is_sync(last
);
374 rbnext
= rb_first(&ad
->sort_list
[data_dir
]);
375 if (rbnext
&& rbnext
!= &last
->rb_node
)
376 next
= rb_entry_rq(rbnext
);
379 return as_choose_req(ad
, next
, prev
);
383 * anticipatory scheduling functions follow
387 * as_antic_expired tells us when we have anticipated too long.
388 * The funny "absolute difference" math on the elapsed time is to handle
389 * jiffy wraps, and disks which have been idle for 0x80000000 jiffies.
391 static int as_antic_expired(struct as_data
*ad
)
395 delta_jif
= jiffies
- ad
->antic_start
;
396 if (unlikely(delta_jif
< 0))
397 delta_jif
= -delta_jif
;
398 if (delta_jif
< ad
->antic_expire
)
405 * as_antic_waitnext starts anticipating that a nice request will soon be
406 * submitted. See also as_antic_waitreq
408 static void as_antic_waitnext(struct as_data
*ad
)
410 unsigned long timeout
;
412 BUG_ON(ad
->antic_status
!= ANTIC_OFF
413 && ad
->antic_status
!= ANTIC_WAIT_REQ
);
415 timeout
= ad
->antic_start
+ ad
->antic_expire
;
417 mod_timer(&ad
->antic_timer
, timeout
);
419 ad
->antic_status
= ANTIC_WAIT_NEXT
;
423 * as_antic_waitreq starts anticipating. We don't start timing the anticipation
424 * until the request that we're anticipating on has finished. This means we
425 * are timing from when the candidate process wakes up hopefully.
427 static void as_antic_waitreq(struct as_data
*ad
)
429 BUG_ON(ad
->antic_status
== ANTIC_FINISHED
);
430 if (ad
->antic_status
== ANTIC_OFF
) {
431 if (!ad
->io_context
|| ad
->ioc_finished
)
432 as_antic_waitnext(ad
);
434 ad
->antic_status
= ANTIC_WAIT_REQ
;
439 * This is called directly by the functions in this file to stop anticipation.
440 * We kill the timer and schedule a call to the request_fn asap.
442 static void as_antic_stop(struct as_data
*ad
)
444 int status
= ad
->antic_status
;
446 if (status
== ANTIC_WAIT_REQ
|| status
== ANTIC_WAIT_NEXT
) {
447 if (status
== ANTIC_WAIT_NEXT
)
448 del_timer(&ad
->antic_timer
);
449 ad
->antic_status
= ANTIC_FINISHED
;
450 /* see as_work_handler */
451 kblockd_schedule_work(&ad
->antic_work
);
456 * as_antic_timeout is the timer function set by as_antic_waitnext.
458 static void as_antic_timeout(unsigned long data
)
460 struct request_queue
*q
= (struct request_queue
*)data
;
461 struct as_data
*ad
= q
->elevator
->elevator_data
;
464 spin_lock_irqsave(q
->queue_lock
, flags
);
465 if (ad
->antic_status
== ANTIC_WAIT_REQ
466 || ad
->antic_status
== ANTIC_WAIT_NEXT
) {
467 struct as_io_context
*aic
;
468 spin_lock(&ad
->io_context
->lock
);
469 aic
= ad
->io_context
->aic
;
471 ad
->antic_status
= ANTIC_FINISHED
;
472 kblockd_schedule_work(&ad
->antic_work
);
474 if (aic
->ttime_samples
== 0) {
475 /* process anticipated on has exited or timed out*/
476 ad
->exit_prob
= (7*ad
->exit_prob
+ 256)/8;
478 if (!test_bit(AS_TASK_RUNNING
, &aic
->state
)) {
479 /* process not "saved" by a cooperating request */
480 ad
->exit_no_coop
= (7*ad
->exit_no_coop
+ 256)/8;
482 spin_unlock(&ad
->io_context
->lock
);
484 spin_unlock_irqrestore(q
->queue_lock
, flags
);
487 static void as_update_thinktime(struct as_data
*ad
, struct as_io_context
*aic
,
490 /* fixed point: 1.0 == 1<<8 */
491 if (aic
->ttime_samples
== 0) {
492 ad
->new_ttime_total
= (7*ad
->new_ttime_total
+ 256*ttime
) / 8;
493 ad
->new_ttime_mean
= ad
->new_ttime_total
/ 256;
495 ad
->exit_prob
= (7*ad
->exit_prob
)/8;
497 aic
->ttime_samples
= (7*aic
->ttime_samples
+ 256) / 8;
498 aic
->ttime_total
= (7*aic
->ttime_total
+ 256*ttime
) / 8;
499 aic
->ttime_mean
= (aic
->ttime_total
+ 128) / aic
->ttime_samples
;
502 static void as_update_seekdist(struct as_data
*ad
, struct as_io_context
*aic
,
507 if (aic
->seek_samples
== 0) {
508 ad
->new_seek_total
= (7*ad
