Loading...
Note: File does not exist in v3.1.
1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Pressure stall information for CPU, memory and IO
4 *
5 * Copyright (c) 2018 Facebook, Inc.
6 * Author: Johannes Weiner <hannes@cmpxchg.org>
7 *
8 * Polling support by Suren Baghdasaryan <surenb@google.com>
9 * Copyright (c) 2018 Google, Inc.
10 *
11 * When CPU, memory and IO are contended, tasks experience delays that
12 * reduce throughput and introduce latencies into the workload. Memory
13 * and IO contention, in addition, can cause a full loss of forward
14 * progress in which the CPU goes idle.
15 *
16 * This code aggregates individual task delays into resource pressure
17 * metrics that indicate problems with both workload health and
18 * resource utilization.
19 *
20 * Model
21 *
22 * The time in which a task can execute on a CPU is our baseline for
23 * productivity. Pressure expresses the amount of time in which this
24 * potential cannot be realized due to resource contention.
25 *
26 * This concept of productivity has two components: the workload and
27 * the CPU. To measure the impact of pressure on both, we define two
28 * contention states for a resource: SOME and FULL.
29 *
30 * In the SOME state of a given resource, one or more tasks are
31 * delayed on that resource. This affects the workload's ability to
32 * perform work, but the CPU may still be executing other tasks.
33 *
34 * In the FULL state of a given resource, all non-idle tasks are
35 * delayed on that resource such that nobody is advancing and the CPU
36 * goes idle. This leaves both workload and CPU unproductive.
37 *
38 * SOME = nr_delayed_tasks != 0
39 * FULL = nr_delayed_tasks != 0 && nr_productive_tasks == 0
40 *
41 * What it means for a task to be productive is defined differently
42 * for each resource. For IO, productive means a running task. For
43 * memory, productive means a running task that isn't a reclaimer. For
44 * CPU, productive means an oncpu task.
45 *
46 * Naturally, the FULL state doesn't exist for the CPU resource at the
47 * system level, but exist at the cgroup level. At the cgroup level,
48 * FULL means all non-idle tasks in the cgroup are delayed on the CPU
49 * resource which is being used by others outside of the cgroup or
50 * throttled by the cgroup cpu.max configuration.
51 *
52 * The percentage of wallclock time spent in those compound stall
53 * states gives pressure numbers between 0 and 100 for each resource,
54 * where the SOME percentage indicates workload slowdowns and the FULL
55 * percentage indicates reduced CPU utilization:
56 *
57 * %SOME = time(SOME) / period
58 * %FULL = time(FULL) / period
59 *
60 * Multiple CPUs
61 *
62 * The more tasks and available CPUs there are, the more work can be
63 * performed concurrently. This means that the potential that can go
64 * unrealized due to resource contention *also* scales with non-idle
65 * tasks and CPUs.
66 *
67 * Consider a scenario where 257 number crunching tasks are trying to
68 * run concurrently on 256 CPUs. If we simply aggregated the task
69 * states, we would have to conclude a CPU SOME pressure number of
70 * 100%, since *somebody* is waiting on a runqueue at all
71 * times. However, that is clearly not the amount of contention the
72 * workload is experiencing: only one out of 256 possible execution
73 * threads will be contended at any given time, or about 0.4%.
74 *
75 * Conversely, consider a scenario of 4 tasks and 4 CPUs where at any
76 * given time *one* of the tasks is delayed due to a lack of memory.
77 * Again, looking purely at the task state would yield a memory FULL
78 * pressure number of 0%, since *somebody* is always making forward
79 * progress. But again this wouldn't capture the amount of execution
80 * potential lost, which is 1 out of 4 CPUs, or 25%.
81 *
82 * To calculate wasted potential (pressure) with multiple processors,
83 * we have to base our calculation on the number of non-idle tasks in
84 * conjunction with the number of available CPUs, which is the number
85 * of potential execution threads. SOME becomes then the proportion of
86 * delayed tasks to possible threads, and FULL is the share of possible
87 * threads that are unproductive due to delays:
88 *
89 * threads = min(nr_nonidle_tasks, nr_cpus)
90 * SOME = min(nr_delayed_tasks / threads, 1)
91 * FULL = (threads - min(nr_productive_tasks, threads)) / threads
92 *
93 * For the 257 number crunchers on 256 CPUs, this yields:
94 *
95 * threads = min(257, 256)
96 * SOME = min(1 / 256, 1) = 0.4%
97 * FULL = (256 - min(256, 256)) / 256 = 0%
98 *
99 * For the 1 out of 4 memory-delayed tasks, this yields:
100 *
101 * threads = min(4, 4)
102 * SOME = min(1 / 4, 1) = 25%
103 * FULL = (4 - min(3, 4)) / 4 = 25%
104 *
105 * [ Substitute nr_cpus with 1, and you can see that it's a natural
106 * extension of the single-CPU model. ]
107 *
108 * Implementation
109 *
110 * To assess the precise time spent in each such state, we would have
111 * to freeze the system on task changes and start/stop the state
112 * clocks accordingly. Obviously that doesn't scale in practice.
113 *
114 * Because the scheduler aims to distribute the compute load evenly
115 * among the available CPUs, we can track task state locally to each
116 * CPU and, at much lower frequency, extrapolate the global state for
117 * the cumulative stall times and the running averages.
118 *
119 * For each runqueue, we track:
120 *
121 * tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0)
122 * tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_productive_tasks[cpu])
123 * tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0)
124 *
125 * and then periodically aggregate:
126 *
127 * tNONIDLE = sum(tNONIDLE[i])
128 *
129 * tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE
130 * tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE
131 *
132 * %SOME = tSOME / period
133 * %FULL = tFULL / period
134 *
135 * This gives us an approximation of pressure that is practical
136 * cost-wise, yet way more sensitive and accurate than periodic
137 * sampling of the aggregate task states would be.
