xref: /openbmc/linux/block/blk-rq-qos.c (revision 97e6f135) 
1 // SPDX-License-Identifier: GPL-2.0
2 
3 #include "blk-rq-qos.h"
4 
5 /*
6  * Increment 'v', if 'v' is below 'below'. Returns true if we succeeded,
7  * false if 'v' + 1 would be bigger than 'below'.
8  */
9 static bool atomic_inc_below(atomic_t *v, unsigned int below)
10 {
11 	unsigned int cur = atomic_read(v);
12 
13 	do {
14 		if (cur >= below)
15 			return false;
16 	} while (!atomic_try_cmpxchg(v, &cur, cur + 1));
17 
18 	return true;
19 }
20 
21 bool rq_wait_inc_below(struct rq_wait *rq_wait, unsigned int limit)
22 {
23 	return atomic_inc_below(&rq_wait->inflight, limit);
24 }
25 
26 void __rq_qos_cleanup(struct rq_qos *rqos, struct bio *bio)
27 {
28 	do {
29 		if (rqos->ops->cleanup)
30 			rqos->ops->cleanup(rqos, bio);
31 		rqos = rqos->next;
32 	} while (rqos);
33 }
34 
35 void __rq_qos_done(struct rq_qos *rqos, struct request *rq)
36 {
37 	do {
38 		if (rqos->ops->done)
39 			rqos->ops->done(rqos, rq);
40 		rqos = rqos->next;
41 	} while (rqos);
42 }
43 
44 void __rq_qos_issue(struct rq_qos *rqos, struct request *rq)
45 {
46 	do {
47 		if (rqos->ops->issue)
48 			rqos->ops->issue(rqos, rq);
49 		rqos = rqos->next;
50 	} while (rqos);
51 }
52 
53 void __rq_qos_requeue(struct rq_qos *rqos, struct request *rq)
54 {
55 	do {
56 		if (rqos->ops->requeue)
57 			rqos->ops->requeue(rqos, rq);
58 		rqos = rqos->next;
59 	} while (rqos);
60 }
61 
62 void __rq_qos_throttle(struct rq_qos *rqos, struct bio *bio)
63 {
64 	do {
65 		if (rqos->ops->throttle)
66 			rqos->ops->throttle(rqos, bio);
67 		rqos = rqos->next;
68 	} while (rqos);
69 }
70 
71 void __rq_qos_track(struct rq_qos *rqos, struct request *rq, struct bio *bio)
72 {
73 	do {
74 		if (rqos->ops->track)
75 			rqos->ops->track(rqos, rq, bio);
76 		rqos = rqos->next;
77 	} while (rqos);
78 }
79 
80 void __rq_qos_merge(struct rq_qos *rqos, struct request *rq, struct bio *bio)
81 {
82 	do {
83 		if (rqos->ops->merge)
84 			rqos->ops->merge(rqos, rq, bio);
85 		rqos = rqos->next;
86 	} while (rqos);
87 }
88 
89 void __rq_qos_done_bio(struct rq_qos *rqos, struct bio *bio)
90 {
91 	do {
92 		if (rqos->ops->done_bio)
93 			rqos->ops->done_bio(rqos, bio);
94 		rqos = rqos->next;
95 	} while (rqos);
96 }
97 
98 void __rq_qos_queue_depth_changed(struct rq_qos *rqos)
99 {
100 	do {
101 		if (rqos->ops->queue_depth_changed)
102 			rqos->ops->queue_depth_changed(rqos);
103 		rqos = rqos->next;
104 	} while (rqos);
105 }
106 
107 /*
108  * Return true, if we can't increase the depth further by scaling
109  */
110 bool rq_depth_calc_max_depth(struct rq_depth *rqd)
111 {
112 	unsigned int depth;
113 	bool ret = false;
114 
115 	/*
116 	 * For QD=1 devices, this is a special case. It's important for those
117 	 * to have one request ready when one completes, so force a depth of
118 	 * 2 for those devices. On the backend, it'll be a depth of 1 anyway,
119 	 * since the device can't have more than that in flight. If we're
120 	 * scaling down, then keep a setting of 1/1/1.