->new_seek_total
+ 256*(u64
)sdist
)/8;
509 ad
->new_seek_mean
= ad
->new_seek_total
/ 256;
513 * Don't allow the seek distance to get too large from the
514 * odd fragment, pagein, etc
516 if (aic
->seek_samples
<= 60) /* second&third seek */
517 sdist
= min(sdist
, (aic
->seek_mean
* 4) + 2*1024*1024);
519 sdist
= min(sdist
, (aic
->seek_mean
* 4) + 2*1024*64);
521 aic
->seek_samples
= (7*aic
->seek_samples
+ 256) / 8;
522 aic
->seek_total
= (7*aic
->seek_total
+ (u64
)256*sdist
) / 8;
523 total
= aic
->seek_total
+ (aic
->seek_samples
/2);
524 do_div(total
, aic
->seek_samples
);
525 aic
->seek_mean
= (sector_t
)total
;
529 * as_update_iohist keeps a decaying histogram of IO thinktimes, and
530 * updates @aic->ttime_mean based on that. It is called when a new
533 static void as_update_iohist(struct as_data
*ad
, struct as_io_context
*aic
,
536 int data_dir
= rq_is_sync(rq
);
537 unsigned long thinktime
= 0;
543 if (data_dir
== REQ_SYNC
) {
544 unsigned long in_flight
= atomic_read(&aic
->nr_queued
)
545 + atomic_read(&aic
->nr_dispatched
);
546 spin_lock(&aic
->lock
);
547 if (test_bit(AS_TASK_IORUNNING
, &aic
->state
) ||
548 test_bit(AS_TASK_IOSTARTED
, &aic
->state
)) {
549 /* Calculate read -> read thinktime */
550 if (test_bit(AS_TASK_IORUNNING
, &aic
->state
)
552 thinktime
= jiffies
- aic
->last_end_request
;
553 thinktime
= min(thinktime
, MAX_THINKTIME
-1);
555 as_update_thinktime(ad
, aic
, thinktime
);
557 /* Calculate read -> read seek distance */
558 if (aic
->last_request_pos
< rq
->sector
)
559 seek_dist
= rq
->sector
- aic
->last_request_pos
;
561 seek_dist
= aic
->last_request_pos
- rq
->sector
;
562 as_update_seekdist(ad
, aic
, seek_dist
);
564 aic
->last_request_pos
= rq
->sector
+ rq
->nr_sectors
;
565 set_bit(AS_TASK_IOSTARTED
, &aic
->state
);
566 spin_unlock(&aic
->lock
);
571 * as_close_req decides if one request is considered "close" to the
572 * previous one issued.
574 static int as_close_req(struct as_data
*ad
, struct as_io_context
*aic
,
577 unsigned long delay
; /* jiffies */
578 sector_t last
= ad
->last_sector
[ad
->batch_data_dir
];
579 sector_t next
= rq
->sector
;
580 sector_t delta
; /* acceptable close offset (in sectors) */
583 if (ad
->antic_status
== ANTIC_OFF
|| !ad
->ioc_finished
)
586 delay
= jiffies
- ad
->antic_start
;
590 else if (delay
<= (20 * HZ
/ 1000) && delay
<= ad
->antic_expire
)
591 delta
= 8192 << delay
;
595 if ((last
<= next
+ (delta
>>1)) && (next
<= last
+ delta
))
603 if (aic
->seek_samples
== 0) {
605 * Process has just started IO. Use past statistics to
606 * gauge success possibility
608 if (ad
->new_seek_mean
> s
) {
609 /* this request is better than what we're expecting */
614 if (aic
->seek_mean
> s
) {
615 /* this request is better than what we're expecting */
624 * as_can_break_anticipation returns true if we have been anticipating this
627 * It also returns true if the process against which we are anticipating
628 * submits a write - that's presumably an fsync, O_SYNC write, etc. We want to
629 * dispatch it ASAP, because we know that application will not be submitting
632 * If the task which has submitted the request has exited, break anticipation.
634 * If this task has queued some other IO, do not enter enticipation.
636 static int as_can_break_anticipation(struct as_data
*ad
, struct request
*rq
)
638 struct io_context
*ioc
;
639 struct as_io_context
*aic
;
641 ioc
= ad
->io_context
;
643 spin_lock(&ioc
->lock
);
645 if (rq
&& ioc
== RQ_IOC(rq
)) {
646 /* request from same process */
647 spin_unlock(&ioc
->lock
);
651 if (ad
->ioc_finished
&& as_antic_expired(ad
)) {
653 * In this situation status should really be FINISHED,
654 * however the timer hasn't had the chance to run yet.