138 */
139
140static int psi_bug __read_mostly;
141
142DEFINE_STATIC_KEY_FALSE(psi_disabled);
143DEFINE_STATIC_KEY_TRUE(psi_cgroups_enabled);
144
145#ifdef CONFIG_PSI_DEFAULT_DISABLED
146static bool psi_enable;
147#else
148static bool psi_enable = true;
149#endif
150static int __init setup_psi(char *str)
151{
152 return kstrtobool(str, &psi_enable) == 0;
153}
154__setup("psi=", setup_psi);
155
156/* Running averages - we need to be higher-res than loadavg */
157#define PSI_FREQ (2*HZ+1) /* 2 sec intervals */
158#define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */
159#define EXP_60s 1981 /* 1/exp(2s/60s) */
160#define EXP_300s 2034 /* 1/exp(2s/300s) */
161
162/* PSI trigger definitions */
163#define WINDOW_MIN_US 500000 /* Min window size is 500ms */
164#define WINDOW_MAX_US 10000000 /* Max window size is 10s */
165#define UPDATES_PER_WINDOW 10 /* 10 updates per window */
166
167/* Sampling frequency in nanoseconds */
168static u64 psi_period __read_mostly;
169
170/* System-level pressure and stall tracking */
171static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu);
172struct psi_group psi_system = {
173 .pcpu = &system_group_pcpu,
174};
175
176static void psi_avgs_work(struct work_struct *work);
177
178static void poll_timer_fn(struct timer_list *t);
179
180static void group_init(struct psi_group *group)
181{
182 int cpu;
183
184 group->enabled = true;
185 for_each_possible_cpu(cpu)
186 seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq);
187 group->avg_last_update = sched_clock();
188 group->avg_next_update = group->avg_last_update + psi_period;
189 INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work);
190 mutex_init(&group->avgs_lock);
191 /* Init trigger-related members */
192 atomic_set(&group->poll_scheduled, 0);
193 mutex_init(&group->trigger_lock);
194 INIT_LIST_HEAD(&group->triggers);
195 group->poll_min_period = U32_MAX;
196 group->polling_next_update = ULLONG_MAX;
197 init_waitqueue_head(&group->poll_wait);
198 timer_setup(&group->poll_timer, poll_timer_fn, 0);
199 rcu_assign_pointer(group->poll_task, NULL);
200}
201
202void __init psi_init(void)
203{
204 if (!psi_enable) {
205 static_branch_enable(&psi_disabled);
206 static_branch_disable(&psi_cgroups_enabled);
207 return;
208 }
209
210 if (!cgroup_psi_enabled())
211 static_branch_disable(&psi_cgroups_enabled);
212
213 psi_period = jiffies_to_nsecs(PSI_FREQ);
214 group_init(&psi_system);
215}
216
217static bool test_state(unsigned int *tasks, enum psi_states state, bool oncpu)
218{
219 switch (state) {
220 case PSI_IO_SOME:
221 return unlikely(tasks[NR_IOWAIT]);
222 case PSI_IO_FULL:
223 return unlikely(tasks[NR_IOWAIT] && !tasks[NR_RUNNING]);
224 case PSI_MEM_SOME:
225 return unlikely(tasks[NR_MEMSTALL]);
226 case PSI_MEM_FULL:
227 return unlikely(tasks[NR_MEMSTALL] &&
228 tasks[NR_RUNNING] == tasks[NR_MEMSTALL_RUNNING]);
229 case PSI_CPU_SOME:
230 return unlikely(tasks[NR_RUNNING] > oncpu);
231 case PSI_CPU_FULL:
232 return unlikely(tasks[NR_RUNNING] && !oncpu);
233 case PSI_NONIDLE:
234 return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
235 tasks[NR_RUNNING];
236 default:
237 return false;
238 }
239}
240
241static void get_recent_times(struct psi_group *group, int cpu,
242 enum psi_aggregators aggregator, u32 *times,
243 u32 *pchanged_states)
244{
245 struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
246 int current_cpu = raw_smp_processor_id();
247 unsigned int tasks[NR_PSI_TASK_COUNTS];
248 u64 now, state_start;
249 enum psi_states s;
250 unsigned int seq;
251 u32 state_mask;
252
253 *pchanged_states = 0;
254
255 /* Snapshot a coherent view of the CPU state */
256 do {
257 seq = read_seqcount_begin(&groupc->seq);
258 now = cpu_clock(cpu);
259 memcpy(times, groupc->times, sizeof(groupc->times));
260 state_mask = groupc->state_mask;
261 state_start = groupc->state_start;
262 if (cpu == current_cpu)
263 memcpy(tasks, groupc->tasks, sizeof(groupc->tasks));
264 } while (read_seqcount_retry(&groupc->seq, seq));
265
266 /* Calculate state time deltas against the previous snapshot */
267 for (s = 0; s < NR_PSI_STATES; s++) {
268 u32 delta;
269 /*
270 * In addition to already concluded states, we also
271 * incorporate currently active states on the CPU,
272 * since states may last for many sampling periods.
273 *
274 * This way we keep our delta sampling buckets small
275 * (u32) and our reported pressure close to what's
276 * actually happening.
277 */
278 if (state_mask & (1 << s))
279 times[s] += now - state_start;
280
281 delta = times[s] - groupc->times_prev[aggregator][s];
282 groupc->times_prev[aggregator][s] = times[s];
283
284 times[s] = delta;
285 if (delta)
286 *pchanged_states |= (1 << s);
287 }
288
289 /*
290 * When collect_percpu_times() from the avgs_work, we don't want to
291 * re-arm avgs_work when all CPUs are IDLE. But the current CPU running
292 * this avgs_work is never IDLE, cause avgs_work can't be shut off.
293 * So for the current CPU, we need to re-arm avgs_work only when
294 * (NR_RUNNING > 1 || NR_IOWAIT > 0 || NR_MEMSTALL > 0), for other CPUs
295 * we can just check PSI_NONIDLE delta.
296 */
297 if (current_work() == &group->avgs_work.work) {
298 bool reschedule;
299
300 if (cpu == current_cpu)
301 reschedule = tasks[NR_RUNNING] +
302 tasks[NR_IOWAIT] +
303 tasks[NR_MEMSTALL] > 1;
304 else
305 reschedule = *pchanged_states & (1 << PSI_NONIDLE);
306
307 if (reschedule)
308 *pchanged_states |= PSI_STATE_RESCHEDULE;
309 }
310}
311
312static void calc_avgs(unsigned long avg[3], int missed_periods,
313 u64 time, u64 period)
314{
315 unsigned long pct;
316
317 /* Fill in zeroes for periods of no activity */
318 if (missed_periods) {
319 avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods);
320 avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods);
321 avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods);
322 }
323
324 /* Sample the most recent active period */
325 pct = div_u64(time * 100, period);
326 pct *= FIXED_1;
327 avg[0] = calc_load(avg[0], EXP_10s, pct);
328 avg[1] = calc_load(avg[1], EXP_60s, pct);
329 avg[2] = calc_load(avg[2], EXP_300s, pct);
330}
331
332static void collect_percpu_times(struct psi_group *group,
333 enum psi_aggregators aggregator,
334 u32 *pchanged_states)
335{
336 u64 deltas[NR_PSI_STATES - 1] = { 0, };
337 unsigned long nonidle_total = 0;
338 u32 changed_states = 0;
339 int cpu;
340 int s;
341
342 /*
343 * Collect the per-cpu time buckets and average them into a
344 * single time sample that is normalized to wallclock time.
345 *
346 * For averaging, each CPU is weighted by its non-idle time in
347 * the sampling period. This eliminates artifacts from uneven
348 * loading, or even entirely idle CPUs.
349 */
350 for_each_possible_cpu(cpu) {
351 u32 times[NR_PSI_STATES];
352 u32 nonidle;
353 u32 cpu_changed_states;
354
355 get_recent_times(group, cpu, aggregator, times,
356 &cpu_changed_states);
357 changed_states |= cpu_changed_states;
358
359 nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]);
360 nonidle_total += nonidle;
361
362 for (s = 0; s < PSI_NONIDLE; s++)
363 deltas[s] += (u64)times[s] * nonidle;
364 }
365
366 /*
367 * Integrate the sample into the running statistics that are
368 * reported to userspace: the cumulative stall times and the
369 * decaying averages.
