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e34cbd30 JA |
1 | /* |
2 | * buffered writeback throttling. loosely based on CoDel. We can't drop | |
3 | * packets for IO scheduling, so the logic is something like this: | |
4 | * | |
5 | * - Monitor latencies in a defined window of time. | |
6 | * - If the minimum latency in the above window exceeds some target, increment | |
7 | * scaling step and scale down queue depth by a factor of 2x. The monitoring | |
8 | * window is then shrunk to 100 / sqrt(scaling step + 1). | |
9 | * - For any window where we don't have solid data on what the latencies | |
10 | * look like, retain status quo. | |
11 | * - If latencies look good, decrement scaling step. | |
12 | * - If we're only doing writes, allow the scaling step to go negative. This | |
13 | * will temporarily boost write performance, snapping back to a stable | |
14 | * scaling step of 0 if reads show up or the heavy writers finish. Unlike | |
15 | * positive scaling steps where we shrink the monitoring window, a negative | |
16 | * scaling step retains the default step==0 window size. | |
17 | * | |
18 | * Copyright (C) 2016 Jens Axboe | |
19 | * | |
20 | */ | |
21 | #include <linux/kernel.h> | |
22 | #include <linux/blk_types.h> | |
23 | #include <linux/slab.h> | |
24 | #include <linux/backing-dev.h> | |
25 | #include <linux/swap.h> | |
26 | ||
27 | #include "blk-wbt.h" | |
28 | ||
29 | #define CREATE_TRACE_POINTS | |
30 | #include <trace/events/wbt.h> | |
31 | ||
32 | enum { | |
33 | /* | |
34 | * Default setting, we'll scale up (to 75% of QD max) or down (min 1) | |
35 | * from here depending on device stats | |
36 | */ | |
37 | RWB_DEF_DEPTH = 16, | |
38 | ||
39 | /* | |
40 | * 100msec window | |
41 | */ | |
42 | RWB_WINDOW_NSEC = 100 * 1000 * 1000ULL, | |
43 | ||
44 | /* | |
45 | * Disregard stats, if we don't meet this minimum | |
46 | */ | |
47 | RWB_MIN_WRITE_SAMPLES = 3, | |
48 | ||
49 | /* | |
50 | * If we have this number of consecutive windows with not enough | |
51 | * information to scale up or down, scale up. | |
52 | */ | |
53 | RWB_UNKNOWN_BUMP = 5, | |
54 | }; | |
55 | ||
56 | static inline bool rwb_enabled(struct rq_wb *rwb) | |
57 | { | |
58 | return rwb && rwb->wb_normal != 0; | |
59 | } | |
60 | ||
61 | /* | |
62 | * Increment 'v', if 'v' is below 'below'. Returns true if we succeeded, | |
63 | * false if 'v' + 1 would be bigger than 'below'. | |
64 | */ | |
65 | static bool atomic_inc_below(atomic_t *v, int below) | |
66 | { | |
67 | int cur = atomic_read(v); | |
68 | ||
69 | for (;;) { | |
70 | int old; | |
71 | ||
72 | if (cur >= below) | |
73 | return false; | |
74 | old = atomic_cmpxchg(v, cur, cur + 1); | |
75 | if (old == cur) | |
76 | break; | |
77 | cur = old; | |
78 | } | |
79 | ||
80 | return true; | |
81 | } | |
82 | ||
83 | static void wb_timestamp(struct rq_wb *rwb, unsigned long *var) | |
84 | { | |
85 | if (rwb_enabled(rwb)) { | |
86 | const unsigned long cur = jiffies; | |
87 | ||
88 | if (cur != *var) | |
89 | *var = cur; | |
90 | } | |
91 | } | |
92 | ||
93 | /* | |
94 | * If a task was rate throttled in balance_dirty_pages() within the last | |
