1 // SPDX-License-Identifier: GPL-2.0 2 /* 3 * Pressure stall information for CPU, memory and IO 4 * 5 * Copyright (c) 2018 Facebook, Inc. 6 * Author: Johannes Weiner <hannes@cmpxchg.org> 7 * 8 * Polling support by Suren Baghdasaryan <surenb@google.com> 9 * Copyright (c) 2018 Google, Inc. 10 * 11 * When CPU, memory and IO are contended, tasks experience delays that 12 * reduce throughput and introduce latencies into the workload. Memory 13 * and IO contention, in addition, can cause a full loss of forward 14 * progress in which the CPU goes idle. 15 * 16 * This code aggregates individual task delays into resource pressure 17 * metrics that indicate problems with both workload health and 18 * resource utilization. 19 * 20 * Model 21 * 22 * The time in which a task can execute on a CPU is our baseline for 23 * productivity. Pressure expresses the amount of time in which this 24 * potential cannot be realized due to resource contention. 25 * 26 * This concept of productivity has two components: the workload and 27 * the CPU. To measure the impact of pressure on both, we define two 28 * contention states for a resource: SOME and FULL. 29 * 30 * In the SOME state of a given resource, one or more tasks are 31 * delayed on that resource. This affects the workload's ability to 32 * perform work, but the CPU may still be executing other tasks. 33 * 34 * In the FULL state of a given resource, all non-idle tasks are 35 * delayed on that resource such that nobody is advancing and the CPU 36 * goes idle. This leaves both workload and CPU unproductive. 37 * 38 * SOME = nr_delayed_tasks != 0 39 * FULL = nr_delayed_tasks != 0 && nr_productive_tasks == 0 40 * 41 * What it means for a task to be productive is defined differently 42 * for each resource. For IO, productive means a running task. For 43 * memory, productive means a running task that isn't a reclaimer. For 44 * CPU, productive means an oncpu task. 45 * 46 * Naturally, the FULL state doesn't exist for the CPU resource at the 47 * system level, but exist at the cgroup level. At the cgroup level, 48 * FULL means all non-idle tasks in the cgroup are delayed on the CPU 49 * resource which is being used by others outside of the cgroup or 50 * throttled by the cgroup cpu.max configuration. 51 * 52 * The percentage of wallclock time spent in those compound stall 53 * states gives pressure numbers between 0 and 100 for each resource, 54 * where the SOME percentage indicates workload slowdowns and the FULL 55 * percentage indicates reduced CPU utilization: 56 * 57 * %SOME = time(SOME) / period 58 * %FULL = time(FULL) / period 59 * 60 * Multiple CPUs 61 * 62 * The more tasks and available CPUs there are, the more work can be 63 * performed concurrently. This means that the potential that can go 64 * unrealized due to resource contention *also* scales with non-idle 65 * tasks and CPUs. 66 * 67 * Consider a scenario where 257 number crunching tasks are trying to 68 * run concurrently on 256 CPUs. If we simply aggregated the task 69 * states, we would have to conclude a CPU SOME pressure number of 70 * 100%, since *somebody* is waiting on a runqueue at all 71 * times. However, that is clearly not the amount of contention the 72 * workload is experiencing: only one out of 256 possible execution 73 * threads will be contended at any given time, or about 0.4%. 74 * 75 * Conversely, consider a scenario of 4 tasks and 4 CPUs where at any 76 * given time *one* of the tasks is delayed due to a lack of memory. 77 * Again, looking purely at the task state would yield a memory FULL 78 * pressure number of 0%, since *somebody* is always making forward 79 * progress. But again this wouldn't capture the amount of execution 80 * potential lost, which is 1 out of 4 CPUs, or 25%. 81 * 82 * To calculate wasted potential (pressure) with multiple processors, 83 * we have to base our calculation on the number of non-idle tasks in 84 * conjunction with the number of available CPUs, which is the number 85 * of potential execution threads. SOME becomes then the proportion of 86 * delayed tasks to possible threads, and FULL is the share of possible 87 * threads that are unproductive due to delays: 88 * 89 * threads = min(nr_nonidle_tasks, nr_cpus) 90 * SOME = min(nr_delayed_tasks / threads, 1) 91 * FULL = (threads - min(nr_productive_tasks, threads)) / threads 92 * 93 * For the 257 number crunchers on 256 CPUs, this yields: 94 * 95 * threads = min(257, 256) 96 * SOME = min(1 / 256, 1) = 0.4% 97 * FULL = (256 - min(256, 256)) / 256 = 0% 98 * 99 * For the 1 out of 4 memory-delayed tasks, this yields: 100 * 101 * threads = min(4, 4) 102 * SOME = min(1 / 4, 1) = 25% 103 * FULL = (4 - min(3, 4)) / 4 = 25% 104 * 105 * [ Substitute nr_cpus with 1, and you can see that it's a natural 106 * extension of the single-CPU model. ] 107 * 108 * Implementation 109 * 110 * To assess the precise time spent in each such state, we would have 111 * to freeze the system on task changes and start/stop the state 112 * clocks accordingly. Obviously that doesn't scale in practice. 113 * 114 * Because the scheduler aims to distribute the compute load evenly 115 * among the available CPUs, we can track task state locally to each 116 * CPU and, at much lower frequency, extrapolate the global state for 117 * the cumulative stall times and the running averages. 118 * 119 * For each runqueue, we track: 120 * 121 * tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0) 122 * tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_productive_tasks[cpu]) 123 * tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0) 124 * 125 * and then periodically aggregate: 126 * 127 * tNONIDLE = sum(tNONIDLE[i]) 128 * 129 * tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE 130 * tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE 131 * 132 * %SOME = tSOME / period 133 * %FULL = tFULL / period 134 * 135 * This gives us an approximation of pressure that is practical 136 * cost-wise, yet way more sensitive and accurate than periodic 137 * sampling of the aggregate task states would be. 138 */ 139 140 static int psi_bug __read_mostly; 141 142 DEFINE_STATIC_KEY_FALSE(psi_disabled); 143 static DEFINE_STATIC_KEY_TRUE(psi_cgroups_enabled); 144 145 #ifdef CONFIG_PSI_DEFAULT_DISABLED 146 static bool psi_enable; 147 #else 148 static bool psi_enable = true; 149 #endif 150 static int __init setup_psi(char *str) 151 { 152 return