blk-wbt.c 17.5 KB
Newer Older
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
/*
 * buffered writeback throttling. loosely based on CoDel. We can't drop
 * packets for IO scheduling, so the logic is something like this:
 *
 * - Monitor latencies in a defined window of time.
 * - If the minimum latency in the above window exceeds some target, increment
 *   scaling step and scale down queue depth by a factor of 2x. The monitoring
 *   window is then shrunk to 100 / sqrt(scaling step + 1).
 * - For any window where we don't have solid data on what the latencies
 *   look like, retain status quo.
 * - If latencies look good, decrement scaling step.
 * - If we're only doing writes, allow the scaling step to go negative. This
 *   will temporarily boost write performance, snapping back to a stable
 *   scaling step of 0 if reads show up or the heavy writers finish. Unlike
 *   positive scaling steps where we shrink the monitoring window, a negative
 *   scaling step retains the default step==0 window size.
 *
 * Copyright (C) 2016 Jens Axboe
 *
 */
#include <linux/kernel.h>
#include <linux/blk_types.h>
#include <linux/slab.h>
#include <linux/backing-dev.h>
#include <linux/swap.h>

#include "blk-wbt.h"

#define CREATE_TRACE_POINTS
#include <trace/events/wbt.h>

enum {
	/*
	 * Default setting, we'll scale up (to 75% of QD max) or down (min 1)
	 * from here depending on device stats
	 */
	RWB_DEF_DEPTH	= 16,

	/*
	 * 100msec window
	 */
	RWB_WINDOW_NSEC		= 100 * 1000 * 1000ULL,

	/*
	 * Disregard stats, if we don't meet this minimum
	 */
	RWB_MIN_WRITE_SAMPLES	= 3,

	/*
	 * If we have this number of consecutive windows with not enough
	 * information to scale up or down, scale up.
	 */
	RWB_UNKNOWN_BUMP	= 5,
};

static inline bool rwb_enabled(struct rq_wb *rwb)
{
	return rwb && rwb->wb_normal != 0;
}

/*
 * Increment 'v', if 'v' is below 'below'. Returns true if we succeeded,
 * false if 'v' + 1 would be bigger than 'below'.
 */
static bool atomic_inc_below(atomic_t *v, int below)
{
	int cur = atomic_read(v);

	for (;;) {
		int old;

		if (cur >= below)
			return false;
		old = atomic_cmpxchg(v, cur, cur + 1);
		if (old == cur)
			break;
		cur = old;
	}

	return true;
}

static void wb_timestamp(struct rq_wb *rwb, unsigned long *var)
{
	if (rwb_enabled(rwb)) {
		const unsigned long cur = jiffies;

		if (cur != *var)
			*var = cur;
	}
}

/*
 * If a task was rate throttled in balance_dirty_pages() within the last
 * second or so, use that to indicate a higher cleaning rate.
 */
static bool wb_recent_wait(struct rq_wb *rwb)
{
99
	struct bdi_writeback *wb = &rwb->queue->backing_dev_info->wb;
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

	return time_before(jiffies, wb->dirty_sleep + HZ);
}

static inline struct rq_wait *get_rq_wait(struct rq_wb *rwb, bool is_kswapd)
{
	return &rwb->rq_wait[is_kswapd];
}

static void rwb_wake_all(struct rq_wb *rwb)
{
	int i;

	for (i = 0; i < WBT_NUM_RWQ; i++) {
		struct rq_wait *rqw = &rwb->rq_wait[i];

		if (waitqueue_active(&rqw->wait))
			wake_up_all(&rqw->wait);
	}
}

void __wbt_done(struct rq_wb *rwb, enum wbt_flags wb_acct)
{
	struct rq_wait *rqw;
	int inflight, limit;

	if (!(wb_acct & WBT_TRACKED))
		return;

	rqw = get_rq_wait(rwb, wb_acct & WBT_KSWAPD);
	inflight = atomic_dec_return(&rqw->inflight);

