forked from torvalds/linux
-
Notifications
You must be signed in to change notification settings - Fork 1
/
as-iosched.c
1517 lines (1286 loc) · 38.5 KB
/
as-iosched.c
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
/*
* Anticipatory & deadline i/o scheduler.
*
* Copyright (C) 2002 Jens Axboe <[email protected]>
* Nick Piggin <[email protected]>
*
*/
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/blkdev.h>
#include <linux/elevator.h>
#include <linux/bio.h>
#include <linux/module.h>
#include <linux/slab.h>
#include <linux/init.h>
#include <linux/compiler.h>
#include <linux/rbtree.h>
#include <linux/interrupt.h>
#define REQ_SYNC 1
#define REQ_ASYNC 0
/*
* See Documentation/block/as-iosched.txt
*/
/*
* max time before a read is submitted.
*/
#define default_read_expire (HZ / 8)
/*
* ditto for writes, these limits are not hard, even
* if the disk is capable of satisfying them.
*/
#define default_write_expire (HZ / 4)
/*
* read_batch_expire describes how long we will allow a stream of reads to
* persist before looking to see whether it is time to switch over to writes.
*/
#define default_read_batch_expire (HZ / 2)
/*
* write_batch_expire describes how long we want a stream of writes to run for.
* This is not a hard limit, but a target we set for the auto-tuning thingy.
* See, the problem is: we can send a lot of writes to disk cache / TCQ in
* a short amount of time...
*/
#define default_write_batch_expire (HZ / 8)
/*
* max time we may wait to anticipate a read (default around 6ms)
*/
#define default_antic_expire ((HZ / 150) ? HZ / 150 : 1)
/*
* Keep track of up to 20ms thinktimes. We can go as big as we like here,
* however huge values tend to interfere and not decay fast enough. A program
* might be in a non-io phase of operation. Waiting on user input for example,
* or doing a lengthy computation. A small penalty can be justified there, and
* will still catch out those processes that constantly have large thinktimes.
*/
#define MAX_THINKTIME (HZ/50UL)
/* Bits in as_io_context.state */
enum as_io_states {
AS_TASK_RUNNING=0, /* Process has not exited */
AS_TASK_IOSTARTED, /* Process has started some IO */
AS_TASK_IORUNNING, /* Process has completed some IO */
};
enum anticipation_status {
ANTIC_OFF=0, /* Not anticipating (normal operation) */
ANTIC_WAIT_REQ, /* The last read has not yet completed */
ANTIC_WAIT_NEXT, /* Currently anticipating a request vs
last read (which has completed) */
ANTIC_FINISHED, /* Anticipating but have found a candidate
* or timed out */
};
struct as_data {
/*
* run time data
*/
struct request_queue *q; /* the "owner" queue */
/*
* requests (as_rq s) are present on both sort_list and fifo_list
*/
struct rb_root sort_list[2];
struct list_head fifo_list[2];
struct request *next_rq[2]; /* next in sort order */
sector_t last_sector[2]; /* last REQ_SYNC & REQ_ASYNC sectors */
unsigned long exit_prob; /* probability a task will exit while
being waited on */
unsigned long exit_no_coop; /* probablility an exited task will
not be part of a later cooperating
request */
unsigned long new_ttime_total; /* mean thinktime on new proc */
unsigned long new_ttime_mean;
u64 new_seek_total; /* mean seek on new proc */
sector_t new_seek_mean;
unsigned long current_batch_expires;
unsigned long last_check_fifo[2];
int changed_batch; /* 1: waiting for old batch to end */
int new_batch; /* 1: waiting on first read complete */
int batch_data_dir; /* current batch REQ_SYNC / REQ_ASYNC */
int write_batch_count; /* max # of reqs in a write batch */
int current_write_count; /* how many requests left this batch */
int write_batch_idled; /* has the write batch gone idle? */
enum anticipation_status antic_status;
unsigned long antic_start; /* jiffies: when it started */
struct timer_list antic_timer; /* anticipatory scheduling timer */
struct work_struct antic_work; /* Deferred unplugging */
struct io_context *io_context; /* Identify the expected process */
int ioc_finished; /* IO associated with io_context is finished */
int nr_dispatched;
/*
* settings that change how the i/o scheduler behaves
*/
unsigned long fifo_expire[2];
unsigned long batch_expire[2];
unsigned long antic_expire;
};
/*
* per-request data.