95 | * second or so, use that to indicate a higher cleaning rate. | |
96 | */ | |
97 | static bool wb_recent_wait(struct rq_wb *rwb) | |
98 | { | |
dc3b17cc | 99 | struct bdi_writeback *wb = &rwb->queue->backing_dev_info->wb; |
e34cbd30 JA |
100 | |
101 | return time_before(jiffies, wb->dirty_sleep + HZ); | |
102 | } | |
103 | ||
104 | static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb, bool is_kswapd) | |
105 | { | |
106 | return &rwb->rq_wait[is_kswapd]; | |
107 | } | |
108 | ||
109 | static void rwb_wake_all(struct rq_wb *rwb) | |
110 | { | |
111 | int i; | |
112 | ||
113 | for (i = 0; i < WBT_NUM_RWQ; i++) { | |
114 | struct rq_wait *rqw = &rwb->rq_wait[i]; | |
115 | ||
116 | if (waitqueue_active(&rqw->wait)) | |
117 | wake_up_all(&rqw->wait); | |
118 | } | |
119 | } | |
120 | ||
121 | void __wbt_done(struct rq_wb *rwb, enum wbt_flags wb_acct) | |
122 | { | |
123 | struct rq_wait *rqw; | |
124 | int inflight, limit; | |
125 | ||
126 | if (!(wb_acct & WBT_TRACKED)) | |
127 | return; | |
128 | ||
129 | rqw = get_rq_wait(rwb, wb_acct & WBT_KSWAPD); | |
130 | inflight = atomic_dec_return(&rqw->inflight); | |
131 | ||
132 | /* | |
133 | * wbt got disabled with IO in flight. Wake up any potential | |
134 | * waiters, we don't have to do more than that. | |
135 | */ | |
136 | if (unlikely(!rwb_enabled(rwb))) { | |
137 | rwb_wake_all(rwb); | |
138 | return; | |
139 | } | |
140 | ||
141 | /* | |
142 | * If the device does write back caching, drop further down | |
143 | * before we wake people up. | |
144 | */ | |
145 | if (rwb->wc && !wb_recent_wait(rwb)) | |
146 | limit = 0; | |
147 | else | |
148 | limit = rwb->wb_normal; | |
149 | ||
150 | /* | |
151 | * Don't wake anyone up if we are above the normal limit. | |
152 | */ | |
153 | if (inflight && inflight >= limit) | |
154 | return; | |
155 | ||
156 | if (waitqueue_active(&rqw->wait)) { | |
157 | int diff = limit - inflight; | |
158 | ||
159 | if (!inflight || diff >= rwb->wb_background / 2) | |
160 | wake_up_all(&rqw->wait); | |
161 | } | |
162 | } | |
163 | ||
164 | /* | |
165 | * Called on completion of a request. Note that it's also called when | |
166 | * a request is merged, when the request gets freed. | |
167 | */ | |
168 | void wbt_done(struct rq_wb *rwb, struct blk_issue_stat *stat) | |
169 | { | |
170 | if (!rwb) | |
171 | return; | |
172 | ||
173 | if (!wbt_is_tracked(stat)) { | |
174 | if (rwb->sync_cookie == stat) { | |
175 | rwb->sync_issue = 0; | |
176 | rwb->sync_cookie = NULL; | |
177 | } | |
178 | ||
179 | if (wbt_is_read(stat)) | |
180 | wb_timestamp(rwb, &rwb->last_comp); | |
181 | wbt_clear_state(stat); | |
182 | } else { | |
183 | WARN_ON_ONCE(stat == rwb->sync_cookie); | |
184 | __wbt_done(rwb, wbt_stat_to_mask(stat)); | |
185 | wbt_clear_state(stat); | |
186 | } | |
187 | } | |
188 | ||
189 | /* | |
190 | * Return true, if we can't increase the depth further by scaling | |
191 | */ | |
192 | static bool calc_wb_limits(struct rq_wb *rwb) | |
193 | { | |
194 | unsigned int depth; | |
195 | bool ret = false; | |
196 | ||
197 | if (!rwb->min_lat_nsec) { | |
