1 // SPDX-License-Identifier: GPL-2.0
6  * - Monitor latencies in a defined window of time.
7  * - If the minimum latency in the above window exceeds some target, increment
8  *   scaling step and scale down queue depth by a factor of 2x. The monitoring
9  *   window is then shrunk to 100 / sqrt(scaling step + 1).
10  * - For any window where we don't have solid data on what the latencies
12  * - If latencies look good, decrement scaling step.
13  * - If we're only doing writes, allow the scaling step to go negative. This
15  *   scaling step of 0 if reads show up or the heavy writers finish. Unlike
17  *   scaling step retains the default step==0 window size.
25 #include <linux/backing-dev.h>
28 #include "blk-wbt.h"
29 #include "blk-rq-qos.h"
36 	rq->wbt_flags = 0;  in wbt_clear_state()
41 	return rq->wbt_flags;  in wbt_flags()
46 	return rq->wbt_flags & WBT_TRACKED;  in wbt_is_tracked()
51 	return rq->wbt_flags & WBT_READ;  in wbt_is_read()
56 	 * Default setting, we'll scale up (to 75% of QD max) or down (min 1)
73 	 * information to scale up or down, scale up.
80 	return rwb && rwb->enable_state != WBT_STATE_OFF_DEFAULT &&  in rwb_enabled()
81 		      rwb->wb_normal != 0;  in rwb_enabled()
100 	struct bdi_writeback *wb = &rwb->rqos.q->disk->bdi->wb;  in wb_recent_wait()
102 	return time_before(jiffies, wb->dirty_sleep + HZ);  in wb_recent_wait()
109 		return &rwb->rq_wait[WBT_RWQ_KSWAPD];  in get_rq_wait()
111 		return &rwb->rq_wait[WBT_RWQ_DISCARD];  in get_rq_wait()
113 	return &rwb->rq_wait[WBT_RWQ_BG];  in get_rq_wait()
121 		struct rq_wait *rqw = &rwb->rq_wait[i];  in rwb_wake_all()
123 		if (wq_has_sleeper(&rqw->wait))  in rwb_wake_all()
124 			wake_up_all(&rqw->wait);  in rwb_wake_all()
133 	inflight = atomic_dec_return(&rqw->inflight);  in wbt_rqw_done()
146 	 * the device does write back caching, drop further down before we  in wbt_rqw_done()
150 		limit = rwb->wb_background;  in wbt_rqw_done()
151 	else if (rwb->wc && !wb_recent_wait(rwb))  in wbt_rqw_done()
154 		limit = rwb->wb_normal;  in wbt_rqw_done()
162 	if (wq_has_sleeper(&rqw->wait)) {  in wbt_rqw_done()
163 		int diff = limit - inflight;  in wbt_rqw_done()
165 		if (!inflight || diff >= rwb->wb_background / 2)  in wbt_rqw_done()
166 			wake_up_all(&rqw->wait);  in wbt_rqw_done()
191 		if (rwb->sync_cookie == rq) {  in wbt_done()
192 			rwb->sync_issue = 0;  in wbt_done()
193 			rwb->sync_cookie = NULL;  in wbt_done()
197 			wb_timestamp(rwb, &rwb->last_comp);  in wbt_done()
199 		WARN_ON_ONCE(rq == rwb->sync_cookie);  in wbt_done()
219 	u64 now, issue = READ_ONCE(rwb->sync_issue);  in rwb_sync_issue_lat()
221 	if (!issue || !rwb->sync_cookie)  in rwb_sync_issue_lat()
225 	return now - issue;  in rwb_sync_issue_lat()
237 	struct backing_dev_info *bdi = rwb->rqos.q->disk->bdi;  in latency_exceeded()
238 	struct rq_depth *rqd = &rwb->rq_depth;  in latency_exceeded()
251 	if (thislat > rwb->cur_win_nsec ||  in latency_exceeded()
252 	    (thislat > rwb->min_lat_nsec && !stat[READ].nr_samples)) {  in latency_exceeded()
274 	 * If the 'min' latency exceeds our target, step down.  in latency_exceeded()
276 	if (stat[READ].min > rwb->min_lat_nsec) {  in latency_exceeded()
282 	if (rqd->scale_step)  in latency_exceeded()
290 	struct backing_dev_info *bdi = rwb->rqos.q->disk->bdi;  in rwb_trace_step()
291 	struct rq_depth *rqd = &rwb->rq_depth;  in rwb_trace_step()