*/
enum arq_state {
AS_RQ_NEW=0, /* New - not referenced and not on any lists */
AS_RQ_QUEUED, /* In the request queue. It belongs to the
scheduler */
AS_RQ_DISPATCHED, /* On the dispatch list. It belongs to the
driver now */
AS_RQ_PRESCHED, /* Debug poisoning for requests being used */
AS_RQ_REMOVED,
AS_RQ_MERGED,
AS_RQ_POSTSCHED, /* when they shouldn't be */
};
#define RQ_IOC(rq) ((struct io_context *) (rq)->elevator_private)
#define RQ_STATE(rq) ((enum arq_state)(rq)->elevator_private2)
#define RQ_SET_STATE(rq, state) ((rq)->elevator_private2 = (void *) state)
static DEFINE_PER_CPU(unsigned long, ioc_count);
static struct completion *ioc_gone;
static DEFINE_SPINLOCK(ioc_gone_lock);
static void as_move_to_dispatch(struct as_data *ad, struct request *rq);
static void as_antic_stop(struct as_data *ad);
/*
* IO Context helper functions
*/
/* Called to deallocate the as_io_context */
static void free_as_io_context(struct as_io_context *aic)
{
kfree(aic);
elv_ioc_count_dec(ioc_count);
if (ioc_gone) {
/*
* AS scheduler is exiting, grab exit lock and check
* the pending io context count. If it hits zero,
* complete ioc_gone and set it back to NULL.
*/
spin_lock(&ioc_gone_lock);
if (ioc_gone && !elv_ioc_count_read(ioc_count)) {
complete(ioc_gone);
ioc_gone = NULL;
}
spin_unlock(&ioc_gone_lock);
}
}
static void as_trim(struct io_context *ioc)
{
spin_lock_irq(&ioc->lock);
if (ioc->aic)
free_as_io_context(ioc->aic);
ioc->aic = NULL;
spin_unlock_irq(&ioc->lock);
}
/* Called when the task exits */
static void exit_as_io_context(struct as_io_context *aic)
{
WARN_ON(!test_bit(AS_TASK_RUNNING, &aic->state));
clear_bit(AS_TASK_RUNNING, &aic->state);
}
static struct as_io_context *alloc_as_io_context(void)
{
struct as_io_context *ret;
ret = kmalloc(sizeof(*ret), GFP_ATOMIC);
if (ret) {
ret->dtor = free_as_io_context;
ret->exit = exit_as_io_context;
ret->state = 1 << AS_TASK_RUNNING;
atomic_set(&ret->nr_queued, 0);
atomic_set(&ret->nr_dispatched, 0);
spin_lock_init(&ret->lock);
ret->ttime_total = 0;
ret->ttime_samples = 0;
ret->ttime_mean = 0;
ret->seek_total = 0;
ret->seek_samples = 0;
ret->seek_mean = 0;
elv_ioc_count_inc(ioc_count);
}
return ret;
}
/*
* If the current task has no AS IO context then create one and initialise it.
* Then take a ref on the task's io context and return it.
*/
static struct io_context *as_get_io_context(int node)
{
struct io_context *ioc = get_io_context(GFP_ATOMIC, node);
if (ioc && !ioc->aic) {
ioc->aic = alloc_as_io_context();
if (!ioc->aic) {
put_io_context(ioc);
ioc = NULL;
}
}
return ioc;
}
static void as_put_io_context(struct request *rq)
{
struct as_io_context *aic;
if (unlikely(!RQ_IOC(rq)))
return;
aic = RQ_IOC(rq)->aic;
if (rq_is_sync(rq) && aic) {
unsigned long flags;
spin_lock_irqsave(&aic->lock, flags);
set_bit(AS_TASK_IORUNNING, &aic->state);
aic->last_end_request = jiffies;
spin_unlock_irqrestore(&aic->lock, flags);
}
put_io_context(RQ_IOC(rq));
}
/*
* rb tree support functions
*/
#define RQ_RB_ROOT(ad, rq) (&(ad)->sort_list[rq_is_sync((rq))])
static void as_add_rq_rb(struct as_data *ad, struct request *rq)
{
struct request *alias;
while ((unlikely(alias = elv_rb_add(RQ_RB_ROOT(ad, rq), rq)))) {
as_move_to_dispatch(ad, alias);
as_antic_stop(ad);
}
}
static inline void as_del_rq_rb(struct as_data *ad, struct request *rq)
{
elv_rb_del(RQ_RB_ROOT(ad, rq), rq);
}
/*
* IO Scheduler proper
*/
#define MAXBACK (1024 * 1024) /*
* Maximum distance the disk will go backward
* for a request.
