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 #include <trace/hooks/psi.h>
155
156 static int psi_bug __read_mostly;
157
158 DEFINE_STATIC_KEY_FALSE(psi_disabled);
159 DEFINE_STATIC_KEY_TRUE(psi_cgroups_enabled);
160
161 #ifdef CONFIG_PSI_DEFAULT_DISABLED
162 static bool psi_enable;
163 #else
164 static bool psi_enable = true;
165 #endif
setup_psi(char * str)166 static int __init setup_psi(char *str)
167 {
168 return kstrtobool(str, &psi_enable) == 0;
169 }
170 __setup("psi=", setup_psi);
171
172 /* Running averages - we need to be higher-res than loadavg */
173 #define PSI_FREQ (2*HZ+1) /* 2 sec intervals */
174 #define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */
175 #define EXP_60s 1981 /* 1/exp(2s/60s) */
176 #define EXP_300s 2034 /* 1/exp(2s/300s) */
177
178 /* PSI trigger definitions */
179 #define WINDOW_MIN_US 500000 /* Min window size is 500ms */
180 #define WINDOW_MAX_US 10000000 /* Max window size is 10s */
181 #define UPDATES_PER_WINDOW 10 /* 10 updates per window */
182
183 /* Sampling frequency in nanoseconds */
184 static u64 psi_period __read_mostly;
185
186 /* System-level pressure and stall tracking */
187 static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu);
188 struct psi_group psi_system = {
189 .pcpu = &system_group_pcpu,
190 };
191 EXPORT_SYMBOL_GPL(psi_system);
192 static void psi_avgs_work(struct work_struct *work);
193
194 static void poll_timer_fn(struct timer_list *t);
195
atomic_set_bit(int i,atomic_t * v)196 static inline void atomic_set_bit(int i, atomic_t *v)
197 {
198 atomic_or(1 << i, v);
199 }
200
atomic_clear_bit(int i,atomic_t * v)201 static inline void atomic_clear_bit(int i, atomic_t *v)
202 {
203 atomic_and(~(1 << i), v);
204 }
205
atomic_fetch_and_set_bit(int i,atomic_t * v)206 static inline int atomic_fetch_and_set_bit(int i, atomic_t *v)
207 {
208 int mask = 1 << i;
209 return atomic_fetch_or(mask, v) & mask;
210 }
211
atomic_fetch_and_clear_bit(int i,atomic_t * v)212 static inline int atomic_fetch_and_clear_bit(int i, atomic_t *v)
213 {
214 int mask = 1 << i;
215 return atomic_fetch_and(~mask, v) & mask;
216 }
217
group_init(struct psi_group * group)218 static void group_init(struct psi_group *group)
219 {
220 int cpu;
221
222 for_each_possible_cpu(cpu)
223 seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq);
224 group->avg_last_update = sched_clock();
225 group->avg_next_update = group->avg_last_update + psi_period;
226 INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work);
227 mutex_init(&group->avgs_lock);
228 /* Init trigger-related members */
229 atomic_set(&group->poll_wakeup, 0);
230 mutex_init(&group->trigger_lock);
231 INIT_LIST_HEAD(&group->triggers);
232 memset(group->nr_triggers, 0, sizeof(group->nr_triggers));
233 group->poll_states = 0;
234 group->poll_min_period = U32_MAX;
235 memset(group->polling_total, 0, sizeof(group->polling_total));
236 group->polling_next_update = ULLONG_MAX;
237 group->polling_until = 0;
238 init_waitqueue_head(&group->poll_wait);
239 timer_setup(&group->poll_timer, poll_timer_fn, 0);
240 rcu_assign_pointer(group->poll_task, NULL);
241 }
242
psi_init(void)243 void __init psi_init(void)
244 {
245 if (!psi_enable) {
246 static_branch_enable(&psi_disabled);
247 return;
248 }
249
250 if (!cgroup_psi_enabled())
251 static_branch_disable(&psi_cgroups_enabled);
252
253 psi_period = jiffies_to_nsecs(PSI_FREQ);
254 group_init(&psi_system);
255 }
256
test_state(unsigned int * tasks,enum psi_states state)257 static bool test_state(unsigned int *tasks, enum psi_states state)
258 {
259 switch (state) {
260 case PSI_IO_SOME:
261 return unlikely(tasks[NR_IOWAIT]);
262 case PSI_IO_FULL:
263 return unlikely(tasks[NR_IOWAIT] && !tasks[NR_RUNNING]);
264 case PSI_MEM_SOME:
265 return unlikely(tasks[NR_MEMSTALL]);
266 case PSI_MEM_FULL:
267 return unlikely(tasks[NR_MEMSTALL] &&
268 tasks[NR_RUNNING] == tasks[NR_MEMSTALL_RUNNING]);
269 case PSI_CPU_SOME:
270 return unlikely(tasks[NR_RUNNING] > tasks[NR_ONCPU]);
271 case PSI_CPU_FULL:
272 return unlikely(tasks[NR_RUNNING] && !tasks[NR_ONCPU]);
273 case PSI_NONIDLE:
274 return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] ||
275 tasks[NR_RUNNING];
276 default:
277 return false;
278 }
279 }
280
get_recent_times(struct psi_group * group,int cpu,enum psi_aggregators aggregator,u32 * times,u32 * pchanged_states)281 static void get_recent_times(struct psi_group *group, int cpu,
282 enum psi_aggregators aggregator, u32 *times,
283 u32 *pchanged_states)
284 {
285 struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu);
286 u64 now, state_start;
287 enum psi_states s;
288 unsigned int seq;
289 u32 state_mask;
290
291 *pchanged_states = 0;
292
293 /* Snapshot a coherent view of the CPU state */
294 do {
295 seq = read_seqcount_begin(&groupc->seq);
296 now = cpu_clock(cpu);
297 memcpy(times, groupc->times, sizeof(groupc->times));
298 state_mask = groupc->state_mask;
299 state_start = groupc->state_start;
300 } while (read_seqcount_retry(&groupc->seq, seq));
301
302 /* Calculate state time deltas against the previous snapshot */
303 for (s = 0; s < NR_PSI_STATES; s++) {
304 u32 delta;
305 /*
306 * In addition to already concluded states, we also
307 * incorporate currently active states on the CPU,
308 * since states may last for many sampling periods.