293 	trace_wbt_step(bdi, msg, rqd->scale_step, rwb->cur_win_nsec,  in rwb_trace_step()
294 			rwb->wb_background, rwb->wb_normal, rqd->max_depth);  in rwb_trace_step()
299 	if (rwb->min_lat_nsec == 0) {  in calc_wb_limits()
300 		rwb->wb_normal = rwb->wb_background = 0;  in calc_wb_limits()
301 	} else if (rwb->rq_depth.max_depth <= 2) {  in calc_wb_limits()
302 		rwb->wb_normal = rwb->rq_depth.max_depth;  in calc_wb_limits()
303 		rwb->wb_background = 1;  in calc_wb_limits()
305 		rwb->wb_normal = (rwb->rq_depth.max_depth + 1) / 2;  in calc_wb_limits()
306 		rwb->wb_background = (rwb->rq_depth.max_depth + 3) / 4;  in calc_wb_limits()
312 	if (!rq_depth_scale_up(&rwb->rq_depth))  in scale_up()
315 	rwb->unknown_cnt = 0;  in scale_up()
322 	if (!rq_depth_scale_down(&rwb->rq_depth, hard_throttle))  in scale_down()
325 	rwb->unknown_cnt = 0;  in scale_down()
326 	rwb_trace_step(rwb, tracepoint_string("scale down"));  in scale_down()
331 	struct rq_depth *rqd = &rwb->rq_depth;  in rwb_arm_timer()
333 	if (rqd->scale_step > 0) {  in rwb_arm_timer()
340 		rwb->cur_win_nsec = div_u64(rwb->win_nsec << 4,  in rwb_arm_timer()
341 					int_sqrt((rqd->scale_step + 1) << 8));  in rwb_arm_timer()
344 		 * For step < 0, we don't want to increase/decrease the  in rwb_arm_timer()
347 		rwb->cur_win_nsec = rwb->win_nsec;  in rwb_arm_timer()
350 	blk_stat_activate_nsecs(rwb->cb, rwb->cur_win_nsec);  in rwb_arm_timer()
355 	struct rq_wb *rwb = cb->data;  in wb_timer_fn()
356 	struct rq_depth *rqd = &rwb->rq_depth;  in wb_timer_fn()
360 	if (!rwb->rqos.q->disk)  in wb_timer_fn()
363 	status = latency_exceeded(rwb, cb->stat);  in wb_timer_fn()
365 	trace_wbt_timer(rwb->rqos.q->disk->bdi, status, rqd->scale_step,  in wb_timer_fn()
369 	 * If we exceeded the latency target, step down. If we did not,  in wb_timer_fn()
370 	 * step one level up. If we don't know enough to say either exceeded  in wb_timer_fn()
382 		 * We started a the center step, but don't have a valid  in wb_timer_fn()
384 		 * Allow step to go negative, to increase write perf.  in wb_timer_fn()
389 		if (++rwb->unknown_cnt < RWB_UNKNOWN_BUMP)  in wb_timer_fn()
394 		 * case, slowly return to center state (step == 0).  in wb_timer_fn()
396 		if (rqd->scale_step > 0)  in wb_timer_fn()
398 		else if (rqd->scale_step < 0)  in wb_timer_fn()
406 	 * Re-arm timer, if we have IO in flight  in wb_timer_fn()
408 	if (rqd->scale_step || inflight)  in wb_timer_fn()
414 	struct rq_depth *rqd = &rwb->rq_depth;  in wbt_update_limits()
416 	rqd->scale_step = 0;  in wbt_update_limits()
417 	rqd->scaled_max = false;  in wbt_update_limits()
430 	return RQWB(rqos)->min_lat_nsec;  in wbt_get_min_lat()
438 	RQWB(rqos)->min_lat_nsec = val;  in wbt_set_min_lat()
439 	RQWB(rqos)->enable_state = WBT_STATE_ON_MANUAL;  in wbt_set_min_lat()
448 	return time_before(now, rwb->last_issue + HZ / 10) ||  in close_io()
449 		time_before(now, rwb->last_comp + HZ / 10);  in close_io()
466 		return rwb->wb_background;  in get_limit()
477 		limit = rwb->rq_depth.max_depth;  in get_limit()
483 		limit = rwb->wb_background;  in get_limit()
485 		limit = rwb->wb_normal;  in get_limit()
499 	return rq_wait_inc_below(rqw, get_limit(data->rwb, data->opf));  in wbt_inflight_cb()
505 	wbt_rqw_done(data->rwb, rqw, data->wb_acct);  in wbt_cleanup_cb()
532 		if ((bio->bi_opf & (REQ_SYNC | REQ_IDLE)) ==  in wbt_should_throttle()
572  * If we do sleep, we'll release and re-grab it.
