5f7f1773be611d1b86caaa670e52cca397364047
[sfrench/cifs-2.6.git] / block / blk-iolatency.c
1 /*
2  * Block rq-qos base io controller
3  *
4  * This works similar to wbt with a few exceptions
5  *
6  * - It's bio based, so the latency covers the whole block layer in addition to
7  *   the actual io.
8  * - We will throttle all IO that comes in here if we need to.
9  * - We use the mean latency over the 100ms window.  This is because writes can
10  *   be particularly fast, which could give us a false sense of the impact of
11  *   other workloads on our protected workload.
12  * - By default there's no throttling, we set the queue_depth to UINT_MAX so
13  *   that we can have as many outstanding bio's as we're allowed to.  Only at
14  *   throttle time do we pay attention to the actual queue depth.
15  *
16  * The hierarchy works like the cpu controller does, we track the latency at
17  * every configured node, and each configured node has it's own independent
18  * queue depth.  This means that we only care about our latency targets at the
19  * peer level.  Some group at the bottom of the hierarchy isn't going to affect
20  * a group at the end of some other path if we're only configred at leaf level.
21  *
22  * Consider the following
23  *
24  *                   root blkg
25  *             /                     \
26  *        fast (target=5ms)     slow (target=10ms)
27  *         /     \                  /        \
28  *       a        b          normal(15ms)   unloved
29  *
30  * "a" and "b" have no target, but their combined io under "fast" cannot exceed
31  * an average latency of 5ms.  If it does then we will throttle the "slow"
32  * group.  In the case of "normal", if it exceeds its 15ms target, we will
33  * throttle "unloved", but nobody else.
34  *
35  * In this example "fast", "slow", and "normal" will be the only groups actually
36  * accounting their io latencies.  We have to walk up the heirarchy to the root
37  * on every submit and complete so we can do the appropriate stat recording and
38  * adjust the queue depth of ourselves if needed.
39  *
40  * There are 2 ways we throttle IO.
41  *
42  * 1) Queue depth throttling.  As we throttle down we will adjust the maximum
43  * number of IO's we're allowed to have in flight.  This starts at (u64)-1 down
44  * to 1.  If the group is only ever submitting IO for itself then this is the
45  * only way we throttle.
46  *
47  * 2) Induced delay throttling.  This is for the case that a group is generating
48  * IO that has to be issued by the root cg to avoid priority inversion. So think
49  * REQ_META or REQ_SWAP.  If we are already at qd == 1 and we're getting a lot
50  * of work done for us on behalf of the root cg and are being asked to scale
51  * down more then we induce a latency at userspace return.  We accumulate the
52  * total amount of time we need to be punished by doing
53  *
54  * total_time += min_lat_nsec - actual_io_completion
55  *
56  * and then at throttle time will do
57  *
58  * throttle_time = min(total_time, NSEC_PER_SEC)
59  *
60  * This induced delay will throttle back the activity that is generating the
61  * root cg issued io's, wethere that's some metadata intensive operation or the
62  * group is using so much memory that it is pushing us into swap.
63  *
64  * Copyright (C) 2018 Josef Bacik
65  */
66 #include <linux/kernel.h>
67 #include <linux/blk_types.h>
68 #include <linux/backing-dev.h>
69 #include <linux/module.h>
70 #include <linux/timer.h>
71 #include <linux/memcontrol.h>
72 #include <linux/sched/loadavg.h>
73 #include <linux/sched/signal.h>
74 #include <trace/events/block.h>
75 #include "blk-rq-qos.h"
76 #include "blk-stat.h"
77
78 #define DEFAULT_SCALE_COOKIE 1000000U
79
80 static struct blkcg_policy blkcg_policy_iolatency;
81 struct iolatency_grp;
82
83 struct blk_iolatency {
84         struct rq_qos rqos;
85         struct timer_list timer;
86         atomic_t enabled;
87 };
88
89 static inline struct blk_iolatency *BLKIOLATENCY(struct rq_qos *rqos)
90 {
91         return container_of(rqos, struct blk_iolatency, rqos);
92 }
93
94 static inline bool blk_iolatency_enabled(struct blk_iolatency *blkiolat)
95 {
96         return atomic_read(&blkiolat->enabled) > 0;
97 }
98
99 struct child_latency_info {
100         spinlock_t lock;
101
102         /* Last time we adjusted the scale of everybody. */
103         u64 last_scale_event;
104
105         /* The latency that we missed. */
106         u64 scale_lat;
107
108         /* Total io's from all of our children for the last summation. */
109         u64 nr_samples;
110
111         /* The guy who actually changed the latency numbers. */
112         struct iolatency_grp *scale_grp;
113
114         /* Cookie to tell if we need to scale up or down. */
115         atomic_t scale_cookie;
116 };
117
118 struct percentile_stats {
119         u64 total;
120         u64 missed;
121 };
122
123 struct latency_stat {
124         union {
125                 struct percentile_stats ps;
126                 struct blk_rq_stat rqs;
127         };
128 };
129
130 struct iolatency_grp {
131         struct blkg_policy_data pd;
132         struct latency_stat __percpu *stats;
133         struct latency_stat cur_stat;
134         struct blk_iolatency *blkiolat;
135         struct rq_depth rq_depth;
136         struct rq_wait rq_wait;
137         atomic64_t window_start;
138         atomic_t scale_cookie;
139         u64 min_lat_nsec;
140         u64 cur_win_nsec;
141
142         /* total running average of our io latency. */
143         u64 lat_avg;
144
145         /* Our current number of IO's for the last summation. */
146         u64 nr_samples;
147
148         bool ssd;
149         struct child_latency_info child_lat;
150 };
151
152 #define BLKIOLATENCY_MIN_WIN_SIZE (100 * NSEC_PER_MSEC)
153 #define BLKIOLATENCY_MAX_WIN_SIZE NSEC_PER_SEC
154 /*
155  * These are the constants used to fake the fixed-point moving average
156  * calculation just like load average.  The call to calc_load() folds
157  * (FIXED_1 (2048) - exp_factor) * new_sample into lat_avg.  The sampling
158  * window size is bucketed to try to approximately calculate average
159  * latency such that 1/exp (decay rate) is [1 min, 2.5 min) when windows
160  * elapse immediately.  Note, windows only elapse with IO activity.  Idle
161  * periods extend the most recent window.
