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eb414681 JW |
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 | * When CPU, memory and IO are contended, tasks experience delays that | |
8 | * reduce throughput and introduce latencies into the workload. Memory | |
9 | * and IO contention, in addition, can cause a full loss of forward | |
10 | * progress in which the CPU goes idle. | |
11 | * | |
12 | * This code aggregates individual task delays into resource pressure | |
13 | * metrics that indicate problems with both workload health and | |
14 | * resource utilization. | |
15 | * | |
16 | * Model | |
17 | * | |
18 | * The time in which a task can execute on a CPU is our baseline for | |
19 | * productivity. Pressure expresses the amount of time in which this | |
20 | * potential cannot be realized due to resource contention. | |
21 | * | |
22 | * This concept of productivity has two components: the workload and | |
23 | * the CPU. To measure the impact of pressure on both, we define two | |
24 | * contention states for a resource: SOME and FULL. | |
25 | * | |
26 | * In the SOME state of a given resource, one or more tasks are | |
27 | * delayed on that resource. This affects the workload's ability to | |
28 | * perform work, but the CPU may still be executing other tasks. | |
29 | * | |
30 | * In the FULL state of a given resource, all non-idle tasks are | |
31 | * delayed on that resource such that nobody is advancing and the CPU | |
32 | * goes idle. This leaves both workload and CPU unproductive. | |
33 | * | |
34 | * (Naturally, the FULL state doesn't exist for the CPU resource.) | |
35 | * | |
36 | * SOME = nr_delayed_tasks != 0 | |
37 | * FULL = nr_delayed_tasks != 0 && nr_running_tasks == 0 | |
38 | * | |
39 | * The percentage of wallclock time spent in those compound stall | |
40 | * states gives pressure numbers between 0 and 100 for each resource, | |
41 | * where the SOME percentage indicates workload slowdowns and the FULL | |
42 | * percentage indicates reduced CPU utilization: | |
43 | * | |
44 | * %SOME = time(SOME) / period | |
45 | * %FULL = time(FULL) / period | |
46 | * | |
47 | * Multiple CPUs | |
48 | * | |
49 | * The more tasks and available CPUs there are, the more work can be | |
50 | * performed concurrently. This means that the potential that can go | |
51 | * unrealized due to resource contention *also* scales with non-idle | |
52 | * tasks and CPUs. | |
53 | * | |
54 | * Consider a scenario where 257 number crunching tasks are trying to | |
55 | * run concurrently on 256 CPUs. If we simply aggregated the task | |
56 | * states, we would have to conclude a CPU SOME pressure number of | |
57 | * 100%, since *somebody* is waiting on a runqueue at all | |
58 | * times. However, that is clearly not the amount of contention the | |
59 | * workload is experiencing: only one out of 256 possible exceution | |
60 | * threads will be contended at any given time, or about 0.4%. | |
61 | * | |
62 | * Conversely, consider a scenario of 4 tasks and 4 CPUs where at any | |
63 | * given time *one* of the tasks is delayed due to a lack of memory. | |
64 | * Again, looking purely at the task state would yield a memory FULL | |
65 | * pressure number of 0%, since *somebody* is always making forward | |
66 | * progress. But again this wouldn't capture the amount of execution | |
67 | * potential lost, which is 1 out of 4 CPUs, or 25%. | |
68 | * | |
69 | * To calculate wasted potential (pressure) with multiple processors, | |
70 | * we have to base our calculation on the number of non-idle tasks in | |
71 | * conjunction with the number of available CPUs, which is the number | |
72 | * of potential execution threads. SOME becomes then the proportion of | |
73 | * delayed tasks to possibe threads, and FULL is the share of possible | |
74 | * threads that are unproductive due to delays: | |