309 *
310 * This way we keep our delta sampling buckets small
311 * (u32) and our reported pressure close to what's
312 * actually happening.
313 */
314 if (state_mask & (1 << s))
315 times[s] += now - state_start;
316
317 delta = times[s] - groupc->times_prev[aggregator][s];
318 groupc->times_prev[aggregator][s] = times[s];
319
320 times[s] = delta;
321 if (delta)
322 *pchanged_states |= (1 << s);
323 }
324 }
325
calc_avgs(unsigned long avg[3],int missed_periods,u64 time,u64 period)326 static void calc_avgs(unsigned long avg[3], int missed_periods,
327 u64 time, u64 period)
328 {
329 unsigned long pct;
330
331 /* Fill in zeroes for periods of no activity */
332 if (missed_periods) {
333 avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods);
334 avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods);
335 avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods);
336 }
337
338 /* Sample the most recent active period */
339 pct = div_u64(time * 100, period);
340 pct *= FIXED_1;
341 avg[0] = calc_load(avg[0], EXP_10s, pct);
342 avg[1] = calc_load(avg[1], EXP_60s, pct);
343 avg[2] = calc_load(avg[2], EXP_300s, pct);
344 }
345
collect_percpu_times(struct psi_group * group,enum psi_aggregators aggregator,u32 * pchanged_states)346 static void collect_percpu_times(struct psi_group *group,
347 enum psi_aggregators aggregator,
348 u32 *pchanged_states)
349 {
350 u64 deltas[NR_PSI_STATES - 1] = { 0, };
351 unsigned long nonidle_total = 0;
352 u32 changed_states = 0;
353 int cpu;
354 int s;
355
356 /*
357 * Collect the per-cpu time buckets and average them into a
358 * single time sample that is normalized to wallclock time.
359 *
360 * For averaging, each CPU is weighted by its non-idle time in
361 * the sampling period. This eliminates artifacts from uneven
362 * loading, or even entirely idle CPUs.
363 */
364 for_each_possible_cpu(cpu) {
365 u32 times[NR_PSI_STATES];
366 u32 nonidle;
367 u32 cpu_changed_states;
368
369 get_recent_times(group, cpu, aggregator, times,
370 &cpu_changed_states);
371 changed_states |= cpu_changed_states;
372
373 nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]);
374 nonidle_total += nonidle;
375
376 for (s = 0; s < PSI_NONIDLE; s++)
377 deltas[s] += (u64)times[s] * nonidle;
378 }
379
380 /*
381 * Integrate the sample into the running statistics that are
382 * reported to userspace: the cumulative stall times and the
383 * decaying averages.
384 *
385 * Pressure percentages are sampled at PSI_FREQ. We might be
386 * called more often when the user polls more frequently than
387 * that; we might be called less often when there is no task
388 * activity, thus no data, and clock ticks are sporadic. The
389 * below handles both.
390 */
391
392 /* total= */
393 for (s = 0; s < NR_PSI_STATES - 1; s++)
394 group->total[aggregator][s] +=
395 div_u64(deltas[s], max(nonidle_total, 1UL));
396
397 if (pchanged_states)
398 *pchanged_states = changed_states;
399 }
400
update_averages(struct psi_group * group,u64 now)401 static u64 update_averages(struct psi_group *group, u64 now)
402 {
403 unsigned long missed_periods = 0;
404 u64 expires, period;
405 u64 avg_next_update;
406 int s;
407
408 /* avgX= */
409 expires = group->avg_next_update;
410 if (now - expires >= psi_period)
411 missed_periods = div_u64(now - expires, psi_period);
412
413 /*
414 * The periodic clock tick can get delayed for various
415 * reasons, especially on loaded systems. To avoid clock
416 * drift, we schedule the clock in fixed psi_period intervals.
417 * But the deltas we sample out of the per-cpu buckets above
418 * are based on the actual time elapsing between clock ticks.
419 */
420 avg_next_update = expires + ((1 + missed_periods) * psi_period);
421 period = now - (group->avg_last_update + (missed_periods * psi_period));
422 group->avg_last_update = now;
423
424 for (s = 0; s < NR_PSI_STATES - 1; s++) {
425 u32 sample;
426
427 sample = group->total[PSI_AVGS][s] - group->avg_total[s];
428 /*
429 * Due to the lockless sampling of the time buckets,
430 * recorded time deltas can slip into the next period,
431 * which under full pressure can result in samples in
432 * excess of the period length.
433 *
434 * We don't want to report non-sensical pressures in
435 * excess of 100%, nor do we want to drop such events
436 * on the floor. Instead we punt any overage into the
437 * future until pressure subsides. By doing this we
438 * don't underreport the occurring pressure curve, we
439 * just report it delayed by one period length.
440 *
441 * The error isn't cumulative. As soon as another
442 * delta slips from a period P to P+1, by definition
443 * it frees up its time T in P.
444 */
445 if (sample > period)
446 sample = period;
447 group->avg_total[s] += sample;
448 calc_avgs(group->avg[s], missed_periods, sample, period);
449 }
450
451 return avg_next_update;
452 }
453
psi_avgs_work(struct work_struct * work)454 static void psi_avgs_work(struct work_struct *work)
455 {
456 struct delayed_work *dwork;
457 struct psi_group *group;
458 u32 changed_states;
459 bool nonidle;
460 u64 now;
461
462 dwork = to_delayed_work(work);
463 group = container_of(dwork, struct psi_group, avgs_work);
464
465 mutex_lock(&group->avgs_lock);
466
467 now = sched_clock();
468
469 collect_percpu_times(group, PSI_AVGS, &changed_states);
470 nonidle = changed_states & (1 << PSI_NONIDLE);
471 /*
472 * If there is task activity, periodically fold the per-cpu
473 * times and feed samples into the running averages. If things
474 * are idle and there is no data to process, stop the clock.