198 | rwb->wb_max = rwb->wb_normal = rwb->wb_background = 0; | |
199 | return false; | |
200 | } | |
201 | ||
202 | /* | |
203 | * For QD=1 devices, this is a special case. It's important for those | |
204 | * to have one request ready when one completes, so force a depth of | |
205 | * 2 for those devices. On the backend, it'll be a depth of 1 anyway, | |
206 | * since the device can't have more than that in flight. If we're | |
207 | * scaling down, then keep a setting of 1/1/1. | |
208 | */ | |
209 | if (rwb->queue_depth == 1) { | |
210 | if (rwb->scale_step > 0) | |
211 | rwb->wb_max = rwb->wb_normal = 1; | |
212 | else { | |
213 | rwb->wb_max = rwb->wb_normal = 2; | |
214 | ret = true; | |
215 | } | |
216 | rwb->wb_background = 1; | |
217 | } else { | |
218 | /* | |
219 | * scale_step == 0 is our default state. If we have suffered | |
220 | * latency spikes, step will be > 0, and we shrink the | |
221 | * allowed write depths. If step is < 0, we're only doing | |
222 | * writes, and we allow a temporarily higher depth to | |
223 | * increase performance. | |
224 | */ | |
225 | depth = min_t(unsigned int, RWB_DEF_DEPTH, rwb->queue_depth); | |
226 | if (rwb->scale_step > 0) | |
227 | depth = 1 + ((depth - 1) >> min(31, rwb->scale_step)); | |
228 | else if (rwb->scale_step < 0) { | |
229 | unsigned int maxd = 3 * rwb->queue_depth / 4; | |
230 | ||
231 | depth = 1 + ((depth - 1) << -rwb->scale_step); | |
232 | if (depth > maxd) { | |
233 | depth = maxd; | |
234 | ret = true; | |
235 | } | |
236 | } | |
237 | ||
238 | /* | |
239 | * Set our max/normal/bg queue depths based on how far | |
240 | * we have scaled down (->scale_step). | |
241 | */ | |
242 | rwb->wb_max = depth; | |
243 | rwb->wb_normal = (rwb->wb_max + 1) / 2; | |
244 | rwb->wb_background = (rwb->wb_max + 3) / 4; | |
245 | } | |
246 | ||
247 | return ret; | |
248 | } | |
249 | ||
4121d385 | 250 | static inline bool stat_sample_valid(struct blk_rq_stat *stat) |
e34cbd30 JA |
251 | { |
252 | /* | |
253 | * We need at least one read sample, and a minimum of | |
254 | * RWB_MIN_WRITE_SAMPLES. We require some write samples to know | |
255 | * that it's writes impacting us, and not just some sole read on | |
256 | * a device that is in a lower power state. | |
257 | */ | |
382cf633 JA |
258 | return stat[BLK_STAT_READ].nr_samples >= 1 && |
259 | stat[BLK_STAT_WRITE].nr_samples >= RWB_MIN_WRITE_SAMPLES; | |
e34cbd30 JA |
260 | } |
261 | ||
262 | static u64 rwb_sync_issue_lat(struct rq_wb *rwb) | |
263 | { | |
264 | u64 now, issue = ACCESS_ONCE(rwb->sync_issue); | |
265 | ||
266 | if (!issue || !rwb->sync_cookie) | |
267 | return 0; | |
268 | ||
269 | now = ktime_to_ns(ktime_get()); | |
270 | return now - issue; | |
271 | } | |
272 | ||
273 | enum { | |
274 | LAT_OK = 1, | |
275 | LAT_UNKNOWN, | |
276 | LAT_UNKNOWN_WRITES, | |
277 | LAT_EXCEEDED, | |
278 | }; | |
279 | ||
280 | static int __latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat) | |
281 | { | |
dc3b17cc | 282 | struct backing_dev_info *bdi = rwb->queue->backing_dev_info; |
e34cbd30 JA |
283 | u64 thislat; |
284 | ||
285 | /* | |
286 | * If our stored sync issue exceeds the window size, or it | |