75 | * | |
76 | * threads = min(nr_nonidle_tasks, nr_cpus) | |
77 | * SOME = min(nr_delayed_tasks / threads, 1) | |
78 | * FULL = (threads - min(nr_running_tasks, threads)) / threads | |
79 | * | |
80 | * For the 257 number crunchers on 256 CPUs, this yields: | |
81 | * | |
82 | * threads = min(257, 256) | |
83 | * SOME = min(1 / 256, 1) = 0.4% | |
84 | * FULL = (256 - min(257, 256)) / 256 = 0% | |
85 | * | |
86 | * For the 1 out of 4 memory-delayed tasks, this yields: | |
87 | * | |
88 | * threads = min(4, 4) | |
89 | * SOME = min(1 / 4, 1) = 25% | |
90 | * FULL = (4 - min(3, 4)) / 4 = 25% | |
91 | * | |
92 | * [ Substitute nr_cpus with 1, and you can see that it's a natural | |
93 | * extension of the single-CPU model. ] | |
94 | * | |
95 | * Implementation | |
96 | * | |
97 | * To assess the precise time spent in each such state, we would have | |
98 | * to freeze the system on task changes and start/stop the state | |
99 | * clocks accordingly. Obviously that doesn't scale in practice. | |
100 | * | |
101 | * Because the scheduler aims to distribute the compute load evenly | |
102 | * among the available CPUs, we can track task state locally to each | |
103 | * CPU and, at much lower frequency, extrapolate the global state for | |
104 | * the cumulative stall times and the running averages. | |
105 | * | |
106 | * For each runqueue, we track: | |
107 | * | |
108 | * tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0) | |
109 | * tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_running_tasks[cpu]) | |
110 | * tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0) | |
111 | * | |
112 | * and then periodically aggregate: | |
113 | * | |
114 | * tNONIDLE = sum(tNONIDLE[i]) | |
115 | * | |
116 | * tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE | |
117 | * tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE | |
118 | * | |
119 | * %SOME = tSOME / period | |
120 | * %FULL = tFULL / period | |
121 | * | |
122 | * This gives us an approximation of pressure that is practical | |
123 | * cost-wise, yet way more sensitive and accurate than periodic | |
124 | * sampling of the aggregate task states would be. | |
125 | */ | |
126 | ||
1b69ac6b | 127 | #include "../workqueue_internal.h" |
eb414681 JW |
128 | #include <linux/sched/loadavg.h> |
129 | #include <linux/seq_file.h> | |
130 | #include <linux/proc_fs.h> | |
131 | #include <linux/seqlock.h> | |
132 | #include <linux/cgroup.h> | |
133 | #include <linux/module.h> | |
134 | #include <linux/sched.h> | |
135 | #include <linux/psi.h> | |
136 | #include "sched.h" | |
137 | ||
138 | static int psi_bug __read_mostly; | |
139 | ||
e0c27447 JW |
140 | DEFINE_STATIC_KEY_FALSE(psi_disabled); |
141 | ||
142 | #ifdef CONFIG_PSI_DEFAULT_DISABLED | |
9289c5e6 | 143 | static bool psi_enable; |
e0c27447 | 144 | #else |
9289c5e6 | 145 | static bool psi_enable = true; |
e0c27447 JW |
146 | #endif |
147 | static int __init setup_psi(char *str) | |
148 | { | |
149 | return kstrtobool(str, &psi_enable) == 0; | |
150 | } | |
151 | __setup("psi=", setup_psi); | |
eb414681 JW |
152 | |
153 | /* Running averages - we need to be higher-res than loadavg */ | |
154 | #define PSI_FREQ (2*HZ+1) /* 2 sec intervals */ | |
155 | #define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */ | |
156 | #define EXP_60s 1981 /* 1/exp(2s/60s) */ | |
157 | #define EXP_300s 2034 /* 1/exp(2s/300s) */ | |
158 | ||
159 | /* Sampling frequency in nanoseconds */ | |
160 | static u64 psi_period __read_mostly; | |
161 | ||
162 | /* System-level pressure and stall tracking */ | |
163 | static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu); | |
164 | static struct psi_group psi_system = { | |
165 | .pcpu = &system_group_pcpu, | |
166 | }; | |
167 | ||
bcc78db6 | 168 | static void psi_avgs_work(struct work_struct *work); |
eb414681 JW |