kstrtobool(str, &psi_enable) == 0; 153 } 154 __setup("psi=", setup_psi); 155 156 /* Running averages - we need to be higher-res than loadavg */ 157 #define PSI_FREQ (2*HZ+1) /* 2 sec intervals */ 158 #define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */ 159 #define EXP_60s 1981 /* 1/exp(2s/60s) */ 160 #define EXP_300s 2034 /* 1/exp(2s/300s) */ 161 162 /* PSI trigger definitions */ 163 #define WINDOW_MAX_US 10000000 /* Max window size is 10s */ 164 #define UPDATES_PER_WINDOW 10 /* 10 updates per window */ 165 166 /* Sampling frequency in nanoseconds */ 167 static u64 psi_period __read_mostly; 168 169 /* System-level pressure and stall tracking */ 170 static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu); 171 struct psi_group psi_system = { 172 .pcpu = &system_group_pcpu, 173 }; 174 175 static void psi_avgs_work(struct work_struct *work); 176 177 static void poll_timer_fn(struct timer_list *t); 178 179 static void group_init(struct psi_group *group) 180 { 181 int cpu; 182 183 group->enabled = true; 184 for_each_possible_cpu(cpu) 185 seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq); 186 group->avg_last_update = sched_clock(); 187 group->avg_next_update = group->avg_last_update + psi_period; 188 mutex_init(&group->avgs_lock); 189 190 /* Init avg trigger-related members */ 191 INIT_LIST_HEAD(&group->avg_triggers); 192 memset(group->avg_nr_triggers, 0, sizeof(group->avg_nr_triggers)); 193 INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work); 194 195 /* Init rtpoll trigger-related members */ 196 atomic_set(&group->rtpoll_scheduled, 0); 197 mutex_init(&group->rtpoll_trigger_lock); 198 INIT_LIST_HEAD(&group->rtpoll_triggers); 199 group->rtpoll_min_period = U32_MAX; 200 group->rtpoll_next_update = ULLONG_MAX; 201 init_waitqueue_head(&group->rtpoll_wait); 202 timer_setup(&group->rtpoll_timer, poll_timer_fn, 0); 203 rcu_assign_pointer(group->rtpoll_task, NULL); 204 } 205 206 void __init psi_init(void) 207 { 208 if (!psi_enable) { 209 static_branch_enable(&psi_disabled); 210 static_branch_disable(&psi_cgroups_enabled); 211 return; 212 } 213 214 if (!cgroup_psi_enabled()) 215 static_branch_disable(&psi_cgroups_enabled); 216 217 psi_period = jiffies_to_nsecs(PSI_FREQ); 218 group_init(&psi_system); 219 } 220 221 static bool test_state(unsigned int *tasks, enum psi_states state, bool oncpu) 222 { 223 switch (state) { 224 case PSI_IO_SOME: 225 return unlikely(tasks[NR_IOWAIT]); 226 case PSI_IO_FULL: 227 return unlikely(tasks[NR_IOWAIT] && !tasks[NR_RUNNING]); 228 case PSI_MEM_SOME: 229 return unlikely(tasks[NR_MEMSTALL]); 230 case PSI_MEM_FULL: 231 return unlikely(tasks[NR_MEMSTALL] && 232 tasks[NR_RUNNING] == tasks[NR_MEMSTALL_RUNNING]); 233 case PSI_CPU_SOME: 234 return unlikely(tasks[NR_RUNNING] > oncpu); 235 case PSI_CPU_FULL: 236 return unlikely(tasks[NR_RUNNING] && !oncpu); 237 case PSI_NONIDLE: 238 return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] || 239 tasks[NR_RUNNING]; 240 default: 241 return false; 242 } 243 } 244 245 static void get_recent_times(struct psi_group *group, int cpu, 246 enum psi_aggregators aggregator, u32 *times, 247 u32 *pchanged_states) 248 { 249 struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu); 250 int current_cpu = raw_smp_processor_id(); 251 unsigned int tasks[NR_PSI_TASK_COUNTS]; 252 u64 now, state_start; 253 enum psi_states s; 254 unsigned int seq; 255 u32 state_mask; 256 257 *pchanged_states = 0; 258 259 /* Snapshot a coherent view of the CPU state */ 260 do { 261 seq = read_seqcount_begin(&groupc->seq); 262 now = cpu_clock(cpu); 263 memcpy(times, groupc->times, sizeof(groupc->times)); 264 state_mask = groupc->state_mask; 265 state_start = groupc->state_start; 266 if (cpu == current_cpu) 267 memcpy(tasks, groupc->tasks, sizeof(groupc->tasks)); 268 } while (read_seqcount_retry(&groupc->seq, seq)); 269 270 /* Calculate state time deltas against the previous snapshot */ 271 for (s = 0; s < NR_PSI_STATES; s++) { 272 u32 delta; 273 /* 274 * In addition to already concluded states, we also 275 * incorporate currently active states on the CPU, 276 * since states may last for many sampling periods. 277 * 278 * This way we keep our delta sampling buckets small 279 * (u32) and our reported pressure close to what's 280 * actually happening. 281 */ 282 if (state_mask & (1 << s)) 283 times[s] += now - state_start; 284 285 delta = times[s] - groupc->times_prev[aggregator][s]; 286 groupc->times_prev[aggregator][s] = times[s]; 287 288 times[s] = delta; 289 if (delta) 290 *pchanged_states |= (1 << s); 291 } 292 293 /* 294 * When collect_percpu_times() from the avgs_work, we don't want to 295 * re-arm avgs_work when all CPUs are IDLE. But the current CPU running 296 * this avgs_work is never IDLE, cause avgs_work can't be shut off. 297 * So for the current CPU, we need to re-arm avgs_work only when 298 * (NR_RUNNING > 1 || NR_IOWAIT > 0 || NR_MEMSTALL > 0), for other CPUs 299 * we can just check PSI_NONIDLE delta. 300 */ 301 if (current_work() == &group->avgs_work.work) { 302 bool reschedule; 303 304 if (cpu == current_cpu) 305 reschedule = tasks[NR_RUNNING] + 306 tasks[NR_IOWAIT] + 307 tasks[NR_MEMSTALL] > 1; 308 else 309 reschedule = *pchanged_states & (1 << PSI_NONIDLE); 310 311 if (reschedule) 312 *pchanged_states |= PSI_STATE_RESCHEDULE; 313 } 314 } 315 316 static void calc_avgs(unsigned long avg[3], int missed_periods, 317 u64 time, u64 period) 318 { 319 unsigned long pct; 320 321 /* Fill in zeroes for periods of no activity */ 322 if (missed_periods) { 323 avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods); 324 avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods); 325 avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods); 326 } 327 328 /* Sample the most recent active period */ 329 pct = div_u64(time * 100, period); 330 pct *= FIXED_1; 331 avg[0] = calc_load(avg[0], EXP_10s, pct); 332 avg[1] = calc_load(avg[1], EXP_60s, pct); 333 avg[2] = calc_load(avg[2], EXP_300s, pct); 334 } 335 336 static void collect_percpu_times(struct psi_group *group, 337 enum psi_aggregators aggregator, 338 u32 *pchanged_states) 339 { 340 u64 deltas[NR_PSI_STATES - 1] = { 0, }; 341 unsigned long nonidle_total = 0; 342 u32 changed_states = 0; 343 int cpu; 344 int s; 345 346 /* 347 * Collect the per-cpu time buckets and average them into a 348 * single time sample that is normalized to wallclock time. 349 * 350 * For averaging, each CPU is weighted by its non-idle time in 351 * the sampling period. This eliminates artifacts from uneven 352 * loading, or even entirely idle CPUs. 353 */ 354 for_each_possible_cpu(cpu) { 355 u32 times[NR_PSI_STATES]; 356 u32 nonidle; 357 u32 cpu_changed_states; 358 359 get_recent_times(group, cpu, aggregator, times, 360 &cpu_changed_states); 361 changed_states |= cpu_changed_states; 362 363 nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]); 364 nonidle_total += nonidle; 365 366 for (s = 0; s < PSI_NONIDLE; s++) 367 deltas[s] += (u64)times[s] * nonidle; 368 } 369 370 /* 371 * Integrate the sample into the running statistics that are 372 * reported to userspace: the cumulative stall times and the 373 * decaying averages. 