287 | * exceeds our min target AND we haven't logged any entries, | |
288 | * flag the latency as exceeded. wbt works off completion latencies, | |
289 | * but for a flooded device, a single sync IO can take a long time | |
290 | * to complete after being issued. If this time exceeds our | |
291 | * monitoring window AND we didn't see any other completions in that | |
292 | * window, then count that sync IO as a violation of the latency. | |
293 | */ | |
294 | thislat = rwb_sync_issue_lat(rwb); | |
295 | if (thislat > rwb->cur_win_nsec || | |
382cf633 | 296 | (thislat > rwb->min_lat_nsec && !stat[BLK_STAT_READ].nr_samples)) { |
d8a0cbfd | 297 | trace_wbt_lat(bdi, thislat); |
e34cbd30 JA |
298 | return LAT_EXCEEDED; |
299 | } | |
300 | ||
301 | /* | |
302 | * No read/write mix, if stat isn't valid | |
303 | */ | |
304 | if (!stat_sample_valid(stat)) { | |
305 | /* | |
306 | * If we had writes in this stat window and the window is | |
307 | * current, we're only doing writes. If a task recently | |
308 | * waited or still has writes in flights, consider us doing | |
309 | * just writes as well. | |
310 | */ | |
382cf633 | 311 | if ((stat[BLK_STAT_WRITE].nr_samples && blk_stat_is_current(stat)) || |
e34cbd30 JA |
312 | wb_recent_wait(rwb) || wbt_inflight(rwb)) |
313 | return LAT_UNKNOWN_WRITES; | |
314 | return LAT_UNKNOWN; | |
315 | } | |
316 | ||
317 | /* | |
318 | * If the 'min' latency exceeds our target, step down. | |
319 | */ | |
382cf633 JA |
320 | if (stat[BLK_STAT_READ].min > rwb->min_lat_nsec) { |
321 | trace_wbt_lat(bdi, stat[BLK_STAT_READ].min); | |
d8a0cbfd | 322 | trace_wbt_stat(bdi, stat); |
e34cbd30 JA |
323 | return LAT_EXCEEDED; |
324 | } | |
325 | ||
326 | if (rwb->scale_step) | |
d8a0cbfd | 327 | trace_wbt_stat(bdi, stat); |
e34cbd30 JA |
328 | |
329 | return LAT_OK; | |
330 | } | |
331 | ||
332 | static int latency_exceeded(struct rq_wb *rwb) | |
333 | { | |
334 | struct blk_rq_stat stat[2]; | |
335 | ||
8054b89f | 336 | blk_queue_stat_get(rwb->queue, stat); |
e34cbd30 JA |
337 | return __latency_exceeded(rwb, stat); |
338 | } | |
339 | ||
340 | static void rwb_trace_step(struct rq_wb *rwb, const char *msg) | |
341 | { | |
dc3b17cc | 342 | struct backing_dev_info *bdi = rwb->queue->backing_dev_info; |
d8a0cbfd JA |
343 | |
344 | trace_wbt_step(bdi, msg, rwb->scale_step, rwb->cur_win_nsec, | |
e34cbd30 JA |
345 | rwb->wb_background, rwb->wb_normal, rwb->wb_max); |
346 | } | |
347 | ||
348 | static void scale_up(struct rq_wb *rwb) | |
349 | { | |
350 | /* | |
351 | * Hit max in previous round, stop here | |
352 | */ | |
353 | if (rwb->scaled_max) | |
354 | return; | |
355 | ||
356 | rwb->scale_step--; | |
357 | rwb->unknown_cnt = 0; | |
8054b89f | 358 | blk_stat_clear(rwb->queue); |
e34cbd30 JA |
359 | |
360 | rwb->scaled_max = calc_wb_limits(rwb); | |
361 | ||
362 | rwb_wake_all(rwb); | |
363 | ||
364 | rwb_trace_step(rwb, "step up"); | |
365 | } | |
366 | ||
367 | /* | |
368 | * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we | |
369 | * had a latency violation. | |
370 | */ | |
371 | static void scale_down(struct rq_wb *rwb, bool hard_throttle) | |