	/*
	 * wbt got disabled with IO in flight. Wake up any potential
	 * waiters, we don't have to do more than that.
	 */
	if (unlikely(!rwb_enabled(rwb))) {
		rwb_wake_all(rwb);
		return;
	}

	/*
	 * If the device does write back caching, drop further down
	 * before we wake people up.
	 */
	if (rwb->wc && !wb_recent_wait(rwb))
		limit = 0;
	else
		limit = rwb->wb_normal;

	/*
	 * Don't wake anyone up if we are above the normal limit.
	 */
	if (inflight && inflight >= limit)
		return;

	if (waitqueue_active(&rqw->wait)) {
		int diff = limit - inflight;

		if (!inflight || diff >= rwb->wb_background / 2)
			wake_up_all(&rqw->wait);
	}
}

/*
 * Called on completion of a request. Note that it's also called when
 * a request is merged, when the request gets freed.
 */
void wbt_done(struct rq_wb *rwb, struct blk_issue_stat *stat)
{
	if (!rwb)
		return;

	if (!wbt_is_tracked(stat)) {
		if (rwb->sync_cookie == stat) {
			rwb->sync_issue = 0;
			rwb->sync_cookie = NULL;
		}

		if (wbt_is_read(stat))
			wb_timestamp(rwb, &rwb->last_comp);
	} else {
		WARN_ON_ONCE(stat == rwb->sync_cookie);
		__wbt_done(rwb, wbt_stat_to_mask(stat));
	}
185
	wbt_clear_state(stat);
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
}

/*
 * Return true, if we can't increase the depth further by scaling
 */
static bool calc_wb_limits(struct rq_wb *rwb)
{
	unsigned int depth;
	bool ret = false;

	if (!rwb->min_lat_nsec) {
		rwb->wb_max = rwb->wb_normal = rwb->wb_background = 0;
		return false;
	}

	/*
	 * For QD=1 devices, this is a special case. It's important for those
	 * to have one request ready when one completes, so force a depth of
	 * 2 for those devices. On the backend, it'll be a depth of 1 anyway,
	 * since the device can't have more than that in flight. If we're
	 * scaling down, then keep a setting of 1/1/1.
	 */
	if (rwb->queue_depth == 1) {
		if (rwb->scale_step > 0)
			rwb->wb_max = rwb->wb_normal = 1;
		else {
			rwb->wb_max = rwb->wb_normal = 2;
			ret = true;
		}
		rwb->wb_background = 1;
	} else {
		/*
		 * scale_step == 0 is our default state. If we have suffered
		 * latency spikes, step will be > 0, and we shrink the
		 * allowed write depths. If step is < 0, we're only doing
		 * writes, and we allow a temporarily higher depth to
		 * increase performance.
		 */
		depth = min_t(unsigned int, RWB_DEF_DEPTH, rwb->queue_depth);
		if (rwb->scale_step > 0)
			depth = 1 + ((depth - 1) >> min(31, rwb->scale_step));
		else if (rwb->scale_step < 0) {
			unsigned int maxd = 3 * rwb->queue_depth / 4;

			depth = 1 + ((depth - 1) << -rwb->scale_step);
			if (depth > maxd) {
				depth = maxd;
				ret = true;
			}
		}

		/*
		 * Set our max/normal/bg queue depths based on how far
		 * we have scaled down (->scale_step).
		 */
		rwb->wb_max = depth;
		rwb->wb_normal = (rwb->wb_max + 1) / 2;
		rwb->wb_background = (rwb->wb_max + 3) / 4;
	}

	return ret;
}

249
static inline bool stat_sample_valid(struct blk_rq_stat *stat)
250 251 252 253 254 255 256
{
	/*
	 * We need at least one read sample, and a minimum of
	 * RWB_MIN_WRITE_SAMPLES. We require some write samples to know
	 * that it's writes impacting us, and not just some sole read on
	 * a device that is in a lower power state.
	 */
257 258
	return (stat[READ].nr_samples >= 1 &&
		stat[WRITE].nr_samples >= RWB_MIN_WRITE_SAMPLES);
259 260 261 262
}

static u64 rwb_sync_issue_lat(struct rq_wb *rwb)
{
263
	u64 now, issue = READ_ONCE(rwb->sync_issue);
264 265 266 267 268 269 270 271 272 273 274 275 276 277 278

	if (!issue || !rwb->sync_cookie)
		return 0;

	now = ktime_to_ns(ktime_get());
	return now - issue;
}

enum {
	LAT_OK = 1,
	LAT_UNKNOWN,
	LAT_UNKNOWN_WRITES,
	LAT_EXCEEDED,
};