169 | |
170 | static void group_init(struct psi_group *group) | |
171 | { | |
172 | int cpu; | |
173 | ||
174 | for_each_possible_cpu(cpu) | |
175 | seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq); | |
bcc78db6 SB |
176 | group->avg_next_update = sched_clock() + psi_period; |
177 | INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work); | |
178 | mutex_init(&group->avgs_lock); | |
eb414681 JW |
179 | } |
180 | ||
181 | void __init psi_init(void) | |
182 | { | |
e0c27447 JW |
183 | if (!psi_enable) { |
184 | static_branch_enable(&psi_disabled); | |
eb414681 | 185 | return; |
e0c27447 | 186 | } |
eb414681 JW |
187 | |
188 | psi_period = jiffies_to_nsecs(PSI_FREQ); | |
189 | group_init(&psi_system); | |
190 | } | |
191 | ||
192 | static bool test_state(unsigned int *tasks, enum psi_states state) | |
193 | { | |
194 | switch (state) { | |
195 | case PSI_IO_SOME: | |
196 | return tasks[NR_IOWAIT]; | |
197 | case PSI_IO_FULL: | |
198 | return tasks[NR_IOWAIT] && !tasks[NR_RUNNING]; | |
199 | case PSI_MEM_SOME: | |
200 | return tasks[NR_MEMSTALL]; | |
201 | case PSI_MEM_FULL: | |
202 | return tasks[NR_MEMSTALL] && !tasks[NR_RUNNING]; | |
203 | case PSI_CPU_SOME: | |
204 | return tasks[NR_RUNNING] > 1; | |
205 | case PSI_NONIDLE: | |
206 | return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] || | |
207 | tasks[NR_RUNNING]; | |
208 | default: | |
209 | return false; | |
210 | } | |
211 | } | |
212 | ||
213 | static void get_recent_times(struct psi_group *group, int cpu, u32 *times) | |
214 | { | |
215 | struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu); | |
eb414681 | 216 | u64 now, state_start; |
33b2d630 | 217 | enum psi_states s; |
eb414681 | 218 | unsigned int seq; |
33b2d630 | 219 | u32 state_mask; |
eb414681 JW |
220 | |
221 | /* Snapshot a coherent view of the CPU state */ | |
222 | do { | |
223 | seq = read_seqcount_begin(&groupc->seq); | |
224 | now = cpu_clock(cpu); | |
225 | memcpy(times, groupc->times, sizeof(groupc->times)); | |
33b2d630 | 226 | state_mask = groupc->state_mask; |
eb414681 JW |
227 | state_start = groupc->state_start; |
228 | } while (read_seqcount_retry(&groupc->seq, seq)); | |
229 | ||
230 | /* Calculate state time deltas against the previous snapshot */ | |
231 | for (s = 0; s < NR_PSI_STATES; s++) { | |
232 | u32 delta; | |
233 | /* | |
234 | * In addition to already concluded states, we also | |
235 | * incorporate currently active states on the CPU, | |
236 | * since states may last for many sampling periods. | |
237 | * | |
238 | * This way we keep our delta sampling buckets small | |
239 | * (u32) and our reported pressure close to what's | |
240 | * actually happening. | |
241 | */ | |
33b2d630 | 242 | if (state_mask & (1 << s)) |
eb414681 JW |
243 | times[s] += now - state_start; |
244 | ||
245 | delta = times[s] - groupc->times_prev[s]; | |
246 | groupc->times_prev[s] = times[s]; | |
247 | ||
248 | times[s] = delta; | |
249 | } | |
250 | } | |
251 | ||
252 | static void calc_avgs(unsigned long avg[3], int missed_periods, | |
253 | u64 time, u64 period) | |
254 | { | |
255 | unsigned long pct; | |
256 | ||
257 | /* Fill in zeroes for periods of no activity */ | |
258 | if (missed_periods) { | |
259 | avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods); | |
260 | avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods); | |
261 | avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods); | |
262 | } | |
263 | ||
264 | /* Sample the most recent active period */ | |
265 | pct = div_u64(time * 100, period); | |
266 | pct *= FIXED_1; | |
267 | avg[0] = calc_load(avg[0], EXP_10s, pct); | |
268 | avg[1] = calc_load(avg[1], EXP_60s, pct); | |
269 | avg[2] = calc_load(avg[2], EXP_300s, pct); | |
270 | } | |
271 | ||
7fc70a39 | 272 | static bool collect_percpu_times(struct psi_group *group) |
eb414681 JW |
273 | { |