370 *
371 * Pressure percentages are sampled at PSI_FREQ. We might be
372 * called more often when the user polls more frequently than
373 * that; we might be called less often when there is no task
374 * activity, thus no data, and clock ticks are sporadic. The
375 * below handles both.
376 */
377
378 /* total= */
379 for (s = 0; s < NR_PSI_STATES - 1; s++)
380 group->total[aggregator][s] +=
381 div_u64(deltas[s], max(nonidle_total, 1UL));
382
383 if (pchanged_states)
384 *pchanged_states = changed_states;
385}
386
387static u64 update_averages(struct psi_group *group, u64 now)
388{
389 unsigned long missed_periods = 0;
390 u64 expires, period;
391 u64 avg_next_update;
392 int s;
393
394 /* avgX= */
395 expires = group->avg_next_update;
396 if (now - expires >= psi_period)
397 missed_periods = div_u64(now - expires, psi_period);
398
399 /*
400 * The periodic clock tick can get delayed for various
401 * reasons, especially on loaded systems. To avoid clock
402 * drift, we schedule the clock in fixed psi_period intervals.
403 * But the deltas we sample out of the per-cpu buckets above
404 * are based on the actual time elapsing between clock ticks.
405 */
406 avg_next_update = expires + ((1 + missed_periods) * psi_period);
407 period = now - (group->avg_last_update + (missed_periods * psi_period));
408 group->avg_last_update = now;
409
410 for (s = 0; s < NR_PSI_STATES - 1; s++) {
411 u32 sample;
412
413 sample = group->total[PSI_AVGS][s] - group->avg_total[s];
414 /*
415 * Due to the lockless sampling of the time buckets,
416 * recorded time deltas can slip into the next period,
417 * which under full pressure can result in samples in
418 * excess of the period length.
419 *
420 * We don't want to report non-sensical pressures in
421 * excess of 100%, nor do we want to drop such events
422 * on the floor. Instead we punt any overage into the
423 * future until pressure subsides. By doing this we
424 * don't underreport the occurring pressure curve, we
425 * just report it delayed by one period length.
426 *
427 * The error isn't cumulative. As soon as another
428 * delta slips from a period P to P+1, by definition
429 * it frees up its time T in P.
430 */
431 if (sample > period)
432 sample = period;
433 group->avg_total[s] += sample;
434 calc_avgs(group->avg[s], missed_periods, sample, period);
435 }
436
437 return avg_next_update;
438}
439
440static void psi_avgs_work(struct work_struct *work)
441{
442 struct delayed_work *dwork;
443 struct psi_group *group;
444 u32 changed_states;
445 u64 now;
446
447 dwork = to_delayed_work(work);
448 group = container_of(dwork, struct psi_group, avgs_work);
449
450 mutex_lock(&group->avgs_lock);
451
452 now = sched_clock();
453
454 collect_percpu_times(group, PSI_AVGS, &changed_states);
455 /*
456 * If there is task activity, periodically fold the per-cpu
457 * times and feed samples into the running averages. If things
458 * are idle and there is no data to process, stop the clock.
459 * Once restarted, we'll catch up the running averages in one
460 * go - see calc_avgs() and missed_periods.
461 */
462 if (now >= group->avg_next_update)
463 group->avg_next_update = update_averages(group, now);
464
465 if (changed_states & PSI_STATE_RESCHEDULE) {
466 schedule_delayed_work(dwork, nsecs_to_jiffies(
467 group->avg_next_update - now) + 1);
468 }
469
470 mutex_unlock(&group->avgs_lock);
471}
472
473/* Trigger tracking window manipulations */
474static void window_reset(struct psi_window *win, u64 now, u64 value,
475 u64 prev_growth)
476{
477 win->start_time = now;
478 win->start_value = value;
479 win->prev_growth = prev_growth;
480}
481
482/*
483 * PSI growth tracking window update and growth calculation routine.
484 *
485 * This approximates a sliding tracking window by interpolating
486 * partially elapsed windows using historical growth data from the
487 * previous intervals. This minimizes memory requirements (by not storing
488 * all the intermediate values in the previous window) and simplifies
489 * the calculations. It works well because PSI signal changes only in
490 * positive direction and over relatively small window sizes the growth
491 * is close to linear.
492 */
493static u64 window_update(struct psi_window *win, u64 now, u64 value)
494{
495 u64 elapsed;
496 u64 growth;
497
498 elapsed = now - win->start_time;
499 growth = value - win->start_value;
500 /*
501 * After each tracking window passes win->start_value and
502 * win->start_time get reset and win->prev_growth stores
503 * the average per-window growth of the previous window.
504 * win->prev_growth is then used to interpolate additional
505 * growth from the previous window assuming it was linear.
506 */
507 if (elapsed > win->size)
508 window_reset(win, now, value, growth);
509 else {
510 u32 remaining;
511
512 remaining = win->size - elapsed;
513 growth += div64_u64(win->prev_growth * remaining, win->size);
514 }
515
516 return growth;
517}
518
519static void init_triggers(struct psi_group *group, u64 now)
520{
521 struct psi_trigger *t;
522
523 list_for_each_entry(t, &group->triggers, node)
524 window_reset(&t->win, now,
525 group->total[PSI_POLL][t->state], 0);
526 memcpy(group->polling_total, group->total[PSI_POLL],
527 sizeof(group->polling_total));
528 group->polling_next_update = now + group->poll_min_period;
529}
530
531static u64 update_triggers(struct psi_group *group, u64 now)
532{
533 struct psi_trigger *t;
534 bool update_total = false;
535 u64 *total = group->total[PSI_POLL];
536
537 /*
538 * On subsequent updates, calculate growth deltas and let
539 * watchers know when their specified thresholds are exceeded.
540 */
541 list_for_each_entry(t, &group->triggers, node) {
542 u64 growth;
543 bool new_stall;
544
545 new_stall = group->polling_total[t->state] != total[t->state];
546
547 /* Check for stall activity or a previous threshold breach */
548 if (!new_stall && !t->pending_event)
549 continue;
550 /*
551 * Check for new stall activity, as well as deferred
552 * events that occurred in the last window after the
553 * trigger had already fired (we want to ratelimit
554 * events without dropping any).
555 */
556 if (new_stall) {
557 /*
558 * Multiple triggers might be looking at the same state,
559 * remember to update group->polling_total[] once we've
560 * been through all of them. Also remember to extend the
561 * polling time if we see new stall activity.
562 */
563 update_total = true;
564
565 /* Calculate growth since last update */
566 growth = window_update(&t->win, now, total[t->state]);
567 if (!t->pending_event) {
568 if (growth < t->threshold)
569 continue;
570
571 t->pending_event = true;
572 }
573 }
574 /* Limit event signaling to once per window */
575 if (now < t->last_event_time + t->win.size)
576 continue;
577
578 /* Generate an event */
579 if (cmpxchg(&t->event, 0, 1) == 0)
580 wake_up_interruptible(&t->event_wait);
581 t->last_event_time = now;
582 /* Reset threshold breach flag once event got generated */
583 t->pending_event = false;
584 }
585
586 if (update_total)
587 memcpy(group->polling_total, total,
588 sizeof(group->polling_total));
589
590 return now + group->poll_min_period;
591}
592
593/* Schedule polling if it's not already scheduled or forced. */
594static void psi_schedule_poll_work(struct psi_group *group, unsigned long delay,
595 bool force)
596{
597 struct task_struct *task;
598
599 /*
600 * atomic_xchg should be called even when !force to provide a
601 * full memory barrier (see the comment inside psi_poll_work).