162  */
163 #define BLKIOLATENCY_NR_EXP_FACTORS 5
164 #define BLKIOLATENCY_EXP_BUCKET_SIZE (BLKIOLATENCY_MAX_WIN_SIZE / \
165                                       (BLKIOLATENCY_NR_EXP_FACTORS - 1))
166 static const u64 iolatency_exp_factors[BLKIOLATENCY_NR_EXP_FACTORS] = {
167         2045, // exp(1/600) - 600 samples
168         2039, // exp(1/240) - 240 samples
169         2031, // exp(1/120) - 120 samples
170         2023, // exp(1/80)  - 80 samples
171         2014, // exp(1/60)  - 60 samples
172 };
173
174 static inline struct iolatency_grp *pd_to_lat(struct blkg_policy_data *pd)
175 {
176         return pd ? container_of(pd, struct iolatency_grp, pd) : NULL;
177 }
178
179 static inline struct iolatency_grp *blkg_to_lat(struct blkcg_gq *blkg)
180 {
181         return pd_to_lat(blkg_to_pd(blkg, &blkcg_policy_iolatency));
182 }
183
184 static inline struct blkcg_gq *lat_to_blkg(struct iolatency_grp *iolat)
185 {
186         return pd_to_blkg(&iolat->pd);
187 }
188
189 static inline void latency_stat_init(struct iolatency_grp *iolat,
190                                      struct latency_stat *stat)
191 {
192         if (iolat->ssd) {
193                 stat->ps.total = 0;
194                 stat->ps.missed = 0;
195         } else
196                 blk_rq_stat_init(&stat->rqs);
197 }
198
199 static inline void latency_stat_sum(struct iolatency_grp *iolat,
200                                     struct latency_stat *sum,
201                                     struct latency_stat *stat)
202 {
203         if (iolat->ssd) {
204                 sum->ps.total += stat->ps.total;
205                 sum->ps.missed += stat->ps.missed;
206         } else
207                 blk_rq_stat_sum(&sum->rqs, &stat->rqs);
208 }
209
210 static inline void latency_stat_record_time(struct iolatency_grp *iolat,
211                                             u64 req_time)
212 {
213         struct latency_stat *stat = get_cpu_ptr(iolat->stats);
214         if (iolat->ssd) {
215                 if (req_time >= iolat->min_lat_nsec)
216                         stat->ps.missed++;
217                 stat->ps.total++;
218         } else
219                 blk_rq_stat_add(&stat->rqs, req_time);
220         put_cpu_ptr(stat);
221 }
222
223 static inline bool latency_sum_ok(struct iolatency_grp *iolat,
224                                   struct latency_stat *stat)
225 {
226         if (iolat->ssd) {
227                 u64 thresh = div64_u64(stat->ps.total, 10);
228                 thresh = max(thresh, 1ULL);
229                 return stat->ps.missed < thresh;
230         }
231         return stat->rqs.mean <= iolat->min_lat_nsec;
232 }
233
234 static inline u64 latency_stat_samples(struct iolatency_grp *iolat,
235                                        struct latency_stat *stat)
236 {
237         if (iolat->ssd)
238                 return stat->ps.total;
239         return stat->rqs.nr_samples;
240 }
241
242 static inline void iolat_update_total_lat_avg(struct iolatency_grp *iolat,
243                                               struct latency_stat *stat)
244 {
245         int exp_idx;
246
247         if (iolat->ssd)
248                 return;
249
250         /*
251          * calc_load() takes in a number stored in fixed point representation.
252          * Because we are using this for IO time in ns, the values stored
253          * are significantly larger than the FIXED_1 denominator (2048).
254          * Therefore, rounding errors in the calculation are negligible and
255          * can be ignored.