121 	 */
122 	if (rqd->queue_depth == 1) {
123 		if (rqd->scale_step > 0)
124 			rqd->max_depth = 1;
125 		else {
126 			rqd->max_depth = 2;
127 			ret = true;
128 		}
129 	} else {
130 		/*
131 		 * scale_step == 0 is our default state. If we have suffered
132 		 * latency spikes, step will be > 0, and we shrink the
133 		 * allowed write depths. If step is < 0, we're only doing
134 		 * writes, and we allow a temporarily higher depth to
135 		 * increase performance.
136 		 */
137 		depth = min_t(unsigned int, rqd->default_depth,
138 			      rqd->queue_depth);
139 		if (rqd->scale_step > 0)
140 			depth = 1 + ((depth - 1) >> min(31, rqd->scale_step));
141 		else if (rqd->scale_step < 0) {
142 			unsigned int maxd = 3 * rqd->queue_depth / 4;
143 
144 			depth = 1 + ((depth - 1) << -rqd->scale_step);
145 			if (depth > maxd) {
146 				depth = maxd;
147 				ret = true;
148 			}
149 		}
150 
151 		rqd->max_depth = depth;
152 	}
153 
154 	return ret;
155 }
156 
157 /* Returns true on success and false if scaling up wasn't possible */
158 bool rq_depth_scale_up(struct rq_depth *rqd)
159 {
160 	/*
161 	 * Hit max in previous round, stop here
162 	 */
163 	if (rqd->scaled_max)
164 		return false;
165 
166 	rqd->scale_step--;
167 
168 	rqd->scaled_max = rq_depth_calc_max_depth(rqd);
169 	return true;
170 }
171 
172 /*
173  * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we
174  * had a latency violation. Returns true on success and returns false if
175  * scaling down wasn't possible.
176  */
177 bool rq_depth_scale_down(struct rq_depth *rqd, bool hard_throttle)
178 {
179 	/*
180 	 * Stop scaling down when we've hit the limit. This also prevents
181 	 * ->scale_step from going to crazy values, if the device can't
182 	 * keep up.
183 	 */
184 	if (rqd->max_depth == 1)
185 		return false;
186 
187 	if (rqd->scale_step < 0 && hard_throttle)
188 		rqd->scale_step = 0;
189 	else
190 		rqd->scale_step++;
191 
192 	rqd->scaled_max = false;
193 	rq_depth_calc_max_depth(rqd);
194 	return true;
195 }
196 
197 struct rq_qos_wait_data {
198 	struct wait_queue_entry wq;
199 	struct task_struct *task;
200 	struct rq_wait *rqw;
201 	acquire_inflight_cb_t *cb;
202 	void *private_data;
203 	bool got_token;
204 };
205 
206 static int rq_qos_wake_function(struct wait_queue_entry *curr,
207 				unsigned int mode, int wake_flags, void *key)
208 {
209 	struct rq_qos_wait_data *data = container_of(curr,
210 						     struct rq_qos_wait_data,
211 						     wq);
212 
213 	/*
214 	 * If we fail to get a budget, return -1 to interrupt the wake up loop
215 	 * in __wake_up_common.
216 	 */
217 	if (!data->cb(data->rqw, data->private_data))
218 		return -1;
219 
220 	data->got_token = true;
221 	smp_wmb();
222 	list_del_init(&curr->entry);
223 	wake_up_process(data->task);
224 	return 1;
225 }
226 
227 /**
228  * rq_qos_wait - throttle on a rqw if we need to
229  * @rqw: rqw to throttle on
230  * @private_data: caller provided specific data
231  * @acquire_inflight_cb: inc the rqw->inflight counter if we can
232  * @cleanup_cb: the callback to cleanup in case we race with a waker
233  *
234  * This provides a uniform place for the rq_qos users to do their throttling.
235  * Since you can end up with a lot of things sleeping at once, this manages the
236  * waking up based on the resources available.  The acquire_inflight_cb should
237  * inc the rqw->inflight if we have the ability to do so, or return false if not
238  * and then we will sleep until the room becomes available.
239  *
240  * cleanup_cb is in case that we race with a waker and need to cleanup the
241  * inflight count accordingly.