274 | u64 deltas[NR_PSI_STATES - 1] = { 0, }; | |
eb414681 | 275 | unsigned long nonidle_total = 0; |
eb414681 JW |
276 | int cpu; |
277 | int s; | |
278 | ||
eb414681 JW |
279 | /* |
280 | * Collect the per-cpu time buckets and average them into a | |
281 | * single time sample that is normalized to wallclock time. | |
282 | * | |
283 | * For averaging, each CPU is weighted by its non-idle time in | |
284 | * the sampling period. This eliminates artifacts from uneven | |
285 | * loading, or even entirely idle CPUs. | |
286 | */ | |
287 | for_each_possible_cpu(cpu) { | |
288 | u32 times[NR_PSI_STATES]; | |
289 | u32 nonidle; | |
290 | ||
291 | get_recent_times(group, cpu, times); | |
292 | ||
293 | nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]); | |
294 | nonidle_total += nonidle; | |
295 | ||
296 | for (s = 0; s < PSI_NONIDLE; s++) | |
297 | deltas[s] += (u64)times[s] * nonidle; | |
298 | } | |
299 | ||
300 | /* | |
301 | * Integrate the sample into the running statistics that are | |
302 | * reported to userspace: the cumulative stall times and the | |
303 | * decaying averages. | |
304 | * | |
305 | * Pressure percentages are sampled at PSI_FREQ. We might be | |
306 | * called more often when the user polls more frequently than | |
307 | * that; we might be called less often when there is no task | |
308 | * activity, thus no data, and clock ticks are sporadic. The | |
309 | * below handles both. | |
310 | */ | |
311 | ||
312 | /* total= */ | |
313 | for (s = 0; s < NR_PSI_STATES - 1; s++) | |
314 | group->total[s] += div_u64(deltas[s], max(nonidle_total, 1UL)); | |
315 | ||
7fc70a39 SB |
316 | return nonidle_total; |
317 | } | |
318 | ||
319 | static u64 update_averages(struct psi_group *group, u64 now) | |
320 | { | |
321 | unsigned long missed_periods = 0; | |
322 | u64 expires, period; | |
323 | u64 avg_next_update; | |
324 | int s; | |
325 | ||
eb414681 | 326 | /* avgX= */ |
bcc78db6 | 327 | expires = group->avg_next_update; |
4e37504d | 328 | if (now - expires >= psi_period) |
eb414681 JW |
329 | missed_periods = div_u64(now - expires, psi_period); |
330 | ||
331 | /* | |
332 | * The periodic clock tick can get delayed for various | |
333 | * reasons, especially on loaded systems. To avoid clock | |
334 | * drift, we schedule the clock in fixed psi_period intervals. | |
335 | * But the deltas we sample out of the per-cpu buckets above | |
336 | * are based on the actual time elapsing between clock ticks. | |
337 | */ | |
7fc70a39 | 338 | avg_next_update = expires + ((1 + missed_periods) * psi_period); |
bcc78db6 SB |
339 | period = now - (group->avg_last_update + (missed_periods * psi_period)); |
340 | group->avg_last_update = now; | |
eb414681 JW |
341 | |
342 | for (s = 0; s < NR_PSI_STATES - 1; s++) { | |
343 | u32 sample; | |
344 | ||
bcc78db6 | 345 | sample = group->total[s] - group->avg_total[s]; |
eb414681 JW |
346 | /* |
347 | * Due to the lockless sampling of the time buckets, | |
348 | * recorded time deltas can slip into the next period, | |
349 | * which under full pressure can result in samples in | |
350 | * excess of the period length. | |
351 | * | |
352 | * We don't want to report non-sensical pressures in | |
353 | * excess of 100%, nor do we want to drop such events | |
354 | * on the floor. Instead we punt any overage into the | |
355 | * future until pressure subsides. By doing this we | |
356 | * don't underreport the occurring pressure curve, we | |
357 | * just report it delayed by one period length. | |
358 | * | |
359 | * The error isn't cumulative. As soon as another | |
360 | * delta slips from a period P to P+1, by definition | |
361 | * it frees up its time T in P. | |
362 | */ | |
363 | if (sample > period) | |
364 | sample = period; | |
bcc78db6 | 365 | group->avg_total[s] += sample; |
eb414681 JW |
366 | calc_avgs(group->avg[s], missed_periods, sample, period); |