602 */
603 if (atomic_xchg(&group->poll_scheduled, 1) && !force)
604 return;
605
606 rcu_read_lock();
607
608 task = rcu_dereference(group->poll_task);
609 /*
610 * kworker might be NULL in case psi_trigger_destroy races with
611 * psi_task_change (hotpath) which can't use locks
612 */
613 if (likely(task))
614 mod_timer(&group->poll_timer, jiffies + delay);
615 else
616 atomic_set(&group->poll_scheduled, 0);
617
618 rcu_read_unlock();
619}
620
621static void psi_poll_work(struct psi_group *group)
622{
623 bool force_reschedule = false;
624 u32 changed_states;
625 u64 now;
626
627 mutex_lock(&group->trigger_lock);
628
629 now = sched_clock();
630
631 if (now > group->polling_until) {
632 /*
633 * We are either about to start or might stop polling if no
634 * state change was recorded. Resetting poll_scheduled leaves
635 * a small window for psi_group_change to sneak in and schedule
636 * an immediate poll_work before we get to rescheduling. One
637 * potential extra wakeup at the end of the polling window
638 * should be negligible and polling_next_update still keeps
639 * updates correctly on schedule.
640 */
641 atomic_set(&group->poll_scheduled, 0);
642 /*
643 * A task change can race with the poll worker that is supposed to
644 * report on it. To avoid missing events, ensure ordering between
645 * poll_scheduled and the task state accesses, such that if the poll
646 * worker misses the state update, the task change is guaranteed to
647 * reschedule the poll worker:
648 *
649 * poll worker:
650 * atomic_set(poll_scheduled, 0)
651 * smp_mb()
652 * LOAD states
653 *
654 * task change:
655 * STORE states
656 * if atomic_xchg(poll_scheduled, 1) == 0:
657 * schedule poll worker
658 *
659 * The atomic_xchg() implies a full barrier.
660 */
661 smp_mb();
662 } else {
663 /* Polling window is not over, keep rescheduling */
664 force_reschedule = true;
665 }
666
667
668 collect_percpu_times(group, PSI_POLL, &changed_states);
669
670 if (changed_states & group->poll_states) {
671 /* Initialize trigger windows when entering polling mode */
672 if (now > group->polling_until)
673 init_triggers(group, now);
674
675 /*
676 * Keep the monitor active for at least the duration of the
677 * minimum tracking window as long as monitor states are
678 * changing.
679 */
680 group->polling_until = now +
681 group->poll_min_period * UPDATES_PER_WINDOW;
682 }
683
684 if (now > group->polling_until) {
685 group->polling_next_update = ULLONG_MAX;
686 goto out;
687 }
688
689 if (now >= group->polling_next_update)
690 group->polling_next_update = update_triggers(group, now);
691
692 psi_schedule_poll_work(group,
693 nsecs_to_jiffies(group->polling_next_update - now) + 1,
694 force_reschedule);
695
696out:
697 mutex_unlock(&group->trigger_lock);
698}
699
700static int psi_poll_worker(void *data)
701{
702 struct psi_group *group = (struct psi_group *)data;
703
704 sched_set_fifo_low(current);
705
706 while (true) {
707 wait_event_interruptible(group->poll_wait,
708 atomic_cmpxchg(&group->poll_wakeup, 1, 0) ||
709 kthread_should_stop());
710 if (kthread_should_stop())
711 break;
712
713 psi_poll_work(group);
714 }
715 return 0;
716}
717
718static void poll_timer_fn(struct timer_list *t)
719{
720 struct psi_group *group = from_timer(group, t, poll_timer);
721
722 atomic_set(&group->poll_wakeup, 1);
723 wake_up_interruptible(&group->poll_wait);
724}
725
726static void record_times(struct psi_group_cpu *groupc, u64 now)
727{
728 u32 delta;
729
730 delta = now - groupc->state_start;
731 groupc->state_start = now;
732
733 if (groupc->state_mask & (1 << PSI_IO_SOME)) {
734 groupc->times[PSI_IO_SOME] += delta;
735 if (groupc->state_mask & (1 << PSI_IO_FULL))
736 groupc->times[PSI_IO_FULL] += delta;
737 }
738
739 if (groupc->state_mask & (1 << PSI_MEM_SOME)) {
740 groupc->times[PSI_MEM_SOME] += delta;
741 if (groupc->state_mask & (1 << PSI_MEM_FULL))
742 groupc->times[PSI_MEM_FULL] += delta;
743 }
744
745 if (groupc->state_mask & (1 << PSI_CPU_SOME)) {
746 groupc->times[PSI_CPU_SOME] += delta;
747 if (groupc->state_mask & (1 << PSI_CPU_FULL))
748 groupc->times[PSI_CPU_FULL] += delta;
749 }
750
751 if (groupc->state_mask & (1 << PSI_NONIDLE))
752 groupc->times[PSI_NONIDLE] += delta;
753}
754
755static void psi_group_change(struct psi_group *group, int cpu,
756 unsigned int clear, unsigned int set, u64 now,
757 bool wake_clock)
758{
759 struct psi_group_cpu *groupc;
760 unsigned int t, m;
761 enum psi_states s;
762 u32 state_mask;
763
764 groupc = per_cpu_ptr(group->pcpu, cpu);
765
766 /*
767 * First we update the task counts according to the state
768 * change requested through the @clear and @set bits.
769 *
770 * Then if the cgroup PSI stats accounting enabled, we
771 * assess the aggregate resource states this CPU's tasks
772 * have been in since the last change, and account any
773 * SOME and FULL time these may have resulted in.
774 */
775 write_seqcount_begin(&groupc->seq);
776
777 /*
778 * Start with TSK_ONCPU, which doesn't have a corresponding
779 * task count - it's just a boolean flag directly encoded in
780 * the state mask. Clear, set, or carry the current state if
781 * no changes are requested.
782 */
783 if (unlikely(clear & TSK_ONCPU)) {
784 state_mask = 0;
785 clear &= ~TSK_ONCPU;
786 } else if (unlikely(set & TSK_ONCPU)) {
787 state_mask = PSI_ONCPU;
788 set &= ~TSK_ONCPU;
789 } else {
790 state_mask = groupc->state_mask & PSI_ONCPU;
791 }
792
793 /*
794 * The rest of the state mask is calculated based on the task
795 * counts. Update those first, then construct the mask.