256          */
257         exp_idx = min_t(int, BLKIOLATENCY_NR_EXP_FACTORS - 1,
258                         div64_u64(iolat->cur_win_nsec,
259                                   BLKIOLATENCY_EXP_BUCKET_SIZE));
260         iolat->lat_avg = calc_load(iolat->lat_avg,
261                                    iolatency_exp_factors[exp_idx],
262                                    stat->rqs.mean);
263 }
264
265 static inline bool iolatency_may_queue(struct iolatency_grp *iolat,
266                                        wait_queue_entry_t *wait,
267                                        bool first_block)
268 {
269         struct rq_wait *rqw = &iolat->rq_wait;
270
271         if (first_block && waitqueue_active(&rqw->wait) &&
272             rqw->wait.head.next != &wait->entry)
273                 return false;
274         return rq_wait_inc_below(rqw, iolat->rq_depth.max_depth);
275 }
276
277 static void __blkcg_iolatency_throttle(struct rq_qos *rqos,
278                                        struct iolatency_grp *iolat,
279                                        bool issue_as_root,
280                                        bool use_memdelay)
281 {
282         struct rq_wait *rqw = &iolat->rq_wait;
283         unsigned use_delay = atomic_read(&lat_to_blkg(iolat)->use_delay);
284         DEFINE_WAIT(wait);
285         bool first_block = true;
286
287         if (use_delay)
288                 blkcg_schedule_throttle(rqos->q, use_memdelay);
289
290         /*
291          * To avoid priority inversions we want to just take a slot if we are
292          * issuing as root.  If we're being killed off there's no point in
293          * delaying things, we may have been killed by OOM so throttling may
294          * make recovery take even longer, so just let the IO's through so the
295          * task can go away.
296          */
297         if (issue_as_root || fatal_signal_pending(current)) {
298                 atomic_inc(&rqw->inflight);
299                 return;
300         }
301
302         if (iolatency_may_queue(iolat, &wait, first_block))
303                 return;
304
305         do {
306                 prepare_to_wait_exclusive(&rqw->wait, &wait,
307                                           TASK_UNINTERRUPTIBLE);
308
309                 if (iolatency_may_queue(iolat, &wait, first_block))
310                         break;
311                 first_block = false;
312                 io_schedule();
313         } while (1);
314
315         finish_wait(&rqw->wait, &wait);
316 }
317
318 #define SCALE_DOWN_FACTOR 2
319 #define SCALE_UP_FACTOR 4
320
321 static inline unsigned long scale_amount(unsigned long qd, bool up)
322 {
323         return max(up ? qd >> SCALE_UP_FACTOR : qd >> SCALE_DOWN_FACTOR, 1UL);
324 }
325
326 /*
327  * We scale the qd down faster than we scale up, so we need to use this helper
328  * to adjust the scale_cookie accordingly so we don't prematurely get
329  * scale_cookie at DEFAULT_SCALE_COOKIE and unthrottle too much.
330  *
331  * Each group has their own local copy of the last scale cookie they saw, so if
332  * the global scale cookie goes up or down they know which way they need to go
333  * based on their last knowledge of it.
334  */
335 static void scale_cookie_change(struct blk_iolatency *blkiolat,
336                                 struct child_latency_info *lat_info,
337                                 bool up)
338 {
339         unsigned long qd = blkiolat->rqos.q->nr_requests;
340         unsigned long scale = scale_amount(qd, up);
341         unsigned long old = atomic_read(&lat_info->scale_cookie);
342         unsigned long max_scale = qd << 1;
343         unsigned long diff = 0;
344
345         if (old < DEFAULT_SCALE_COOKIE)
346                 diff = DEFAULT_SCALE_COOKIE - old;
347
348         if (up) {
349                 if (scale + old > DEFAULT_SCALE_COOKIE)
350                         atomic_set(&lat_info->scale_cookie,
351                                    DEFAULT_SCALE_COOKIE);
352                 else if (diff > qd)
353                         atomic_inc(&lat_info->scale_cookie);
354                 else
355                         atomic_add(scale, &lat_info->scale_cookie);
356         } else {
357                 /*
358                  * We don't want to dig a hole so deep that it takes us hours to
359                  * dig out of it.  Just enough that we don't throttle/unthrottle
360                  * with jagged workloads but can still unthrottle once pressure
361                  * has sufficiently dissipated.
362                  */
363                 if (diff > qd) {
364                         if (diff < max_scale)
365                                 atomic_dec(&lat_info->scale_cookie);
366                 } else {
367                         atomic_sub(scale, &lat_info->scale_cookie);
368                 }
369         }
370 }
371
372 /*
373  * Change the queue depth of the iolatency_grp.  We add/subtract 1/16th of the
374  * queue depth at a time so we don't get wild swings and hopefully dial in to
375  * fairer distribution of the overall queue depth.