475 * Once restarted, we'll catch up the running averages in one
476 * go - see calc_avgs() and missed_periods.
477 */
478 if (now >= group->avg_next_update)
479 group->avg_next_update = update_averages(group, now);
480
481 if (nonidle) {
482 schedule_delayed_work(dwork, nsecs_to_jiffies(
483 group->avg_next_update - now) + 1);
484 }
485
486 mutex_unlock(&group->avgs_lock);
487 }
488
489 /* Trigger tracking window manipulations */
window_reset(struct psi_window * win,u64 now,u64 value,u64 prev_growth)490 static void window_reset(struct psi_window *win, u64 now, u64 value,
491 u64 prev_growth)
492 {
493 win->start_time = now;
494 win->start_value = value;
495 win->prev_growth = prev_growth;
496 }
497
498 /*
499 * PSI growth tracking window update and growth calculation routine.
500 *
501 * This approximates a sliding tracking window by interpolating
502 * partially elapsed windows using historical growth data from the
503 * previous intervals. This minimizes memory requirements (by not storing
504 * all the intermediate values in the previous window) and simplifies
505 * the calculations. It works well because PSI signal changes only in
506 * positive direction and over relatively small window sizes the growth
507 * is close to linear.
508 */
window_update(struct psi_window * win,u64 now,u64 value)509 static u64 window_update(struct psi_window *win, u64 now, u64 value)
510 {
511 u64 elapsed;
512 u64 growth;
513
514 elapsed = now - win->start_time;
515 growth = value - win->start_value;
516 /*
517 * After each tracking window passes win->start_value and
518 * win->start_time get reset and win->prev_growth stores
519 * the average per-window growth of the previous window.
520 * win->prev_growth is then used to interpolate additional
521 * growth from the previous window assuming it was linear.
522 */
523 if (elapsed > win->size)
524 window_reset(win, now, value, growth);
525 else {
526 u32 remaining;
527
528 remaining = win->size - elapsed;
529 growth += div64_u64(win->prev_growth * remaining, win->size);
530 }
531
532 return growth;
533 }
534
init_triggers(struct psi_group * group,u64 now)535 static void init_triggers(struct psi_group *group, u64 now)
536 {
537 struct psi_trigger *t;
538
539 list_for_each_entry(t, &group->triggers, node)
540 window_reset(&t->win, now,
541 group->total[PSI_POLL][t->state], 0);
542 memcpy(group->polling_total, group->total[PSI_POLL],
543 sizeof(group->polling_total));
544 group->polling_next_update = now + group->poll_min_period;
545 }
546
update_triggers(struct psi_group * group,u64 now)547 static u64 update_triggers(struct psi_group *group, u64 now)
548 {
549 struct psi_trigger *t;
550 bool new_stall = false;
551 u64 *total = group->total[PSI_POLL];
552
553 /*
554 * On subsequent updates, calculate growth deltas and let
555 * watchers know when their specified thresholds are exceeded.
556 */
557 list_for_each_entry(t, &group->triggers, node) {
558 u64 growth;
559
560 /* Check for stall activity */
561 if (group->polling_total[t->state] == total[t->state])
562 continue;
563
564 /*
565 * Multiple triggers might be looking at the same state,
566 * remember to update group->polling_total[] once we've
567 * been through all of them. Also remember to extend the
568 * polling time if we see new stall activity.
569 */
570 new_stall = true;
571
572 /* Calculate growth since last update */
573 growth = window_update(&t->win, now, total[t->state]);
574 if (growth < t->threshold)
575 continue;
576
577 /* Limit event signaling to once per window */
578 if (now < t->last_event_time + t->win.size)
579 continue;
580
581 trace_android_vh_psi_event(t);
582
583 /* Generate an event */
584 if (cmpxchg(&t->event, 0, 1) == 0)
585 wake_up_interruptible(&t->event_wait);
586 t->last_event_time = now;
587 }
588
589 trace_android_vh_psi_group(group);
590
591 if (new_stall)
592 memcpy(group->polling_total, total,
593 sizeof(group->polling_total));
594
595 return now + group->poll_min_period;
596 }
597
598 /* Schedule polling if it's not already scheduled or forced. */
psi_schedule_poll_work(struct psi_group * group,unsigned long delay,bool force)599 static void psi_schedule_poll_work(struct psi_group *group, unsigned long delay,
600 bool force)
601 {
602 struct task_struct *task;
603
604 /*
605 * atomic_xchg should be called even when !force to provide a
606 * full memory barrier (see the comment inside psi_poll_work).
607 */
608 if (atomic_fetch_and_set_bit(POLL_SCHEDULED, &group->poll_wakeup) &&
609 !force)
610 return;
611
612 rcu_read_lock();
613
614 task = rcu_dereference(group->poll_task);
615 /*
616 * kworker might be NULL in case psi_trigger_destroy races with
617 * psi_task_change (hotpath) which can't use locks
618 */
619 if (likely(task))
620 mod_timer(&group->poll_timer, jiffies + delay);
621 else
622 atomic_clear_bit(POLL_SCHEDULED, &group->poll_wakeup);
623
624 rcu_read_unlock();
625 }
626
psi_poll_work(struct psi_group * group)627 static void psi_poll_work(struct psi_group *group)
628 {
629 bool force_reschedule = false;
630 u32 changed_states;
631 u64 now;
632
633 mutex_lock(&group->trigger_lock);
634
635 now = sched_clock();
636
637 if (now > group->polling_until) {
638 /*
639 * We are either about to start or might stop polling if no
640 * state change was recorded. Resetting poll_scheduled leaves
641 * a small window for psi_group_change to sneak in and schedule
642 * an immegiate poll_work before we get to rescheduling. One
643 * potential extra wakeup at the end of the polling window
644 * should be negligible and polling_next_update still keeps
645 * updates correctly on schedule.