656 spin_unlock(&ioc
->lock
);
662 spin_unlock(&ioc
->lock
);
666 if (atomic_read(&aic
->nr_queued
) > 0) {
667 /* process has more requests queued */
668 spin_unlock(&ioc
->lock
);
672 if (atomic_read(&aic
->nr_dispatched
) > 0) {
673 /* process has more requests dispatched */
674 spin_unlock(&ioc
->lock
);
678 if (rq
&& rq_is_sync(rq
) && as_close_req(ad
, aic
, rq
)) {
680 * Found a close request that is not one of ours.
682 * This makes close requests from another process update
683 * our IO history. Is generally useful when there are
684 * two or more cooperating processes working in the same
687 if (!test_bit(AS_TASK_RUNNING
, &aic
->state
)) {
688 if (aic
->ttime_samples
== 0)
689 ad
->exit_prob
= (7*ad
->exit_prob
+ 256)/8;
691 ad
->exit_no_coop
= (7*ad
->exit_no_coop
)/8;
694 as_update_iohist(ad
, aic
, rq
);
695 spin_unlock(&ioc
->lock
);
699 if (!test_bit(AS_TASK_RUNNING
, &aic
->state
)) {
700 /* process anticipated on has exited */
701 if (aic
->ttime_samples
== 0)
702 ad
->exit_prob
= (7*ad
->exit_prob
+ 256)/8;
704 if (ad
->exit_no_coop
> 128) {
705 spin_unlock(&ioc
->lock
);
710 if (aic
->ttime_samples
== 0) {
711 if (ad
->new_ttime_mean
> ad
->antic_expire
) {
712 spin_unlock(&ioc
->lock
);
715 if (ad
->exit_prob
* ad
->exit_no_coop
> 128*256) {
716 spin_unlock(&ioc
->lock
);
719 } else if (aic
->ttime_mean
> ad
->antic_expire
) {
720 /* the process thinks too much between requests */
721 spin_unlock(&ioc
->lock
);
724 spin_unlock(&ioc
->lock
);
729 * as_can_anticipate indicates whether we should either run rq
730 * or keep anticipating a better request.
732 static int as_can_anticipate(struct as_data
*ad
, struct request
*rq
)
736 * Last request submitted was a write
740 if (ad
->antic_status
== ANTIC_FINISHED
)
742 * Don't restart if we have just finished. Run the next request
746 if (as_can_break_anticipation(ad
, rq
))
748 * This request is a good candidate. Don't keep anticipating,
754 * OK from here, we haven't finished, and don't have a decent request!
755 * Status is either ANTIC_OFF so start waiting,
756 * ANTIC_WAIT_REQ so continue waiting for request to finish
757 * or ANTIC_WAIT_NEXT so continue waiting for an acceptable request.
764 * as_update_rq must be called whenever a request (rq) is added to
765 * the sort_list. This function keeps caches up to date, and checks if the
766 * request might be one we are "anticipating"
768 static void as_update_rq(struct as_data
*ad
, struct request
*rq
)
770 const int data_dir
= rq_is_sync(rq
);
772 /* keep the next_rq cache up to date */
773 ad
->next_rq
[data_dir
] = as_choose_req(ad
, rq
, ad
->next_rq
[data_dir
]);
776 * have we been anticipating this request?
777 * or does it come from the same process as the one we are anticipating
780 if (ad
->antic_status
== ANTIC_WAIT_REQ
781 || ad
->antic_status
== ANTIC_WAIT_NEXT
) {
782 if (as_can_break_anticipation(ad
, rq
))
788 * Gathers timings and resizes the write batch automatically
790 static void update_write_batch(struct as_data
*ad
)
792 unsigned long batch
= ad
->batch_expire
[REQ_ASYNC
];
795 write_time
= (jiffies
- ad
->current_batch_expires
) + batch
;
799 if (write_time
> batch
&& !ad
->write_batch_idled
) {
800 if (write_time
> batch
* 3)
801 ad
->write_batch_count
/= 2;
803 ad
->write_batch_count
--;
804 } else if (write_time
< batch
&& ad
->current_write_count
== 0) {
805 if (batch
> write_time
* 3)
806 ad
->write_batch_count
*= 2;
808 ad
->write_batch_count
++;
811 if (ad
->write_batch_count
< 1)
812 ad
->write_batch_count
= 1;
816 * as_completed_request is to be called when a request has completed and
817 * returned something to the requesting process, be it an error or data.