*/
#define BACK_PENALTY 2
/*
* as_choose_req selects the preferred one of two requests of the same data_dir
* ignoring time - eg. timeouts, which is the job of as_dispatch_request
*/
static struct request *
as_choose_req(struct as_data *ad, struct request *rq1, struct request *rq2)
{
int data_dir;
sector_t last, s1, s2, d1, d2;
int r1_wrap=0, r2_wrap=0; /* requests are behind the disk head */
const sector_t maxback = MAXBACK;
if (rq1 == NULL || rq1 == rq2)
return rq2;
if (rq2 == NULL)
return rq1;
data_dir = rq_is_sync(rq1);
last = ad->last_sector[data_dir];
s1 = rq1->sector;
s2 = rq2->sector;
BUG_ON(data_dir != rq_is_sync(rq2));
/*
* Strict one way elevator _except_ in the case where we allow
* short backward seeks which are biased as twice the cost of a
* similar forward seek.
*/
if (s1 >= last)
d1 = s1 - last;
else if (s1+maxback >= last)
d1 = (last - s1)*BACK_PENALTY;
else {
r1_wrap = 1;
d1 = 0; /* shut up, gcc */
}
if (s2 >= last)
d2 = s2 - last;
else if (s2+maxback >= last)
d2 = (last - s2)*BACK_PENALTY;
else {
r2_wrap = 1;
d2 = 0;
}
/* Found required data */
if (!r1_wrap && r2_wrap)
return rq1;
else if (!r2_wrap && r1_wrap)
return rq2;
else if (r1_wrap && r2_wrap) {
/* both behind the head */
if (s1 <= s2)
return rq1;
else
return rq2;
}
/* Both requests in front of the head */
if (d1 < d2)
return rq1;
else if (d2 < d1)
return rq2;
else {
if (s1 >= s2)
return rq1;
else
return rq2;
}
}
/*
* as_find_next_rq finds the next request after @prev in elevator order.
* this with as_choose_req form the basis for how the scheduler chooses
* what request to process next. Anticipation works on top of this.
*/
static struct request *
as_find_next_rq(struct as_data *ad, struct request *last)
{
struct rb_node *rbnext = rb_next(&last->rb_node);
struct rb_node *rbprev = rb_prev(&last->rb_node);
struct request *next = NULL, *prev = NULL;
BUG_ON(RB_EMPTY_NODE(&last->rb_node));
if (rbprev)
prev = rb_entry_rq(rbprev);
if (rbnext)
next = rb_entry_rq(rbnext);
else {
const int data_dir = rq_is_sync(last);
rbnext = rb_first(&ad->sort_list[data_dir]);
if (rbnext && rbnext != &last->rb_node)
next = rb_entry_rq(rbnext);
}
return as_choose_req(ad, next, prev);
}
/*
* anticipatory scheduling functions follow
*/
/*
* as_antic_expired tells us when we have anticipated too long.
* The funny "absolute difference" math on the elapsed time is to handle
* jiffy wraps, and disks which have been idle for 0x80000000 jiffies.
*/
static int as_antic_expired(struct as_data *ad)
{
long delta_jif;
delta_jif = jiffies - ad->antic_start;
if (unlikely(delta_jif < 0))
delta_jif = -delta_jif;
if (delta_jif < ad->antic_expire)
return 0;
return 1;
}
/*
* as_antic_waitnext starts anticipating that a nice request will soon be
* submitted. See also as_antic_waitreq
*/
static void as_antic_waitnext(struct as_data *ad)
{
unsigned long timeout;
BUG_ON(ad->antic_status != ANTIC_OFF
&& ad->antic_status != ANTIC_WAIT_REQ);
timeout = ad->antic_start + ad->antic_expire;
mod_timer(&ad->antic_timer, timeout);
ad->antic_status = ANTIC_WAIT_NEXT;
}
/*
* as_antic_waitreq starts anticipating. We don't start timing the anticipation
* until the request that we're anticipating on has finished. This means we
* are timing from when the candidate process wakes up hopefully.