646 */
647 atomic_clear_bit(POLL_SCHEDULED, &group->poll_wakeup);
648 /*
649 * A task change can race with the poll worker that is supposed to
650 * report on it. To avoid missing events, ensure ordering between
651 * poll_scheduled and the task state accesses, such that if the poll
652 * worker misses the state update, the task change is guaranteed to
653 * reschedule the poll worker:
654 *
655 * poll worker:
656 * atomic_set(poll_scheduled, 0)
657 * smp_mb()
658 * LOAD states
659 *
660 * task change:
661 * STORE states
662 * if atomic_xchg(poll_scheduled, 1) == 0:
663 * schedule poll worker
664 *
665 * The atomic_xchg() implies a full barrier.
666 */
667 smp_mb();
668 } else {
669 /* Polling window is not over, keep rescheduling */
670 force_reschedule = true;
671 }
672
673
674 collect_percpu_times(group, PSI_POLL, &changed_states);
675
676 if (changed_states & group->poll_states) {
677 /* Initialize trigger windows when entering polling mode */
678 if (now > group->polling_until)
679 init_triggers(group, now);
680
681 /*
682 * Keep the monitor active for at least the duration of the
683 * minimum tracking window as long as monitor states are
684 * changing.
685 */
686 group->polling_until = now +
687 group->poll_min_period * UPDATES_PER_WINDOW;
688 }
689
690 if (now > group->polling_until) {
691 group->polling_next_update = ULLONG_MAX;
692 goto out;
693 }
694
695 if (now >= group->polling_next_update)
696 group->polling_next_update = update_triggers(group, now);
697
698 psi_schedule_poll_work(group,
699 nsecs_to_jiffies(group->polling_next_update - now) + 1,
700 force_reschedule);
701
702 out:
703 mutex_unlock(&group->trigger_lock);
704 }
705
psi_poll_worker(void * data)706 static int psi_poll_worker(void *data)
707 {
708 struct psi_group *group = (struct psi_group *)data;
709
710 sched_set_fifo_low(current);
711
712 while (true) {
713 wait_event_interruptible(group->poll_wait,
714 atomic_fetch_and_clear_bit(POLL_WAKEUP, &group->poll_wakeup) ||
715 kthread_should_stop());
716 if (kthread_should_stop())
717 break;
718
719 psi_poll_work(group);
720 }
721 return 0;
722 }
723
poll_timer_fn(struct timer_list * t)724 static void poll_timer_fn(struct timer_list *t)
725 {
726 struct psi_group *group = from_timer(group, t, poll_timer);
727
728 atomic_set_bit(POLL_WAKEUP, &group->poll_wakeup);
729 wake_up_interruptible(&group->poll_wait);
730 }
731
record_times(struct psi_group_cpu * groupc,u64 now)732 static void record_times(struct psi_group_cpu *groupc, u64 now)
733 {
734 u32 delta;
735
736 delta = now - groupc->state_start;
737 groupc->state_start = now;
738
739 if (groupc->state_mask & (1 << PSI_IO_SOME)) {
740 groupc->times[PSI_IO_SOME] += delta;
741 if (groupc->state_mask & (1 << PSI_IO_FULL))
742 groupc->times[PSI_IO_FULL] += delta;
743 }
744
745 if (groupc->state_mask & (1 << PSI_MEM_SOME)) {
746 groupc->times[PSI_MEM_SOME] += delta;
747 if (groupc->state_mask & (1 << PSI_MEM_FULL))
748 groupc->times[PSI_MEM_FULL] += delta;
749 }
750
751 if (groupc->state_mask & (1 << PSI_CPU_SOME)) {
752 groupc->times[PSI_CPU_SOME] += delta;
753 if (groupc->state_mask & (1 << PSI_CPU_FULL))
754 groupc->times[PSI_CPU_FULL] += delta;
755 }
756
757 if (groupc->state_mask & (1 << PSI_NONIDLE))
758 groupc->times[PSI_NONIDLE] += delta;
759 }
760
psi_group_change(struct psi_group * group,int cpu,unsigned int clear,unsigned int set,u64 now,bool wake_clock)761 static void psi_group_change(struct psi_group *group, int cpu,
762 unsigned int clear, unsigned int set, u64 now,
763 bool wake_clock)
764 {
765 struct psi_group_cpu *groupc;
766 u32 state_mask = 0;
767 unsigned int t, m;
768 enum psi_states s;
769
770 groupc = per_cpu_ptr(group->pcpu, cpu);
771
772 /*
773 * First we assess the aggregate resource states this CPU's
774 * tasks have been in since the last change, and account any
775 * SOME and FULL time these may have resulted in.
776 *
777 * Then we update the task counts according to the state
778 * change requested through the @clear and @set bits.
779 */
780 write_seqcount_begin(&groupc->seq);
781
782 record_times(groupc, now);
783
784 for (t = 0, m = clear; m; m &= ~(1 << t), t++) {
785 if (!(m & (1 << t)))
786 continue;
787 if (groupc->tasks[t]) {
788 groupc->tasks[t]--;
789 } else if (!psi_bug) {
790 printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u %u] clear=%x set=%x\n",
791 cpu, t, groupc->tasks[0],
792 groupc->tasks[1], groupc->tasks[2],
793 groupc->tasks[3], groupc->tasks[4],
794 clear, set);
795 psi_bug = 1;
796 }
797 }
798
799 for (t = 0; set; set &= ~(1 << t), t++)
800 if (set & (1 << t))
801 groupc->tasks[t]++;
802
803 /* Calculate state mask representing active states */
804 for (s = 0; s < NR_PSI_STATES; s++) {
805 if (test_state(groupc->tasks, s))
806 state_mask |= (1 << s);
807 }
808
809 /*
810 * Since we care about lost potential, a memstall is FULL
811 * when there are no other working tasks, but also when
812 * the CPU is actively reclaiming and nothing productive
813 * could run even if it were runnable. So when the current
814 * task in a cgroup is in_memstall, the corresponding groupc
815 * on that cpu is in PSI_MEM_FULL state.