367 | } | |
7fc70a39 SB |
368 | |
369 | return avg_next_update; | |
eb414681 JW |
370 | } |
371 | ||
bcc78db6 | 372 | static void psi_avgs_work(struct work_struct *work) |
eb414681 JW |
373 | { |
374 | struct delayed_work *dwork; | |
375 | struct psi_group *group; | |
376 | bool nonidle; | |
7fc70a39 | 377 | u64 now; |
eb414681 JW |
378 | |
379 | dwork = to_delayed_work(work); | |
bcc78db6 | 380 | group = container_of(dwork, struct psi_group, avgs_work); |
eb414681 | 381 | |
7fc70a39 SB |
382 | mutex_lock(&group->avgs_lock); |
383 | ||
384 | now = sched_clock(); | |
385 | ||
386 | nonidle = collect_percpu_times(group); | |
eb414681 JW |
387 | /* |
388 | * If there is task activity, periodically fold the per-cpu | |
389 | * times and feed samples into the running averages. If things | |
390 | * are idle and there is no data to process, stop the clock. | |
391 | * Once restarted, we'll catch up the running averages in one | |
392 | * go - see calc_avgs() and missed_periods. | |
393 | */ | |
7fc70a39 SB |
394 | if (now >= group->avg_next_update) |
395 | group->avg_next_update = update_averages(group, now); | |
eb414681 JW |
396 | |
397 | if (nonidle) { | |
7fc70a39 SB |
398 | schedule_delayed_work(dwork, nsecs_to_jiffies( |
399 | group->avg_next_update - now) + 1); | |
eb414681 | 400 | } |
7fc70a39 SB |
401 | |
402 | mutex_unlock(&group->avgs_lock); | |
eb414681 JW |
403 | } |
404 | ||
405 | static void record_times(struct psi_group_cpu *groupc, int cpu, | |
406 | bool memstall_tick) | |
407 | { | |
408 | u32 delta; | |
409 | u64 now; | |
410 | ||
411 | now = cpu_clock(cpu); | |
412 | delta = now - groupc->state_start; | |
413 | groupc->state_start = now; | |
414 | ||
33b2d630 | 415 | if (groupc->state_mask & (1 << PSI_IO_SOME)) { |
eb414681 | 416 | groupc->times[PSI_IO_SOME] += delta; |
33b2d630 | 417 | if (groupc->state_mask & (1 << PSI_IO_FULL)) |
eb414681 JW |
418 | groupc->times[PSI_IO_FULL] += delta; |
419 | } | |
420 | ||
33b2d630 | 421 | if (groupc->state_mask & (1 << PSI_MEM_SOME)) { |
eb414681 | 422 | groupc->times[PSI_MEM_SOME] += delta; |
33b2d630 | 423 | if (groupc->state_mask & (1 << PSI_MEM_FULL)) |
eb414681 JW |
424 | groupc->times[PSI_MEM_FULL] += delta; |
425 | else if (memstall_tick) { | |
426 | u32 sample; | |
427 | /* | |
428 | * Since we care about lost potential, a | |
429 | * memstall is FULL when there are no other | |
430 | * working tasks, but also when the CPU is | |
431 | * actively reclaiming and nothing productive | |
432 | * could run even if it were runnable. | |
433 | * | |
434 | * When the timer tick sees a reclaiming CPU, | |
435 | * regardless of runnable tasks, sample a FULL | |
436 | * tick (or less if it hasn't been a full tick | |
437 | * since the last state change). | |
438 | */ | |
439 | sample = min(delta, (u32)jiffies_to_nsecs(1)); | |
440 | groupc->times[PSI_MEM_FULL] += sample; | |
441 | } | |
442 | } | |
443 | ||
33b2d630 | 444 | if (groupc->state_mask & (1 << PSI_CPU_SOME)) |
eb414681 JW |
445 | groupc->times[PSI_CPU_SOME] += delta; |
446 | ||
33b2d630 | 447 | if (groupc->state_mask & (1 << PSI_NONIDLE)) |
eb414681 JW |
448 | groupc->times[PSI_NONIDLE] += delta; |
449 | } | |
450 | ||
451 | static void psi_group_change(struct psi_group *group, int cpu, | |
452 | unsigned int clear, unsigned int set) | |
453 | { | |
454 | struct psi_group_cpu *groupc; | |
455 | unsigned int t, m; | |
33b2d630 SB |
456 | enum psi_states s; |
457 | u32 state_mask = 0; | |
eb414681 JW |
458 | |
459 | groupc = per_cpu_ptr(group->pcpu, cpu); | |
460 | ||
461 | /* | |
462 | * First we assess the aggregate resource states this CPU's | |
463 | * tasks have been in since the last change, and account any | |
464 | * SOME and FULL time these may have resulted in. | |
465 | * | |
466 | * Then we update the task counts according to the state | |
