xref: /openbmc/linux/block/blk-rq-qos.c (revision f9a82c48) 
1 #include "blk-rq-qos.h"
2 
3 /*
4  * Increment 'v', if 'v' is below 'below'. Returns true if we succeeded,
5  * false if 'v' + 1 would be bigger than 'below'.
6  */
7 static bool atomic_inc_below(atomic_t *v, unsigned int below)
8 {
9 	unsigned int cur = atomic_read(v);
10 
11 	for (;;) {
12 		unsigned int old;
13 
14 		if (cur >= below)
15 			return false;
16 		old = atomic_cmpxchg(v, cur, cur + 1);
17 		if (old == cur)
18 			break;
19 		cur = old;
20 	}
21 
22 	return true;
23 }
24 
25 bool rq_wait_inc_below(struct rq_wait *rq_wait, unsigned int limit)
26 {
27 	return atomic_inc_below(&rq_wait->inflight, limit);
28 }
29 
30 void __rq_qos_cleanup(struct rq_qos *rqos, struct bio *bio)
31 {
32 	do {
33 		if (rqos->ops->cleanup)
34 			rqos->ops->cleanup(rqos, bio);
35 		rqos = rqos->next;
36 	} while (rqos);
37 }
38 
39 void __rq_qos_done(struct rq_qos *rqos, struct request *rq)
40 {
41 	do {
42 		if (rqos->ops->done)
43 			rqos->ops->done(rqos, rq);
44 		rqos = rqos->next;
45 	} while (rqos);
46 }
47 
48 void __rq_qos_issue(struct rq_qos *rqos, struct request *rq)
49 {
50 	do {
51 		if (rqos->ops->issue)
52 			rqos->ops->issue(rqos, rq);
53 		rqos = rqos->next;
54 	} while (rqos);
55 }
56 
57 void __rq_qos_requeue(struct rq_qos *rqos, struct request *rq)
58 {
59 	do {
60 		if (rqos->ops->requeue)
61 			rqos->ops->requeue(rqos, rq);
62 		rqos = rqos->next;
63 	} while (rqos);
64 }
65 
66 void __rq_qos_throttle(struct rq_qos *rqos, struct bio *bio)
67 {
68 	do {
69 		if (rqos->ops->throttle)
70 			rqos->ops->throttle(rqos, bio);
71 		rqos = rqos->next;
72 	} while (rqos);
73 }
74 
75 void __rq_qos_track(struct rq_qos *rqos, struct request *rq, struct bio *bio)
76 {
77 	do {
78 		if (rqos->ops->track)
79 			rqos->ops->track(rqos, rq, bio);
80 		rqos = rqos->next;
81 	} while (rqos);
82 }
83 
84 void __rq_qos_done_bio(struct rq_qos *rqos, struct bio *bio)
85 {
86 	do {
87 		if (rqos->ops->done_bio)
88 			rqos->ops->done_bio(rqos, bio);
89 		rqos = rqos->next;
90 	} while (rqos);
91 }
92 
93 /*
94  * Return true, if we can't increase the depth further by scaling
95  */
96 bool rq_depth_calc_max_depth(struct rq_depth *rqd)
97 {
98 	unsigned int depth;
99 	bool ret = false;
100 
101 	/*
102 	 * For QD=1 devices, this is a special case. It's important for those
103 	 * to have one request ready when one completes, so force a depth of
104 	 * 2 for those devices. On the backend, it'll be a depth of 1 anyway,
105 	 * since the device can't have more than that in flight. If we're
106 	 * scaling down, then keep a setting of 1/1/1.
107 	 */
108 	if (rqd->queue_depth == 1) {
109 		if (rqd->scale_step > 0)
110 			rqd->max_depth = 1;
111 		else {
112 			rqd->max_depth = 2;
113 			ret = true;
114 		}
115 	} else {
116 		/*
117 		 * scale_step == 0 is our default state. If we have suffered
118 		 * latency spikes, step will be > 0, and we shrink the
119 		 * allowed write depths. If step is < 0, we're only doing
120 		 * writes, and we allow a temporarily higher depth to
121 		 * increase performance.
122 		 */
123 		depth = min_t(unsigned int, rqd->default_depth,
124 			      rqd->queue_depth);
125 		if (rqd->scale_step > 0)
126 			depth = 1 + ((depth - 1) >> min(31, rqd->scale_step));
127 		else if (rqd->scale_step < 0) {
128 			unsigned int maxd = 3 * rqd->queue_depth / 4;
129 
130 			depth = 1 + ((depth - 1) << -rqd->scale_step);
131 			if (depth > maxd) {
132 				depth = maxd;
133 				ret = true;
134 			}
135 		}
136 
137 		rqd->max_depth = depth;
138 	}
139 
140 	return ret;
141 }
142 
143 void rq_depth_scale_up(struct rq_depth *rqd)
144 {
145 	/*
146 	 * Hit max in previous round, stop here
147 	 */
148 	if (rqd->scaled_max)
149 		return;
150 
151 	rqd->scale_step--;
152 
153 	rqd->scaled_max = rq_depth_calc_max_depth(rqd);
154 }
155 
156 /*
157  * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we
158  * had a latency violation.