819 static void as_completed_request(struct request_queue
*q
, struct request
*rq
)
821 struct as_data
*ad
= q
->elevator
->elevator_data
;
823 WARN_ON(!list_empty(&rq
->queuelist
));
825 if (RQ_STATE(rq
) != AS_RQ_REMOVED
) {
826 printk("rq->state %d\n", RQ_STATE(rq
));
831 if (ad
->changed_batch
&& ad
->nr_dispatched
== 1) {
832 kblockd_schedule_work(&ad
->antic_work
);
833 ad
->changed_batch
= 0;
835 if (ad
->batch_data_dir
== REQ_SYNC
)
838 WARN_ON(ad
->nr_dispatched
== 0);
842 * Start counting the batch from when a request of that direction is
843 * actually serviced. This should help devices with big TCQ windows
844 * and writeback caches
846 if (ad
->new_batch
&& ad
->batch_data_dir
== rq_is_sync(rq
)) {
847 update_write_batch(ad
);
848 ad
->current_batch_expires
= jiffies
+
849 ad
->batch_expire
[REQ_SYNC
];
853 if (ad
->io_context
== RQ_IOC(rq
) && ad
->io_context
) {
854 ad
->antic_start
= jiffies
;
855 ad
->ioc_finished
= 1;
856 if (ad
->antic_status
== ANTIC_WAIT_REQ
) {
858 * We were waiting on this request, now anticipate
861 as_antic_waitnext(ad
);
865 as_put_io_context(rq
);
867 RQ_SET_STATE(rq
, AS_RQ_POSTSCHED
);
871 * as_remove_queued_request removes a request from the pre dispatch queue
872 * without updating refcounts. It is expected the caller will drop the
873 * reference unless it replaces the request at somepart of the elevator
874 * (ie. the dispatch queue)
876 static void as_remove_queued_request(struct request_queue
*q
,
879 const int data_dir
= rq_is_sync(rq
);
880 struct as_data
*ad
= q
->elevator
->elevator_data
;
881 struct io_context
*ioc
;
883 WARN_ON(RQ_STATE(rq
) != AS_RQ_QUEUED
);
886 if (ioc
&& ioc
->aic
) {
887 BUG_ON(!atomic_read(&ioc
->aic
->nr_queued
));
888 atomic_dec(&ioc
->aic
->nr_queued
);
892 * Update the "next_rq" cache if we are about to remove its
895 if (ad
->next_rq
[data_dir
] == rq
)
896 ad
->next_rq
[data_dir
] = as_find_next_rq(ad
, rq
);
899 as_del_rq_rb(ad
, rq
);
903 * as_fifo_expired returns 0 if there are no expired requests on the fifo,
904 * 1 otherwise. It is ratelimited so that we only perform the check once per
905 * `fifo_expire' interval. Otherwise a large number of expired requests
906 * would create a hopeless seekstorm.
908 * See as_antic_expired comment.
910 static int as_fifo_expired(struct as_data
*ad
, int adir
)
915 delta_jif
= jiffies
- ad
->last_check_fifo
[adir
];
916 if (unlikely(delta_jif
< 0))
917 delta_jif
= -delta_jif
;
918 if (delta_jif
< ad
->fifo_expire
[adir
])
921 ad
->last_check_fifo
[adir
] = jiffies
;
923 if (list_empty(&ad
->fifo_list
[adir
]))
926 rq
= rq_entry_fifo(ad
->fifo_list
[adir
].next
);
928 return time_after(jiffies
, rq_fifo_time(rq
));
932 * as_batch_expired returns true if the current batch has expired. A batch
933 * is a set of reads or a set of writes.
935 static inline int as_batch_expired(struct as_data
*ad
)
937 if (ad
->changed_batch
|| ad
->new_batch
)
940 if (ad
->batch_data_dir
== REQ_SYNC
)
941 /* TODO! add a check so a complete fifo gets written? */
942 return time_after(jiffies
, ad
->current_batch_expires
);
944 return time_after(jiffies
, ad
->current_batch_expires
)
945 || ad
->current_write_count
== 0;
949 * move an entry to dispatch queue
951 static void as_move_to_dispatch(struct as_data
*ad
, struct request
*rq
)
953 const int data_dir
= rq_is_sync(rq
);
955 BUG_ON(RB_EMPTY_NODE(&rq
->rb_node
));
958 ad
->antic_status
= ANTIC_OFF
;
961 * This has to be set in order to be correctly updated by
964 ad
->last_sector
[data_dir
] = rq
->sector
+ rq
->nr_sectors
;
966 if (data_dir
== REQ_SYNC
) {
967 struct io_context
*ioc
= RQ_IOC(rq
);
968 /* In case we have to anticipate after this */
969 copy_io_context(&ad
->io_context
, &ioc
);
971 if (ad
->io_context
) {
972 put_io_context(ad
->io_context
);
973 ad
->io_context
= NULL
;
976 if (ad
->current_write_count
!= 0)
977 ad
->current_write_count
--;
979 ad
->ioc_finished
= 0;
981 ad
->next_rq
[data_dir
] = as_find_next_rq(ad
, rq
);
984 * take it off the sort and fifo list, add to dispatch queue
986 as_remove_queued_request(ad
->q
, rq
);
987 WARN_ON(RQ_STATE(rq
) != AS_RQ_QUEUED
);
989 elv_dispatch_sort(ad
->q
, rq
);
991 RQ_SET_STATE(rq
, AS_RQ_DISPATCHED
);
992 if (RQ_IOC(rq
) && RQ_IOC(rq
)->aic
)
993 atomic_inc(&RQ_IOC(rq
)->aic
->nr_dispatched
);
998 * as_dispatch_request selects the best request according to
999 * read/write expire, batch expire, etc, and moves it to the dispatch
1000 * queue. Returns 1 if a request was found, 0 otherwise.