582 			wb_timestamp(rwb, &rwb->last_issue);  in wbt_wait()
586 	__wbt_wait(rwb, flags, bio->bi_opf);  in wbt_wait()
588 	if (!blk_stat_is_active(rwb->cb))  in wbt_wait()
595 	rq->wbt_flags |= bio_to_wbt_flags(rwb, bio);  in wbt_track()
612 	if (wbt_is_read(rq) && !rwb->sync_issue) {  in wbt_issue()
613 		rwb->sync_cookie = rq;  in wbt_issue()
614 		rwb->sync_issue = rq->io_start_time_ns;  in wbt_issue()
623 	if (rq == rwb->sync_cookie) {  in wbt_requeue()
624 		rwb->sync_issue = 0;  in wbt_requeue()
625 		rwb->sync_cookie = NULL;  in wbt_requeue()
633 		RQWB(rqos)->wc = write_cache_on;  in wbt_set_write_cache()
645 		if (RQWB(rqos)->enable_state == WBT_STATE_OFF_DEFAULT)  in wbt_enable_default()
646 			RQWB(rqos)->enable_state = WBT_STATE_ON_DEFAULT;  in wbt_enable_default()
650 	/* Queue not registered? Maybe shutting down... */  in wbt_enable_default()
662 	 * We default to 2msec for non-rotational storage, and 75msec  in wbt_default_latency_nsec()
681 	return -1;  in wbt_data_dir()
686 	RQWB(rqos)->rq_depth.queue_depth = blk_queue_depth(rqos->q);  in wbt_queue_depth_changed()
693 	struct request_queue *q = rqos->q;  in wbt_exit()
695 	blk_stat_remove_callback(q, rwb->cb);  in wbt_exit()
696 	blk_stat_free_callback(rwb->cb);  in wbt_exit()
710 	if (rwb->enable_state == WBT_STATE_ON_DEFAULT) {  in wbt_disable_default()
711 		blk_stat_deactivate(rwb->cb);  in wbt_disable_default()
712 		rwb->enable_state = WBT_STATE_OFF_DEFAULT;  in wbt_disable_default()
723 	seq_printf(m, "%llu\n", rwb->cur_win_nsec);  in wbt_curr_win_nsec_show()
732 	seq_printf(m, "%d\n", rwb->enable_state);  in wbt_enabled_show()
740 	seq_printf(m, "%u\n", rqos->id);  in wbt_id_show()
752 			   atomic_read(&rwb->rq_wait[i].inflight));  in wbt_inflight_show()
761 	seq_printf(m, "%lu\n", rwb->min_lat_nsec);  in wbt_min_lat_nsec_show()
770 	seq_printf(m, "%u\n", rwb->unknown_cnt);  in wbt_unknown_cnt_show()
779 	seq_printf(m, "%u\n", rwb->wb_normal);  in wbt_normal_show()
788 	seq_printf(m, "%u\n", rwb->wb_background);  in wbt_background_show()
827 		return -ENOMEM;  in wbt_init()
829 	rwb->cb = blk_stat_alloc_callback(wb_timer_fn, wbt_data_dir, 2, rwb);  in wbt_init()
830 	if (!rwb->cb) {  in wbt_init()
832 		return -ENOMEM;  in wbt_init()
836 		rq_wait_init(&rwb->rq_wait[i]);  in wbt_init()
838 	rwb->rqos.id = RQ_QOS_WBT;  in wbt_init()
839 	rwb->rqos.ops = &wbt_rqos_ops;  in wbt_init()
840 	rwb->rqos.q = q;  in wbt_init()
841 	rwb->last_comp = rwb->last_issue = jiffies;  in wbt_init()
842 	rwb->win_nsec = RWB_WINDOW_NSEC;  in wbt_init()
843 	rwb->enable_state = WBT_STATE_ON_DEFAULT;  in wbt_init()
844 	rwb->wc = test_bit(QUEUE_FLAG_WC, &q->queue_flags);  in wbt_init()
845 	rwb->rq_depth.default_depth = RWB_DEF_DEPTH;  in wbt_init()
846 	rwb->min_lat_nsec = wbt_default_latency_nsec(q);  in wbt_init()
848 	wbt_queue_depth_changed(&rwb->rqos);  in wbt_init()
853 	ret = rq_qos_add(q, &rwb->rqos);  in wbt_init()
857 	blk_stat_add_callback(q, rwb->cb);  in wbt_init()
862 	blk_stat_free_callback(rwb->cb);  in wbt_init()