279
static int latency_exceeded(struct rq_wb *rwb, struct blk_rq_stat *stat)
280
{
281
	struct backing_dev_info *bdi = rwb->queue->backing_dev_info;
282 283 284 285 286 287 288 289 290 291 292 293 294
	u64 thislat;

	/*
	 * If our stored sync issue exceeds the window size, or it
	 * exceeds our min target AND we haven't logged any entries,
	 * flag the latency as exceeded. wbt works off completion latencies,
	 * but for a flooded device, a single sync IO can take a long time
	 * to complete after being issued. If this time exceeds our
	 * monitoring window AND we didn't see any other completions in that
	 * window, then count that sync IO as a violation of the latency.
	 */
	thislat = rwb_sync_issue_lat(rwb);
	if (thislat > rwb->cur_win_nsec ||
295
	    (thislat > rwb->min_lat_nsec && !stat[READ].nr_samples)) {
J
Jens Axboe 已提交
296
		trace_wbt_lat(bdi, thislat);
297 298 299 300 301 302 303 304 305 306 307 308 309
		return LAT_EXCEEDED;
	}

	/*
	 * No read/write mix, if stat isn't valid
	 */
	if (!stat_sample_valid(stat)) {
		/*
		 * If we had writes in this stat window and the window is
		 * current, we're only doing writes. If a task recently
		 * waited or still has writes in flights, consider us doing
		 * just writes as well.
		 */
310 311
		if (stat[WRITE].nr_samples || wb_recent_wait(rwb) ||
		    wbt_inflight(rwb))
312 313 314 315 316 317 318
			return LAT_UNKNOWN_WRITES;
		return LAT_UNKNOWN;
	}

	/*
	 * If the 'min' latency exceeds our target, step down.
	 */
319 320
	if (stat[READ].min > rwb->min_lat_nsec) {
		trace_wbt_lat(bdi, stat[READ].min);
J
Jens Axboe 已提交
321
		trace_wbt_stat(bdi, stat);
322 323 324 325
		return LAT_EXCEEDED;
	}

	if (rwb->scale_step)
J
Jens Axboe 已提交
326
		trace_wbt_stat(bdi, stat);
327 328 329 330 331 332

	return LAT_OK;
}

static void rwb_trace_step(struct rq_wb *rwb, const char *msg)
{
333
	struct backing_dev_info *bdi = rwb->queue->backing_dev_info;
J
Jens Axboe 已提交
334 335

	trace_wbt_step(bdi, msg, rwb->scale_step, rwb->cur_win_nsec,
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
			rwb->wb_background, rwb->wb_normal, rwb->wb_max);
}

static void scale_up(struct rq_wb *rwb)
{
	/*
	 * Hit max in previous round, stop here
	 */
	if (rwb->scaled_max)
		return;

	rwb->scale_step--;
	rwb->unknown_cnt = 0;

	rwb->scaled_max = calc_wb_limits(rwb);

	rwb_wake_all(rwb);

	rwb_trace_step(rwb, "step up");
}

/*
 * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we
 * had a latency violation.
 */
static void scale_down(struct rq_wb *rwb, bool hard_throttle)
{
	/*
	 * Stop scaling down when we've hit the limit. This also prevents
	 * ->scale_step from going to crazy values, if the device can't
	 * keep up.
	 */
	if (rwb->wb_max == 1)
		return;

	if (rwb->scale_step < 0 && hard_throttle)
		rwb->scale_step = 0;
	else
		rwb->scale_step++;

	rwb->scaled_max = false;
	rwb->unknown_cnt = 0;
	calc_wb_limits(rwb);
	rwb_trace_step(rwb, "step down");
}

static void rwb_arm_timer(struct rq_wb *rwb)
{
	if (rwb->scale_step > 0) {
		/*
		 * We should speed this up, using some variant of a fast
		 * integer inverse square root calculation. Since we only do
		 * this for every window expiration, it's not a huge deal,
		 * though.
		 */
		rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4,
					int_sqrt((rwb->scale_step + 1) << 8));
	} else {
		/*
		 * For step < 0, we don't want to increase/decrease the
		 * window size.
		 */
		rwb->cur_win_nsec = rwb->win_nsec;
	}