1002 static int as_dispatch_request(struct request_queue
*q
, int force
)
1004 struct as_data
*ad
= q
->elevator
->elevator_data
;
1005 const int reads
= !list_empty(&ad
->fifo_list
[REQ_SYNC
]);
1006 const int writes
= !list_empty(&ad
->fifo_list
[REQ_ASYNC
]);
1009 if (unlikely(force
)) {
1011 * Forced dispatch, accounting is useless. Reset
1012 * accounting states and dump fifo_lists. Note that
1013 * batch_data_dir is reset to REQ_SYNC to avoid
1014 * screwing write batch accounting as write batch
1015 * accounting occurs on W->R transition.
1019 ad
->batch_data_dir
= REQ_SYNC
;
1020 ad
->changed_batch
= 0;
1023 while (ad
->next_rq
[REQ_SYNC
]) {
1024 as_move_to_dispatch(ad
, ad
->next_rq
[REQ_SYNC
]);
1027 ad
->last_check_fifo
[REQ_SYNC
] = jiffies
;
1029 while (ad
->next_rq
[REQ_ASYNC
]) {
1030 as_move_to_dispatch(ad
, ad
->next_rq
[REQ_ASYNC
]);
1033 ad
->last_check_fifo
[REQ_ASYNC
] = jiffies
;
1038 /* Signal that the write batch was uncontended, so we can't time it */
1039 if (ad
->batch_data_dir
== REQ_ASYNC
&& !reads
) {
1040 if (ad
->current_write_count
== 0 || !writes
)
1041 ad
->write_batch_idled
= 1;
1044 if (!(reads
|| writes
)
1045 || ad
->antic_status
== ANTIC_WAIT_REQ
1046 || ad
->antic_status
== ANTIC_WAIT_NEXT
1047 || ad
->changed_batch
)
1050 if (!(reads
&& writes
&& as_batch_expired(ad
))) {
1052 * batch is still running or no reads or no writes
1054 rq
= ad
->next_rq
[ad
->batch_data_dir
];
1056 if (ad
->batch_data_dir
== REQ_SYNC
&& ad
->antic_expire
) {
1057 if (as_fifo_expired(ad
, REQ_SYNC
))
1060 if (as_can_anticipate(ad
, rq
)) {
1061 as_antic_waitreq(ad
);
1067 /* we have a "next request" */
1068 if (reads
&& !writes
)
1069 ad
->current_batch_expires
=
1070 jiffies
+ ad
->batch_expire
[REQ_SYNC
];
1071 goto dispatch_request
;
1076 * at this point we are not running a batch. select the appropriate
1077 * data direction (read / write)
1081 BUG_ON(RB_EMPTY_ROOT(&ad
->sort_list
[REQ_SYNC
]));
1083 if (writes
&& ad
->batch_data_dir
== REQ_SYNC
)
1085 * Last batch was a read, switch to writes
1087 goto dispatch_writes
;
1089 if (ad
->batch_data_dir
== REQ_ASYNC
) {
1090 WARN_ON(ad
->new_batch
);
1091 ad
->changed_batch
= 1;
1093 ad
->batch_data_dir
= REQ_SYNC
;
1094 rq
= rq_entry_fifo(ad
->fifo_list
[REQ_SYNC
].next
);
1095 ad
->last_check_fifo
[ad
->batch_data_dir
] = jiffies
;
1096 goto dispatch_request
;
1100 * the last batch was a read
1105 BUG_ON(RB_EMPTY_ROOT(&ad
->sort_list
[REQ_ASYNC
]));
1107 if (ad
->batch_data_dir
== REQ_SYNC
) {
1108 ad
->changed_batch
= 1;
1111 * new_batch might be 1 when the queue runs out of
1112 * reads. A subsequent submission of a write might
1113 * cause a change of batch before the read is finished.
1117 ad
->batch_data_dir
= REQ_ASYNC
;
1118 ad
->current_write_count
= ad
->write_batch_count
;
1119 ad
->write_batch_idled
= 0;
1120 rq
= rq_entry_fifo(ad
->fifo_list
[REQ_ASYNC
].next
);
1121 ad
->last_check_fifo
[REQ_ASYNC
] = jiffies
;
1122 goto dispatch_request
;
1130 * If a request has expired, service it.
