root/block/blk-rq-qos.c

DEFINITIONS

1. atomic_inc_below
2. rq_wait_inc_below
3. __rq_qos_cleanup
4. __rq_qos_done
5. __rq_qos_issue
6. __rq_qos_requeue
7. __rq_qos_throttle
8. __rq_qos_track
9. __rq_qos_merge
10. __rq_qos_done_bio
11. __rq_qos_queue_depth_changed
12. rq_depth_calc_max_depth
13. rq_depth_scale_up
14. rq_depth_scale_down
15. rq_qos_wake_function
16. rq_qos_wait
17. rq_qos_exit

   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 }