374 * 375 * Pressure percentages are sampled at PSI_FREQ. We might be 376 * called more often when the user polls more frequently than 377 * that; we might be called less often when there is no task 378 * activity, thus no data, and clock ticks are sporadic. The 379 * below handles both. 380 */ 381 382 /* total= */ 383 for (s = 0; s < NR_PSI_STATES - 1; s++) 384 group->total[aggregator][s] += 385 div_u64(deltas[s], max(nonidle_total, 1UL)); 386 387 if (pchanged_states) 388 *pchanged_states = changed_states; 389 } 390 391 /* Trigger tracking window manipulations */ 392 static void window_reset(struct psi_window *win, u64 now, u64 value, 393 u64 prev_growth) 394 { 395 win->start_time = now; 396 win->start_value = value; 397 win->prev_growth = prev_growth; 398 } 399 400 /* 401 * PSI growth tracking window update and growth calculation routine. 402 * 403 * This approximates a sliding tracking window by interpolating 404 * partially elapsed windows using historical growth data from the 405 * previous intervals. This minimizes memory requirements (by not storing 406 * all the intermediate values in the previous window) and simplifies 407 * the calculations. It works well because PSI signal changes only in 408 * positive direction and over relatively small window sizes the growth 409 * is close to linear. 410 */ 411 static u64 window_update(struct psi_window *win, u64 now, u64 value) 412 { 413 u64 elapsed; 414 u64 growth; 415 416 elapsed = now - win->start_time; 417 growth = value - win->start_value; 418 /* 419 * After each tracking window passes win->start_value and 420 * win->start_time get reset and win->prev_growth stores 421 * the average per-window growth of the previous window. 422 * win->prev_growth is then used to interpolate additional 423 * growth from the previous window assuming it was linear. 424 */ 425 if (elapsed > win->size) 426 window_reset(win, now, value, growth); 427 else { 428 u32 remaining; 429 430 remaining = win->size - elapsed; 431 growth += div64_u64(win->prev_growth * remaining, win->size); 432 } 433 434 return growth; 435 } 436 437 static void update_triggers(struct psi_group *group, u64 now, 438 enum psi_aggregators aggregator) 439 { 440 struct psi_trigger *t; 441 u64 *total = group->total[aggregator]; 442 struct list_head *triggers; 443 u64 *aggregator_total; 444 445 if (aggregator == PSI_AVGS) { 446 triggers = &group->avg_triggers; 447 aggregator_total = group->avg_total; 448 } else { 449 triggers = &group->rtpoll_triggers; 450 aggregator_total = group->rtpoll_total; 451 } 452 453 /* 454 * On subsequent updates, calculate growth deltas and let 455 * watchers know when their specified thresholds are exceeded. 456 */ 457 list_for_each_entry(t, triggers, node) { 458 u64 growth; 459 bool new_stall; 460 461 new_stall = aggregator_total[t->state] != total[t->state]; 462 463 /* Check for stall activity or a previous threshold breach */ 464 if (!new_stall && !t->pending_event) 465 continue; 466 /* 467 * Check for new stall activity, as well as deferred 468 * events that occurred in the last window after the 469 * trigger had already fired (we want to ratelimit 470 * events without dropping any). 471 */ 472 if (new_stall) { 473 /* Calculate growth since last update */ 474 growth = window_update(&t->win, now, total[t->state]); 475 if (!t->pending_event) { 476 if (growth < t->threshold) 477 continue; 478 479 t->pending_event = true; 480 } 481 } 482 /* Limit event signaling to once per window */ 483 if (now < t->last_event_time + t->win.size) 484 continue; 485 486 /* Generate an event */ 487 if (cmpxchg(&t->event, 0, 1) == 0) { 488 if (t->of) 489 kernfs_notify(t->of->kn); 490 else 491 wake_up_interruptible(&t->event_wait); 492 } 493 t->last_event_time = now; 494 /* Reset threshold breach flag once event got generated */ 495 t->pending_event = false; 496 } 497 } 498 499 static u64 update_averages(struct psi_group *group, u64 now) 500 { 501 unsigned long missed_periods = 0; 502 u64 expires, period; 503 u64 avg_next_update; 504 int s; 505 506 /* avgX= */ 507 expires = group->avg_next_update; 508 if (now - expires >= psi_period) 509 missed_periods = div_u64(now - expires, psi_period); 510 511 /* 512 * The periodic clock tick can get delayed for various 513 * reasons, especially on loaded systems. To avoid clock 514 * drift, we schedule the clock in fixed psi_period intervals. 515 * But the deltas we sample out of the per-cpu buckets above 516 * are based on the actual time elapsing between clock ticks. 517 */ 518 avg_next_update = expires + ((1 + missed_periods) * psi_period); 519 period = now - (group->avg_last_update + (missed_periods * psi_period)); 520 group->avg_last_update = now; 521 522 for (s = 0; s < NR_PSI_STATES - 1; s++) { 523 u32 sample; 524 525 sample = group->total[PSI_AVGS][s] - group->avg_total[s]; 526 /* 527 * Due to the lockless sampling of the time buckets, 528 * recorded time deltas can slip into the next period, 529 * which under full pressure can result in samples in 530 * excess of the period length. 531 * 532 * We don't want to report non-sensical pressures in 533 * excess of 100%, nor do we want to drop such events 534 * on the floor. Instead we punt any overage into the 535 * future until pressure subsides. By doing this we 536 * don't underreport the occurring pressure curve, we 537 * just report it delayed by one period length. 