1133 if (as_fifo_expired(ad
, ad
->batch_data_dir
)) {
1135 rq
= rq_entry_fifo(ad
->fifo_list
[ad
->batch_data_dir
].next
);
1138 if (ad
->changed_batch
) {
1139 WARN_ON(ad
->new_batch
);
1141 if (ad
->nr_dispatched
)
1144 if (ad
->batch_data_dir
== REQ_ASYNC
)
1145 ad
->current_batch_expires
= jiffies
+
1146 ad
->batch_expire
[REQ_ASYNC
];
1150 ad
->changed_batch
= 0;
1154 * rq is the selected appropriate request.
1156 as_move_to_dispatch(ad
, rq
);
1162 * add rq to rbtree and fifo
1164 static void as_add_request(struct request_queue
*q
, struct request
*rq
)
1166 struct as_data
*ad
= q
->elevator
->elevator_data
;
1169 RQ_SET_STATE(rq
, AS_RQ_NEW
);
1171 data_dir
= rq_is_sync(rq
);
1173 rq
->elevator_private
= as_get_io_context(q
->node
);
1176 as_update_iohist(ad
, RQ_IOC(rq
)->aic
, rq
);
1177 atomic_inc(&RQ_IOC(rq
)->aic
->nr_queued
);
1180 as_add_rq_rb(ad
, rq
);
1183 * set expire time and add to fifo list
1185 rq_set_fifo_time(rq
, jiffies
+ ad
->fifo_expire
[data_dir
]);
1186 list_add_tail(&rq
->queuelist
, &ad
->fifo_list
[data_dir
]);
1188 as_update_rq(ad
, rq
); /* keep state machine up to date */
1189 RQ_SET_STATE(rq
, AS_RQ_QUEUED
);
1192 static void as_activate_request(struct request_queue
*q
, struct request
*rq
)
1194 WARN_ON(RQ_STATE(rq
) != AS_RQ_DISPATCHED
);
1195 RQ_SET_STATE(rq
, AS_RQ_REMOVED
);
1196 if (RQ_IOC(rq
) && RQ_IOC(rq
)->aic
)
1197 atomic_dec(&RQ_IOC(rq
)->aic
->nr_dispatched
);
1200 static void as_deactivate_request(struct request_queue
*q
, struct request
*rq
)
1202 WARN_ON(RQ_STATE(rq
) != AS_RQ_REMOVED
);
1203 RQ_SET_STATE(rq
, AS_RQ_DISPATCHED
);
1204 if (RQ_IOC(rq
) && RQ_IOC(rq
)->aic
)
1205 atomic_inc(&RQ_IOC(rq
)->aic
->nr_dispatched
);
1209 * as_queue_empty tells us if there are requests left in the device. It may
1210 * not be the case that a driver can get the next request even if the queue
1211 * is not empty - it is used in the block layer to check for plugging and
1212 * merging opportunities
1214 static int as_queue_empty(struct request_queue
*q
)
1216 struct as_data
*ad
= q
->elevator
->elevator_data
;
1218 return list_empty(&ad
->fifo_list
[REQ_ASYNC
])
1219 && list_empty(&ad
->fifo_list
[REQ_SYNC
]);
1223 as_merge(struct request_queue
*q
, struct request
**req
, struct bio
*bio
)
1225 struct as_data
*ad
= q
->elevator
->elevator_data
;
1226 sector_t rb_key
= bio
->bi_sector
+ bio_sectors(bio
);
1227 struct request
*__rq
;
1230 * check for front merge
1232 __rq
= elv_rb_find(&ad
->sort_list
[bio_data_dir(bio
)], rb_key
);
1233 if (__rq
&& elv_rq_merge_ok(__rq
, bio
)) {
1235 return ELEVATOR_FRONT_MERGE
;
1238 return ELEVATOR_NO_MERGE
;
1241 static void as_merged_request(struct request_queue
*q
, struct request
*req
,
1244 struct as_data
*ad
= q
->elevator
->elevator_data
;
1247 * if the merge was a front merge, we need to reposition request
1249 if (type
== ELEVATOR_FRONT_MERGE
) {
1250 as_del_rq_rb(ad
, req
);
1251 as_add_rq_rb(ad
, req
);
1253 * Note! At this stage of this and the next function, our next
1254 * request may not be optimal - eg the request may have "grown"
1255 * behind the disk head. We currently don't bother adjusting.
1260 static void as_merged_requests(struct request_queue
*q
, struct request
*req
,
1261 struct request
*next
)
1264 * if next expires before rq, assign its expire time to arq
1265 * and move into next position (next will be deleted) in fifo
1267 if (!list_empty(&req
->queuelist
) && !list_empty(&next
->queuelist
)) {
1268 if (time_before(rq_fifo_time(next
), rq_fifo_time(req
))) {
1269 struct io_context
*rioc
= RQ_IOC(req
);
1270 struct io_context
*nioc
= RQ_IOC(next
);
1272 list_move(&req
->queuelist
, &next
->queuelist
);
1273 rq_set_fifo_time(req
, rq_fifo_time(next
));
1275 * Don't copy here but swap, because when anext is
1276 * removed below, it must contain the unused context
1279 double_spin_lock(&rioc
->lock
, &nioc
->lock
,
1281 swap_io_context(&rioc
, &nioc
);
1282 double_spin_unlock(&rioc
->lock
, &nioc
->lock
,
1289 * kill knowledge of next, this one is a goner
1291 as_remove_queued_request(q
, next
);
1292 as_put_io_context(next
);
1294 RQ_SET_STATE(next
, AS_RQ_MERGED
);
1298 * This is executed in a "deferred" process context, by kblockd. It calls the
1299 * driver's request_fn so the driver can submit that request.