401
	blk_stat_activate_nsecs(rwb->cb, rwb->cur_win_nsec);
402 403
}

404
static void wb_timer_fn(struct blk_stat_callback *cb)
405
{
406
	struct rq_wb *rwb = cb->data;
407 408 409
	unsigned int inflight = wbt_inflight(rwb);
	int status;

410
	status = latency_exceeded(rwb, cb->stat);
411

412
	trace_wbt_timer(rwb->queue->backing_dev_info, status, rwb->scale_step,
J
Jens Axboe 已提交
413
			inflight);
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

	/*
	 * If we exceeded the latency target, step down. If we did not,
	 * step one level up. If we don't know enough to say either exceeded
	 * or ok, then don't do anything.
	 */
	switch (status) {
	case LAT_EXCEEDED:
		scale_down(rwb, true);
		break;
	case LAT_OK:
		scale_up(rwb);
		break;
	case LAT_UNKNOWN_WRITES:
		/*
		 * We started a the center step, but don't have a valid
		 * read/write sample, but we do have writes going on.
		 * Allow step to go negative, to increase write perf.
		 */
		scale_up(rwb);
		break;
	case LAT_UNKNOWN:
		if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP)
			break;
		/*
		 * We get here when previously scaled reduced depth, and we
		 * currently don't have a valid read/write sample. For that
		 * case, slowly return to center state (step == 0).
		 */
		if (rwb->scale_step > 0)
			scale_up(rwb);
		else if (rwb->scale_step < 0)
			scale_down(rwb, false);
		break;
	default:
		break;
	}

	/*
	 * Re-arm timer, if we have IO in flight
	 */
	if (rwb->scale_step || inflight)
		rwb_arm_timer(rwb);
}

void wbt_update_limits(struct rq_wb *rwb)
{
	rwb->scale_step = 0;
	rwb->scaled_max = false;
	calc_wb_limits(rwb);

	rwb_wake_all(rwb);
}

static bool close_io(struct rq_wb *rwb)
{
	const unsigned long now = jiffies;

	return time_before(now, rwb->last_issue + HZ / 10) ||
		time_before(now, rwb->last_comp + HZ / 10);
}

#define REQ_HIPRIO	(REQ_SYNC | REQ_META | REQ_PRIO)

static inline unsigned int get_limit(struct rq_wb *rwb, unsigned long rw)
{
	unsigned int limit;

	/*
	 * At this point we know it's a buffered write. If this is
W
weiping zhang 已提交
484
	 * kswapd trying to free memory, or REQ_SYNC is set, then
485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504
	 * it's WB_SYNC_ALL writeback, and we'll use the max limit for
	 * that. If the write is marked as a background write, then use
	 * the idle limit, or go to normal if we haven't had competing
	 * IO for a bit.
	 */
	if ((rw & REQ_HIPRIO) || wb_recent_wait(rwb) || current_is_kswapd())
		limit = rwb->wb_max;
	else if ((rw & REQ_BACKGROUND) || close_io(rwb)) {
		/*
		 * If less than 100ms since we completed unrelated IO,
		 * limit us to half the depth for background writeback.
		 */
		limit = rwb->wb_background;
	} else
		limit = rwb->wb_normal;

	return limit;
}

static inline bool may_queue(struct rq_wb *rwb, struct rq_wait *rqw,
505
			     wait_queue_entry_t *wait, unsigned long rw)
506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521
{
	/*
	 * inc it here even if disabled, since we'll dec it at completion.
	 * this only happens if the task was sleeping in __wbt_wait(),
	 * and someone turned it off at the same time.
	 */
	if (!rwb_enabled(rwb)) {
		atomic_inc(&rqw->inflight);
		return true;
	}