816 */
817 if (unlikely(groupc->tasks[NR_ONCPU] && cpu_curr(cpu)->in_memstall))
818 state_mask |= (1 << PSI_MEM_FULL);
819
820 groupc->state_mask = state_mask;
821
822 write_seqcount_end(&groupc->seq);
823
824 if (state_mask & group->poll_states)
825 psi_schedule_poll_work(group, 1, false);
826
827 if (wake_clock && !delayed_work_pending(&group->avgs_work))
828 schedule_delayed_work(&group->avgs_work, PSI_FREQ);
829 }
830
iterate_groups(struct task_struct * task,void ** iter)831 static struct psi_group *iterate_groups(struct task_struct *task, void **iter)
832 {
833 if (*iter == &psi_system)
834 return NULL;
835
836 #ifdef CONFIG_CGROUPS
837 if (static_branch_likely(&psi_cgroups_enabled)) {
838 struct cgroup *cgroup = NULL;
839
840 if (!*iter)
841 cgroup = task->cgroups->dfl_cgrp;
842 else
843 cgroup = cgroup_parent(*iter);
844
845 if (cgroup && cgroup_parent(cgroup)) {
846 *iter = cgroup;
847 return cgroup_psi(cgroup);
848 }
849 }
850 #endif
851 *iter = &psi_system;
852 return &psi_system;
853 }
854
psi_flags_change(struct task_struct * task,int clear,int set)855 static void psi_flags_change(struct task_struct *task, int clear, int set)
856 {
857 if (((task->psi_flags & set) ||
858 (task->psi_flags & clear) != clear) &&
859 !psi_bug) {
860 printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n",
861 task->pid, task->comm, task_cpu(task),
862 task->psi_flags, clear, set);
863 psi_bug = 1;
864 }
865
866 task->psi_flags &= ~clear;
867 task->psi_flags |= set;
868 }
869
psi_task_change(struct task_struct * task,int clear,int set)870 void psi_task_change(struct task_struct *task, int clear, int set)
871 {
872 int cpu = task_cpu(task);
873 struct psi_group *group;
874 bool wake_clock = true;
875 void *iter = NULL;
876 u64 now;
877
878 if (!task->pid)
879 return;
880
881 psi_flags_change(task, clear, set);
882
883 now = cpu_clock(cpu);
884 /*
885 * Periodic aggregation shuts off if there is a period of no
886 * task changes, so we wake it back up if necessary. However,
887 * don't do this if the task change is the aggregation worker
888 * itself going to sleep, or we'll ping-pong forever.
889 */
890 if (unlikely((clear & TSK_RUNNING) &&
891 (task->flags & PF_WQ_WORKER) &&
892 wq_worker_last_func(task) == psi_avgs_work))
893 wake_clock = false;
894
895 while ((group = iterate_groups(task, &iter)))
896 psi_group_change(group, cpu, clear, set, now, wake_clock);
897 }
898
psi_task_switch(struct task_struct * prev,struct task_struct * next,bool sleep)899 void psi_task_switch(struct task_struct *prev, struct task_struct *next,
900 bool sleep)
901 {
902 struct psi_group *group, *common = NULL;
903 int cpu = task_cpu(prev);
904 void *iter;
905 u64 now = cpu_clock(cpu);
906
907 if (next->pid) {
908 bool identical_state;
909
910 psi_flags_change(next, 0, TSK_ONCPU);
911 /*
912 * When switching between tasks that have an identical
913 * runtime state, the cgroup that contains both tasks
914 * runtime state, the cgroup that contains both tasks
915 * we reach the first common ancestor. Iterate @next's
916 * ancestors only until we encounter @prev's ONCPU.
917 */
918 identical_state = prev->psi_flags == next->psi_flags;
919 iter = NULL;
920 while ((group = iterate_groups(next, &iter))) {
921 if (identical_state &&
922 per_cpu_ptr(group->pcpu, cpu)->tasks[NR_ONCPU]) {
923 common = group;
924 break;
925 }
926
927 psi_group_change(group, cpu, 0, TSK_ONCPU, now, true);
928 }
929 }
930
931 if (prev->pid) {
932 int clear = TSK_ONCPU, set = 0;
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 psi_flags_change(prev, clear, set);
949
950 iter = NULL;
951 while ((group = iterate_groups(prev, &iter)) && group != common)
952 psi_group_change(group, cpu, clear, set, now, true);
953
954 /*
955 * TSK_ONCPU is handled up to the common ancestor. If we're tasked
956 * with dequeuing too, finish that for the rest of the hierarchy.
957 */
958 if (sleep) {
959 clear &= ~TSK_ONCPU;
960 for (; group; group = iterate_groups(prev, &iter))
961 psi_group_change(group, cpu, clear, set, now, true);
962 }
963 }
964 }
965
966 /**
967 * psi_memstall_enter - mark the beginning of a memory stall section
968 * @flags: flags to handle nested sections
969 *
970 * Marks the calling task as being stalled due to a lack of memory,
971 * such as waiting for a refault or performing reclaim.
972 */
psi_memstall_enter(unsigned long * flags)973 void psi_memstall_enter(unsigned long *flags)
974 {
975 struct rq_flags rf;
976 struct rq *rq;
977
978 if (static_branch_likely(&psi_disabled))
979 return;
980
981 *flags = current->in_memstall;
982 if (*flags)
983 return;
984 /*
985 * in_memstall setting & accounting needs to be atomic wrt
986 * changes to the task's scheduling state, otherwise we can
987 * race with CPU migration.
988 */
989 rq = this_rq_lock_irq(&rf);
990
991 current->in_memstall = 1;
992 psi_task_change(current, 0, TSK_MEMSTALL | TSK_MEMSTALL_RUNNING);
993
994 rq_unlock_irq(rq, &rf);
995 }
996
997 /**
998 * psi_memstall_leave - mark the end of an memory stall section
999 * @flags: flags to handle nested memdelay sections
1000 *
1001 * Marks the calling task as no longer stalled due to lack of memory.