372 | { | |
373 | /* | |
374 | * Stop scaling down when we've hit the limit. This also prevents | |
375 | * ->scale_step from going to crazy values, if the device can't | |
376 | * keep up. | |
377 | */ | |
378 | if (rwb->wb_max == 1) | |
379 | return; | |
380 | ||
381 | if (rwb->scale_step < 0 && hard_throttle) | |
382 | rwb->scale_step = 0; | |
383 | else | |
384 | rwb->scale_step++; | |
385 | ||
386 | rwb->scaled_max = false; | |
387 | rwb->unknown_cnt = 0; | |
8054b89f | 388 | blk_stat_clear(rwb->queue); |
e34cbd30 JA |
389 | calc_wb_limits(rwb); |
390 | rwb_trace_step(rwb, "step down"); | |
391 | } | |
392 | ||
393 | static void rwb_arm_timer(struct rq_wb *rwb) | |
394 | { | |
395 | unsigned long expires; | |
396 | ||
397 | if (rwb->scale_step > 0) { | |
398 | /* | |
399 | * We should speed this up, using some variant of a fast | |
400 | * integer inverse square root calculation. Since we only do | |
401 | * this for every window expiration, it's not a huge deal, | |
402 | * though. | |
403 | */ | |
404 | rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4, | |
405 | int_sqrt((rwb->scale_step + 1) << 8)); | |
406 | } else { | |
407 | /* | |
408 | * For step < 0, we don't want to increase/decrease the | |
409 | * window size. | |
410 | */ | |
411 | rwb->cur_win_nsec = rwb->win_nsec; | |
412 | } | |
413 | ||
414 | expires = jiffies + nsecs_to_jiffies(rwb->cur_win_nsec); | |
415 | mod_timer(&rwb->window_timer, expires); | |
416 | } | |
417 | ||
418 | static void wb_timer_fn(unsigned long data) | |
419 | { | |
420 | struct rq_wb *rwb = (struct rq_wb *) data; | |
421 | unsigned int inflight = wbt_inflight(rwb); | |
422 | int status; | |
423 | ||
424 | status = latency_exceeded(rwb); | |
425 | ||
dc3b17cc | 426 | trace_wbt_timer(rwb->queue->backing_dev_info, status, rwb->scale_step, |
d8a0cbfd | 427 | inflight); |
e34cbd30 JA |
428 | |
429 | /* | |
430 | * If we exceeded the latency target, step down. If we did not, | |
431 | * step one level up. If we don't know enough to say either exceeded | |
432 | * or ok, then don't do anything. | |
433 | */ | |
434 | switch (status) { | |
435 | case LAT_EXCEEDED: | |
436 | scale_down(rwb, true); | |
437 | break; | |
438 | case LAT_OK: | |
439 | scale_up(rwb); | |
440 | break; | |
441 | case LAT_UNKNOWN_WRITES: | |
442 | /* | |
443 | * We started a the center step, but don't have a valid | |
444 | * read/write sample, but we do have writes going on. | |
445 | * Allow step to go negative, to increase write perf. | |
446 | */ | |
447 | scale_up(rwb); | |
448 | break; | |
449 | case LAT_UNKNOWN: | |
450 | if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP) | |
451 | break; | |
452 | /* | |
453 | * We get here when previously scaled reduced depth, and we | |
454 | * currently don't have a valid read/write sample. For that | |
455 | * case, slowly return to center state (step == 0). | |
456 | */ | |
457 | if (rwb->scale_step > 0) | |
458 | scale_up(rwb); | |
459 | else if (rwb->scale_step < 0) | |
460 | scale_down(rwb, false); | |
461 | break; | |
462 | default: | |
463 | break; | |
464 | } | |
465 | ||