376  */
377 static void scale_change(struct iolatency_grp *iolat, bool up)
378 {
379         unsigned long qd = iolat->blkiolat->rqos.q->nr_requests;
380         unsigned long scale = scale_amount(qd, up);
381         unsigned long old = iolat->rq_depth.max_depth;
382
383         if (old > qd)
384                 old = qd;
385
386         if (up) {
387                 if (old == 1 && blkcg_unuse_delay(lat_to_blkg(iolat)))
388                         return;
389
390                 if (old < qd) {
391                         old += scale;
392                         old = min(old, qd);
393                         iolat->rq_depth.max_depth = old;
394                         wake_up_all(&iolat->rq_wait.wait);
395                 }
396         } else {
397                 old >>= 1;
398                 iolat->rq_depth.max_depth = max(old, 1UL);
399         }
400 }
401
402 /* Check our parent and see if the scale cookie has changed. */
403 static void check_scale_change(struct iolatency_grp *iolat)
404 {
405         struct iolatency_grp *parent;
406         struct child_latency_info *lat_info;
407         unsigned int cur_cookie;
408         unsigned int our_cookie = atomic_read(&iolat->scale_cookie);
409         u64 scale_lat;
410         unsigned int old;
411         int direction = 0;
412
413         if (lat_to_blkg(iolat)->parent == NULL)
414                 return;
415
416         parent = blkg_to_lat(lat_to_blkg(iolat)->parent);
417         if (!parent)
418                 return;
419
420         lat_info = &parent->child_lat;
421         cur_cookie = atomic_read(&lat_info->scale_cookie);
422         scale_lat = READ_ONCE(lat_info->scale_lat);
423
424         if (cur_cookie < our_cookie)
425                 direction = -1;
426         else if (cur_cookie > our_cookie)
427                 direction = 1;
428         else
429                 return;
430
431         old = atomic_cmpxchg(&iolat->scale_cookie, our_cookie, cur_cookie);
432
433         /* Somebody beat us to the punch, just bail. */
434         if (old != our_cookie)
435                 return;
436
437         if (direction < 0 && iolat->min_lat_nsec) {
438                 u64 samples_thresh;
439
440                 if (!scale_lat || iolat->min_lat_nsec <= scale_lat)
441                         return;
442
443                 /*
444                  * Sometimes high priority groups are their own worst enemy, so
445                  * instead of taking it out on some poor other group that did 5%
446                  * or less of the IO's for the last summation just skip this
447                  * scale down event.
448                  */
449                 samples_thresh = lat_info->nr_samples * 5;
450                 samples_thresh = max(1ULL, div64_u64(samples_thresh, 100));
451                 if (iolat->nr_samples <= samples_thresh)
452                         return;
453         }
454
455         /* We're as low as we can go. */
456         if (iolat->rq_depth.max_depth == 1 && direction < 0) {
457                 blkcg_use_delay(lat_to_blkg(iolat));
458                 return;
459         }
460
461         /* We're back to the default cookie, unthrottle all the things. */
462         if (cur_cookie == DEFAULT_SCALE_COOKIE) {
463                 blkcg_clear_delay(lat_to_blkg(iolat));
464                 iolat->rq_depth.max_depth = UINT_MAX;
465                 wake_up_all(&iolat->rq_wait.wait);
466                 return;
467         }
468
469         scale_change(iolat, direction > 0);
470 }
471
472 static void blkcg_iolatency_throttle(struct rq_qos *rqos, struct bio *bio)
473 {
474         struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
475         struct blkcg *blkcg;
476         struct blkcg_gq *blkg;
477         struct request_queue *q = rqos->q;
478         bool issue_as_root = bio_issue_as_root_blkg(bio);
479
480         if (!blk_iolatency_enabled(blkiolat))
481                 return;
482
483         rcu_read_lock();
484         blkcg = bio_blkcg(bio);
485         bio_associate_blkcg(bio, &blkcg->css);
486         blkg = blkg_lookup(blkcg, q);
487         if (unlikely(!blkg)) {
488                 spin_lock_irq(&q->queue_lock);
489                 blkg = blkg_lookup_create(blkcg, q);
490                 if (IS_ERR(blkg))
491                         blkg = NULL;
492                 spin_unlock_irq(&q->queue_lock);
493         }
494         if (!blkg)
495                 goto out;
496
497         bio_issue_init(&bio->bi_issue, bio_sectors(bio));
498         bio_associate_blkg(bio, blkg);
499 out:
500         rcu_read_unlock();
501         while (blkg && blkg->parent) {
502                 struct iolatency_grp *iolat = blkg_to_lat(blkg);
503                 if (!iolat) {
504                         blkg = blkg->parent;
505                         continue;
506                 }
507
508                 check_scale_change(iolat);
509                 __blkcg_iolatency_throttle(rqos, iolat, issue_as_root,
510                                      (bio->bi_opf & REQ_SWAP) == REQ_SWAP);
511                 blkg = blkg->parent;
512         }
513         if (!timer_pending(&blkiolat->timer))
514                 mod_timer(&blkiolat->timer, jiffies + HZ);
515 }
516
517 static void iolatency_record_time(struct iolatency_grp *iolat,
518                                   struct bio_issue *issue, u64 now,
519                                   bool issue_as_root)
520 {
521         u64 start = bio_issue_time(issue);
522         u64 req_time;
523
524         /*
525          * Have to do this so we are truncated to the correct time that our
526          * issue is truncated to.