467 | * change requested through the @clear and @set bits. | |
468 | */ | |
469 | write_seqcount_begin(&groupc->seq); | |
470 | ||
471 | record_times(groupc, cpu, false); | |
472 | ||
473 | for (t = 0, m = clear; m; m &= ~(1 << t), t++) { | |
474 | if (!(m & (1 << t))) | |
475 | continue; | |
476 | if (groupc->tasks[t] == 0 && !psi_bug) { | |
477 | printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u] clear=%x set=%x\n", | |
478 | cpu, t, groupc->tasks[0], | |
479 | groupc->tasks[1], groupc->tasks[2], | |
480 | clear, set); | |
481 | psi_bug = 1; | |
482 | } | |
483 | groupc->tasks[t]--; | |
484 | } | |
485 | ||
486 | for (t = 0; set; set &= ~(1 << t), t++) | |
487 | if (set & (1 << t)) | |
488 | groupc->tasks[t]++; | |
489 | ||
33b2d630 SB |
490 | /* Calculate state mask representing active states */ |
491 | for (s = 0; s < NR_PSI_STATES; s++) { | |
492 | if (test_state(groupc->tasks, s)) | |
493 | state_mask |= (1 << s); | |
494 | } | |
495 | groupc->state_mask = state_mask; | |
496 | ||
eb414681 | 497 | write_seqcount_end(&groupc->seq); |
eb414681 JW |
498 | } |
499 | ||
2ce7135a JW |
500 | static struct psi_group *iterate_groups(struct task_struct *task, void **iter) |
501 | { | |
502 | #ifdef CONFIG_CGROUPS | |
503 | struct cgroup *cgroup = NULL; | |
504 | ||
505 | if (!*iter) | |
506 | cgroup = task->cgroups->dfl_cgrp; | |
507 | else if (*iter == &psi_system) | |
508 | return NULL; | |
509 | else | |
510 | cgroup = cgroup_parent(*iter); | |
511 | ||
512 | if (cgroup && cgroup_parent(cgroup)) { | |
513 | *iter = cgroup; | |
514 | return cgroup_psi(cgroup); | |
515 | } | |
516 | #else | |
517 | if (*iter) | |
518 | return NULL; | |
519 | #endif | |
520 | *iter = &psi_system; | |
521 | return &psi_system; | |
522 | } | |
523 | ||
eb414681 JW |
524 | void psi_task_change(struct task_struct *task, int clear, int set) |
525 | { | |
526 | int cpu = task_cpu(task); | |
2ce7135a | 527 | struct psi_group *group; |
1b69ac6b | 528 | bool wake_clock = true; |
2ce7135a | 529 | void *iter = NULL; |
eb414681 JW |
530 | |
531 | if (!task->pid) | |
532 | return; | |
533 | ||
534 | if (((task->psi_flags & set) || | |
535 | (task->psi_flags & clear) != clear) && | |
536 | !psi_bug) { | |
537 | printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n", | |
538 | task->pid, task->comm, cpu, | |
539 | task->psi_flags, clear, set); | |
540 | psi_bug = 1; | |
541 | } | |
542 | ||
543 | task->psi_flags &= ~clear; | |
544 | task->psi_flags |= set; | |
545 | ||
1b69ac6b JW |
546 | /* |
547 | * Periodic aggregation shuts off if there is a period of no | |
548 | * task changes, so we wake it back up if necessary. However, | |
549 | * don't do this if the task change is the aggregation worker | |
550 | * itself going to sleep, or we'll ping-pong forever. | |
551 | */ | |
552 | if (unlikely((clear & TSK_RUNNING) && | |
553 | (task->flags & PF_WQ_WORKER) && | |
bcc78db6 | 554 | wq_worker_last_func(task) == psi_avgs_work)) |
1b69ac6b JW |
555 | wake_clock = false; |
556 | ||
557 | while ((group = iterate_groups(task, &iter))) { | |
2ce7135a | 558 | psi_group_change(group, cpu, clear, set); |
bcc78db6 SB |
559 | if (wake_clock && !delayed_work_pending(&group->avgs_work)) |
560 | schedule_delayed_work(&group->avgs_work, PSI_FREQ); | |
1b69ac6b | 561 | } |
eb414681 JW |
562 | } |
563 | ||
564 | void psi_memstall_tick(struct task_struct *task, int cpu) | |
565 | { | |
2ce7135a JW |
566 | struct psi_group *group; |
567 | void *iter = NULL; | |
eb414681 | 568 | |
2ce7135a JW |
569 | while ((group = iterate_groups(task, &iter))) { |
570 | struct psi_group_cpu *groupc; | |
571 | ||
572 | groupc = per_cpu_ptr(group->pcpu, cpu); | |
573 | write_seqcount_begin(&groupc->seq); | |
574 | record_times(groupc, cpu, true); | |
575 | write_seqcount_end(&groupc->seq); | |
576 | } | |
eb414681 JW |
577 | } |
578 | ||
579 | /** | |
