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