	/*
	 * If the waitqueue is already active and we are not the next
	 * in line to be woken up, wait for our turn.
	 */
	if (waitqueue_active(&rqw->wait) &&
522
	    rqw->wait.head.next != &wait->entry)
523 524 525 526 527 528 529 530 531 532
		return false;

	return atomic_inc_below(&rqw->inflight, get_limit(rwb, rw));
}

/*
 * Block if we will exceed our limit, or if we are currently waiting for
 * the timer to kick off queuing again.
 */
static void __wbt_wait(struct rq_wb *rwb, unsigned long rw, spinlock_t *lock)
533 534
	__releases(lock)
	__acquires(lock)
535 536 537 538 539 540 541 542 543 544 545 546 547 548
{
	struct rq_wait *rqw = get_rq_wait(rwb, current_is_kswapd());
	DEFINE_WAIT(wait);

	if (may_queue(rwb, rqw, &wait, rw))
		return;

	do {
		prepare_to_wait_exclusive(&rqw->wait, &wait,
						TASK_UNINTERRUPTIBLE);

		if (may_queue(rwb, rqw, &wait, rw))
			break;

549
		if (lock) {
550
			spin_unlock_irq(lock);
551
			io_schedule();
552
			spin_lock_irq(lock);
553 554
		} else
			io_schedule();
555 556 557 558 559 560 561 562 563 564
	} while (1);

	finish_wait(&rqw->wait, &wait);
}

static inline bool wbt_should_throttle(struct rq_wb *rwb, struct bio *bio)
{
	const int op = bio_op(bio);

	/*
565
	 * If not a WRITE, do nothing
566
	 */
567
	if (op != REQ_OP_WRITE)
568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584
		return false;

	/*
	 * Don't throttle WRITE_ODIRECT
	 */
	if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) == (REQ_SYNC | REQ_IDLE))
		return false;

	return true;
}

/*
 * Returns true if the IO request should be accounted, false if not.
 * May sleep, if we have exceeded the writeback limits. Caller can pass
 * in an irq held spinlock, if it holds one when calling this function.
 * If we do sleep, we'll release and re-grab it.
 */
585
enum wbt_flags wbt_wait(struct rq_wb *rwb, struct bio *bio, spinlock_t *lock)
586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602
{
	unsigned int ret = 0;

	if (!rwb_enabled(rwb))
		return 0;

	if (bio_op(bio) == REQ_OP_READ)
		ret = WBT_READ;

	if (!wbt_should_throttle(rwb, bio)) {
		if (ret & WBT_READ)
			wb_timestamp(rwb, &rwb->last_issue);
		return ret;
	}

	__wbt_wait(rwb, bio->bi_opf, lock);

603
	if (!blk_stat_is_active(rwb->cb))
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
		rwb_arm_timer(rwb);

	if (current_is_kswapd())
		ret |= WBT_KSWAPD;

	return ret | WBT_TRACKED;
}

void wbt_issue(struct rq_wb *rwb, struct blk_issue_stat *stat)
{
	if (!rwb_enabled(rwb))
		return;

	/*
	 * Track sync issue, in case it takes a long time to complete. Allows
	 * us to react quicker, if a sync IO takes a long time to complete.
	 * Note that this is just a hint. 'stat' can go away when the
	 * request completes, so it's important we never dereference it. We
	 * only use the address to compare with, which is why we store the
	 * sync_issue time locally.
	 */
	if (wbt_is_read(stat) && !rwb->sync_issue) {
		rwb->sync_cookie = stat;
		rwb->sync_issue = blk_stat_time(stat);
	}
}

void wbt_requeue(struct rq_wb *rwb, struct blk_issue_stat *stat)
{
	if (!rwb_enabled(rwb))
		return;
	if (stat == rwb->sync_cookie) {
		rwb->sync_issue = 0;
		rwb->sync_cookie = NULL;
	}
}

void wbt_set_queue_depth(struct rq_wb *rwb, unsigned int depth)
{
	if (rwb) {
		rwb->queue_depth = depth;
		wbt_update_limits(rwb);
	}
}

void wbt_set_write_cache(struct rq_wb *rwb, bool write_cache_on)
{
	if (rwb)
		rwb->wc = write_cache_on;
}