527          */
528         now = __bio_issue_time(now);
529
530         if (now <= start)
531                 return;
532
533         req_time = now - start;
534
535         /*
536          * We don't want to count issue_as_root bio's in the cgroups latency
537          * statistics as it could skew the numbers downwards.
538          */
539         if (unlikely(issue_as_root && iolat->rq_depth.max_depth != UINT_MAX)) {
540                 u64 sub = iolat->min_lat_nsec;
541                 if (req_time < sub)
542                         blkcg_add_delay(lat_to_blkg(iolat), now, sub - req_time);
543                 return;
544         }
545
546         latency_stat_record_time(iolat, req_time);
547 }
548
549 #define BLKIOLATENCY_MIN_ADJUST_TIME (500 * NSEC_PER_MSEC)
550 #define BLKIOLATENCY_MIN_GOOD_SAMPLES 5
551
552 static void iolatency_check_latencies(struct iolatency_grp *iolat, u64 now)
553 {
554         struct blkcg_gq *blkg = lat_to_blkg(iolat);
555         struct iolatency_grp *parent;
556         struct child_latency_info *lat_info;
557         struct latency_stat stat;
558         unsigned long flags;
559         int cpu;
560
561         latency_stat_init(iolat, &stat);
562         preempt_disable();
563         for_each_online_cpu(cpu) {
564                 struct latency_stat *s;
565                 s = per_cpu_ptr(iolat->stats, cpu);
566                 latency_stat_sum(iolat, &stat, s);
567                 latency_stat_init(iolat, s);
568         }
569         preempt_enable();
570
571         parent = blkg_to_lat(blkg->parent);
572         if (!parent)
573                 return;
574
575         lat_info = &parent->child_lat;
576
577         iolat_update_total_lat_avg(iolat, &stat);
578
579         /* Everything is ok and we don't need to adjust the scale. */
580         if (latency_sum_ok(iolat, &stat) &&
581             atomic_read(&lat_info->scale_cookie) == DEFAULT_SCALE_COOKIE)
582                 return;
583
584         /* Somebody beat us to the punch, just bail. */
585         spin_lock_irqsave(&lat_info->lock, flags);
586
587         latency_stat_sum(iolat, &iolat->cur_stat, &stat);
588         lat_info->nr_samples -= iolat->nr_samples;
589         lat_info->nr_samples += latency_stat_samples(iolat, &iolat->cur_stat);
590         iolat->nr_samples = latency_stat_samples(iolat, &iolat->cur_stat);
591
592         if ((lat_info->last_scale_event >= now ||
593             now - lat_info->last_scale_event < BLKIOLATENCY_MIN_ADJUST_TIME))
594                 goto out;
595
596         if (latency_sum_ok(iolat, &iolat->cur_stat) &&
597             latency_sum_ok(iolat, &stat)) {
598                 if (latency_stat_samples(iolat, &iolat->cur_stat) <
599                     BLKIOLATENCY_MIN_GOOD_SAMPLES)
600                         goto out;
601                 if (lat_info->scale_grp == iolat) {
602                         lat_info->last_scale_event = now;
603                         scale_cookie_change(iolat->blkiolat, lat_info, true);
604                 }
605         } else if (lat_info->scale_lat == 0 ||
606                    lat_info->scale_lat >= iolat->min_lat_nsec) {
607                 lat_info->last_scale_event = now;
608                 if (!lat_info->scale_grp ||
609                     lat_info->scale_lat > iolat->min_lat_nsec) {
610                         WRITE_ONCE(lat_info->scale_lat, iolat->min_lat_nsec);
611                         lat_info->scale_grp = iolat;
612                 }
613                 scale_cookie_change(iolat->blkiolat, lat_info, false);
614         }
615         latency_stat_init(iolat, &iolat->cur_stat);
616 out:
617         spin_unlock_irqrestore(&lat_info->lock, flags);
618 }
619
620 static void blkcg_iolatency_done_bio(struct rq_qos *rqos, struct bio *bio)
621 {
622         struct blkcg_gq *blkg;
623         struct rq_wait *rqw;
624         struct iolatency_grp *iolat;
625         u64 window_start;
626         u64 now = ktime_to_ns(ktime_get());
627         bool issue_as_root = bio_issue_as_root_blkg(bio);
628         bool enabled = false;
629
630         blkg = bio->bi_blkg;
631         if (!blkg)
632                 return;
633
634         iolat = blkg_to_lat(bio->bi_blkg);
635         if (!iolat)
636                 return;
637
638         enabled = blk_iolatency_enabled(iolat->blkiolat);
639         while (blkg && blkg->parent) {
640                 iolat = blkg_to_lat(blkg);
641                 if (!iolat) {
642                         blkg = blkg->parent;
643                         continue;
644                 }
645                 rqw = &iolat->rq_wait;
646
647                 atomic_dec(&rqw->inflight);
648                 if (!enabled || iolat->min_lat_nsec == 0)
649                         goto next;
650                 iolatency_record_time(iolat, &bio->bi_issue, now,
651                                       issue_as_root);
652                 window_start = atomic64_read(&iolat->window_start);
