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