466 | /* | |
467 | * Re-arm timer, if we have IO in flight | |
468 | */ | |
469 | if (rwb->scale_step || inflight) | |
470 | rwb_arm_timer(rwb); | |
471 | } | |
472 | ||
473 | void wbt_update_limits(struct rq_wb *rwb) | |
474 | { | |
475 | rwb->scale_step = 0; | |
476 | rwb->scaled_max = false; | |
477 | calc_wb_limits(rwb); | |
478 | ||
479 | rwb_wake_all(rwb); | |
480 | } | |
481 | ||
482 | static bool close_io(struct rq_wb *rwb) | |
483 | { | |
484 | const unsigned long now = jiffies; | |
485 | ||
486 | return time_before(now, rwb->last_issue + HZ / 10) || | |
487 | time_before(now, rwb->last_comp + HZ / 10); | |
488 | } | |
489 | ||
490 | #define REQ_HIPRIO (REQ_SYNC | REQ_META | REQ_PRIO) | |
491 | ||
492 | static inline unsigned int get_limit(struct rq_wb *rwb, unsigned long rw) | |
493 | { | |
494 | unsigned int limit; | |
495 | ||
496 | /* | |
497 | * At this point we know it's a buffered write. If this is | |
498 | * kswapd trying to free memory, or REQ_SYNC is set, set, then | |
499 | * it's WB_SYNC_ALL writeback, and we'll use the max limit for | |
500 | * that. If the write is marked as a background write, then use | |
501 | * the idle limit, or go to normal if we haven't had competing | |
502 | * IO for a bit. | |
503 | */ | |
504 | if ((rw & REQ_HIPRIO) || wb_recent_wait(rwb) || current_is_kswapd()) | |
505 | limit = rwb->wb_max; | |
506 | else if ((rw & REQ_BACKGROUND) || close_io(rwb)) { | |
507 | /* | |
508 | * If less than 100ms since we completed unrelated IO, | |
509 | * limit us to half the depth for background writeback. | |
510 | */ | |
511 | limit = rwb->wb_background; | |
512 | } else | |
513 | limit = rwb->wb_normal; | |
514 | ||
515 | return limit; | |
516 | } | |
517 | ||
518 | static inline bool may_queue(struct rq_wb *rwb, struct rq_wait *rqw, | |
519 | wait_queue_t *wait, unsigned long rw) | |
520 | { | |
521 | /* | |
522 | * inc it here even if disabled, since we'll dec it at completion. | |
523 | * this only happens if the task was sleeping in __wbt_wait(), | |
524 | * and someone turned it off at the same time. | |
525 | */ | |
526 | if (!rwb_enabled(rwb)) { | |
527 | atomic_inc(&rqw->inflight); | |
528 | return true; | |
529 | } | |
530 | ||
531 | /* | |
532 | * If the waitqueue is already active and we are not the next | |
533 | * in line to be woken up, wait for our turn. | |
534 | */ | |
535 | if (waitqueue_active(&rqw->wait) && | |
536 | rqw->wait.task_list.next != &wait->task_list) | |
537 | return false; | |
538 | ||
539 | return atomic_inc_below(&rqw->inflight, get_limit(rwb, rw)); | |
540 | } | |
541 | ||
542 | /* | |
543 | * Block if we will exceed our limit, or if we are currently waiting for | |
544 | * the timer to kick off queuing again. | |
545 | */ | |
546 | static void __wbt_wait(struct rq_wb *rwb, unsigned long rw, spinlock_t *lock) | |
9eca5350 BVA |
547 | __releases(lock) |
548 | __acquires(lock) | |
e34cbd30 JA |
549 | { |
550 | struct rq_wait *rqw = get_rq_wait(rwb, current_is_kswapd()); | |
551 | DEFINE_WAIT(wait); | |
552 | ||
553 | if (may_queue(rwb, rqw, &wait, rw)) | |
554 | return; | |
555 | ||
556 | do { | |