580 | * psi_memstall_enter - mark the beginning of a memory stall section | |
581 | * @flags: flags to handle nested sections | |
582 | * | |
583 | * Marks the calling task as being stalled due to a lack of memory, | |
584 | * such as waiting for a refault or performing reclaim. | |
585 | */ | |
586 | void psi_memstall_enter(unsigned long *flags) | |
587 | { | |
588 | struct rq_flags rf; | |
589 | struct rq *rq; | |
590 | ||
e0c27447 | 591 | if (static_branch_likely(&psi_disabled)) |
eb414681 JW |
592 | return; |
593 | ||
594 | *flags = current->flags & PF_MEMSTALL; | |
595 | if (*flags) | |
596 | return; | |
597 | /* | |
598 | * PF_MEMSTALL setting & accounting needs to be atomic wrt | |
599 | * changes to the task's scheduling state, otherwise we can | |
600 | * race with CPU migration. | |
601 | */ | |
602 | rq = this_rq_lock_irq(&rf); | |
603 | ||
604 | current->flags |= PF_MEMSTALL; | |
605 | psi_task_change(current, 0, TSK_MEMSTALL); | |
606 | ||
607 | rq_unlock_irq(rq, &rf); | |
608 | } | |
609 | ||
610 | /** | |
611 | * psi_memstall_leave - mark the end of an memory stall section | |
612 | * @flags: flags to handle nested memdelay sections | |
613 | * | |
614 | * Marks the calling task as no longer stalled due to lack of memory. | |
615 | */ | |
616 | void psi_memstall_leave(unsigned long *flags) | |
617 | { | |
618 | struct rq_flags rf; | |
619 | struct rq *rq; | |
620 | ||
e0c27447 | 621 | if (static_branch_likely(&psi_disabled)) |
eb414681 JW |
622 | return; |
623 | ||
624 | if (*flags) | |
625 | return; | |
626 | /* | |
627 | * PF_MEMSTALL clearing & accounting needs to be atomic wrt | |
628 | * changes to the task's scheduling state, otherwise we could | |
629 | * race with CPU migration. | |
630 | */ | |
631 | rq = this_rq_lock_irq(&rf); | |
632 | ||
633 | current->flags &= ~PF_MEMSTALL; | |
634 | psi_task_change(current, TSK_MEMSTALL, 0); | |
635 | ||
636 | rq_unlock_irq(rq, &rf); | |
637 | } | |
638 | ||
2ce7135a JW |
639 | #ifdef CONFIG_CGROUPS |
640 | int psi_cgroup_alloc(struct cgroup *cgroup) | |
641 | { | |
e0c27447 | 642 | if (static_branch_likely(&psi_disabled)) |
2ce7135a JW |
643 | return 0; |
644 | ||
645 | cgroup->psi.pcpu = alloc_percpu(struct psi_group_cpu); | |
646 | if (!cgroup->psi.pcpu) | |
647 | return -ENOMEM; | |
648 | group_init(&cgroup->psi); | |
649 | return 0; | |
650 | } | |
651 | ||
652 | void psi_cgroup_free(struct cgroup *cgroup) | |
653 | { | |
e0c27447 | 654 | if (static_branch_likely(&psi_disabled)) |
2ce7135a JW |
655 | return; |
656 | ||
bcc78db6 | 657 | cancel_delayed_work_sync(&cgroup->psi.avgs_work); |
2ce7135a JW |
658 | free_percpu(cgroup->psi.pcpu); |
659 | } | |
660 | ||
661 | /** | |
662 | * cgroup_move_task - move task to a different cgroup | |
663 | * @task: the task | |
664 | * @to: the target css_set | |
665 | * | |
666 | * Move task to a new cgroup and safely migrate its associated stall | |
667 | * state between the different groups. | |
668 | * | |
669 | * This function acquires the task's rq lock to lock out concurrent | |
670 | * changes to the task's scheduling state and - in case the task is | |
671 | * running - concurrent changes to its stall state. | |
672 | */ | |
673 | void cgroup_move_task(struct task_struct *task, struct css_set *to) | |
674 | { | |
2ce7135a JW |
675 | unsigned int task_flags = 0; |
676 | struct rq_flags rf; | |
677 | struct rq *rq; | |
678 | ||
e0c27447 | 679 | if (static_branch_likely(&psi_disabled)) { |
8fcb2312 OJ |
680 | /* |
681 | * Lame to do this here, but the scheduler cannot be locked | |
682 | * from the outside, so we move cgroups from inside sched/. | |
683 | */ | |
684 | rcu_assign_pointer(task->cgroups, to); | |
685 | return; | |
686 | } | |
2ce7135a | 687 | |
8fcb2312 | 688 | rq = task_rq_lock(task, &rf); |
2ce7135a | 689 | |
8fcb2312 OJ |
690 | if (task_on_rq_queued(task)) |