*/
static void as_antic_waitreq(struct as_data *ad)
{
BUG_ON(ad->antic_status == ANTIC_FINISHED);
if (ad->antic_status == ANTIC_OFF) {
if (!ad->io_context || ad->ioc_finished)
as_antic_waitnext(ad);
else
ad->antic_status = ANTIC_WAIT_REQ;
}
}
/*
* This is called directly by the functions in this file to stop anticipation.
* We kill the timer and schedule a call to the request_fn asap.
*/
static void as_antic_stop(struct as_data *ad)
{
int status = ad->antic_status;
if (status == ANTIC_WAIT_REQ || status == ANTIC_WAIT_NEXT) {
if (status == ANTIC_WAIT_NEXT)
del_timer(&ad->antic_timer);
ad->antic_status = ANTIC_FINISHED;
/* see as_work_handler */
kblockd_schedule_work(&ad->antic_work);
}
}
/*
* as_antic_timeout is the timer function set by as_antic_waitnext.
*/
static void as_antic_timeout(unsigned long data)
{
struct request_queue *q = (struct request_queue *)data;
struct as_data *ad = q->elevator->elevator_data;
unsigned long flags;
spin_lock_irqsave(q->queue_lock, flags);
if (ad->antic_status == ANTIC_WAIT_REQ
|| ad->antic_status == ANTIC_WAIT_NEXT) {
struct as_io_context *aic;
spin_lock(&ad->io_context->lock);
aic = ad->io_context->aic;
ad->antic_status = ANTIC_FINISHED;
kblockd_schedule_work(&ad->antic_work);
if (aic->ttime_samples == 0) {
/* process anticipated on has exited or timed out*/
ad->exit_prob = (7*ad->exit_prob + 256)/8;
}
if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
/* process not "saved" by a cooperating request */
ad->exit_no_coop = (7*ad->exit_no_coop + 256)/8;
}
spin_unlock(&ad->io_context->lock);
}
spin_unlock_irqrestore(q->queue_lock, flags);
}
static void as_update_thinktime(struct as_data *ad, struct as_io_context *aic,
unsigned long ttime)
{
/* fixed point: 1.0 == 1<<8 */
if (aic->ttime_samples == 0) {
ad->new_ttime_total = (7*ad->new_ttime_total + 256*ttime) / 8;
ad->new_ttime_mean = ad->new_ttime_total / 256;
ad->exit_prob = (7*ad->exit_prob)/8;
}
aic->ttime_samples = (7*aic->ttime_samples + 256) / 8;
aic->ttime_total = (7*aic->ttime_total + 256*ttime) / 8;
aic->ttime_mean = (aic->ttime_total + 128) / aic->ttime_samples;
}
static void as_update_seekdist(struct as_data *ad, struct as_io_context *aic,
sector_t sdist)
{
u64 total;
if (aic->seek_samples == 0) {
ad->new_seek_total = (7*ad->new_seek_total + 256*(u64)sdist)/8;
ad->new_seek_mean = ad->new_seek_total / 256;
}
/*
* Don't allow the seek distance to get too large from the
* odd fragment, pagein, etc
*/
if (aic->seek_samples <= 60) /* second&third seek */
sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*1024);
else
sdist = min(sdist, (aic->seek_mean * 4) + 2*1024*64);
aic->seek_samples = (7*aic->seek_samples + 256) / 8;
aic->seek_total = (7*aic->seek_total + (u64)256*sdist) / 8;
total = aic->seek_total + (aic->seek_samples/2);
do_div(total, aic->seek_samples);
aic->seek_mean = (sector_t)total;
}
/*
* as_update_iohist keeps a decaying histogram of IO thinktimes, and
* updates @aic->ttime_mean based on that. It is called when a new
* request is queued.