538 * 539 * The error isn't cumulative. As soon as another 540 * delta slips from a period P to P+1, by definition 541 * it frees up its time T in P. 542 */ 543 if (sample > period) 544 sample = period; 545 group->avg_total[s] += sample; 546 calc_avgs(group->avg[s], missed_periods, sample, period); 547 } 548 549 return avg_next_update; 550 } 551 552 static void psi_avgs_work(struct work_struct *work) 553 { 554 struct delayed_work *dwork; 555 struct psi_group *group; 556 u32 changed_states; 557 u64 now; 558 559 dwork = to_delayed_work(work); 560 group = container_of(dwork, struct psi_group, avgs_work); 561 562 mutex_lock(&group->avgs_lock); 563 564 now = sched_clock(); 565 566 collect_percpu_times(group, PSI_AVGS, &changed_states); 567 /* 568 * If there is task activity, periodically fold the per-cpu 569 * times and feed samples into the running averages. If things 570 * are idle and there is no data to process, stop the clock. 571 * Once restarted, we'll catch up the running averages in one 572 * go - see calc_avgs() and missed_periods. 573 */ 574 if (now >= group->avg_next_update) { 575 update_triggers(group, now, PSI_AVGS); 576 group->avg_next_update = update_averages(group, now); 577 } 578 579 if (changed_states & PSI_STATE_RESCHEDULE) { 580 schedule_delayed_work(dwork, nsecs_to_jiffies( 581 group->avg_next_update - now) + 1); 582 } 583 584 mutex_unlock(&group->avgs_lock); 585 } 586 587 static void init_rtpoll_triggers(struct psi_group *group, u64 now) 588 { 589 struct psi_trigger *t; 590 591 list_for_each_entry(t, &group->rtpoll_triggers, node) 592 window_reset(&t->win, now, 593 group->total[PSI_POLL][t->state], 0); 594 memcpy(group->rtpoll_total, group->total[PSI_POLL], 595 sizeof(group->rtpoll_total)); 596 group->rtpoll_next_update = now + group->rtpoll_min_period; 597 } 598 599 /* Schedule rtpolling if it's not already scheduled or forced. */ 600 static void psi_schedule_rtpoll_work(struct psi_group *group, unsigned long delay, 601 bool force) 602 { 603 struct task_struct *task; 604 605 /* 606 * atomic_xchg should be called even when !force to provide a 607 * full memory barrier (see the comment inside psi_rtpoll_work). 608 */ 609 if (atomic_xchg(&group->rtpoll_scheduled, 1) && !force) 610 return; 611 612 rcu_read_lock(); 613 614 task = rcu_dereference(group->rtpoll_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->rtpoll_timer, jiffies + delay); 621 else 622 atomic_set(&group->rtpoll_scheduled, 0); 623 624 rcu_read_unlock(); 625 } 626 627 static void psi_rtpoll_work(struct psi_group *group) 628 { 629 bool force_reschedule = false; 630 u32 changed_states; 631 u64 now; 632 633 mutex_lock(&group->rtpoll_trigger_lock); 634 635 now = sched_clock(); 636 637 if (now > group->rtpoll_until) { 638 /* 639 * We are either about to start or might stop rtpolling if no 640 * state change was recorded. Resetting rtpoll_scheduled leaves 641 * a small window for psi_group_change to sneak in and schedule 642 * an immediate rtpoll_work before we get to rescheduling. One 643 * potential extra wakeup at the end of the rtpolling window 644 * should be negligible and rtpoll_next_update still keeps 645 * updates correctly on schedule. 646 */ 647 atomic_set(&group->rtpoll_scheduled, 0); 648 /* 649 * A task change can race with the rtpoll worker that is supposed to 650 * report on it. To avoid missing events, ensure ordering between 651 * rtpoll_scheduled and the task state accesses, such that if the 652 * rtpoll worker misses the state update, the task change is 653 * guaranteed to reschedule the rtpoll worker: 654 * 655 * rtpoll worker: 656 * atomic_set(rtpoll_scheduled, 0) 657 * smp_mb() 658 * LOAD states 659 * 660 * task change: 661 * STORE states 662 * if atomic_xchg(rtpoll_scheduled, 1) == 0: 663 * schedule rtpoll worker 664 * 665 * The atomic_xchg() implies a full barrier. 666 */ 667 smp_mb(); 668 } else { 669 /* The rtpolling 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->rtpoll_states) { 677 /* Initialize trigger windows when entering rtpolling mode */ 678 if (now > group->rtpoll_until) 679 init_rtpoll_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->rtpoll_until = now + 687 group->rtpoll_min_period * UPDATES_PER_WINDOW; 688 } 689 690 if (now > group->rtpoll_until) { 691 group->rtpoll_next_update = ULLONG_MAX; 692 goto out; 693 } 694 695 if (now >= group->rtpoll_next_update) { 696 if (changed_states & group->rtpoll_states) { 697 update_triggers(group, now, PSI_POLL); 698 memcpy(group->rtpoll_total, group->total[PSI_POLL], 699 sizeof(group->rtpoll_total)); 700 } 701 group->rtpoll_next_update = now + group->rtpoll_min_period; 702 } 703 704 psi_schedule_rtpoll_work(group, 705 nsecs_to_jiffies(group->rtpoll_next_update - now) + 1, 706 force_reschedule); 707 708 out: 709 mutex_unlock(&group->rtpoll_trigger_lock); 710 } 711 712 static int psi_rtpoll_worker(void *data) 713 { 714 struct psi_group *group = (struct psi_group *)data; 715 716 sched_set_fifo_low(current); 717 718 while (true) { 719 wait_event_interruptible(group->rtpoll_wait, 720 atomic_cmpxchg(&group->rtpoll_wakeup, 1, 0) || 721 kthread_should_stop()); 722 if (kthread_should_stop()) 723 break; 724 725 psi_rtpoll_work(group); 726 } 727 return 0; 728 } 729 730 static void poll_timer_fn(struct timer_list *t) 731 { 732 struct psi_group *group = from_timer(group, t, rtpoll_timer); 733 734 atomic_set(&group->rtpoll_wakeup, 1); 735 wake_up_interruptible(&group->rtpoll_wait); 736 } 737 738 static void record_times(struct psi_group_cpu *groupc, u64 now) 739 { 740 u32 delta; 741 742 delta = now - groupc->state_start; 743 groupc->state_start = now; 744 745 if (groupc->state_mask & (1 << PSI_IO_SOME)) { 746 groupc->times[PSI_IO_SOME] += delta; 747 if (groupc->state_mask & (1 << PSI_IO_FULL)) 748 groupc->times[PSI_IO_FULL] += delta; 749 } 750 751 if (groupc->state_mask & (1 << PSI_MEM_SOME)) { 752 groupc->times[PSI_MEM_SOME] += delta; 753 if (groupc->state_mask & (1 << PSI_MEM_FULL)) 754 groupc->times[PSI_MEM_FULL] += delta; 755 } 756 757 if (groupc->state_mask & (1 << PSI_CPU_SOME)) { 758 groupc->times[PSI_CPU_SOME] += delta; 759 if (groupc->state_mask & (1 << PSI_CPU_FULL)) 760 groupc->times[PSI_CPU_FULL] += delta; 761 } 762 763 if (groupc->state_mask & (1 << PSI_NONIDLE)) 764 groupc->times[PSI_NONIDLE] += delta; 765 } 766 767 static void psi_group_change(struct psi_group *group, int cpu, 768 unsigned int clear, unsigned int set, u64 now, 769 bool wake_clock) 770 { 771 struct psi_group_cpu *groupc; 772 unsigned int t, m; 773 enum psi_states s; 774 u32 state_mask; 775 776 groupc = per_cpu_ptr(group->pcpu, cpu); 777 778 /* 779 * First we update the task counts according to the state 780 * change requested through the @clear and @set bits. 781 * 782 * Then if the cgroup PSI stats accounting enabled, we 783 * assess the aggregate resource states this CPU's tasks 784 * have been in since the last change, and account any 785 * SOME and FULL time these may have resulted in. 786 */ 787 write_seqcount_begin(&groupc->seq); 788 789 /* 790 * Start with TSK_ONCPU, which doesn't have a corresponding 791 * task count - it's just a boolean flag directly encoded in 792 * the state mask. Clear, set, or carry the current state if 793 * no changes are requested. 