1301 * IMPORTANT! This guy will reenter the elevator, so set up all queue global
1302 * state before calling, and don't rely on any state over calls.
1304 * FIXME! dispatch queue is not a queue at all!
1306 static void as_work_handler(struct work_struct
*work
)
1308 struct as_data
*ad
= container_of(work
, struct as_data
, antic_work
);
1309 struct request_queue
*q
= ad
->q
;
1310 unsigned long flags
;
1312 spin_lock_irqsave(q
->queue_lock
, flags
);
1313 blk_start_queueing(q
);
1314 spin_unlock_irqrestore(q
->queue_lock
, flags
);
1317 static int as_may_queue(struct request_queue
*q
, int rw
)
1319 int ret
= ELV_MQUEUE_MAY
;
1320 struct as_data
*ad
= q
->elevator
->elevator_data
;
1321 struct io_context
*ioc
;
1322 if (ad
->antic_status
== ANTIC_WAIT_REQ
||
1323 ad
->antic_status
== ANTIC_WAIT_NEXT
) {
1324 ioc
= as_get_io_context(q
->node
);
1325 if (ad
->io_context
== ioc
)
1326 ret
= ELV_MQUEUE_MUST
;
1327 put_io_context(ioc
);
1333 static void as_exit_queue(elevator_t
*e
)
1335 struct as_data
*ad
= e
->elevator_data
;
1337 del_timer_sync(&ad
->antic_timer
);
1338 kblockd_flush_work(&ad
->antic_work
);
1340 BUG_ON(!list_empty(&ad
->fifo_list
[REQ_SYNC
]));
1341 BUG_ON(!list_empty(&ad
->fifo_list
[REQ_ASYNC
]));
1343 put_io_context(ad
->io_context
);
1348 * initialize elevator private data (as_data).
1350 static void *as_init_queue(struct request_queue
*q
)
1354 ad
= kmalloc_node(sizeof(*ad
), GFP_KERNEL
| __GFP_ZERO
, q
->node
);
1358 ad
->q
= q
; /* Identify what queue the data belongs to */
1360 /* anticipatory scheduling helpers */
1361 ad
->antic_timer
.function
= as_antic_timeout
;
1362 ad
->antic_timer
.data
= (unsigned long)q
;
1363 init_timer(&ad
->antic_timer
);
1364 INIT_WORK(&ad
->antic_work
, as_work_handler
);
1366 INIT_LIST_HEAD(&ad
->fifo_list
[REQ_SYNC
]);
1367 INIT_LIST_HEAD(&ad
->fifo_list
[REQ_ASYNC
]);
1368 ad
->sort_list
[REQ_SYNC
] = RB_ROOT
;
1369 ad
->sort_list
[REQ_ASYNC
] = RB_ROOT
;
1370 ad
->fifo_expire
[REQ_SYNC
] = default_read_expire
;
1371 ad
->fifo_expire
[REQ_ASYNC
] = default_write_expire
;
1372 ad
->antic_expire
= default_antic_expire
;
1373 ad
->batch_expire
[REQ_SYNC
] = default_read_batch_expire
;
1374 ad
->batch_expire
[REQ_ASYNC
] = default_write_batch_expire
;
1376 ad
->current_batch_expires
= jiffies
+ ad
->batch_expire
[REQ_SYNC
];
1377 ad
->write_batch_count
= ad
->batch_expire
[REQ_ASYNC
] / 10;
1378 if (ad
->write_batch_count
< 2)
1379 ad
->write_batch_count
= 2;
1389 as_var_show(unsigned int var
, char *page
)
1391 return sprintf(page
, "%d\n", var
);
1395 as_var_store(unsigned long *var
, const char *page
, size_t count
)
1397 char *p
= (char *) page
;
1399 *var
= simple_strtoul(p
, &p
, 10);
1403 static ssize_t
est_time_show(elevator_t
*e
, char *page
)
1405 struct as_data
*ad
= e
->elevator_data
;
1408 pos
+= sprintf(page
+pos
, "%lu %% exit probability\n",
1409 100*ad
->exit_prob
/256);
1410 pos
+= sprintf(page
+pos
, "%lu %% probability of exiting without a "
1411 "cooperating process submitting IO\n",
1412 100*ad
->exit_no_coop
/256);
1413 pos
+= sprintf(page
+pos
, "%lu ms new thinktime\n", ad
->new_ttime_mean
);
1414 pos
+= sprintf(page
+pos
, "%llu sectors new seek distance\n",