*/
static void as_update_iohist(struct as_data *ad, struct as_io_context *aic,
struct request *rq)
{
int data_dir = rq_is_sync(rq);
unsigned long thinktime = 0;
sector_t seek_dist;
if (aic == NULL)
return;
if (data_dir == REQ_SYNC) {
unsigned long in_flight = atomic_read(&aic->nr_queued)
+ atomic_read(&aic->nr_dispatched);
spin_lock(&aic->lock);
if (test_bit(AS_TASK_IORUNNING, &aic->state) ||
test_bit(AS_TASK_IOSTARTED, &aic->state)) {
/* Calculate read -> read thinktime */
if (test_bit(AS_TASK_IORUNNING, &aic->state)
&& in_flight == 0) {
thinktime = jiffies - aic->last_end_request;
thinktime = min(thinktime, MAX_THINKTIME-1);
}
as_update_thinktime(ad, aic, thinktime);
/* Calculate read -> read seek distance */
if (aic->last_request_pos < rq->sector)
seek_dist = rq->sector - aic->last_request_pos;
else
seek_dist = aic->last_request_pos - rq->sector;
as_update_seekdist(ad, aic, seek_dist);
}
aic->last_request_pos = rq->sector + rq->nr_sectors;
set_bit(AS_TASK_IOSTARTED, &aic->state);
spin_unlock(&aic->lock);
}
}
/*
* as_close_req decides if one request is considered "close" to the
* previous one issued.
*/
static int as_close_req(struct as_data *ad, struct as_io_context *aic,
struct request *rq)
{
unsigned long delay; /* jiffies */
sector_t last = ad->last_sector[ad->batch_data_dir];
sector_t next = rq->sector;
sector_t delta; /* acceptable close offset (in sectors) */
sector_t s;
if (ad->antic_status == ANTIC_OFF || !ad->ioc_finished)
delay = 0;
else
delay = jiffies - ad->antic_start;
if (delay == 0)
delta = 8192;
else if (delay <= (20 * HZ / 1000) && delay <= ad->antic_expire)
delta = 8192 << delay;
else
return 1;
if ((last <= next + (delta>>1)) && (next <= last + delta))
return 1;
if (last < next)
s = next - last;
else
s = last - next;
if (aic->seek_samples == 0) {
/*
* Process has just started IO. Use past statistics to
* gauge success possibility
*/
if (ad->new_seek_mean > s) {
/* this request is better than what we're expecting */
return 1;
}
} else {
if (aic->seek_mean > s) {
/* this request is better than what we're expecting */
return 1;
}
}
return 0;
}
/*
* as_can_break_anticipation returns true if we have been anticipating this
* request.
*
* It also returns true if the process against which we are anticipating
* submits a write - that's presumably an fsync, O_SYNC write, etc. We want to
* dispatch it ASAP, because we know that application will not be submitting
* any new reads.
*
* If the task which has submitted the request has exited, break anticipation.
*
* If this task has queued some other IO, do not enter enticipation.
*/
static int as_can_break_anticipation(struct as_data *ad, struct request *rq)
{
struct io_context *ioc;
struct as_io_context *aic;
ioc = ad->io_context;
BUG_ON(!ioc);
spin_lock(&ioc->lock);
if (rq && ioc == RQ_IOC(rq)) {
/* request from same process */
spin_unlock(&ioc->lock);
return 1;
}
if (ad->ioc_finished && as_antic_expired(ad)) {
/*
* In this situation status should really be FINISHED,
* however the timer hasn't had the chance to run yet.
*/
spin_unlock(&ioc->lock);
return 1;
}
aic = ioc->aic;
if (!aic) {
spin_unlock(&ioc->lock);
return 0;
}
if (atomic_read(&aic->nr_queued) > 0) {
/* process has more requests queued */
spin_unlock(&ioc->lock);
return 1;
}
if (atomic_read(&aic->nr_dispatched) > 0) {
/* process has more requests dispatched */
spin_unlock(&ioc->lock);
return 1;
}
if (rq && rq_is_sync(rq) && as_close_req(ad, aic, rq)) {
/*
* Found a close request that is not one of ours.
*
* This makes close requests from another process update
* our IO history. Is generally useful when there are
* two or more cooperating processes working in the same
* area.