655
/*
656
 * Disable wbt, if enabled by default.
657 658
 */
void wbt_disable_default(struct request_queue *q)
659
{
660 661
	struct rq_wb *rwb = q->rq_wb;

662 663
	if (rwb && rwb->enable_state == WBT_STATE_ON_DEFAULT)
		wbt_exit(q);
664
}
665
EXPORT_SYMBOL_GPL(wbt_disable_default);
666

667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685
/*
 * Enable wbt if defaults are configured that way
 */
void wbt_enable_default(struct request_queue *q)
{
	/* Throttling already enabled? */
	if (q->rq_wb)
		return;

	/* Queue not registered? Maybe shutting down... */
	if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags))
		return;

	if ((q->mq_ops && IS_ENABLED(CONFIG_BLK_WBT_MQ)) ||
	    (q->request_fn && IS_ENABLED(CONFIG_BLK_WBT_SQ)))
		wbt_init(q);
}
EXPORT_SYMBOL_GPL(wbt_enable_default);

686 687 688 689 690 691 692 693 694 695 696 697
u64 wbt_default_latency_nsec(struct request_queue *q)
{
	/*
	 * We default to 2msec for non-rotational storage, and 75msec
	 * for rotational storage.
	 */
	if (blk_queue_nonrot(q))
		return 2000000ULL;
	else
		return 75000000ULL;
}

J
Jens Axboe 已提交
698 699 700 701 702
static int wbt_data_dir(const struct request *rq)
{
	return rq_data_dir(rq);
}

J
Jens Axboe 已提交
703
int wbt_init(struct request_queue *q)
704 705 706 707 708 709 710 711 712 713
{
	struct rq_wb *rwb;
	int i;

	BUILD_BUG_ON(WBT_NR_BITS > BLK_STAT_RES_BITS);

	rwb = kzalloc(sizeof(*rwb), GFP_KERNEL);
	if (!rwb)
		return -ENOMEM;

J
Jens Axboe 已提交
714
	rwb->cb = blk_stat_alloc_callback(wb_timer_fn, wbt_data_dir, 2, rwb);
715 716 717 718 719
	if (!rwb->cb) {
		kfree(rwb);
		return -ENOMEM;
	}

720 721 722 723 724 725
	for (i = 0; i < WBT_NUM_RWQ; i++) {
		atomic_set(&rwb->rq_wait[i].inflight, 0);
		init_waitqueue_head(&rwb->rq_wait[i].wait);
	}

	rwb->last_comp = rwb->last_issue = jiffies;
J
Jens Axboe 已提交
726
	rwb->queue = q;
727
	rwb->win_nsec = RWB_WINDOW_NSEC;
728
	rwb->enable_state = WBT_STATE_ON_DEFAULT;
729 730 731
	wbt_update_limits(rwb);

	/*
732
	 * Assign rwb and add the stats callback.
733 734
	 */
	q->rq_wb = rwb;
735
	blk_stat_add_callback(q, rwb->cb);
736

737
	rwb->min_lat_nsec = wbt_default_latency_nsec(q);
738 739 740 741 742 743 744 745 746 747 748 749

	wbt_set_queue_depth(rwb, blk_queue_depth(q));
	wbt_set_write_cache(rwb, test_bit(QUEUE_FLAG_WC, &q->queue_flags));

	return 0;
}

void wbt_exit(struct request_queue *q)
{
	struct rq_wb *rwb = q->rq_wb;

	if (rwb) {
750 751
		blk_stat_remove_callback(q, rwb->cb);
		blk_stat_free_callback(rwb->cb);
752 753 754 755
		q->rq_wb = NULL;
		kfree(rwb);
	}
}