794 */ 795 if (unlikely(clear & TSK_ONCPU)) { 796 state_mask = 0; 797 clear &= ~TSK_ONCPU; 798 } else if (unlikely(set & TSK_ONCPU)) { 799 state_mask = PSI_ONCPU; 800 set &= ~TSK_ONCPU; 801 } else { 802 state_mask = groupc->state_mask & PSI_ONCPU; 803 } 804 805 /* 806 * The rest of the state mask is calculated based on the task 807 * counts. Update those first, then construct the mask. 808 */ 809 for (t = 0, m = clear; m; m &= ~(1 << t), t++) { 810 if (!(m & (1 << t))) 811 continue; 812 if (groupc->tasks[t]) { 813 groupc->tasks[t]--; 814 } else if (!psi_bug) { 815 printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u] clear=%x set=%x\n", 816 cpu, t, groupc->tasks[0], 817 groupc->tasks[1], groupc->tasks[2], 818 groupc->tasks[3], clear, set); 819 psi_bug = 1; 820 } 821 } 822 823 for (t = 0; set; set &= ~(1 << t), t++) 824 if (set & (1 << t)) 825 groupc->tasks[t]++; 826 827 if (!group->enabled) { 828 /* 829 * On the first group change after disabling PSI, conclude 830 * the current state and flush its time. This is unlikely 831 * to matter to the user, but aggregation (get_recent_times) 832 * may have already incorporated the live state into times_prev; 833 * avoid a delta sample underflow when PSI is later re-enabled. 834 */ 835 if (unlikely(groupc->state_mask & (1 << PSI_NONIDLE))) 836 record_times(groupc, now); 837 838 groupc->state_mask = state_mask; 839 840 write_seqcount_end(&groupc->seq); 841 return; 842 } 843 844 for (s = 0; s < NR_PSI_STATES; s++) { 845 if (test_state(groupc->tasks, s, state_mask & PSI_ONCPU)) 846 state_mask |= (1 << s); 847 } 848 849 /* 850 * Since we care about lost potential, a memstall is FULL 851 * when there are no other working tasks, but also when 852 * the CPU is actively reclaiming and nothing productive 853 * could run even if it were runnable. So when the current 854 * task in a cgroup is in_memstall, the corresponding groupc 855 * on that cpu is in PSI_MEM_FULL state. 856 */ 857 if (unlikely((state_mask & PSI_ONCPU) && cpu_curr(cpu)->in_memstall)) 858 state_mask |= (1 << PSI_MEM_FULL); 859 860 record_times(groupc, now); 861 862 groupc->state_mask = state_mask; 863 864 write_seqcount_end(&groupc->seq); 865 866 if (state_mask & group->rtpoll_states) 867 psi_schedule_rtpoll_work(group, 1, false); 868 869 if (wake_clock && !delayed_work_pending(&group->avgs_work)) 870 schedule_delayed_work(&group->avgs_work, PSI_FREQ); 871 } 872 873 static inline struct psi_group *task_psi_group(struct task_struct *task) 874 { 875 #ifdef CONFIG_CGROUPS 876 if (static_branch_likely(&psi_cgroups_enabled)) 877 return cgroup_psi(task_dfl_cgroup(task)); 878 #endif 879 return &psi_system; 880 } 881 882 static void psi_flags_change(struct task_struct *task, int clear, int set) 883 { 884 if (((task->psi_flags & set) || 885 (task->psi_flags & clear) != clear) && 886 !psi_bug) { 887 printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n", 888 task->pid, task->comm, task_cpu(task), 889 task->psi_flags, clear, set); 890 psi_bug = 1; 891 } 892 893 task->psi_flags &= ~clear; 894 task->psi_flags |= set; 895 } 896 897 void psi_task_change(struct task_struct *task, int clear, int set) 898 { 899 int cpu = task_cpu(task); 900 struct psi_group *group; 901 u64 now; 902 903 if (!task->pid) 904 return; 905 906 psi_flags_change(task, clear, set); 907 908 now = cpu_clock(cpu); 909 910 group = task_psi_group(task); 911 do { 912 psi_group_change(group, cpu, clear, set, now, true); 913 } while ((group = group->parent)); 914 } 915 916 void psi_task_switch(struct task_struct *prev, struct task_struct *next, 917 bool sleep) 918 { 919 struct psi_group *group, *common = NULL; 920 int cpu = task_cpu(prev); 921 u64 now = cpu_clock(cpu); 922 923 if (next->pid) { 924 psi_flags_change(next, 0, TSK_ONCPU); 925 /* 926 * Set TSK_ONCPU on @next's cgroups. If @next shares any 927 * ancestors with @prev, those will already have @prev's 928 * TSK_ONCPU bit set, and we can stop the iteration there. 929 */ 930 group = task_psi_group(next); 931 do { 932 if (per_cpu_ptr(group->pcpu, cpu)->state_mask & 933 PSI_ONCPU) { 934 common = group; 935 break; 936 } 937 938 psi_group_change(group, cpu, 0, TSK_ONCPU, now, true); 939 } while ((group = group->parent)); 940 } 941 942 if (prev->pid) { 943 int clear = TSK_ONCPU, set = 0; 944 bool wake_clock = true; 945 946 /* 947 * When we're going to sleep, psi_dequeue() lets us 948 * handle TSK_RUNNING, TSK_MEMSTALL_RUNNING and 949 * TSK_IOWAIT here, where we can combine it with 950 * TSK_ONCPU and save walking common ancestors twice. 951 */ 952 if (sleep) { 953 clear |= TSK_RUNNING; 954 if (prev->in_memstall) 955 clear |= TSK_MEMSTALL_RUNNING; 956 if (prev->in_iowait) 957 set |= TSK_IOWAIT; 958 959 /* 960 * Periodic aggregation shuts off if there is a period of no 961 * task changes, so we wake it back up if necessary. However, 962 * don't do this if the task change is the aggregation worker 963 * itself going to sleep, or we'll ping-pong forever. 964 */ 965 if (unlikely((prev->flags & PF_WQ_WORKER) && 966 wq_worker_last_func(prev) == psi_avgs_work)) 967 wake_clock = false; 968 } 969 970 psi_flags_change(prev, clear, set); 971 972 group = task_psi_group(prev); 973 do { 974 if (group == common) 975 break; 976 psi_group_change(group, cpu, clear, set, now, wake_clock); 977 } while ((group = group->parent)); 978 979 /* 980 * TSK_ONCPU is handled up to the common ancestor. If there are 981 * any other differences between the two tasks (e.g. prev goes 982 * to sleep, or only one task is memstall), finish propagating 983 * those differences all the way up to the root. 984 */ 985 if ((prev->psi_flags ^ next->psi_flags) & ~TSK_ONCPU) { 986 clear &= ~TSK_ONCPU; 987 for (; group; group = group->parent) 988 psi_group_change(group, cpu, clear, set, now, wake_clock); 989 } 990 } 991 } 992 993 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 994 void psi_account_irqtime(struct task_struct *task, u32 