796 */
797 for (t = 0, m = clear; m; m &= ~(1 << t), t++) {
798 if (!(m & (1 << t)))
799 continue;
800 if (groupc->tasks[t]) {
801 groupc->tasks[t]--;
802 } else if (!psi_bug) {
803 printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u] clear=%x set=%x\n",
804 cpu, t, groupc->tasks[0],
805 groupc->tasks[1], groupc->tasks[2],
806 groupc->tasks[3], clear, set);
807 psi_bug = 1;
808 }
809 }
810
811 for (t = 0; set; set &= ~(1 << t), t++)
812 if (set & (1 << t))
813 groupc->tasks[t]++;
814
815 if (!group->enabled) {
816 /*
817 * On the first group change after disabling PSI, conclude
818 * the current state and flush its time. This is unlikely
819 * to matter to the user, but aggregation (get_recent_times)
820 * may have already incorporated the live state into times_prev;
821 * avoid a delta sample underflow when PSI is later re-enabled.
822 */
823 if (unlikely(groupc->state_mask & (1 << PSI_NONIDLE)))
824 record_times(groupc, now);
825
826 groupc->state_mask = state_mask;
827
828 write_seqcount_end(&groupc->seq);
829 return;
830 }
831
832 for (s = 0; s < NR_PSI_STATES; s++) {
833 if (test_state(groupc->tasks, s, state_mask & PSI_ONCPU))
834 state_mask |= (1 << s);
835 }
836
837 /*
838 * Since we care about lost potential, a memstall is FULL
839 * when there are no other working tasks, but also when
840 * the CPU is actively reclaiming and nothing productive
841 * could run even if it were runnable. So when the current
842 * task in a cgroup is in_memstall, the corresponding groupc
843 * on that cpu is in PSI_MEM_FULL state.
844 */
845 if (unlikely((state_mask & PSI_ONCPU) && cpu_curr(cpu)->in_memstall))
846 state_mask |= (1 << PSI_MEM_FULL);
847
848 record_times(groupc, now);
849
850 groupc->state_mask = state_mask;
851
852 write_seqcount_end(&groupc->seq);
853
854 if (state_mask & group->poll_states)
855 psi_schedule_poll_work(group, 1, false);
856
857 if (wake_clock && !delayed_work_pending(&group->avgs_work))
858 schedule_delayed_work(&group->avgs_work, PSI_FREQ);
859}
860
861static inline struct psi_group *task_psi_group(struct task_struct *task)
862{
863#ifdef CONFIG_CGROUPS
864 if (static_branch_likely(&psi_cgroups_enabled))
865 return cgroup_psi(task_dfl_cgroup(task));
866#endif
867 return &psi_system;
868}
869
870static void psi_flags_change(struct task_struct *task, int clear, int set)
871{
872 if (((task->psi_flags & set) ||
873 (task->psi_flags & clear) != clear) &&
874 !psi_bug) {
875 printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n",
876 task->pid, task->comm, task_cpu(task),
877 task->psi_flags, clear, set);
878 psi_bug = 1;
879 }
880
881 task->psi_flags &= ~clear;
882 task->psi_flags |= set;
883}
884
885void psi_task_change(struct task_struct *task, int clear, int set)
886{
887 int cpu = task_cpu(task);
888 struct psi_group *group;
889 u64 now;
890
891 if (!task->pid)
892 return;
893
894 psi_flags_change(task, clear, set);
895
896 now = cpu_clock(cpu);
897
898 group = task_psi_group(task);
899 do {
900 psi_group_change(group, cpu, clear, set, now, true);
901 } while ((group = group->parent));
902}
903
904void psi_task_switch(struct task_struct *prev, struct task_struct *next,
905 bool sleep)
906{
907 struct psi_group *group, *common = NULL;
908 int cpu = task_cpu(prev);
909 u64 now = cpu_clock(cpu);
910
911 if (next->pid) {
912 psi_flags_change(next, 0, TSK_ONCPU);
913 /*
914 * Set TSK_ONCPU on @next's cgroups. If @next shares any
915 * ancestors with @prev, those will already have @prev's
916 * TSK_ONCPU bit set, and we can stop the iteration there.
917 */
918 group = task_psi_group(next);
919 do {
920 if (per_cpu_ptr(group->pcpu, cpu)->state_mask &
921 PSI_ONCPU) {
922 common = group;
923 break;
924 }
925
926 psi_group_change(group, cpu, 0, TSK_ONCPU, now, true);
927 } while ((group = group->parent));
928 }
929
930 if (prev->pid) {
931 int clear = TSK_ONCPU, set = 0;
932 bool wake_clock = true;
933
934 /*
935 * When we're going to sleep, psi_dequeue() lets us
936 * handle TSK_RUNNING, TSK_MEMSTALL_RUNNING and
937 * TSK_IOWAIT here, where we can combine it with
938 * TSK_ONCPU and save walking common ancestors twice.
939 */
940 if (sleep) {
941 clear |= TSK_RUNNING;
942 if (prev->in_memstall)
943 clear |= TSK_MEMSTALL_RUNNING;
944 if (prev->in_iowait)
945 set |= TSK_IOWAIT;
946
947 /*
948 * Periodic aggregation shuts off if there is a period of no
949 * task changes, so we wake it back up if necessary. However,
950 * don't do this if the task change is the aggregation worker
951 * itself going to sleep, or we'll ping-pong forever.
952 */
953 if (unlikely((prev->flags & PF_WQ_WORKER) &&
954 wq_worker_last_func(prev) == psi_avgs_work))
955 wake_clock = false;
956 }
957
958 psi_flags_change(prev, clear, set);
959
960 group = task_psi_group(prev);
961 do {
962 if (group == common)
963 break;
964 psi_group_change(group, cpu, clear, set, now, wake_clock);
965 } while ((group = group->parent));
966
967 /*
968 * TSK_ONCPU is handled up to the common ancestor. If there are
969 * any other differences between the two tasks (e.g. prev goes
970 * to sleep, or only one task is memstall), finish propagating
971 * those differences all the way up to the root.
972 */
973 if ((prev->psi_flags ^ next->psi_flags) & ~TSK_ONCPU) {
974 clear &= ~TSK_ONCPU;
975 for (; group; group = group->parent)
976 psi_group_change(group, cpu, clear, set, now, wake_clock);
977 }
978 }
979}
980
981#ifdef CONFIG_IRQ_TIME_ACCOUNTING
982void psi_account_irqtime(struct task_struct *task, u32 delta)
983{
984 int cpu = task_cpu(task);
985 struct psi_group *group;
986 struct psi_group_cpu *groupc;
987 u64 now;
988
989 if (!task->pid)
990 return;
991
992 now = cpu_clock(cpu);
993
994 group = task_psi_group(task);
995 do {
996 if (!group->enabled)
997 continue;
998
999 groupc = per_cpu_ptr(group->pcpu, cpu);
1000
1001 write_seqcount_begin(&groupc->seq);
1002
1003 record_times(groupc, now);
1004 groupc->times[PSI_IRQ_FULL] += delta;
1005
1006 write_seqcount_end(&groupc->seq);
1007
1008 if (group->poll_states & (1 << PSI_IRQ_FULL))
1009 psi_schedule_poll_work(group, 1, false);
1010 } while ((group = group->parent));
1011}
1012#endif
1013
1014/**
1015 * psi_memstall_enter - mark the beginning of a memory stall section
1016 * @flags: flags to handle nested sections
1017 *
1018 * Marks the calling task as being stalled due to a lack of memory,
1019 * such as waiting for a refault or performing reclaim.
