xref: /openbmc/linux/block/blk-rq-qos.c (revision 25a3d6ba) 
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 	for (;;) {
14 		unsigned int old;
15 
16 		if (cur >= below)
17 			return false;
18 		old = atomic_cmpxchg(v, cur, cur + 1);
19 		if (old == cur)
20 			break;
21 		cur = old;
22 	}
23 
24 	return true;
25 }
26 
27 bool rq_wait_inc_below(struct rq_wait *rq_wait, unsigned int limit)
28 {
29 	return atomic_inc_below(&rq_wait->inflight, limit);
30 }
31 
32 void __rq_qos_cleanup(struct rq_qos *rqos, struct bio *bio)
33 {
34 	do {
35 		if (rqos->ops->cleanup)
36 			rqos->ops->cleanup(rqos, bio);
37 		rqos = rqos->next;
38 	} while (rqos);
39 }
40 
41 void __rq_qos_done(struct rq_qos *rqos, struct request *rq)
42 {
43 	do {
44 		if (rqos->ops->done)
45 			rqos->ops->done(rqos, rq);
46 		rqos = rqos->next;
47 	} while (rqos);
48 }
49 
50 void __rq_qos_issue(struct rq_qos *rqos, struct request *rq)
51 {
52 	do {
53 		if (rqos->ops->issue)
54 			rqos->ops->issue(rqos, rq);
55 		rqos = rqos->next;
56 	} while (rqos);
57 }
58 
59 void __rq_qos_requeue(struct rq_qos *rqos, struct request *rq)
60 {
61 	do {
62 		if (rqos->ops->requeue)
63 			rqos->ops->requeue(rqos, rq);
64 		rqos = rqos->next;
65 	} while (rqos);
66 }
67 
68 void __rq_qos_throttle(struct rq_qos *rqos, struct bio *bio)
69 {
70 	do {
71 		if (rqos->ops->throttle)
72 			rqos->ops->throttle(rqos, bio);
73 		rqos = rqos->next;
74 	} while (rqos);
75 }
76 
77 void __rq_qos_track(struct rq_qos *rqos, struct request *rq, struct bio *bio)
78 {
79 	do {
80 		if (rqos->ops->track)
81 			rqos->ops->track(rqos, rq, bio);
82 		rqos = rqos->next;
83 	} while (rqos);
84 }
85 
86 void __rq_qos_done_bio(struct rq_qos *rqos, struct bio *bio)
87 {
88 	do {
89 		if (rqos->ops->done_bio)
90 			rqos->ops->done_bio(rqos, bio);
91 		rqos = rqos->next;
92 	} while (rqos);
93 }
94 
95 /*
96  * Return true, if we can't increase the depth further by scaling
97  */
98 bool rq_depth_calc_max_depth(struct rq_depth *rqd)
99 {
100 	unsigned int depth;
101 	bool ret = false;
102 
103 	/*
104 	 * For QD=1 devices, this is a special case. It's important for those
105 	 * to have one request ready when one completes, so force a depth of
106 	 * 2 for those devices. On the backend, it'll be a depth of 1 anyway,
107 	 * since the device can't have more than that in flight. If we're
108 	 * scaling down, then keep a setting of 1/1/1.
109 	 */
110 	if (rqd->queue_depth == 1) {
111 		if (rqd->scale_step > 0)
112 			rqd->max_depth = 1;
113 		else {
114 			rqd->max_depth = 2;
115 			ret = true;
116 		}
117 	} else {
118 		/*
119 		 * scale_step == 0 is our default state. If we have suffered
120 		 * latency spikes, step will be > 0, and we shrink the
121 		 * allowed write depths. If step is < 0, we're only doing
122 		 * writes, and we allow a temporarily higher depth to
123 		 * increase performance.
124 		 */
125 		depth = min_t(unsigned int, rqd->default_depth,
126 			      rqd->queue_depth);
127 		if (rqd->scale_step > 0)
128 			depth = 1 + ((depth - 1) >> min(31, rqd->scale_step));
129 		else if (rqd->scale_step < 0) {
130 			unsigned int maxd = 3 * rqd->queue_depth / 4;
131 
132 			depth = 1 + ((depth - 1) << -rqd->scale_step);
133 			if (depth > maxd) {
134 				depth = maxd;
135 				ret = true;
136 			}
137 		}
138 
139 		rqd->max_depth = depth;
140 	}
141 
142 	return ret;
143 }
144 
145 void rq_depth_scale_up(struct rq_depth *rqd)
146 {
147 	/*
148 	 * Hit max in previous round, stop here
149 	 */
150 	if (rqd->scaled_max)
151 		return;
152 
153 	rqd->scale_step--;
154 
155 	rqd->scaled_max = rq_depth_calc_max_depth(rqd);
156 }
157 
158 /*
159  * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we
160  * had a latency violation.