*/
if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
if (aic->ttime_samples == 0)
ad->exit_prob = (7*ad->exit_prob + 256)/8;
ad->exit_no_coop = (7*ad->exit_no_coop)/8;
}
as_update_iohist(ad, aic, rq);
spin_unlock(&ioc->lock);
return 1;
}
if (!test_bit(AS_TASK_RUNNING, &aic->state)) {
/* process anticipated on has exited */
if (aic->ttime_samples == 0)
ad->exit_prob = (7*ad->exit_prob + 256)/8;
if (ad->exit_no_coop > 128) {
spin_unlock(&ioc->lock);
return 1;
}
}
if (aic->ttime_samples == 0) {
if (ad->new_ttime_mean > ad->antic_expire) {
spin_unlock(&ioc->lock);
return 1;
}
if (ad->exit_prob * ad->exit_no_coop > 128*256) {
spin_unlock(&ioc->lock);
return 1;
}
} else if (aic->ttime_mean > ad->antic_expire) {
/* the process thinks too much between requests */
spin_unlock(&ioc->lock);
return 1;
}
spin_unlock(&ioc->lock);
return 0;
}
/*
* as_can_anticipate indicates whether we should either run rq
* or keep anticipating a better request.
*/
static int as_can_anticipate(struct as_data *ad, struct request *rq)
{
if (!ad->io_context)
/*
* Last request submitted was a write
*/
return 0;
if (ad->antic_status == ANTIC_FINISHED)
/*
* Don't restart if we have just finished. Run the next request
*/
return 0;
if (as_can_break_anticipation(ad, rq))
/*
* This request is a good candidate. Don't keep anticipating,
* run it.
*/
return 0;
/*
* OK from here, we haven't finished, and don't have a decent request!
* Status is either ANTIC_OFF so start waiting,
* ANTIC_WAIT_REQ so continue waiting for request to finish
* or ANTIC_WAIT_NEXT so continue waiting for an acceptable request.
*/
return 1;
}
/*
* as_update_rq must be called whenever a request (rq) is added to
* the sort_list. This function keeps caches up to date, and checks if the
* request might be one we are "anticipating"
*/
static void as_update_rq(struct as_data *ad, struct request *rq)
{
const int data_dir = rq_is_sync(rq);
/* keep the next_rq cache up to date */
ad->next_rq[data_dir] = as_choose_req(ad, rq, ad->next_rq[data_dir]);
/*
* have we been anticipating this request?
* or does it come from the same process as the one we are anticipating
* for?
*/
if (ad->antic_status == ANTIC_WAIT_REQ
|| ad->antic_status == ANTIC_WAIT_NEXT) {
if (as_can_break_anticipation(ad, rq))
as_antic_stop(ad);
}
}
/*
* Gathers timings and resizes the write batch automatically
*/
static void update_write_batch(struct as_data *ad)
{
unsigned long batch = ad->batch_expire[REQ_ASYNC];
long write_time;
write_time = (jiffies - ad->current_batch_expires) + batch;
if (write_time < 0)
write_time = 0;
if (write_time > batch && !ad->write_batch_idled) {
if (write_time > batch * 3)
ad->write_batch_count /= 2;
else
ad->write_batch_count--;
} else if (write_time < batch && ad->current_write_count == 0) {
if (batch > write_time * 3)
ad->write_batch_count *= 2;
else
ad->write_batch_count++;
}
if (ad->write_batch_count < 1)
ad->write_batch_count = 1;
}
/*
* as_completed_request is to be called when a request has completed and
* returned something to the requesting process, be it an error or data.