653                 if (now > window_start &&
654                     (now - window_start) >= iolat->cur_win_nsec) {
655                         if (atomic64_cmpxchg(&iolat->window_start,
656                                         window_start, now) == window_start)
657                                 iolatency_check_latencies(iolat, now);
658                 }
659 next:
660                 wake_up(&rqw->wait);
661                 blkg = blkg->parent;
662         }
663 }
664
665 static void blkcg_iolatency_cleanup(struct rq_qos *rqos, struct bio *bio)
666 {
667         struct blkcg_gq *blkg;
668
669         blkg = bio->bi_blkg;
670         while (blkg && blkg->parent) {
671                 struct rq_wait *rqw;
672                 struct iolatency_grp *iolat;
673
674                 iolat = blkg_to_lat(blkg);
675                 if (!iolat)
676                         goto next;
677
678                 rqw = &iolat->rq_wait;
679                 atomic_dec(&rqw->inflight);
680                 wake_up(&rqw->wait);
681 next:
682                 blkg = blkg->parent;
683         }
684 }
685
686 static void blkcg_iolatency_exit(struct rq_qos *rqos)
687 {
688         struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
689
690         del_timer_sync(&blkiolat->timer);
691         blkcg_deactivate_policy(rqos->q, &blkcg_policy_iolatency);
692         kfree(blkiolat);
693 }
694
695 static struct rq_qos_ops blkcg_iolatency_ops = {
696         .throttle = blkcg_iolatency_throttle,
697         .cleanup = blkcg_iolatency_cleanup,
698         .done_bio = blkcg_iolatency_done_bio,
699         .exit = blkcg_iolatency_exit,
700 };
701
702 static void blkiolatency_timer_fn(struct timer_list *t)
703 {
704         struct blk_iolatency *blkiolat = from_timer(blkiolat, t, timer);
705         struct blkcg_gq *blkg;
706         struct cgroup_subsys_state *pos_css;
707         u64 now = ktime_to_ns(ktime_get());
708
709         rcu_read_lock();
710         blkg_for_each_descendant_pre(blkg, pos_css,
711                                      blkiolat->rqos.q->root_blkg) {
712                 struct iolatency_grp *iolat;
713                 struct child_latency_info *lat_info;
714                 unsigned long flags;
715                 u64 cookie;
716
717                 /*
718                  * We could be exiting, don't access the pd unless we have a
719                  * ref on the blkg.
720                  */
721                 if (!blkg_try_get(blkg))
722                         continue;
723
724                 iolat = blkg_to_lat(blkg);
725                 if (!iolat)
726                         goto next;
727
728                 lat_info = &iolat->child_lat;
729                 cookie = atomic_read(&lat_info->scale_cookie);
730
731                 if (cookie >= DEFAULT_SCALE_COOKIE)
732                         goto next;
733
734                 spin_lock_irqsave(&lat_info->lock, flags);
735                 if (lat_info->last_scale_event >= now)
736                         goto next_lock;
737
738                 /*
739                  * We scaled down but don't have a scale_grp, scale up and carry
740                  * on.
741                  */
742                 if (lat_info->scale_grp == NULL) {
743                         scale_cookie_change(iolat->blkiolat, lat_info, true);
744                         goto next_lock;
745                 }
746
747                 /*
748                  * It's been 5 seconds since our last scale event, clear the
749                  * scale grp in case the group that needed the scale down isn't
750                  * doing any IO currently.
751                  */
752                 if (now - lat_info->last_scale_event >=
753                     ((u64)NSEC_PER_SEC * 5))
754                         lat_info->scale_grp = NULL;
755 next_lock:
756                 spin_unlock_irqrestore(&lat_info->lock, flags);
757 next:
758                 blkg_put(blkg);
759         }
760         rcu_read_unlock();
761 }
762
763 int blk_iolatency_init(struct request_queue *q)
764 {
765         struct blk_iolatency *blkiolat;
766         struct rq_qos *rqos;
767         int ret;
768
769         blkiolat = kzalloc(sizeof(*blkiolat), GFP_KERNEL);
770         if (!blkiolat)
771                 return -ENOMEM;
772
773         rqos = &blkiolat->rqos;
774         rqos->id = RQ_QOS_CGROUP;
775         rqos->ops = &blkcg_iolatency_ops;
776         rqos->q = q;
777
778         rq_qos_add(q, rqos);
779
780         ret = blkcg_activate_policy(q, &blkcg_policy_iolatency);
781         if (ret) {
782                 rq_qos_del(q, rqos);
783                 kfree(blkiolat);
784                 return ret;
785         }
786
787         timer_setup(&blkiolat->timer, blkiolatency_timer_fn, 0);
788
789         return 0;
790 }
791
792 static void iolatency_set_min_lat_nsec(struct blkcg_gq *blkg, u64 val)
793 {