242  */
243 void rq_qos_wait(struct rq_wait *rqw, void *private_data,
244 		 acquire_inflight_cb_t *acquire_inflight_cb,
245 		 cleanup_cb_t *cleanup_cb)
246 {
247 	struct rq_qos_wait_data data = {
248 		.wq = {
249 			.func	= rq_qos_wake_function,
250 			.entry	= LIST_HEAD_INIT(data.wq.entry),
251 		},
252 		.task = current,
253 		.rqw = rqw,
254 		.cb = acquire_inflight_cb,
255 		.private_data = private_data,
256 	};
257 	bool has_sleeper;
258 
259 	has_sleeper = wq_has_sleeper(&rqw->wait);
260 	if (!has_sleeper && acquire_inflight_cb(rqw, private_data))
261 		return;
262 
263 	has_sleeper = !prepare_to_wait_exclusive(&rqw->wait, &data.wq,
264 						 TASK_UNINTERRUPTIBLE);
265 	do {
266 		/* The memory barrier in set_task_state saves us here. */
267 		if (data.got_token)
268 			break;
269 		if (!has_sleeper && acquire_inflight_cb(rqw, private_data)) {
270 			finish_wait(&rqw->wait, &data.wq);
271 
272 			/*
273 			 * We raced with wbt_wake_function() getting a token,
274 			 * which means we now have two. Put our local token
275 			 * and wake anyone else potentially waiting for one.
276 			 */
277 			smp_rmb();
278 			if (data.got_token)
279 				cleanup_cb(rqw, private_data);
280 			break;
281 		}
282 		io_schedule();
283 		has_sleeper = true;
284 		set_current_state(TASK_UNINTERRUPTIBLE);
285 	} while (1);
286 	finish_wait(&rqw->wait, &data.wq);
287 }
288 
289 void rq_qos_exit(struct request_queue *q)
290 {
291 	mutex_lock(&q->rq_qos_mutex);
292 	while (q->rq_qos) {
293 		struct rq_qos *rqos = q->rq_qos;
294 		q->rq_qos = rqos->next;
295 		rqos->ops->exit(rqos);
296 	}
297 	mutex_unlock(&q->rq_qos_mutex);
298 }
299 
300 int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id,
301 		const struct rq_qos_ops *ops)
302 {
303 	struct request_queue *q = disk->queue;
304 
305 	lockdep_assert_held(&q->rq_qos_mutex);
306 
307 	rqos->disk = disk;
308 	rqos->id = id;
309 	rqos->ops = ops;
310 
311 	/*
312 	 * No IO can be in-flight when adding rqos, so freeze queue, which
313 	 * is fine since we only support rq_qos for blk-mq queue.
314 	 */
315 	blk_mq_freeze_queue(q);
316 
317 	if (rq_qos_id(q, rqos->id))
318 		goto ebusy;
319 	rqos->next = q->rq_qos;
320 	q->rq_qos = rqos;
321 
322 	blk_mq_unfreeze_queue(q);
323 
324 	if (rqos->ops->debugfs_attrs) {
325 		mutex_lock(&q->debugfs_mutex);
326 		blk_mq_debugfs_register_rqos(rqos);
327 		mutex_unlock(&q->debugfs_mutex);
328 	}
329 
330 	return 0;
331 ebusy:
332 	blk_mq_unfreeze_queue(q);
333 	return -EBUSY;
334 }
335 
336 void rq_qos_del(struct rq_qos *rqos)
337 {
338 	struct request_queue *q = rqos->disk->queue;
339 	struct rq_qos **cur;
340 
341 	lockdep_assert_held(&q->rq_qos_mutex);
342 
343 	blk_mq_freeze_queue(q);
344 	for (cur = &q->rq_qos; *cur; cur = &(*cur)->next) {
345 		if (*cur == rqos) {
346 			*cur = rqos->next;
347 			break;
348 		}
349 	}
350 	blk_mq_unfreeze_queue(q);
351 
352 	mutex_lock(&q->debugfs_mutex);
353 	blk_mq_debugfs_unregister_rqos(rqos);
354 	mutex_unlock(&q->debugfs_mutex);
355 }
356