1002 */
psi_memstall_leave(unsigned long * flags)1003 void psi_memstall_leave(unsigned long *flags)
1004 {
1005 struct rq_flags rf;
1006 struct rq *rq;
1007
1008 if (static_branch_likely(&psi_disabled))
1009 return;
1010
1011 if (*flags)
1012 return;
1013 /*
1014 * in_memstall clearing & accounting needs to be atomic wrt
1015 * changes to the task's scheduling state, otherwise we could
1016 * race with CPU migration.
1017 */
1018 rq = this_rq_lock_irq(&rf);
1019
1020 current->in_memstall = 0;
1021 psi_task_change(current, TSK_MEMSTALL | TSK_MEMSTALL_RUNNING, 0);
1022
1023 rq_unlock_irq(rq, &rf);
1024 }
1025
1026 #ifdef CONFIG_CGROUPS
psi_cgroup_alloc(struct cgroup * cgroup)1027 int psi_cgroup_alloc(struct cgroup *cgroup)
1028 {
1029 if (static_branch_likely(&psi_disabled))
1030 return 0;
1031
1032 cgroup->psi.pcpu = alloc_percpu(struct psi_group_cpu);
1033 if (!cgroup->psi.pcpu)
1034 return -ENOMEM;
1035 group_init(&cgroup->psi);
1036 return 0;
1037 }
1038
psi_cgroup_free(struct cgroup * cgroup)1039 void psi_cgroup_free(struct cgroup *cgroup)
1040 {
1041 if (static_branch_likely(&psi_disabled))
1042 return;
1043
1044 cancel_delayed_work_sync(&cgroup->psi.avgs_work);
1045 free_percpu(cgroup->psi.pcpu);
1046 /* All triggers must be removed by now */
1047 WARN_ONCE(cgroup->psi.poll_states, "psi: trigger leak\n");
1048 }
1049
1050 /**
1051 * cgroup_move_task - move task to a different cgroup
1052 * @task: the task
1053 * @to: the target css_set
1054 *
1055 * Move task to a new cgroup and safely migrate its associated stall
1056 * state between the different groups.
1057 *
1058 * This function acquires the task's rq lock to lock out concurrent
1059 * changes to the task's scheduling state and - in case the task is
1060 * running - concurrent changes to its stall state.
1061 */
cgroup_move_task(struct task_struct * task,struct css_set * to)1062 void cgroup_move_task(struct task_struct *task, struct css_set *to)
1063 {
1064 unsigned int task_flags;
1065 struct rq_flags rf;
1066 struct rq *rq;
1067
1068 if (static_branch_likely(&psi_disabled)) {
1069 /*
1070 * Lame to do this here, but the scheduler cannot be locked
1071 * from the outside, so we move cgroups from inside sched/.
1072 */
1073 rcu_assign_pointer(task->cgroups, to);
1074 return;
1075 }
1076
1077 rq = task_rq_lock(task, &rf);
1078
1079 /*
1080 * We may race with schedule() dropping the rq lock between
1081 * deactivating prev and switching to next. Because the psi
1082 * updates from the deactivation are deferred to the switch
1083 * callback to save cgroup tree updates, the task's scheduling
1084 * state here is not coherent with its psi state:
1085 *
1086 * schedule() cgroup_move_task()
1087 * rq_lock()
1088 * deactivate_task()
1089 * p->on_rq = 0
1090 * psi_dequeue() // defers TSK_RUNNING & TSK_IOWAIT updates
1091 * pick_next_task()
1092 * rq_unlock()
1093 * rq_lock()
1094 * psi_task_change() // old cgroup
1095 * task->cgroups = to
1096 * psi_task_change() // new cgroup
1097 * rq_unlock()
1098 * rq_lock()
1099 * psi_sched_switch() // does deferred updates in new cgroup
1100 *
1101 * Don't rely on the scheduling state. Use psi_flags instead.
1102 */
1103 task_flags = task->psi_flags;
1104
1105 if (task_flags)
1106 psi_task_change(task, task_flags, 0);
1107
1108 /* See comment above */
1109 rcu_assign_pointer(task->cgroups, to);
1110
1111 if (task_flags)
1112 psi_task_change(task, 0, task_flags);
1113
1114 task_rq_unlock(rq, task, &rf);
1115 }
1116 #endif /* CONFIG_CGROUPS */
1117
psi_show(struct seq_file * m,struct psi_group * group,enum psi_res res)1118 int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
1119 {
1120 int full;
1121 u64 now;
1122
1123 if (static_branch_likely(&psi_disabled))
1124 return -EOPNOTSUPP;
1125
1126 /* Update averages before reporting them */
1127 mutex_lock(&group->avgs_lock);
1128 now = sched_clock();
1129 collect_percpu_times(group, PSI_AVGS, NULL);
1130 if (now >= group->avg_next_update)
1131 group->avg_next_update = update_averages(group, now);
1132 mutex_unlock(&group->avgs_lock);
1133
1134 for (full = 0; full < 2; full++) {
1135 unsigned long avg[3] = { 0, };
1136 u64 total = 0;
1137 int w;
1138
1139 /* CPU FULL is undefined at the system level */
1140 if (!(group == &psi_system && res == PSI_CPU && full)) {
1141 for (w = 0; w < 3; w++)
1142 avg[w] = group->avg[res * 2 + full][w];
1143 total = div_u64(group->total[PSI_AVGS][res * 2 + full],