557 | prepare_to_wait_exclusive(&rqw->wait, &wait, | |
558 | TASK_UNINTERRUPTIBLE); | |
559 | ||
560 | if (may_queue(rwb, rqw, &wait, rw)) | |
561 | break; | |
562 | ||
9eca5350 | 563 | if (lock) { |
e34cbd30 | 564 | spin_unlock_irq(lock); |
9eca5350 | 565 | io_schedule(); |
e34cbd30 | 566 | spin_lock_irq(lock); |
9eca5350 BVA |
567 | } else |
568 | io_schedule(); | |
e34cbd30 JA |
569 | } while (1); |
570 | ||
571 | finish_wait(&rqw->wait, &wait); | |
572 | } | |
573 | ||
574 | static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio) | |
575 | { | |
576 | const int op = bio_op(bio); | |
577 | ||
578 | /* | |
be07e14f | 579 | * If not a WRITE, do nothing |
e34cbd30 | 580 | */ |
be07e14f | 581 | if (op != REQ_OP_WRITE) |
e34cbd30 JA |
582 | return false; |
583 | ||
584 | /* | |
585 | * Don't throttle WRITE_ODIRECT | |
586 | */ | |
587 | if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) == (REQ_SYNC | REQ_IDLE)) | |
588 | return false; | |
589 | ||
590 | return true; | |
591 | } | |
592 | ||
593 | /* | |
594 | * Returns true if the IO request should be accounted, false if not. | |
595 | * May sleep, if we have exceeded the writeback limits. Caller can pass | |
596 | * in an irq held spinlock, if it holds one when calling this function. | |
597 | * If we do sleep, we'll release and re-grab it. | |
598 | */ | |
f2e0a0b2 | 599 | enum wbt_flags wbt_wait(struct rq_wb *rwb, struct bio *bio, spinlock_t *lock) |
e34cbd30 JA |
600 | { |
601 | unsigned int ret = 0; | |
602 | ||
603 | if (!rwb_enabled(rwb)) | |
604 | return 0; | |
605 | ||
606 | if (bio_op(bio) == REQ_OP_READ) | |
607 | ret = WBT_READ; | |
608 | ||
609 | if (!wbt_should_throttle(rwb, bio)) { | |
610 | if (ret & WBT_READ) | |
611 | wb_timestamp(rwb, &rwb->last_issue); | |
612 | return ret; | |
613 | } | |
614 | ||
615 | __wbt_wait(rwb, bio->bi_opf, lock); | |
616 | ||
617 | if (!timer_pending(&rwb->window_timer)) | |
618 | rwb_arm_timer(rwb); | |
619 | ||
620 | if (current_is_kswapd()) | |
621 | ret |= WBT_KSWAPD; | |
622 | ||
623 | return ret | WBT_TRACKED; | |
624 | } | |
625 | ||
626 | void wbt_issue(struct rq_wb *rwb, struct blk_issue_stat *stat) | |
627 | { | |
628 | if (!rwb_enabled(rwb)) | |
629 | return; | |
630 | ||
631 | /* | |
632 | * Track sync issue, in case it takes a long time to complete. Allows | |
633 | * us to react quicker, if a sync IO takes a long time to complete. | |
634 | * Note that this is just a hint. 'stat' can go away when the | |
635 | * request completes, so it's important we never dereference it. We | |
636 | * only use the address to compare with, which is why we store the | |
637 | * sync_issue time locally. | |
638 | */ | |
639 | if (wbt_is_read(stat) && !rwb->sync_issue) { | |
640 | rwb->sync_cookie = stat; | |
641 | rwb->sync_issue = blk_stat_time(stat); | |
642 | } | |
643 | } | |
644 | ||
645 | void wbt_requeue(struct rq_wb *rwb, struct blk_issue_stat *stat) | |
646 | { | |
647 | if (!rwb_enabled(rwb)) | |
648 | return; | |
649 | if (stat == rwb->sync_cookie) { | |
650 | rwb->sync_issue = 0; | |
651 | rwb->sync_cookie = NULL; | |
652 | } | |
653 | } | |
654 | ||