691 | task_flags = TSK_RUNNING; | |
692 | else if (task->in_iowait) | |
693 | task_flags = TSK_IOWAIT; | |
2ce7135a | 694 | |
8fcb2312 OJ |
695 | if (task->flags & PF_MEMSTALL) |
696 | task_flags |= TSK_MEMSTALL; | |
2ce7135a | 697 | |
8fcb2312 OJ |
698 | if (task_flags) |
699 | psi_task_change(task, task_flags, 0); | |
700 | ||
701 | /* See comment above */ | |
2ce7135a JW |
702 | rcu_assign_pointer(task->cgroups, to); |
703 | ||
8fcb2312 OJ |
704 | if (task_flags) |
705 | psi_task_change(task, 0, task_flags); | |
2ce7135a | 706 | |
8fcb2312 | 707 | task_rq_unlock(rq, task, &rf); |
2ce7135a JW |
708 | } |
709 | #endif /* CONFIG_CGROUPS */ | |
710 | ||
711 | int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res) | |
eb414681 JW |
712 | { |
713 | int full; | |
7fc70a39 | 714 | u64 now; |
eb414681 | 715 | |
e0c27447 | 716 | if (static_branch_likely(&psi_disabled)) |
eb414681 JW |
717 | return -EOPNOTSUPP; |
718 | ||
7fc70a39 SB |
719 | /* Update averages before reporting them */ |
720 | mutex_lock(&group->avgs_lock); | |
721 | now = sched_clock(); | |
722 | collect_percpu_times(group); | |
723 | if (now >= group->avg_next_update) | |
724 | group->avg_next_update = update_averages(group, now); | |
725 | mutex_unlock(&group->avgs_lock); | |
eb414681 JW |
726 | |
727 | for (full = 0; full < 2 - (res == PSI_CPU); full++) { | |
728 | unsigned long avg[3]; | |
729 | u64 total; | |
730 | int w; | |
731 | ||
732 | for (w = 0; w < 3; w++) | |
733 | avg[w] = group->avg[res * 2 + full][w]; | |
734 | total = div_u64(group->total[res * 2 + full], NSEC_PER_USEC); | |
735 | ||
736 | seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n", | |
737 | full ? "full" : "some", | |
738 | LOAD_INT(avg[0]), LOAD_FRAC(avg[0]), | |
739 | LOAD_INT(avg[1]), LOAD_FRAC(avg[1]), | |
740 | LOAD_INT(avg[2]), LOAD_FRAC(avg[2]), | |
741 | total); | |
742 | } | |
743 | ||
744 | return 0; | |
745 | } | |
746 | ||
747 | static int psi_io_show(struct seq_file *m, void *v) | |
748 | { | |
749 | return psi_show(m, &psi_system, PSI_IO); | |
750 | } | |
751 | ||
752 | static int psi_memory_show(struct seq_file *m, void *v) | |
753 | { | |
754 | return psi_show(m, &psi_system, PSI_MEM); | |
755 | } | |
756 | ||
757 | static int psi_cpu_show(struct seq_file *m, void *v) | |
758 | { | |
759 | return psi_show(m, &psi_system, PSI_CPU); | |
760 | } | |
761 | ||
762 | static int psi_io_open(struct inode *inode, struct file *file) | |
763 | { | |
764 | return single_open(file, psi_io_show, NULL); | |
765 | } | |
766 | ||
767 | static int psi_memory_open(struct inode *inode, struct file *file) | |
768 | { | |
769 | return single_open(file, psi_memory_show, NULL); | |
770 | } | |
771 | ||
772 | static int psi_cpu_open(struct inode *inode, struct file *file) | |
773 | { | |
774 | return single_open(file, psi_cpu_show, NULL); | |
775 | } | |
776 | ||
777 | static const struct file_operations psi_io_fops = { | |
778 | .open = psi_io_open, | |
779 | .read = seq_read, | |
780 | .llseek = seq_lseek, | |
781 | .release = single_release, | |
782 | }; | |
783 | ||
784 | static const struct file_operations psi_memory_fops = { | |
785 | .open = psi_memory_open, | |
786 | .read = seq_read, | |
787 | .llseek = seq_lseek, | |
788 | .release = single_release, | |
789 | }; | |
790 | ||
791 | static const struct file_operations psi_cpu_fops = { | |
792 | .open = psi_cpu_open, | |
793 | .read = seq_read, | |
794 | .llseek = seq_lseek, | |
795 | .release = single_release, | |
796 | }; | |
797 | ||
798 | static int __init psi_proc_init(void) | |
799 | { | |
800 | proc_mkdir("pressure", NULL); | |
801 | proc_create("pressure/io", 0, NULL, &psi_io_fops); | |
802 | proc_create("pressure/memory", 0, NULL, &psi_memory_fops); | |
803 | proc_create("pressure/cpu", 0, NULL, &psi_cpu_fops); | |
804 | return 0; | |
805 | } | |
806 | module_init(psi_proc_init); |