delta) 995 { 996 int cpu = task_cpu(task); 997 struct psi_group *group; 998 struct psi_group_cpu *groupc; 999 u64 now; 1000 1001 if (static_branch_likely(&psi_disabled)) 1002 return; 1003 1004 if (!task->pid) 1005 return; 1006 1007 now = cpu_clock(cpu); 1008 1009 group = task_psi_group(task); 1010 do { 1011 if (!group->enabled) 1012 continue; 1013 1014 groupc = per_cpu_ptr(group->pcpu, cpu); 1015 1016 write_seqcount_begin(&groupc->seq); 1017 1018 record_times(groupc, now); 1019 groupc->times[PSI_IRQ_FULL] += delta; 1020 1021 write_seqcount_end(&groupc->seq); 1022 1023 if (group->rtpoll_states & (1 << PSI_IRQ_FULL)) 1024 psi_schedule_rtpoll_work(group, 1, false); 1025 } while ((group = group->parent)); 1026 } 1027 #endif 1028 1029 /** 1030 * psi_memstall_enter - mark the beginning of a memory stall section 1031 * @flags: flags to handle nested sections 1032 * 1033 * Marks the calling task as being stalled due to a lack of memory, 1034 * such as waiting for a refault or performing reclaim. 1035 */ 1036 void psi_memstall_enter(unsigned long *flags) 1037 { 1038 struct rq_flags rf; 1039 struct rq *rq; 1040 1041 if (static_branch_likely(&psi_disabled)) 1042 return; 1043 1044 *flags = current->in_memstall; 1045 if (*flags) 1046 return; 1047 /* 1048 * in_memstall setting & accounting needs to be atomic wrt 1049 * changes to the task's scheduling state, otherwise we can 1050 * race with CPU migration. 1051 */ 1052 rq = this_rq_lock_irq(&rf); 1053 1054 current->in_memstall = 1; 1055 psi_task_change(current, 0, TSK_MEMSTALL | TSK_MEMSTALL_RUNNING); 1056 1057 rq_unlock_irq(rq, &rf); 1058 } 1059 EXPORT_SYMBOL_GPL(psi_memstall_enter); 1060 1061 /** 1062 * psi_memstall_leave - mark the end of an memory stall section 1063 * @flags: flags to handle nested memdelay sections 1064 * 1065 * Marks the calling task as no longer stalled due to lack of memory. 1066 */ 1067 void psi_memstall_leave(unsigned long *flags) 1068 { 1069 struct rq_flags rf; 1070 struct rq *rq; 1071 1072 if (static_branch_likely(&psi_disabled)) 1073 return; 1074 1075 if (*flags) 1076 return; 1077 /* 1078 * in_memstall clearing & accounting needs to be atomic wrt 1079 * changes to the task's scheduling state, otherwise we could 1080 * race with CPU migration. 1081 */ 1082 rq = this_rq_lock_irq(&rf); 1083 1084 current->in_memstall = 0; 1085 psi_task_change(current, TSK_MEMSTALL | TSK_MEMSTALL_RUNNING, 0); 1086 1087 rq_unlock_irq(rq, &rf); 1088 } 1089 EXPORT_SYMBOL_GPL(psi_memstall_leave); 1090 1091 #ifdef CONFIG_CGROUPS 1092 int psi_cgroup_alloc(struct cgroup *cgroup) 1093 { 1094 if (!static_branch_likely(&psi_cgroups_enabled)) 1095 return 0; 1096 1097 cgroup->psi = kzalloc(sizeof(struct psi_group), GFP_KERNEL); 1098 if (!cgroup->psi) 1099 return -ENOMEM; 1100 1101 cgroup->psi->pcpu = alloc_percpu(struct psi_group_cpu); 1102 if (!cgroup->psi->pcpu) { 1103 kfree(cgroup->psi); 1104 return -ENOMEM; 1105 } 1106 group_init(cgroup->psi); 1107 cgroup->psi->parent = cgroup_psi(cgroup_parent(cgroup)); 1108 return 0; 1109 } 1110 1111 void psi_cgroup_free(struct cgroup *cgroup) 1112 { 1113 if (!static_branch_likely(&psi_cgroups_enabled)) 1114 return; 1115 1116 cancel_delayed_work_sync(&cgroup->psi->avgs_work); 1117 free_percpu(cgroup->psi->pcpu); 1118 /* All triggers must be removed by now */ 1119 WARN_ONCE(cgroup->psi->rtpoll_states, "psi: trigger leak\n"); 1120 kfree(cgroup->psi); 1121 } 1122 1123 /** 1124 * cgroup_move_task - move task to a different cgroup 1125 * @task: the task 1126 * @to: the target css_set 1127 * 1128 * Move task to a new cgroup and safely migrate its associated stall 1129 * state between the different groups. 1130 * 1131 * This function acquires the task's rq lock to lock out concurrent 1132 * changes to the task's scheduling state and - in case the task is 1133 * running - concurrent changes to its stall state. 1134 */ 1135 void cgroup_move_task(struct task_struct *task, struct css_set *to) 1136 { 1137 unsigned int task_flags; 1138 struct rq_flags rf; 1139 struct rq *rq; 1140 1141 if (!static_branch_likely(&psi_cgroups_enabled)) { 1142 /* 1143 * Lame to do this here, but the scheduler cannot be locked 1144 * from the outside, so we move cgroups from inside sched/. 1145 */ 1146 rcu_assign_pointer(task->cgroups, to); 1147 return; 1148 } 1149 1150 rq = task_rq_lock(task, &rf); 1151 1152 /* 1153 * We may race with schedule() dropping the rq lock between 1154 * deactivating prev and switching to next. Because the psi 1155 * updates from the deactivation are deferred to the switch 1156 * callback to save cgroup tree updates, the task's scheduling 1157 * state here is not coherent with its psi state: 1158 * 1159 * schedule() cgroup_move_task() 1160 * rq_lock() 1161 * deactivate_task() 1162 * p->on_rq = 0 1163 * psi_dequeue() // defers TSK_RUNNING & TSK_IOWAIT updates 1164 * pick_next_task() 1165 * rq_unlock() 1166 * rq_lock() 1167 * psi_task_change() // old cgroup 1168 * task->cgroups = to 1169 * psi_task_change() // new cgroup 1170 * rq_unlock() 1171 * rq_lock() 1172 * psi_sched_switch() // does deferred updates in new cgroup 1173 * 1174 * Don't rely on the scheduling state. Use psi_flags instead. 1175 */ 1176 task_flags = task->psi_flags; 1177 1178 if (task_flags) 1179 psi_task_change(task, task_flags, 0); 1180 1181 /* See comment above */ 1182 rcu_assign_pointer(task->cgroups, to); 1183 1184 if (task_flags) 1185 psi_task_change(task, 0, task_flags); 1186 1187 task_rq_unlock(rq, task, &rf); 1188 } 1189 1190 void psi_cgroup_restart(struct psi_group *group) 1191 { 1192 int cpu; 1193 1194 /* 1195 * After we disable psi_group->enabled, we don't actually 1196 * stop percpu tasks accounting in each psi_group_cpu, 1197 * instead only stop test_state() loop, record_times() 1198 * and averaging worker, see psi_group_change() for details. 1199 * 1200 * When disable cgroup PSI, this function has nothing to sync 1201 * since cgroup pressure files are hidden and percpu psi_group_cpu 1202 * would see !psi_group->enabled and only do task accounting. 1203 * 1204 * When re-enable cgroup PSI, this function use psi_group_change() 1205 * to get correct state mask from test_state() loop on tasks[], 1206 * and restart groupc->state_start from now, use .clear = .set = 0 1207 * here since no task status really changed. 