1020 */
1021void psi_memstall_enter(unsigned long *flags)
1022{
1023 struct rq_flags rf;
1024 struct rq *rq;
1025
1026 if (static_branch_likely(&psi_disabled))
1027 return;
1028
1029 *flags = current->in_memstall;
1030 if (*flags)
1031 return;
1032 /*
1033 * in_memstall setting & accounting needs to be atomic wrt
1034 * changes to the task's scheduling state, otherwise we can
1035 * race with CPU migration.
1036 */
1037 rq = this_rq_lock_irq(&rf);
1038
1039 current->in_memstall = 1;
1040 psi_task_change(current, 0, TSK_MEMSTALL | TSK_MEMSTALL_RUNNING);
1041
1042 rq_unlock_irq(rq, &rf);
1043}
1044EXPORT_SYMBOL_GPL(psi_memstall_enter);
1045
1046/**
1047 * psi_memstall_leave - mark the end of an memory stall section
1048 * @flags: flags to handle nested memdelay sections
1049 *
1050 * Marks the calling task as no longer stalled due to lack of memory.
1051 */
1052void psi_memstall_leave(unsigned long *flags)
1053{
1054 struct rq_flags rf;
1055 struct rq *rq;
1056
1057 if (static_branch_likely(&psi_disabled))
1058 return;
1059
1060 if (*flags)
1061 return;
1062 /*
1063 * in_memstall clearing & accounting needs to be atomic wrt
1064 * changes to the task's scheduling state, otherwise we could
1065 * race with CPU migration.
1066 */
1067 rq = this_rq_lock_irq(&rf);
1068
1069 current->in_memstall = 0;
1070 psi_task_change(current, TSK_MEMSTALL | TSK_MEMSTALL_RUNNING, 0);
1071
1072 rq_unlock_irq(rq, &rf);
1073}
1074EXPORT_SYMBOL_GPL(psi_memstall_leave);
1075
1076#ifdef CONFIG_CGROUPS
1077int psi_cgroup_alloc(struct cgroup *cgroup)
1078{
1079 if (!static_branch_likely(&psi_cgroups_enabled))
1080 return 0;
1081
1082 cgroup->psi = kzalloc(sizeof(struct psi_group), GFP_KERNEL);
1083 if (!cgroup->psi)
1084 return -ENOMEM;
1085
1086 cgroup->psi->pcpu = alloc_percpu(struct psi_group_cpu);
1087 if (!cgroup->psi->pcpu) {
1088 kfree(cgroup->psi);
1089 return -ENOMEM;
1090 }
1091 group_init(cgroup->psi);
1092 cgroup->psi->parent = cgroup_psi(cgroup_parent(cgroup));
1093 return 0;
1094}
1095
1096void psi_cgroup_free(struct cgroup *cgroup)
1097{
1098 if (!static_branch_likely(&psi_cgroups_enabled))
1099 return;
1100
1101 cancel_delayed_work_sync(&cgroup->psi->avgs_work);
1102 free_percpu(cgroup->psi->pcpu);
1103 /* All triggers must be removed by now */
1104 WARN_ONCE(cgroup->psi->poll_states, "psi: trigger leak\n");
1105 kfree(cgroup->psi);
1106}
1107
1108/**
1109 * cgroup_move_task - move task to a different cgroup
1110 * @task: the task
1111 * @to: the target css_set
1112 *
1113 * Move task to a new cgroup and safely migrate its associated stall
1114 * state between the different groups.
1115 *
1116 * This function acquires the task's rq lock to lock out concurrent
1117 * changes to the task's scheduling state and - in case the task is
1118 * running - concurrent changes to its stall state.
1119 */
1120void cgroup_move_task(struct task_struct *task, struct css_set *to)
1121{
1122 unsigned int task_flags;
1123 struct rq_flags rf;
1124 struct rq *rq;
1125
1126 if (!static_branch_likely(&psi_cgroups_enabled)) {
1127 /*
1128 * Lame to do this here, but the scheduler cannot be locked
1129 * from the outside, so we move cgroups from inside sched/.
1130 */
1131 rcu_assign_pointer(task->cgroups, to);
1132 return;
1133 }
1134
1135 rq = task_rq_lock(task, &rf);
1136
1137 /*
1138 * We may race with schedule() dropping the rq lock between
1139 * deactivating prev and switching to next. Because the psi
1140 * updates from the deactivation are deferred to the switch
1141 * callback to save cgroup tree updates, the task's scheduling
1142 * state here is not coherent with its psi state:
1143 *
1144 * schedule() cgroup_move_task()
1145 * rq_lock()
1146 * deactivate_task()
1147 * p->on_rq = 0
1148 * psi_dequeue() // defers TSK_RUNNING & TSK_IOWAIT updates
1149 * pick_next_task()
1150 * rq_unlock()
1151 * rq_lock()
1152 * psi_task_change() // old cgroup
1153 * task->cgroups = to
1154 * psi_task_change() // new cgroup
1155 * rq_unlock()
1156 * rq_lock()
1157 * psi_sched_switch() // does deferred updates in new cgroup
1158 *
1159 * Don't rely on the scheduling state. Use psi_flags instead.
1160 */
1161 task_flags = task->psi_flags;
1162
1163 if (task_flags)
1164 psi_task_change(task, task_flags, 0);
1165
1166 /* See comment above */
1167 rcu_assign_pointer(task->cgroups, to);
1168
1169 if (task_flags)
1170 psi_task_change(task, 0, task_flags);
1171
1172 task_rq_unlock(rq, task, &rf);
1173}
1174
1175void psi_cgroup_restart(struct psi_group *group)
1176{
1177 int cpu;
1178
1179 /*
1180 * After we disable psi_group->enabled, we don't actually
1181 * stop percpu tasks accounting in each psi_group_cpu,
1182 * instead only stop test_state() loop, record_times()
1183 * and averaging worker, see psi_group_change() for details.
1184 *
1185 * When disable cgroup PSI, this function has nothing to sync
1186 * since cgroup pressure files are hidden and percpu psi_group_cpu
1187 * would see !psi_group->enabled and only do task accounting.
1188 *
1189 * When re-enable cgroup PSI, this function use psi_group_change()
1190 * to get correct state mask from test_state() loop on tasks[],
1191 * and restart groupc->state_start from now, use .clear = .set = 0
1192 * here since no task status really changed.