1144 NSEC_PER_USEC);
1145 }
1146
1147 seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n",
1148 full ? "full" : "some",
1149 LOAD_INT(avg[0]), LOAD_FRAC(avg[0]),
1150 LOAD_INT(avg[1]), LOAD_FRAC(avg[1]),
1151 LOAD_INT(avg[2]), LOAD_FRAC(avg[2]),
1152 total);
1153 }
1154
1155 return 0;
1156 }
1157
psi_trigger_create(struct psi_group * group,char * buf,size_t nbytes,enum psi_res res)1158 struct psi_trigger *psi_trigger_create(struct psi_group *group,
1159 char *buf, size_t nbytes, enum psi_res res)
1160 {
1161 struct psi_trigger *t;
1162 enum psi_states state;
1163 u32 threshold_us;
1164 u32 window_us;
1165
1166 if (static_branch_likely(&psi_disabled))
1167 return ERR_PTR(-EOPNOTSUPP);
1168
1169 if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2)
1170 state = PSI_IO_SOME + res * 2;
1171 else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2)
1172 state = PSI_IO_FULL + res * 2;
1173 else
1174 return ERR_PTR(-EINVAL);
1175
1176 if (state >= PSI_NONIDLE)
1177 return ERR_PTR(-EINVAL);
1178
1179 if (window_us < WINDOW_MIN_US ||
1180 window_us > WINDOW_MAX_US)
1181 return ERR_PTR(-EINVAL);
1182
1183 /* Check threshold */
1184 if (threshold_us == 0 || threshold_us > window_us)
1185 return ERR_PTR(-EINVAL);
1186
1187 t = kmalloc(sizeof(*t), GFP_KERNEL);
1188 if (!t)
1189 return ERR_PTR(-ENOMEM);
1190
1191 t->group = group;
1192 t->state = state;
1193 t->threshold = threshold_us * NSEC_PER_USEC;
1194 t->win.size = window_us * NSEC_PER_USEC;
1195 window_reset(&t->win, 0, 0, 0);
1196
1197 t->event = 0;
1198 t->last_event_time = 0;
1199 init_waitqueue_head(&t->event_wait);
1200
1201 mutex_lock(&group->trigger_lock);
1202
1203 if (!rcu_access_pointer(group->poll_task)) {
1204 struct task_struct *task;
1205
1206 task = kthread_create(psi_poll_worker, group, "psimon");
1207 if (IS_ERR(task)) {
1208 kfree(t);
1209 mutex_unlock(&group->trigger_lock);
1210 return ERR_CAST(task);
1211 }
1212 atomic_clear_bit(POLL_WAKEUP, &group->poll_wakeup);
1213 wake_up_process(task);
1214 rcu_assign_pointer(group->poll_task, task);
1215 }
1216
1217 list_add(&t->node, &group->triggers);
1218 group->poll_min_period = min(group->poll_min_period,
1219 div_u64(t->win.size, UPDATES_PER_WINDOW));
1220 group->nr_triggers[t->state]++;
1221 group->poll_states |= (1 << t->state);
1222
1223 mutex_unlock(&group->trigger_lock);
1224
1225 return t;
1226 }
1227
psi_trigger_destroy(struct psi_trigger * t)1228 void psi_trigger_destroy(struct psi_trigger *t)
1229 {
1230 struct psi_group *group;
1231 struct task_struct *task_to_destroy = NULL;
1232
1233 /*
1234 * We do not check psi_disabled since it might have been disabled after
1235 * the trigger got created.
1236 */
1237 if (!t)
1238 return;
1239
1240 group = t->group;
1241 /*
1242 * Wakeup waiters to stop polling and clear the queue to prevent it from
1243 * being accessed later. Can happen if cgroup is deleted from under a
1244 * polling process.
1245 */
1246 wake_up_pollfree(&t->event_wait);
1247
1248 mutex_lock(&group->trigger_lock);
1249
1250 if (!list_empty(&t->node)) {
1251 struct psi_trigger *tmp;
1252 u64 period = ULLONG_MAX;
1253
1254 list_del(&t->node);
1255 group->nr_triggers[t->state]--;
1256 if (!group->nr_triggers[t->state])
1257 group->poll_states &= ~(1 << t->state);
1258 /* reset min update period for the remaining triggers */
1259 list_for_each_entry(tmp, &group->triggers, node)
1260 period = min(period, div_u64(tmp->win.size,
1261 UPDATES_PER_WINDOW));
1262 group->poll_min_period = period;
1263 /* Destroy poll_task when the last trigger is destroyed */
1264 if (group->poll_states == 0) {
1265 group->polling_until = 0;
1266 task_to_destroy = rcu_dereference_protected(
1267 group->poll_task,
1268 lockdep_is_held(&group->trigger_lock));
1269 rcu_assign_pointer(group->poll_task, NULL);
1270 del_timer(&group->poll_timer);
1271 }
1272 }
1273
1274 mutex_unlock(&group->trigger_lock);
1275
1276 /*
1277 * Wait for psi_schedule_poll_work RCU to complete its read-side
1278 * critical section before destroying the trigger and optionally the
1279 * poll_task.
1280 */
1281 synchronize_rcu();
1282 /*
1283 * Stop kthread 'psimon' after releasing trigger_lock to prevent a
1284 * deadlock while waiting for psi_poll_work to acquire trigger_lock
1285 */
1286 if (task_to_destroy) {
1287 /*
1288 * After the RCU grace period has expired, the worker
1289 * can no longer be found through group->poll_task.