159  */
160 void rq_depth_scale_down(struct rq_depth *rqd, bool hard_throttle)
161 {
162 	/*
163 	 * Stop scaling down when we've hit the limit. This also prevents
164 	 * ->scale_step from going to crazy values, if the device can't
165 	 * keep up.
166 	 */
167 	if (rqd->max_depth == 1)
168 		return;
169 
170 	if (rqd->scale_step < 0 && hard_throttle)
171 		rqd->scale_step = 0;
172 	else
173 		rqd->scale_step++;
174 
175 	rqd->scaled_max = false;
176 	rq_depth_calc_max_depth(rqd);
177 }
178 
179 struct rq_qos_wait_data {
180 	struct wait_queue_entry wq;
181 	struct task_struct *task;
182 	struct rq_wait *rqw;
183 	acquire_inflight_cb_t *cb;
184 	void *private_data;
185 	bool got_token;
186 };
187 
188 static int rq_qos_wake_function(struct wait_queue_entry *curr,
189 				unsigned int mode, int wake_flags, void *key)
190 {
191 	struct rq_qos_wait_data *data = container_of(curr,
192 						     struct rq_qos_wait_data,
193 						     wq);
194 
195 	/*
196 	 * If we fail to get a budget, return -1 to interrupt the wake up loop
197 	 * in __wake_up_common.
198 	 */
199 	if (!data->cb(data->rqw, data->private_data))
200 		return -1;
201 
202 	data->got_token = true;
203 	list_del_init(&curr->entry);
204 	wake_up_process(data->task);
205 	return 1;
206 }
207 
208 /**
209  * rq_qos_wait - throttle on a rqw if we need to
210  * @private_data - caller provided specific data
211  * @acquire_inflight_cb - inc the rqw->inflight counter if we can
212  * @cleanup_cb - the callback to cleanup in case we race with a waker
213  *
214  * This provides a uniform place for the rq_qos users to do their throttling.
215  * Since you can end up with a lot of things sleeping at once, this manages the
216  * waking up based on the resources available.  The acquire_inflight_cb should
217  * inc the rqw->inflight if we have the ability to do so, or return false if not
218  * and then we will sleep until the room becomes available.
219  *
220  * cleanup_cb is in case that we race with a waker and need to cleanup the
221  * inflight count accordingly.
222  */
223 void rq_qos_wait(struct rq_wait *rqw, void *private_data,
224 		 acquire_inflight_cb_t *acquire_inflight_cb,
225 		 cleanup_cb_t *cleanup_cb)
226 {
227 	struct rq_qos_wait_data data = {
228 		.wq = {
229 			.func	= rq_qos_wake_function,
230 			.entry	= LIST_HEAD_INIT(data.wq.entry),
231 		},
232 		.task = current,
233 		.rqw = rqw,
234 		.cb = acquire_inflight_cb,
235 		.private_data = private_data,
236 	};
237 	bool has_sleeper;
238 
239 	has_sleeper = wq_has_sleeper(&rqw->wait);
240 	if (!has_sleeper && acquire_inflight_cb(rqw, private_data))
241 		return;
242 
243 	prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE);
244 	do {
245 		if (data.got_token)
246 			break;
247 		if (!has_sleeper && acquire_inflight_cb(rqw, private_data)) {
248 			finish_wait(&rqw->wait, &data.wq);
249 
250 			/*
251 			 * We raced with wbt_wake_function() getting a token,
252 			 * which means we now have two. Put our local token
253 			 * and wake anyone else potentially waiting for one.
254 			 */
255 			if (data.got_token)
256 				cleanup_cb(rqw, private_data);
257 			break;
258 		}
259 		io_schedule();
260 		has_sleeper = false;
261 	} while (1);
262 	finish_wait(&rqw->wait, &data.wq);
263 }
264 
265 void rq_qos_exit(struct request_queue *q)
266 {
267 	blk_mq_debugfs_unregister_queue_rqos(q);
268 
269 	while (q->rq_qos) {
270 		struct rq_qos *rqos = q->rq_qos;
271 		q->rq_qos = rqos->next;
272 		rqos->ops->exit(rqos);
273 	}
274 }
275