1193 */
1194 if (!group->enabled)
1195 return;
1196
1197 for_each_possible_cpu(cpu) {
1198 struct rq *rq = cpu_rq(cpu);
1199 struct rq_flags rf;
1200 u64 now;
1201
1202 rq_lock_irq(rq, &rf);
1203 now = cpu_clock(cpu);
1204 psi_group_change(group, cpu, 0, 0, now, true);
1205 rq_unlock_irq(rq, &rf);
1206 }
1207}
1208#endif /* CONFIG_CGROUPS */
1209
1210int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
1211{
1212 bool only_full = false;
1213 int full;
1214 u64 now;
1215
1216 if (static_branch_likely(&psi_disabled))
1217 return -EOPNOTSUPP;
1218
1219 /* Update averages before reporting them */
1220 mutex_lock(&group->avgs_lock);
1221 now = sched_clock();
1222 collect_percpu_times(group, PSI_AVGS, NULL);
1223 if (now >= group->avg_next_update)
1224 group->avg_next_update = update_averages(group, now);
1225 mutex_unlock(&group->avgs_lock);
1226
1227#ifdef CONFIG_IRQ_TIME_ACCOUNTING
1228 only_full = res == PSI_IRQ;
1229#endif
1230
1231 for (full = 0; full < 2 - only_full; full++) {
1232 unsigned long avg[3] = { 0, };
1233 u64 total = 0;
1234 int w;
1235
1236 /* CPU FULL is undefined at the system level */
1237 if (!(group == &psi_system && res == PSI_CPU && full)) {
1238 for (w = 0; w < 3; w++)
1239 avg[w] = group->avg[res * 2 + full][w];
1240 total = div_u64(group->total[PSI_AVGS][res * 2 + full],
1241 NSEC_PER_USEC);
1242 }
1243
1244 seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n",
1245 full || only_full ? "full" : "some",
1246 LOAD_INT(avg[0]), LOAD_FRAC(avg[0]),
1247 LOAD_INT(avg[1]), LOAD_FRAC(avg[1]),
1248 LOAD_INT(avg[2]), LOAD_FRAC(avg[2]),
1249 total);
1250 }
1251
1252 return 0;
1253}
1254
1255struct psi_trigger *psi_trigger_create(struct psi_group *group,
1256 char *buf, enum psi_res res)
1257{
1258 struct psi_trigger *t;
1259 enum psi_states state;
1260 u32 threshold_us;
1261 u32 window_us;
1262
1263 if (static_branch_likely(&psi_disabled))
1264 return ERR_PTR(-EOPNOTSUPP);
1265
1266 if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2)
1267 state = PSI_IO_SOME + res * 2;
1268 else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2)
1269 state = PSI_IO_FULL + res * 2;
1270 else
1271 return ERR_PTR(-EINVAL);
1272
1273#ifdef CONFIG_IRQ_TIME_ACCOUNTING
1274 if (res == PSI_IRQ && --state != PSI_IRQ_FULL)
1275 return ERR_PTR(-EINVAL);
1276#endif
1277
1278 if (state >= PSI_NONIDLE)
1279 return ERR_PTR(-EINVAL);
1280
1281 if (window_us < WINDOW_MIN_US ||
1282 window_us > WINDOW_MAX_US)
1283 return ERR_PTR(-EINVAL);
1284
1285 /* Check threshold */
1286 if (threshold_us == 0 || threshold_us > window_us)
1287 return ERR_PTR(-EINVAL);
1288
1289 t = kmalloc(sizeof(*t), GFP_KERNEL);
1290 if (!t)
1291 return ERR_PTR(-ENOMEM);
1292
1293 t->group = group;
1294 t->state = state;
1295 t->threshold = threshold_us * NSEC_PER_USEC;
1296 t->win.size = window_us * NSEC_PER_USEC;
1297 window_reset(&t->win, sched_clock(),
1298 group->total[PSI_POLL][t->state], 0);
1299
1300 t->event = 0;
1301 t->last_event_time = 0;
1302 init_waitqueue_head(&t->event_wait);
1303 t->pending_event = false;
1304
1305 mutex_lock(&group->trigger_lock);
1306
1307 if (!rcu_access_pointer(group->poll_task)) {
1308 struct task_struct *task;
1309
1310 task = kthread_create(psi_poll_worker, group, "psimon");
1311 if (IS_ERR(task)) {
1312 kfree(t);
1313 mutex_unlock(&group->trigger_lock);
1314 return ERR_CAST(task);
1315 }
1316 atomic_set(&group->poll_wakeup, 0);
1317 wake_up_process(task);
1318 rcu_assign_pointer(group->poll_task, task);
1319 }
1320
1321 list_add(&t->node, &group->triggers);
1322 group->poll_min_period = min(group->poll_min_period,
1323 div_u64(t->win.size, UPDATES_PER_WINDOW));
1324 group->nr_triggers[t->state]++;
1325 group->poll_states |= (1 << t->state);
1326
1327 mutex_unlock(&group->trigger_lock);
1328
1329 return t;
1330}
1331
1332void psi_trigger_destroy(struct psi_trigger *t)
1333{
1334 struct psi_group *group;
1335 struct task_struct *task_to_destroy = NULL;
1336
1337 /*
1338 * We do not check psi_disabled since it might have been disabled after
1339 * the trigger got created.
1340 */
1341 if (!t)
1342 return;
1343
1344 group = t->group;
1345 /*
1346 * Wakeup waiters to stop polling and clear the queue to prevent it from
1347 * being accessed later. Can happen if cgroup is deleted from under a
1348 * polling process.
1349 */
1350 wake_up_pollfree(&t->event_wait);
1351
1352 mutex_lock(&group->trigger_lock);
1353
1354 if (!list_empty(&t->node)) {
1355 struct psi_trigger *tmp;
1356 u64 period = ULLONG_MAX;
1357
1358 list_del(&t->node);
1359 group->nr_triggers[t->state]--;
1360 if (!group->nr_triggers[t->state])
1361 group->poll_states &= ~(1 << t->state);
1362 /* reset min update period for the remaining triggers */
1363 list_for_each_entry(tmp, &group->triggers, node)
1364 period = min(period, div_u64(tmp->win.size,
1365 UPDATES_PER_WINDOW));
1366 group->poll_min_period = period;
1367 /* Destroy poll_task when the last trigger is destroyed */
1368 if (group->poll_states == 0) {
1369 group->polling_until = 0;
1370 task_to_destroy = rcu_dereference_protected(
1371 group->poll_task,
1372 lockdep_is_held(&group->trigger_lock));
1373 rcu_assign_pointer(group->poll_task, NULL);
1374 del_timer(&group->poll_timer);
1375 }
1376 }
1377
1378 mutex_unlock(&group->trigger_lock);
1379
1380 /*
1381 * Wait for psi_schedule_poll_work RCU to complete its read-side
1382 * critical section before destroying the trigger and optionally the
1383 * poll_task.
1384 */
1385 synchronize_rcu();
1386 /*
1387 * Stop kthread 'psimon' after releasing trigger_lock to prevent a
1388 * deadlock while waiting for psi_poll_work to acquire trigger_lock
1389 */
1390 if (task_to_destroy) {
1391 /*
1392 * After the RCU grace period has expired, the worker
1393 * can no longer be found through group->poll_task.
