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Linux/block/blk-rq-qos.c

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  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_merge(struct rq_qos *rqos, struct request *rq, struct bio *bio)
 87 {
 88         do {
 89                 if (rqos->ops->merge)
 90                         rqos->ops->merge(rqos, rq, bio);
 91                 rqos = rqos->next;
 92         } while (rqos);
 93 }
 94 
 95 void __rq_qos_done_bio(struct rq_qos *rqos, struct bio *bio)
 96 {
 97         do {
 98                 if (rqos->ops->done_bio)
 99                         rqos->ops->done_bio(rqos, bio);
100                 rqos = rqos->next;
101         } while (rqos);
102 }
103 
104 void __rq_qos_queue_depth_changed(struct rq_qos *rqos)
105 {
106         do {
107                 if (rqos->ops->queue_depth_changed)
108                         rqos->ops->queue_depth_changed(rqos);
109                 rqos = rqos->next;
110         } while (rqos);
111 }
112 
113 /*
114  * Return true, if we can't increase the depth further by scaling
115  */
116 bool rq_depth_calc_max_depth(struct rq_depth *rqd)
117 {
118         unsigned int depth;
119         bool ret = false;
120 
121         /*
122          * For QD=1 devices, this is a special case. It's important for those
123          * to have one request ready when one completes, so force a depth of
124          * 2 for those devices. On the backend, it'll be a depth of 1 anyway,
125          * since the device can't have more than that in flight. If we're
126          * scaling down, then keep a setting of 1/1/1.
127          */
128         if (rqd->queue_depth == 1) {
129                 if (rqd->scale_step > 0)
130                         rqd->max_depth = 1;
131                 else {
132                         rqd->max_depth = 2;
133                         ret = true;
134                 }
135         } else {
136                 /*
137                  * scale_step == 0 is our default state. If we have suffered
138                  * latency spikes, step will be > 0, and we shrink the
139                  * allowed write depths. If step is < 0, we're only doing
140                  * writes, and we allow a temporarily higher depth to
141                  * increase performance.
142                  */
143                 depth = min_t(unsigned int, rqd->default_depth,
144                               rqd->queue_depth);
145                 if (rqd->scale_step > 0)
146                         depth = 1 + ((depth - 1) >> min(31, rqd->scale_step));
147                 else if (rqd->scale_step < 0) {
148                         unsigned int maxd = 3 * rqd->queue_depth / 4;
149 
150                         depth = 1 + ((depth - 1) << -rqd->scale_step);
151                         if (depth > maxd) {
152                                 depth = maxd;
153                                 ret = true;
154                         }
155                 }
156 
157                 rqd->max_depth = depth;
158         }
159 
160         return ret;
161 }
162 
163 /* Returns true on success and false if scaling up wasn't possible */
164 bool rq_depth_scale_up(struct rq_depth *rqd)
165 {
166         /*
167          * Hit max in previous round, stop here
168          */
169         if (rqd->scaled_max)
170                 return false;
171 
172         rqd->scale_step--;
173 
174         rqd->scaled_max = rq_depth_calc_max_depth(rqd);
175         return true;
176 }
177 
178 /*
179  * Scale rwb down. If 'hard_throttle' is set, do it quicker, since we
180  * had a latency violation. Returns true on success and returns false if
181  * scaling down wasn't possible.
182  */
183 bool rq_depth_scale_down(struct rq_depth *rqd, bool hard_throttle)
184 {
185         /*
186          * Stop scaling down when we've hit the limit. This also prevents
187          * ->scale_step from going to crazy values, if the device can't
188          * keep up.