*/
static void as_completed_request(struct request_queue *q, struct request *rq)
{
struct as_data *ad = q->elevator->elevator_data;
WARN_ON(!list_empty(&rq->queuelist));
if (RQ_STATE(rq) != AS_RQ_REMOVED) {
printk("rq->state %d\n", RQ_STATE(rq));
WARN_ON(1);
goto out;
}
if (ad->changed_batch && ad->nr_dispatched == 1) {
ad->current_batch_expires = jiffies +
ad->batch_expire[ad->batch_data_dir];
kblockd_schedule_work(&ad->antic_work);
ad->changed_batch = 0;
if (ad->batch_data_dir == REQ_SYNC)
ad->new_batch = 1;
}
WARN_ON(ad->nr_dispatched == 0);
ad->nr_dispatched--;
/*
* Start counting the batch from when a request of that direction is
* actually serviced. This should help devices with big TCQ windows
* and writeback caches
*/
if (ad->new_batch && ad->batch_data_dir == rq_is_sync(rq)) {
update_write_batch(ad);
ad->current_batch_expires = jiffies +
ad->batch_expire[REQ_SYNC];
ad->new_batch = 0;
}
if (ad->io_context == RQ_IOC(rq) && ad->io_context) {
ad->antic_start = jiffies;
ad->ioc_finished = 1;
if (ad->antic_status == ANTIC_WAIT_REQ) {
/*
* We were waiting on this request, now anticipate
* the next one
*/
as_antic_waitnext(ad);
}
}
as_put_io_context(rq);
out:
RQ_SET_STATE(rq, AS_RQ_POSTSCHED);
}
/*
* as_remove_queued_request removes a request from the pre dispatch queue
* without updating refcounts. It is expected the caller will drop the
* reference unless it replaces the request at somepart of the elevator
* (ie. the dispatch queue)
*/
static void as_remove_queued_request(struct request_queue *q,
struct request *rq)
{
const int data_dir = rq_is_sync(rq);
struct as_data *ad = q->elevator->elevator_data;
struct io_context *ioc;
WARN_ON(RQ_STATE(rq) != AS_RQ_QUEUED);
ioc = RQ_IOC(rq);
if (ioc && ioc->aic) {
BUG_ON(!atomic_read(&ioc->aic->nr_queued));
atomic_dec(&ioc->aic->nr_queued);
}
/*
* Update the "next_rq" cache if we are about to remove its
* entry
*/
if (ad->next_rq[data_dir] == rq)
ad->next_rq[data_dir] = as_find_next_rq(ad, rq);
rq_fifo_clear(rq);
as_del_rq_rb(ad, rq);
}
/*
* as_fifo_expired returns 0 if there are no expired requests on the fifo,
* 1 otherwise. It is ratelimited so that we only perform the check once per
* `fifo_expire' interval. Otherwise a large number of expired requests
* would create a hopeless seekstorm.
*
* See as_antic_expired comment.
*/
static int as_fifo_expired(struct as_data *ad, int adir)
{
struct request *rq;
long delta_jif;
delta_jif = jiffies - ad->last_check_fifo[adir];
if (unlikely(delta_jif < 0))
delta_jif = -delta_jif;
if (delta_jif < ad->fifo_expire[adir])
return 0;
ad->last_check_fifo[adir] = jiffies;
if (list_empty(&ad->fifo_list[adir]))
return 0;
rq = rq_entry_fifo(ad->fifo_list[adir].next);
return time_after(jiffies, rq_fifo_time(rq));
}
/*
* as_batch_expired returns true if the current batch has expired. A batch
* is a set of reads or a set of writes.
*/
static inline int as_batch_expired(struct as_data *ad)
{
if (ad->changed_batch || ad->new_batch)
return 0;
if (ad->batch_data_dir == REQ_SYNC)
/* TODO! add a check so a complete fifo gets written? */
return time_after(jiffies, ad->current_batch_expires);
return time_after(jiffies, ad->current_batch_expires)
|| ad->current_write_count == 0;
}
/*
* move an entry to dispatch queue
*/
static void as_move_to_dispatch(struct as_data *ad, struct request *rq)
{
const int data_dir = rq_is_sync(rq);
BUG_ON(RB_EMPTY_NODE(&rq->rb_node));
as_antic_stop(ad);
ad->antic_status = ANTIC_OFF;
/*
* This has to be set in order to be correctly updated by
* as_find_next_rq
*/
ad->last_sector[data_dir] = rq->sector + rq->nr_sectors;
if (data_dir == REQ_SYNC) {
struct io_context *ioc = RQ_IOC(rq);
/* In case we have to anticipate after this */
copy_io_context(&ad->io_context, &ioc);
} else {
if (ad->io_context) {
put_io_context(ad->io_context);
ad->io_context = NULL;
}
if (ad->current_write_count != 0)
ad->current_write_count--;
}
ad->ioc_finished = 0;
ad->next_rq[data_dir] = as_find_next_rq(ad, rq);
/*
* take it off the sort and fifo list, add to dispatch queue