1394 */
1395 kthread_stop(task_to_destroy);
1396 atomic_set(&group->poll_scheduled, 0);
1397 }
1398 kfree(t);
1399}
1400
1401__poll_t psi_trigger_poll(void **trigger_ptr,
1402 struct file *file, poll_table *wait)
1403{
1404 __poll_t ret = DEFAULT_POLLMASK;
1405 struct psi_trigger *t;
1406
1407 if (static_branch_likely(&psi_disabled))
1408 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
1409
1410 t = smp_load_acquire(trigger_ptr);
1411 if (!t)
1412 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
1413
1414 poll_wait(file, &t->event_wait, wait);
1415
1416 if (cmpxchg(&t->event, 1, 0) == 1)
1417 ret |= EPOLLPRI;
1418
1419 return ret;
1420}
1421
1422#ifdef CONFIG_PROC_FS
1423static int psi_io_show(struct seq_file *m, void *v)
1424{
1425 return psi_show(m, &psi_system, PSI_IO);
1426}
1427
1428static int psi_memory_show(struct seq_file *m, void *v)
1429{
1430 return psi_show(m, &psi_system, PSI_MEM);
1431}
1432
1433static int psi_cpu_show(struct seq_file *m, void *v)
1434{
1435 return psi_show(m, &psi_system, PSI_CPU);
1436}
1437
1438static int psi_open(struct file *file, int (*psi_show)(struct seq_file *, void *))
1439{
1440 if (file->f_mode & FMODE_WRITE && !capable(CAP_SYS_RESOURCE))
1441 return -EPERM;
1442
1443 return single_open(file, psi_show, NULL);
1444}
1445
1446static int psi_io_open(struct inode *inode, struct file *file)
1447{
1448 return psi_open(file, psi_io_show);
1449}
1450
1451static int psi_memory_open(struct inode *inode, struct file *file)
1452{
1453 return psi_open(file, psi_memory_show);
1454}
1455
1456static int psi_cpu_open(struct inode *inode, struct file *file)
1457{
1458 return psi_open(file, psi_cpu_show);
1459}
1460
1461static ssize_t psi_write(struct file *file, const char __user *user_buf,
1462 size_t nbytes, enum psi_res res)
1463{
1464 char buf[32];
1465 size_t buf_size;
1466 struct seq_file *seq;
1467 struct psi_trigger *new;
1468
1469 if (static_branch_likely(&psi_disabled))
1470 return -EOPNOTSUPP;
1471
1472 if (!nbytes)
1473 return -EINVAL;
1474
1475 buf_size = min(nbytes, sizeof(buf));
1476 if (copy_from_user(buf, user_buf, buf_size))
1477 return -EFAULT;
1478
1479 buf[buf_size - 1] = '\0';
1480
1481 seq = file->private_data;
1482
1483 /* Take seq->lock to protect seq->private from concurrent writes */
1484 mutex_lock(&seq->lock);
1485
1486 /* Allow only one trigger per file descriptor */
1487 if (seq->private) {
1488 mutex_unlock(&seq->lock);
1489 return -EBUSY;
1490 }
1491
1492 new = psi_trigger_create(&psi_system, buf, res);
1493 if (IS_ERR(new)) {
1494 mutex_unlock(&seq->lock);
1495 return PTR_ERR(new);
1496 }
1497
1498 smp_store_release(&seq->private, new);
1499 mutex_unlock(&seq->lock);
1500
1501 return nbytes;
1502}
1503
1504static ssize_t psi_io_write(struct file *file, const char __user *user_buf,
1505 size_t nbytes, loff_t *ppos)
1506{
1507 return psi_write(file, user_buf, nbytes, PSI_IO);
1508}
1509
1510static ssize_t psi_memory_write(struct file *file, const char __user *user_buf,
1511 size_t nbytes, loff_t *ppos)
1512{
1513 return psi_write(file, user_buf, nbytes, PSI_MEM);
1514}
1515
1516static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf,
1517 size_t nbytes, loff_t *ppos)
1518{
1519 return psi_write(file, user_buf, nbytes, PSI_CPU);
1520}
1521
1522static __poll_t psi_fop_poll(struct file *file, poll_table *wait)
1523{
1524 struct seq_file *seq = file->private_data;
1525
1526 return psi_trigger_poll(&seq->private, file, wait);
1527}
1528
1529static int psi_fop_release(struct inode *inode, struct file *file)
1530{
1531 struct seq_file *seq = file->private_data;
1532
1533 psi_trigger_destroy(seq->private);
1534 return single_release(inode, file);
1535}
1536
1537static const struct proc_ops psi_io_proc_ops = {
1538 .proc_open = psi_io_open,
1539 .proc_read = seq_read,
1540 .proc_lseek = seq_lseek,
1541 .proc_write = psi_io_write,
1542 .proc_poll = psi_fop_poll,
1543 .proc_release = psi_fop_release,
1544};
1545
1546static const struct proc_ops psi_memory_proc_ops = {
1547 .proc_open = psi_memory_open,
1548 .proc_read = seq_read,
1549 .proc_lseek = seq_lseek,
1550 .proc_write = psi_memory_write,
1551 .proc_poll = psi_fop_poll,
1552 .proc_release = psi_fop_release,
1553};
1554
1555static const struct proc_ops psi_cpu_proc_ops = {
1556 .proc_open = psi_cpu_open,
1557 .proc_read = seq_read,
1558 .proc_lseek = seq_lseek,
1559 .proc_write = psi_cpu_write,
1560 .proc_poll = psi_fop_poll,
1561 .proc_release = psi_fop_release,
1562};
1563
1564#ifdef CONFIG_IRQ_TIME_ACCOUNTING
1565static int psi_irq_show(struct seq_file *m, void *v)
1566{
1567 return psi_show(m, &psi_system, PSI_IRQ);
1568}
1569
1570static int psi_irq_open(struct inode *inode, struct file *file)
1571{
1572 return psi_open(file, psi_irq_show);
1573}
1574
1575static ssize_t psi_irq_write(struct file *file, const char __user *user_buf,
1576 size_t nbytes, loff_t *ppos)
1577{
1578 return psi_write(file, user_buf, nbytes, PSI_IRQ);
1579}
1580
1581static const struct proc_ops psi_irq_proc_ops = {
1582 .proc_open = psi_irq_open,
1583 .proc_read = seq_read,
1584 .proc_lseek = seq_lseek,
1585 .proc_write = psi_irq_write,
1586 .proc_poll = psi_fop_poll,
1587 .proc_release = psi_fop_release,
1588};
1589#endif
1590
1591static int __init psi_proc_init(void)
1592{
1593 if (psi_enable) {
1594 proc_mkdir("pressure", NULL);
1595 proc_create("pressure/io", 0666, NULL, &psi_io_proc_ops);
1596 proc_create("pressure/memory", 0666, NULL, &psi_memory_proc_ops);
1597 proc_create("pressure/cpu", 0666, NULL, &psi_cpu_proc_ops);
1598#ifdef CONFIG_IRQ_TIME_ACCOUNTING
1599 proc_create("pressure/irq", 0666, NULL, &psi_irq_proc_ops);
1600#endif
1601 }
1602 return 0;
1603}
1604module_init(psi_proc_init);
1605
1606#endif /* CONFIG_PROC_FS */