794         struct iolatency_grp *iolat = blkg_to_lat(blkg);
795         struct blk_iolatency *blkiolat = iolat->blkiolat;
796         u64 oldval = iolat->min_lat_nsec;
797
798         iolat->min_lat_nsec = val;
799         iolat->cur_win_nsec = max_t(u64, val << 4, BLKIOLATENCY_MIN_WIN_SIZE);
800         iolat->cur_win_nsec = min_t(u64, iolat->cur_win_nsec,
801                                     BLKIOLATENCY_MAX_WIN_SIZE);
802
803         if (!oldval && val)
804                 atomic_inc(&blkiolat->enabled);
805         if (oldval && !val)
806                 atomic_dec(&blkiolat->enabled);
807 }
808
809 static void iolatency_clear_scaling(struct blkcg_gq *blkg)
810 {
811         if (blkg->parent) {
812                 struct iolatency_grp *iolat = blkg_to_lat(blkg->parent);
813                 struct child_latency_info *lat_info;
814                 if (!iolat)
815                         return;
816
817                 lat_info = &iolat->child_lat;
818                 spin_lock(&lat_info->lock);
819                 atomic_set(&lat_info->scale_cookie, DEFAULT_SCALE_COOKIE);
820                 lat_info->last_scale_event = 0;
821                 lat_info->scale_grp = NULL;
822                 lat_info->scale_lat = 0;
823                 spin_unlock(&lat_info->lock);
824         }
825 }
826
827 static ssize_t iolatency_set_limit(struct kernfs_open_file *of, char *buf,
828                              size_t nbytes, loff_t off)
829 {
830         struct blkcg *blkcg = css_to_blkcg(of_css(of));
831         struct blkcg_gq *blkg;
832         struct blkg_conf_ctx ctx;
833         struct iolatency_grp *iolat;
834         char *p, *tok;
835         u64 lat_val = 0;
836         u64 oldval;
837         int ret;
838
839         ret = blkg_conf_prep(blkcg, &blkcg_policy_iolatency, buf, &ctx);
840         if (ret)
841                 return ret;
842
843         iolat = blkg_to_lat(ctx.blkg);
844         p = ctx.body;
845
846         ret = -EINVAL;
847         while ((tok = strsep(&p, " "))) {
848                 char key[16];
849                 char val[21];   /* 18446744073709551616 */
850
851                 if (sscanf(tok, "%15[^=]=%20s", key, val) != 2)
852                         goto out;
853
854                 if (!strcmp(key, "target")) {
855                         u64 v;
856
857                         if (!strcmp(val, "max"))
858                                 lat_val = 0;
859                         else if (sscanf(val, "%llu", &v) == 1)
860                                 lat_val = v * NSEC_PER_USEC;
861                         else
862                                 goto out;
863                 } else {
864                         goto out;
865                 }
866         }
867
868         /* Walk up the tree to see if our new val is lower than it should be. */
869         blkg = ctx.blkg;
870         oldval = iolat->min_lat_nsec;
871
872         iolatency_set_min_lat_nsec(blkg, lat_val);
873         if (oldval != iolat->min_lat_nsec) {
874                 iolatency_clear_scaling(blkg);
875         }
876
877         ret = 0;
878 out:
879         blkg_conf_finish(&ctx);
880         return ret ?: nbytes;
881 }
882
883 static u64 iolatency_prfill_limit(struct seq_file *sf,
884                                   struct blkg_policy_data *pd, int off)
885 {
886         struct iolatency_grp *iolat = pd_to_lat(pd);
887         const char *dname = blkg_dev_name(pd->blkg);
888
889         if (!dname || !iolat->min_lat_nsec)
890                 return 0;
891         seq_printf(sf, "%s target=%llu\n",
892                    dname, div_u64(iolat->min_lat_nsec, NSEC_PER_USEC));
893         return 0;
894 }
895
896 static int iolatency_print_limit(struct seq_file *sf, void *v)
897 {
898         blkcg_print_blkgs(sf, css_to_blkcg(seq_css(sf)),
899                           iolatency_prfill_limit,
900                           &blkcg_policy_iolatency, seq_cft(sf)->private, false);
901         return 0;
902 }
903
904 static size_t iolatency_ssd_stat(struct iolatency_grp *iolat, char *buf,
905                                  size_t size)
906 {
907         struct latency_stat stat;
908         int cpu;
909
910         latency_stat_init(iolat, &stat);
911         preempt_disable();
912         for_each_online_cpu(cpu) {
913                 struct latency_stat *s;
914                 s = per_cpu_ptr(iolat->stats, cpu);
915                 latency_stat_sum(iolat, &stat, s);
916         }
917         preempt_enable();
918
919         if (iolat->rq_depth.max_depth == UINT_MAX)
920                 return scnprintf(buf, size, " missed=%llu total=%llu depth=max",
921                                  (unsigned long long)stat.ps.missed,
922                                  (unsigned long long)stat.ps.total);
923         return scnprintf(buf, size, " missed=%llu total=%llu depth=%u",
924                          (unsigned long long)stat.ps.missed,
925                          (unsigned long long)stat.ps.total,