1415 (unsigned long long)ad
->new_seek_mean
);
1420 #define SHOW_FUNCTION(__FUNC, __VAR) \
1421 static ssize_t __FUNC(elevator_t *e, char *page) \
1423 struct as_data *ad = e->elevator_data; \
1424 return as_var_show(jiffies_to_msecs((__VAR)), (page)); \
1426 SHOW_FUNCTION(as_read_expire_show
, ad
->fifo_expire
[REQ_SYNC
]);
1427 SHOW_FUNCTION(as_write_expire_show
, ad
->fifo_expire
[REQ_ASYNC
]);
1428 SHOW_FUNCTION(as_antic_expire_show
, ad
->antic_expire
);
1429 SHOW_FUNCTION(as_read_batch_expire_show
, ad
->batch_expire
[REQ_SYNC
]);
1430 SHOW_FUNCTION(as_write_batch_expire_show
, ad
->batch_expire
[REQ_ASYNC
]);
1431 #undef SHOW_FUNCTION
1433 #define STORE_FUNCTION(__FUNC, __PTR, MIN, MAX) \
1434 static ssize_t __FUNC(elevator_t *e, const char *page, size_t count) \
1436 struct as_data *ad = e->elevator_data; \
1437 int ret = as_var_store(__PTR, (page), count); \
1438 if (*(__PTR) < (MIN)) \
1440 else if (*(__PTR) > (MAX)) \
1442 *(__PTR) = msecs_to_jiffies(*(__PTR)); \
1445 STORE_FUNCTION(as_read_expire_store
, &ad
->fifo_expire
[REQ_SYNC
], 0, INT_MAX
);
1446 STORE_FUNCTION(as_write_expire_store
, &ad
->fifo_expire
[REQ_ASYNC
], 0, INT_MAX
);
1447 STORE_FUNCTION(as_antic_expire_store
, &ad
->antic_expire
, 0, INT_MAX
);
1448 STORE_FUNCTION(as_read_batch_expire_store
,
1449 &ad
->batch_expire
[REQ_SYNC
], 0, INT_MAX
);
1450 STORE_FUNCTION(as_write_batch_expire_store
,
1451 &ad
->batch_expire
[REQ_ASYNC
], 0, INT_MAX
);
1452 #undef STORE_FUNCTION
1454 #define AS_ATTR(name) \
1455 __ATTR(name, S_IRUGO|S_IWUSR, as_##name##_show, as_##name##_store)
1457 static struct elv_fs_entry as_attrs
[] = {
1458 __ATTR_RO(est_time
),
1459 AS_ATTR(read_expire
),
1460 AS_ATTR(write_expire
),
1461 AS_ATTR(antic_expire
),
1462 AS_ATTR(read_batch_expire
),
1463 AS_ATTR(write_batch_expire
),
1467 static struct elevator_type iosched_as
= {
1469 .elevator_merge_fn
= as_merge
,
1470 .elevator_merged_fn
= as_merged_request
,
1471 .elevator_merge_req_fn
= as_merged_requests
,
1472 .elevator_dispatch_fn
= as_dispatch_request
,
1473 .elevator_add_req_fn
= as_add_request
,
1474 .elevator_activate_req_fn
= as_activate_request
,
1475 .elevator_deactivate_req_fn
= as_deactivate_request
,
1476 .elevator_queue_empty_fn
= as_queue_empty
,
1477 .elevator_completed_req_fn
= as_completed_request
,
1478 .elevator_former_req_fn
= elv_rb_former_request
,
1479 .elevator_latter_req_fn
= elv_rb_latter_request
,
1480 .elevator_may_queue_fn
= as_may_queue
,
1481 .elevator_init_fn
= as_init_queue
,
1482 .elevator_exit_fn
= as_exit_queue
,
1486 .elevator_attrs
= as_attrs
,
1487 .elevator_name
= "anticipatory",
1488 .elevator_owner
= THIS_MODULE
,
1491 static int __init
as_init(void)
1493 elv_register(&iosched_as
);
1498 static void __exit
as_exit(void)
1500 DECLARE_COMPLETION_ONSTACK(all_gone
);
1501 elv_unregister(&iosched_as
);
1502 ioc_gone
= &all_gone
;
1503 /* ioc_gone's update must be visible before reading ioc_count */
1505 if (elv_ioc_count_read(ioc_count
))
1506 wait_for_completion(ioc_gone
);
1510 module_init(as_init
);
1511 module_exit(as_exit
);
1513 MODULE_AUTHOR("Nick Piggin");
1514 MODULE_LICENSE("GPL");
1515 MODULE_DESCRIPTION("anticipatory IO scheduler");