1208 */ 1209 if (!group->enabled) 1210 return; 1211 1212 for_each_possible_cpu(cpu) { 1213 struct rq *rq = cpu_rq(cpu); 1214 struct rq_flags rf; 1215 u64 now; 1216 1217 rq_lock_irq(rq, &rf); 1218 now = cpu_clock(cpu); 1219 psi_group_change(group, cpu, 0, 0, now, true); 1220 rq_unlock_irq(rq, &rf); 1221 } 1222 } 1223 #endif /* CONFIG_CGROUPS */ 1224 1225 int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res) 1226 { 1227 bool only_full = false; 1228 int full; 1229 u64 now; 1230 1231 if (static_branch_likely(&psi_disabled)) 1232 return -EOPNOTSUPP; 1233 1234 /* Update averages before reporting them */ 1235 mutex_lock(&group->avgs_lock); 1236 now = sched_clock(); 1237 collect_percpu_times(group, PSI_AVGS, NULL); 1238 if (now >= group->avg_next_update) 1239 group->avg_next_update = update_averages(group, now); 1240 mutex_unlock(&group->avgs_lock); 1241 1242 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 1243 only_full = res == PSI_IRQ; 1244 #endif 1245 1246 for (full = 0; full < 2 - only_full; full++) { 1247 unsigned long avg[3] = { 0, }; 1248 u64 total = 0; 1249 int w; 1250 1251 /* CPU FULL is undefined at the system level */ 1252 if (!(group == &psi_system && res == PSI_CPU && full)) { 1253 for (w = 0; w < 3; w++) 1254 avg[w] = group->avg[res * 2 + full][w]; 1255 total = div_u64(group->total[PSI_AVGS][res * 2 + full], 1256 NSEC_PER_USEC); 1257 } 1258 1259 seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n", 1260 full || only_full ? "full" : "some", 1261 LOAD_INT(avg[0]), LOAD_FRAC(avg[0]), 1262 LOAD_INT(avg[1]), LOAD_FRAC(avg[1]), 1263 LOAD_INT(avg[2]), LOAD_FRAC(avg[2]), 1264 total); 1265 } 1266 1267 return 0; 1268 } 1269 1270 struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf, 1271 enum psi_res res, struct file *file, 1272 struct kernfs_open_file *of) 1273 { 1274 struct psi_trigger *t; 1275 enum psi_states state; 1276 u32 threshold_us; 1277 bool privileged; 1278 u32 window_us; 1279 1280 if (static_branch_likely(&psi_disabled)) 1281 return ERR_PTR(-EOPNOTSUPP); 1282 1283 /* 1284 * Checking the privilege here on file->f_cred implies that a privileged user 1285 * could open the file and delegate the write to an unprivileged one. 1286 */ 1287 privileged = cap_raised(file->f_cred->cap_effective, CAP_SYS_RESOURCE); 1288 1289 if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2) 1290 state = PSI_IO_SOME + res * 2; 1291 else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2) 1292 state = PSI_IO_FULL + res * 2; 1293 else 1294 return ERR_PTR(-EINVAL); 1295 1296 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 1297 if (res == PSI_IRQ && --state != PSI_IRQ_FULL) 1298 return ERR_PTR(-EINVAL); 1299 #endif 1300 1301 if (state >= PSI_NONIDLE) 1302 return ERR_PTR(-EINVAL); 1303 1304 if (window_us == 0 || window_us > WINDOW_MAX_US) 1305 return ERR_PTR(-EINVAL); 1306 1307 /* 1308 * Unprivileged users can only use 2s windows so that averages aggregation 1309 * work is used, and no RT threads need to be spawned. 1310 */ 1311 if (!privileged && window_us % 2000000) 1312 return ERR_PTR(-EINVAL); 1313 1314 /* Check threshold */ 1315 if (threshold_us == 0 || threshold_us > window_us) 1316 return ERR_PTR(-EINVAL); 1317 1318 t = kmalloc(sizeof(*t), GFP_KERNEL); 1319 if (!t) 1320 return ERR_PTR(-ENOMEM); 1321 1322 t->group = group; 1323 t->state = state; 1324 t->threshold = threshold_us * NSEC_PER_USEC; 1325 t->win.size = window_us * NSEC_PER_USEC; 1326 window_reset(&t->win, sched_clock(), 1327 group->total[PSI_POLL][t->state], 0); 1328 1329 t->event = 0; 1330 t->last_event_time = 0; 1331 t->of = of; 1332 if (!of) 1333 init_waitqueue_head(&t->event_wait); 1334 t->pending_event = false; 1335 t->aggregator = privileged ? PSI_POLL : PSI_AVGS; 1336 1337 if (privileged) { 1338 mutex_lock(&group->rtpoll_trigger_lock); 1339 1340 if (!rcu_access_pointer(group->rtpoll_task)) { 1341 struct task_struct *task; 1342 1343 task = kthread_create(psi_rtpoll_worker, group, "psimon"); 1344 if (IS_ERR(task)) { 1345 kfree(t); 1346 mutex_unlock(&group->rtpoll_trigger_lock); 1347 return ERR_CAST(task); 1348 } 1349 atomic_set(&group->rtpoll_wakeup, 0); 1350 wake_up_process(task); 1351 rcu_assign_pointer(group->rtpoll_task, task); 1352 } 1353 1354 list_add(&t->node, &group->rtpoll_triggers); 1355 group->rtpoll_min_period = min(group->rtpoll_min_period, 1356 div_u64(t->win.size, UPDATES_PER_WINDOW)); 1357 group->rtpoll_nr_triggers[t->state]++; 1358 group->rtpoll_states |= (1 << t->state); 1359 1360 mutex_unlock(&group->rtpoll_trigger_lock); 1361 } else { 1362 mutex_lock(&group->avgs_lock); 1363 1364 list_add(&t->node, &group->avg_triggers); 1365 group->avg_nr_triggers[t->state]++; 1366 1367 mutex_unlock(&group->avgs_lock); 1368 } 1369 return t; 1370 } 1371 1372 void psi_trigger_destroy(struct psi_trigger *t) 1373 { 1374 struct psi_group *group; 1375 struct task_struct *task_to_destroy = NULL; 1376 1377 /* 1378 * We do not check psi_disabled since it might have been disabled after 1379 * the trigger got created. 1380 */ 1381 if (!t) 1382 return; 1383 1384 group = t->group; 1385 /* 1386 * Wakeup waiters to stop polling and clear the queue to prevent it from 1387 * being accessed later. Can happen if cgroup is deleted from under a 1388 * polling process. 1389 */ 1390 if (t->of) 1391 kernfs_notify(t->of->kn); 1392 else 1393 wake_up_interruptible(&t->event_wait); 1394 1395 if (t->aggregator == PSI_AVGS) { 1396 mutex_lock(&group->avgs_lock); 1397 if (!list_empty(&t->node)) { 1398 list_del(&t->node); 1399 group->avg_nr_triggers[t->state]--; 1400 } 1401 mutex_unlock(&group->avgs_lock); 1402 } else { 1403 mutex_lock(&group->rtpoll_trigger_lock); 1404 if (!list_empty(&t->node)) { 1405 struct psi_trigger *tmp; 1406 u64 period = ULLONG_MAX; 1407 1408 list_del(&t->node); 1409 group->rtpoll_nr_triggers[t->state]--; 1410 if (!group->rtpoll_nr_triggers[t->state]) 1411 group->rtpoll_states &= ~(1 << t->state); 1412 /* 1413 * Reset min update period for the remaining triggers 1414 * iff the destroying trigger had the min window size. 1415 */ 1416 if (group->rtpoll_min_period == div_u64(t->win.size, UPDATES_PER_WINDOW)) { 1417 list_for_each_entry(tmp, &group->rtpoll_triggers, node) 1418 period = min(period, div_u64(tmp->win.size, 1419 UPDATES_PER_WINDOW)); 1420 group->rtpoll_min_period = period; 1421 } 1422 /* Destroy rtpoll_task when the last trigger is destroyed */ 1423 if (group->rtpoll_states == 0) { 1424 group->rtpoll_until = 0; 1425 task_to_destroy = rcu_dereference_protected( 1426 group->rtpoll_task, 1427 lockdep_is_held(&group->rtpoll_trigger_lock)); 1428 