655 | void wbt_set_queue_depth(struct rq_wb *rwb, unsigned int depth) | |
656 | { | |
657 | if (rwb) { | |
658 | rwb->queue_depth = depth; | |
659 | wbt_update_limits(rwb); | |
660 | } | |
661 | } | |
662 | ||
663 | void wbt_set_write_cache(struct rq_wb *rwb, bool write_cache_on) | |
664 | { | |
665 | if (rwb) | |
666 | rwb->wc = write_cache_on; | |
667 | } | |
668 | ||
fa224eed JA |
669 | /* |
670 | * Disable wbt, if enabled by default. Only called from CFQ, if we have | |
671 | * cgroups enabled | |
672 | */ | |
673 | void wbt_disable_default(struct request_queue *q) | |
e34cbd30 | 674 | { |
fa224eed JA |
675 | struct rq_wb *rwb = q->rq_wb; |
676 | ||
d62118b6 | 677 | if (rwb && rwb->enable_state == WBT_STATE_ON_DEFAULT) { |
e34cbd30 JA |
678 | del_timer_sync(&rwb->window_timer); |
679 | rwb->win_nsec = rwb->min_lat_nsec = 0; | |
680 | wbt_update_limits(rwb); | |
681 | } | |
682 | } | |
fa224eed | 683 | EXPORT_SYMBOL_GPL(wbt_disable_default); |
e34cbd30 | 684 | |
80e091d1 JA |
685 | u64 wbt_default_latency_nsec(struct request_queue *q) |
686 | { | |
687 | /* | |
688 | * We default to 2msec for non-rotational storage, and 75msec | |
689 | * for rotational storage. | |
690 | */ | |
691 | if (blk_queue_nonrot(q)) | |
692 | return 2000000ULL; | |
693 | else | |
694 | return 75000000ULL; | |
695 | } | |
696 | ||
8054b89f | 697 | int wbt_init(struct request_queue *q) |
e34cbd30 JA |
698 | { |
699 | struct rq_wb *rwb; | |
700 | int i; | |
701 | ||
702 | /* | |
703 | * For now, we depend on the stats window being larger than | |
704 | * our monitoring window. Ensure that this isn't inadvertently | |
705 | * violated. | |
706 | */ | |
707 | BUILD_BUG_ON(RWB_WINDOW_NSEC > BLK_STAT_NSEC); | |
708 | BUILD_BUG_ON(WBT_NR_BITS > BLK_STAT_RES_BITS); | |
709 | ||
e34cbd30 JA |
710 | rwb = kzalloc(sizeof(*rwb), GFP_KERNEL); |
711 | if (!rwb) | |
712 | return -ENOMEM; | |
713 | ||
714 | for (i = 0; i < WBT_NUM_RWQ; i++) { | |
715 | atomic_set(&rwb->rq_wait[i].inflight, 0); | |
716 | init_waitqueue_head(&rwb->rq_wait[i].wait); | |
717 | } | |
718 | ||
719 | setup_timer(&rwb->window_timer, wb_timer_fn, (unsigned long) rwb); | |
720 | rwb->wc = 1; | |
721 | rwb->queue_depth = RWB_DEF_DEPTH; | |
722 | rwb->last_comp = rwb->last_issue = jiffies; | |
d8a0cbfd | 723 | rwb->queue = q; |
e34cbd30 | 724 | rwb->win_nsec = RWB_WINDOW_NSEC; |
d62118b6 | 725 | rwb->enable_state = WBT_STATE_ON_DEFAULT; |
e34cbd30 JA |
726 | wbt_update_limits(rwb); |
727 | ||
728 | /* | |
729 | * Assign rwb, and turn on stats tracking for this queue | |
730 | */ | |
731 | q->rq_wb = rwb; | |
732 | blk_stat_enable(q); | |
733 | ||
80e091d1 | 734 | rwb->min_lat_nsec = wbt_default_latency_nsec(q); |
e34cbd30 JA |
735 | |
736 | wbt_set_queue_depth(rwb, blk_queue_depth(q)); | |
737 | wbt_set_write_cache(rwb, test_bit(QUEUE_FLAG_WC, &q->queue_flags)); | |
738 | ||
739 | return 0; | |
740 | } | |
741 | ||
742 | void wbt_exit(struct request_queue *q) | |
743 | { | |
744 | struct rq_wb *rwb = q->rq_wb; | |
745 | ||
746 | if (rwb) { | |
747 | del_timer_sync(&rwb->window_timer); | |
748 | q->rq_wb = NULL; | |
749 | kfree(rwb); | |
750 | } | |
751 | } |