926                          iolat->rq_depth.max_depth);
927 }
928
929 static size_t iolatency_pd_stat(struct blkg_policy_data *pd, char *buf,
930                                 size_t size)
931 {
932         struct iolatency_grp *iolat = pd_to_lat(pd);
933         unsigned long long avg_lat;
934         unsigned long long cur_win;
935
936         if (iolat->ssd)
937                 return iolatency_ssd_stat(iolat, buf, size);
938
939         avg_lat = div64_u64(iolat->lat_avg, NSEC_PER_USEC);
940         cur_win = div64_u64(iolat->cur_win_nsec, NSEC_PER_MSEC);
941         if (iolat->rq_depth.max_depth == UINT_MAX)
942                 return scnprintf(buf, size, " depth=max avg_lat=%llu win=%llu",
943                                  avg_lat, cur_win);
944
945         return scnprintf(buf, size, " depth=%u avg_lat=%llu win=%llu",
946                          iolat->rq_depth.max_depth, avg_lat, cur_win);
947 }
948
949
950 static struct blkg_policy_data *iolatency_pd_alloc(gfp_t gfp, int node)
951 {
952         struct iolatency_grp *iolat;
953
954         iolat = kzalloc_node(sizeof(*iolat), gfp, node);
955         if (!iolat)
956                 return NULL;
957         iolat->stats = __alloc_percpu_gfp(sizeof(struct latency_stat),
958                                        __alignof__(struct latency_stat), gfp);
959         if (!iolat->stats) {
960                 kfree(iolat);
961                 return NULL;
962         }
963         return &iolat->pd;
964 }
965
966 static void iolatency_pd_init(struct blkg_policy_data *pd)
967 {
968         struct iolatency_grp *iolat = pd_to_lat(pd);
969         struct blkcg_gq *blkg = lat_to_blkg(iolat);
970         struct rq_qos *rqos = blkcg_rq_qos(blkg->q);
971         struct blk_iolatency *blkiolat = BLKIOLATENCY(rqos);
972         u64 now = ktime_to_ns(ktime_get());
973         int cpu;
974
975         if (blk_queue_nonrot(blkg->q))
976                 iolat->ssd = true;
977         else
978                 iolat->ssd = false;
979
980         for_each_possible_cpu(cpu) {
981                 struct latency_stat *stat;
982                 stat = per_cpu_ptr(iolat->stats, cpu);
983                 latency_stat_init(iolat, stat);
984         }
985
986         latency_stat_init(iolat, &iolat->cur_stat);
987         rq_wait_init(&iolat->rq_wait);
988         spin_lock_init(&iolat->child_lat.lock);
989         iolat->rq_depth.queue_depth = blkg->q->nr_requests;
990         iolat->rq_depth.max_depth = UINT_MAX;
991         iolat->rq_depth.default_depth = iolat->rq_depth.queue_depth;
992         iolat->blkiolat = blkiolat;
993         iolat->cur_win_nsec = 100 * NSEC_PER_MSEC;
994         atomic64_set(&iolat->window_start, now);
995
996         /*
997          * We init things in list order, so the pd for the parent may not be
998          * init'ed yet for whatever reason.
999          */
1000         if (blkg->parent && blkg_to_pd(blkg->parent, &blkcg_policy_iolatency)) {
1001                 struct iolatency_grp *parent = blkg_to_lat(blkg->parent);
1002                 atomic_set(&iolat->scale_cookie,
1003                            atomic_read(&parent->child_lat.scale_cookie));
1004         } else {
1005                 atomic_set(&iolat->scale_cookie, DEFAULT_SCALE_COOKIE);
1006         }
1007
1008         atomic_set(&iolat->child_lat.scale_cookie, DEFAULT_SCALE_COOKIE);
1009 }
1010
1011 static void iolatency_pd_offline(struct blkg_policy_data *pd)
1012 {
1013         struct iolatency_grp *iolat = pd_to_lat(pd);
1014         struct blkcg_gq *blkg = lat_to_blkg(iolat);
1015
1016         iolatency_set_min_lat_nsec(blkg, 0);
1017         iolatency_clear_scaling(blkg);
1018 }
1019
1020 static void iolatency_pd_free(struct blkg_policy_data *pd)
1021 {
1022         struct iolatency_grp *iolat = pd_to_lat(pd);
1023         free_percpu(iolat->stats);
1024         kfree(iolat);
1025 }
1026
1027 static struct cftype iolatency_files[] = {
1028         {
1029                 .name = "latency",
1030                 .flags = CFTYPE_NOT_ON_ROOT,
1031                 .seq_show = iolatency_print_limit,
1032                 .write = iolatency_set_limit,
1033         },
1034         {}
1035 };
1036
1037 static struct blkcg_policy blkcg_policy_iolatency = {
1038         .dfl_cftypes    = iolatency_files,
1039         .pd_alloc_fn    = iolatency_pd_alloc,
1040         .pd_init_fn     = iolatency_pd_init,
1041         .pd_offline_fn  = iolatency_pd_offline,
1042         .pd_free_fn     = iolatency_pd_free,
1043         .pd_stat_fn     = iolatency_pd_stat,
1044 };
1045
1046 static int __init iolatency_init(void)
1047 {
1048         return blkcg_policy_register(&blkcg_policy_iolatency);
1049 }
1050
1051 static void __exit iolatency_exit(void)
1052 {
1053         return blkcg_policy_unregister(&blkcg_policy_iolatency);
1054 }
1055
1056 module_init(iolatency_init);
1057 module_exit(iolatency_exit);