rcu_assign_pointer(group->rtpoll_task, NULL); 1429 del_timer(&group->rtpoll_timer); 1430 } 1431 } 1432 mutex_unlock(&group->rtpoll_trigger_lock); 1433 } 1434 1435 /* 1436 * Wait for psi_schedule_rtpoll_work RCU to complete its read-side 1437 * critical section before destroying the trigger and optionally the 1438 * rtpoll_task. 1439 */ 1440 synchronize_rcu(); 1441 /* 1442 * Stop kthread 'psimon' after releasing rtpoll_trigger_lock to prevent 1443 * a deadlock while waiting for psi_rtpoll_work to acquire 1444 * rtpoll_trigger_lock 1445 */ 1446 if (task_to_destroy) { 1447 /* 1448 * After the RCU grace period has expired, the worker 1449 * can no longer be found through group->rtpoll_task. 1450 */ 1451 kthread_stop(task_to_destroy); 1452 atomic_set(&group->rtpoll_scheduled, 0); 1453 } 1454 kfree(t); 1455 } 1456 1457 __poll_t psi_trigger_poll(void **trigger_ptr, 1458 struct file *file, poll_table *wait) 1459 { 1460 __poll_t ret = DEFAULT_POLLMASK; 1461 struct psi_trigger *t; 1462 1463 if (static_branch_likely(&psi_disabled)) 1464 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; 1465 1466 t = smp_load_acquire(trigger_ptr); 1467 if (!t) 1468 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; 1469 1470 if (t->of) 1471 kernfs_generic_poll(t->of, wait); 1472 else 1473 poll_wait(file, &t->event_wait, wait); 1474 1475 if (cmpxchg(&t->event, 1, 0) == 1) 1476 ret |= EPOLLPRI; 1477 1478 return ret; 1479 } 1480 1481 #ifdef CONFIG_PROC_FS 1482 static int psi_io_show(struct seq_file *m, void *v) 1483 { 1484 return psi_show(m, &psi_system, PSI_IO); 1485 } 1486 1487 static int psi_memory_show(struct seq_file *m, void *v) 1488 { 1489 return psi_show(m, &psi_system, PSI_MEM); 1490 } 1491 1492 static int psi_cpu_show(struct seq_file *m, void *v) 1493 { 1494 return psi_show(m, &psi_system, PSI_CPU); 1495 } 1496 1497 static int psi_io_open(struct inode *inode, struct file *file) 1498 { 1499 return single_open(file, psi_io_show, NULL); 1500 } 1501 1502 static int psi_memory_open(struct inode *inode, struct file *file) 1503 { 1504 return single_open(file, psi_memory_show, NULL); 1505 } 1506 1507 static int psi_cpu_open(struct inode *inode, struct file *file) 1508 { 1509 return single_open(file, psi_cpu_show, NULL); 1510 } 1511 1512 static ssize_t psi_write(struct file *file, const char __user *user_buf, 1513 size_t nbytes, enum psi_res res) 1514 { 1515 char buf[32]; 1516 size_t buf_size; 1517 struct seq_file *seq; 1518 struct psi_trigger *new; 1519 1520 if (static_branch_likely(&psi_disabled)) 1521 return -EOPNOTSUPP; 1522 1523 if (!nbytes) 1524 return -EINVAL; 1525 1526 buf_size = min(nbytes, sizeof(buf)); 1527 if (copy_from_user(buf, user_buf, buf_size)) 1528 return -EFAULT; 1529 1530 buf[buf_size - 1] = '\0'; 1531 1532 seq = file->private_data; 1533 1534 /* Take seq->lock to protect seq->private from concurrent writes */ 1535 mutex_lock(&seq->lock); 1536 1537 /* Allow only one trigger per file descriptor */ 1538 if (seq->private) { 1539 mutex_unlock(&seq->lock); 1540 return -EBUSY; 1541 } 1542 1543 new = psi_trigger_create(&psi_system, buf, res, file, NULL); 1544 if (IS_ERR(new)) { 1545 mutex_unlock(&seq->lock); 1546 return PTR_ERR(new); 1547 } 1548 1549 smp_store_release(&seq->private, new); 1550 mutex_unlock(&seq->lock); 1551 1552 return nbytes; 1553 } 1554 1555 static ssize_t psi_io_write(struct file *file, const char __user *user_buf, 1556 size_t nbytes, loff_t *ppos) 1557 { 1558 return psi_write(file, user_buf, nbytes, PSI_IO); 1559 } 1560 1561 static ssize_t psi_memory_write(struct file *file, const char __user *user_buf, 1562 size_t nbytes, loff_t *ppos) 1563 { 1564 return psi_write(file, user_buf, nbytes, PSI_MEM); 1565 } 1566 1567 static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf, 1568 size_t nbytes, loff_t *ppos) 1569 { 1570 return psi_write(file, user_buf, nbytes, PSI_CPU); 1571 } 1572 1573 static __poll_t psi_fop_poll(struct file *file, poll_table *wait) 1574 { 1575 struct seq_file *seq = file->private_data; 1576 1577 return psi_trigger_poll(&seq->private, file, wait); 1578 } 1579 1580 static int psi_fop_release(struct inode *inode, struct file *file) 1581 { 1582 struct seq_file *seq = file->private_data; 1583 1584 psi_trigger_destroy(seq->private); 1585 return single_release(inode, file); 1586 } 1587 1588 static const struct proc_ops psi_io_proc_ops = { 1589 .proc_open = psi_io_open, 1590 .proc_read = seq_read, 1591 .proc_lseek = seq_lseek, 1592 .proc_write = psi_io_write, 1593 .proc_poll = psi_fop_poll, 1594 .proc_release = psi_fop_release, 1595 }; 1596 1597 static const struct proc_ops psi_memory_proc_ops = { 1598 .proc_open = psi_memory_open, 1599 .proc_read = seq_read, 1600 .proc_lseek = seq_lseek, 1601 .proc_write = psi_memory_write, 1602 .proc_poll = psi_fop_poll, 1603 .proc_release = psi_fop_release, 1604 }; 1605 1606 static const struct proc_ops psi_cpu_proc_ops = { 1607 .proc_open = psi_cpu_open, 1608 .proc_read = seq_read, 1609 .proc_lseek = seq_lseek, 1610 .proc_write = psi_cpu_write, 1611 .proc_poll = psi_fop_poll, 1612 .proc_release = psi_fop_release, 1613 }; 1614 1615 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 1616 static int psi_irq_show(struct seq_file *m, void *v) 1617 { 1618 return psi_show(m, &psi_system, PSI_IRQ); 1619 } 1620 1621 static int psi_irq_open(struct inode *inode, struct file *file) 1622 { 1623 return single_open(file, psi_irq_show, NULL); 1624 } 1625 1626 static ssize_t psi_irq_write(struct file *file, const char __user *user_buf, 1627 size_t nbytes, loff_t *ppos) 1628 { 1629 return psi_write(file, user_buf, nbytes, PSI_IRQ); 1630 } 1631 1632 static const struct proc_ops psi_irq_proc_ops = { 1633 .proc_open = psi_irq_open, 1634 .proc_read = seq_read, 1635 .proc_lseek = seq_lseek, 1636 .proc_write = psi_irq_write, 1637 .proc_poll = psi_fop_poll, 1638 .proc_release = psi_fop_release, 1639 }; 1640 #endif 1641 1642 static int __init psi_proc_init(void) 1643 { 1644 if (psi_enable) { 1645 proc_mkdir("pressure", NULL); 1646 proc_create("pressure/io", 0666, NULL, &psi_io_proc_ops); 1647 proc_create("pressure/memory", 0666, NULL, &psi_memory_proc_ops); 1648 proc_create("pressure/cpu", 0666, NULL, &psi_cpu_proc_ops); 1649 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 1650 proc_create("pressure/irq", 0666, NULL, &psi_irq_proc_ops); 1651 #endif 1652 } 1653 return 0; 1654 } 1655 module_init(psi_proc_init); 1656 1657 #endif /* CONFIG_PROC_FS */ 1658