161  */
162 void rq_depth_scale_down(struct rq_depth *rqd, bool hard_throttle)
163 {
164 	/*
165 	 * Stop scaling down when we've hit the limit. This also prevents
166 	 * ->scale_step from going to crazy values, if the device can't
167 	 * keep up.
168 	 */
169 	if (rqd->max_depth == 1)
170 		return;
171 
172 	if (rqd->scale_step < 0 && hard_throttle)
173 		rqd->scale_step = 0;
174 	else
175 		rqd->scale_step++;
176 
177 	rqd->scaled_max = false;
178 	rq_depth_calc_max_depth(rqd);
179 }
180 
181 struct rq_qos_wait_data {
182 	struct wait_queue_entry wq;
183 	struct task_struct *task;
184 	struct rq_wait *rqw;
185 	acquire_inflight_cb_t *cb;
186 	void *private_data;
187 	bool got_token;
188 };
189 
190 static int rq_qos_wake_function(struct wait_queue_entry *curr,
191 				unsigned int mode, int wake_flags, void *key)
192 {
193 	struct rq_qos_wait_data *data = container_of(curr,
194 						     struct rq_qos_wait_data,
195 						     wq);
196 
197 	/*
198 	 * If we fail to get a budget, return -1 to interrupt the wake up loop
199 	 * in __wake_up_common.
200 	 */
201 	if (!data->cb(data->rqw, data->private_data))
202 		return -1;
203 
204 	data->got_token = true;
205 	smp_wmb();
206 	list_del_init(&curr->entry);
207 	wake_up_process(data->task);
208 	return 1;
209 }
210 
211 /**
212  * rq_qos_wait - throttle on a rqw if we need to
213  * @rqw: rqw to throttle on
214  * @private_data: caller provided specific data
215  * @acquire_inflight_cb: inc the rqw->inflight counter if we can
216  * @cleanup_cb: the callback to cleanup in case we race with a waker
217  *
218  * This provides a uniform place for the rq_qos users to do their throttling.
219  * Since you can end up with a lot of things sleeping at once, this manages the
220  * waking up based on the resources available.  The acquire_inflight_cb should
221  * inc the rqw->inflight if we have the ability to do so, or return false if not
222  * and then we will sleep until the room becomes available.
223  *
224  * cleanup_cb is in case that we race with a waker and need to cleanup the
225  * inflight count accordingly.
226  */
227 void rq_qos_wait(struct rq_wait *rqw, void *private_data,
228 		 acquire_inflight_cb_t *acquire_inflight_cb,
229 		 cleanup_cb_t *cleanup_cb)
230 {
231 	struct rq_qos_wait_data data = {
232 		.wq = {
233 			.func	= rq_qos_wake_function,
234 			.entry	= LIST_HEAD_INIT(data.wq.entry),
235 		},
236 		.task = current,
237 		.rqw = rqw,
238 		.cb = acquire_inflight_cb,
239 		.private_data = private_data,
240 	};
241 	bool has_sleeper;
242 
243 	has_sleeper = wq_has_sleeper(&rqw->wait);
244 	if (!has_sleeper && acquire_inflight_cb(rqw, private_data))
245 		return;
246 
247 	prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE);
248 	has_sleeper = !wq_has_single_sleeper(&rqw->wait);
249 	do {
250 		/* The memory barrier in set_task_state saves us here. */
251 		if (data.got_token)
252 			break;
253 		if (!has_sleeper && acquire_inflight_cb(rqw, private_data)) {
254 			finish_wait(&rqw->wait, &data.wq);
255 
256 			/*
257 			 * We raced with wbt_wake_function() getting a token,
258 			 * which means we now have two. Put our local token
259 			 * and wake anyone else potentially waiting for one.
260 			 */
261 			smp_rmb();
262 			if (data.got_token)
263 				cleanup_cb(rqw, private_data);
264 			break;
265 		}
266 		io_schedule();
267 		has_sleeper = true;
268 		set_current_state(TASK_UNINTERRUPTIBLE);
269 	} while (1);
270 	finish_wait(&rqw->wait, &data.wq);
271 }
272 
273 void rq_qos_exit(struct request_queue *q)
274 {
275 	blk_mq_debugfs_unregister_queue_rqos(q);
276 
277 	while (q->rq_qos) {
278 		struct rq_qos *rqos = q->rq_qos;
279 		q->rq_qos = rqos->next;
280 		rqos->ops->exit(rqos);
281 	}
282 }
283