189          */
190         if (rqd->max_depth == 1)
191                 return false;
192 
193         if (rqd->scale_step < 0 && hard_throttle)
194                 rqd->scale_step = 0;
195         else
196                 rqd->scale_step++;
197 
198         rqd->scaled_max = false;
199         rq_depth_calc_max_depth(rqd);
200         return true;
201 }
202 
203 struct rq_qos_wait_data {
204         struct wait_queue_entry wq;
205         struct task_struct *task;
206         struct rq_wait *rqw;
207         acquire_inflight_cb_t *cb;
208         void *private_data;
209         bool got_token;
210 };
211 
212 static int rq_qos_wake_function(struct wait_queue_entry *curr,
213                                 unsigned int mode, int wake_flags, void *key)
214 {
215         struct rq_qos_wait_data *data = container_of(curr,
216                                                      struct rq_qos_wait_data,
217                                                      wq);
218 
219         /*
220          * If we fail to get a budget, return -1 to interrupt the wake up loop
221          * in __wake_up_common.
222          */
223         if (!data->cb(data->rqw, data->private_data))
224                 return -1;
225 
226         data->got_token = true;
227         smp_wmb();
228         list_del_init(&curr->entry);
229         wake_up_process(data->task);
230         return 1;
231 }
232 
233 /**
234  * rq_qos_wait - throttle on a rqw if we need to
235  * @rqw: rqw to throttle on
236  * @private_data: caller provided specific data
237  * @acquire_inflight_cb: inc the rqw->inflight counter if we can
238  * @cleanup_cb: the callback to cleanup in case we race with a waker
239  *
240  * This provides a uniform place for the rq_qos users to do their throttling.
241  * Since you can end up with a lot of things sleeping at once, this manages the
242  * waking up based on the resources available.  The acquire_inflight_cb should
243  * inc the rqw->inflight if we have the ability to do so, or return false if not
244  * and then we will sleep until the room becomes available.
245  *
246  * cleanup_cb is in case that we race with a waker and need to cleanup the
247  * inflight count accordingly.
248  */
249 void rq_qos_wait(struct rq_wait *rqw, void *private_data,
250                  acquire_inflight_cb_t *acquire_inflight_cb,
251                  cleanup_cb_t *cleanup_cb)
252 {
253         struct rq_qos_wait_data data = {
254                 .wq = {
255                         .func   = rq_qos_wake_function,
256                         .entry  = LIST_HEAD_INIT(data.wq.entry),
257                 },
258                 .task = current,
259                 .rqw = rqw,
260                 .cb = acquire_inflight_cb,
261                 .private_data = private_data,
262         };
263         bool has_sleeper;
264 
265         has_sleeper = wq_has_sleeper(&rqw->wait);
266         if (!has_sleeper && acquire_inflight_cb(rqw, private_data))
267                 return;
268 
269         prepare_to_wait_exclusive(&rqw->wait, &data.wq, TASK_UNINTERRUPTIBLE);
270         has_sleeper = !wq_has_single_sleeper(&rqw->wait);
271         do {
272                 /* The memory barrier in set_task_state saves us here. */
273                 if (data.got_token)
274                         break;
275                 if (!has_sleeper && acquire_inflight_cb(rqw, private_data)) {
276                         finish_wait(&rqw->wait, &data.wq);
277 
278                         /*
279                          * We raced with wbt_wake_function() getting a token,
280                          * which means we now have two. Put our local token
281                          * and wake anyone else potentially waiting for one.
282                          */
283                         smp_rmb();
284                         if (data.got_token)
285                                 cleanup_cb(rqw, private_data);
286                         break;
287                 }
288                 io_schedule();
289                 has_sleeper = true;
290                 set_current_state(TASK_UNINTERRUPTIBLE);
291         } while (1);
292         finish_wait(&rqw->wait, &data.wq);
293 }
294 
295 void rq_qos_exit(struct request_queue *q)
296 {
297         blk_mq_debugfs_unregister_queue_rqos(q);
298 
299         while (q->rq_qos) {
300                 struct rq_qos *rqos = q->rq_qos;
301                 q->rq_qos = rqos->next;
302                 rqos->ops->exit(rqos);
303         }
304 }
305 

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