1290 */
1291 kthread_stop(task_to_destroy);
1292 atomic_clear_bit(POLL_SCHEDULED, &group->poll_wakeup);
1293 }
1294 kfree(t);
1295 }
1296
psi_trigger_poll(void ** trigger_ptr,struct file * file,poll_table * wait)1297 __poll_t psi_trigger_poll(void **trigger_ptr,
1298 struct file *file, poll_table *wait)
1299 {
1300 __poll_t ret = DEFAULT_POLLMASK;
1301 struct psi_trigger *t;
1302
1303 if (static_branch_likely(&psi_disabled))
1304 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
1305
1306 t = smp_load_acquire(trigger_ptr);
1307 if (!t)
1308 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
1309
1310 poll_wait(file, &t->event_wait, wait);
1311
1312 if (cmpxchg(&t->event, 1, 0) == 1)
1313 ret |= EPOLLPRI;
1314
1315 return ret;
1316 }
1317
1318 #ifdef CONFIG_PROC_FS
psi_io_show(struct seq_file * m,void * v)1319 static int psi_io_show(struct seq_file *m, void *v)
1320 {
1321 return psi_show(m, &psi_system, PSI_IO);
1322 }
1323
psi_memory_show(struct seq_file * m,void * v)1324 static int psi_memory_show(struct seq_file *m, void *v)
1325 {
1326 return psi_show(m, &psi_system, PSI_MEM);
1327 }
1328
psi_cpu_show(struct seq_file * m,void * v)1329 static int psi_cpu_show(struct seq_file *m, void *v)
1330 {
1331 return psi_show(m, &psi_system, PSI_CPU);
1332 }
1333
psi_io_open(struct inode * inode,struct file * file)1334 static int psi_io_open(struct inode *inode, struct file *file)
1335 {
1336 return single_open(file, psi_io_show, NULL);
1337 }
1338
psi_memory_open(struct inode * inode,struct file * file)1339 static int psi_memory_open(struct inode *inode, struct file *file)
1340 {
1341 return single_open(file, psi_memory_show, NULL);
1342 }
1343
psi_cpu_open(struct inode * inode,struct file * file)1344 static int psi_cpu_open(struct inode *inode, struct file *file)
1345 {
1346 return single_open(file, psi_cpu_show, NULL);
1347 }
1348
psi_write(struct file * file,const char __user * user_buf,size_t nbytes,enum psi_res res)1349 static ssize_t psi_write(struct file *file, const char __user *user_buf,
1350 size_t nbytes, enum psi_res res)
1351 {
1352 char buf[32];
1353 size_t buf_size;
1354 struct seq_file *seq;
1355 struct psi_trigger *new;
1356
1357 if (static_branch_likely(&psi_disabled))
1358 return -EOPNOTSUPP;
1359
1360 if (!nbytes)
1361 return -EINVAL;
1362
1363 buf_size = min(nbytes, sizeof(buf));
1364 if (copy_from_user(buf, user_buf, buf_size))
1365 return -EFAULT;
1366
1367 buf[buf_size - 1] = '\0';
1368
1369 seq = file->private_data;
1370
1371 /* Take seq->lock to protect seq->private from concurrent writes */
1372 mutex_lock(&seq->lock);
1373
1374 /* Allow only one trigger per file descriptor */
1375 if (seq->private) {
1376 mutex_unlock(&seq->lock);
1377 return -EBUSY;
1378 }
1379
1380 new = psi_trigger_create(&psi_system, buf, nbytes, res);
1381 if (IS_ERR(new)) {
1382 mutex_unlock(&seq->lock);
1383 return PTR_ERR(new);
1384 }
1385
1386 smp_store_release(&seq->private, new);
1387 mutex_unlock(&seq->lock);
1388
1389 return nbytes;
1390 }
1391
psi_io_write(struct file * file,const char __user * user_buf,size_t nbytes,loff_t * ppos)1392 static ssize_t psi_io_write(struct file *file, const char __user *user_buf,
1393 size_t nbytes, loff_t *ppos)
1394 {
1395 return psi_write(file, user_buf, nbytes, PSI_IO);
1396 }
1397
psi_memory_write(struct file * file,const char __user * user_buf,size_t nbytes,loff_t * ppos)1398 static ssize_t psi_memory_write(struct file *file, const char __user *user_buf,
1399 size_t nbytes, loff_t *ppos)
1400 {
1401 return psi_write(file, user_buf, nbytes, PSI_MEM);
1402 }
1403
psi_cpu_write(struct file * file,const char __user * user_buf,size_t nbytes,loff_t * ppos)1404 static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf,
1405 size_t nbytes, loff_t *ppos)
1406 {
1407 return psi_write(file, user_buf, nbytes, PSI_CPU);
1408 }
1409
psi_fop_poll(struct file * file,poll_table * wait)1410 static __poll_t psi_fop_poll(struct file *file, poll_table *wait)
1411 {
1412 struct seq_file *seq = file->private_data;
1413
1414 return psi_trigger_poll(&seq->private, file, wait);
1415 }
1416
psi_fop_release(struct inode * inode,struct file * file)1417 static int psi_fop_release(struct inode *inode, struct file *file)
1418 {
1419 struct seq_file *seq = file->private_data;
1420
1421 psi_trigger_destroy(seq->private);
1422 return single_release(inode, file);
1423 }
1424
1425 static const struct proc_ops psi_io_proc_ops = {
1426 .proc_open = psi_io_open,
1427 .proc_read = seq_read,
1428 .proc_lseek = seq_lseek,
1429 .proc_write = psi_io_write,
1430 .proc_poll = psi_fop_poll,
1431 .proc_release = psi_fop_release,
1432 };
1433
1434 static const struct proc_ops psi_memory_proc_ops = {
1435 .proc_open = psi_memory_open,
1436 .proc_read = seq_read,
1437 .proc_lseek = seq_lseek,
1438 .proc_write = psi_memory_write,
1439 .proc_poll = psi_fop_poll,
1440 .proc_release = psi_fop_release,
1441 };
1442
1443 static const struct proc_ops psi_cpu_proc_ops = {
1444 .proc_open = psi_cpu_open,
1445 .proc_read = seq_read,
1446 .proc_lseek = seq_lseek,
1447 .proc_write = psi_cpu_write,
1448 .proc_poll = psi_fop_poll,
1449 .proc_release = psi_fop_release,
1450 };
1451
psi_proc_init(void)1452 static int __init psi_proc_init(void)
1453 {
1454 if (psi_enable) {
1455 proc_mkdir("pressure", NULL);
1456 proc_create("pressure/io", 0, NULL, &psi_io_proc_ops);
1457 proc_create("pressure/memory", 0, NULL, &psi_memory_proc_ops);
1458 proc_create("pressure/cpu", 0, NULL, &psi_cpu_proc_ops);
1459 }
1460 return 0;
1461 }
1462 module_init(psi_proc_init);
1463
1464 #endif /* CONFIG_PROC_FS */
1465