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 on-CPU 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 wall clock 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 #include <linux/sched/clock.h> 140 #include <linux/workqueue.h> 141 #include <linux/psi.h> 142 #include "sched.h" 143 144 static int psi_bug __read_mostly; 145 146 DEFINE_STATIC_KEY_FALSE(psi_disabled); 147 static DEFINE_STATIC_KEY_TRUE(psi_cgroups_enabled); 148 149 #ifdef CONFIG_PSI_DEFAULT_DISABLED 150 static bool psi_enable; 151 #else 152 static bool psi_enable = true; 153 #endif 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_MAX_US 10000000 /* Max window size is 10s */ 168 #define UPDATES_PER_WINDOW 10 /* 10 updates per window */ 169 170 /* Sampling frequency in nanoseconds */ 171 static u64 psi_period __read_mostly; 172 173 /* System-level pressure and stall tracking */ 174 static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu); 175 struct psi_group psi_system = { 176 .pcpu = &system_group_pcpu, 177 }; 178 179 static DEFINE_PER_CPU(seqcount_t, psi_seq) = SEQCNT_ZERO(psi_seq); 180 181 static inline void psi_write_begin(int cpu) 182 { 183 write_seqcount_begin(per_cpu_ptr(&psi_seq, cpu)); 184 } 185 186 static inline void psi_write_end(int cpu) 187 { 188 write_seqcount_end(per_cpu_ptr(&psi_seq, cpu)); 189 } 190 191 static inline u32 psi_read_begin(int cpu) 192 { 193 return read_seqcount_begin(per_cpu_ptr(&psi_seq, cpu)); 194 } 195 196 static inline bool psi_read_retry(int cpu, u32 seq) 197 { 198 return read_seqcount_retry(per_cpu_ptr(&psi_seq, cpu), seq); 199 } 200 201 static void psi_avgs_work(struct work_struct *work); 202 203 static void poll_timer_fn(struct timer_list *t); 204 205 static void group_init(struct psi_group *group) 206 { 207 group->enabled = true; 208 group->avg_last_update = sched_clock(); 209 group->avg_next_update = group->avg_last_update + psi_period; 210 mutex_init(&group->avgs_lock); 211 212 /* Init avg trigger-related members */ 213 INIT_LIST_HEAD(&group->avg_triggers); 214 memset(group->avg_nr_triggers, 0, sizeof(group->avg_nr_triggers)); 215 INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work); 216 217 /* Init rtpoll trigger-related members */ 218 atomic_set(&group->rtpoll_scheduled, 0); 219 mutex_init(&group->rtpoll_trigger_lock); 220 INIT_LIST_HEAD(&group->rtpoll_triggers); 221 group->rtpoll_min_period = U32_MAX; 222 group->rtpoll_next_update = ULLONG_MAX; 223 init_waitqueue_head(&group->rtpoll_wait); 224 timer_setup(&group->rtpoll_timer, poll_timer_fn, 0); 225 rcu_assign_pointer(group->rtpoll_task, NULL); 226 } 227 228 void __init psi_init(void) 229 { 230 if (!psi_enable) { 231 static_branch_enable(&psi_disabled); 232 static_branch_disable(&psi_cgroups_enabled); 233 return; 234 } 235 236 if (!cgroup_psi_enabled()) 237 static_branch_disable(&psi_cgroups_enabled); 238 239 psi_period = jiffies_to_nsecs(PSI_FREQ); 240 group_init(&psi_system); 241 } 242 243 static u32 test_states(unsigned int *tasks, u32 state_mask) 244 { 245 const bool oncpu = state_mask & PSI_ONCPU; 246 247 if (tasks[NR_IOWAIT]) { 248 state_mask |= BIT(PSI_IO_SOME); 249 if (!tasks[NR_RUNNING]) 250 state_mask |= BIT(PSI_IO_FULL); 251 } 252 253 if (tasks[NR_MEMSTALL]) { 254 state_mask |= BIT(PSI_MEM_SOME); 255 if (tasks[NR_RUNNING] == tasks[NR_MEMSTALL_RUNNING]) 256 state_mask |= BIT(PSI_MEM_FULL); 257 } 258 259 if (tasks[NR_RUNNING] > oncpu) 260 state_mask |= BIT(PSI_CPU_SOME); 261 262 if (tasks[NR_RUNNING] && !oncpu) 263 state_mask |= BIT(PSI_CPU_FULL); 264 265 if (tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] || tasks[NR_RUNNING]) 266 state_mask |= BIT(PSI_NONIDLE); 267 268 return state_mask; 269 } 270 271 static void get_recent_times(struct psi_group *group, int cpu, 272 enum psi_aggregators aggregator, u32 *times, 273 u32 *pchanged_states) 274 { 275 struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu); 276 int current_cpu = raw_smp_processor_id(); 277 unsigned int tasks[NR_PSI_TASK_COUNTS]; 278 u64 now, state_start; 279 enum psi_states s; 280 unsigned int seq; 281 u32 state_mask; 282 283 *pchanged_states = 0; 284 285 /* Snapshot a coherent view of the CPU state */ 286 do { 287 seq = psi_read_begin(cpu); 288 now = cpu_clock(cpu); 289 memcpy(times, groupc->times, sizeof(groupc->times)); 290 state_mask = groupc->state_mask; 291 state_start = groupc->state_start; 292 if (cpu == current_cpu) 293 memcpy(tasks, groupc->tasks, sizeof(groupc->tasks)); 294 } while (psi_read_retry(cpu, seq)); 295 296 /* Calculate state time deltas against the previous snapshot */ 297 for (s = 0; s < NR_PSI_STATES; s++) { 298 u32 delta; 299 /* 300 * In addition to already concluded states, we also 301 * incorporate currently active states on the CPU, 302 * since states may last for many sampling periods. 303 * 304 * This way we keep our delta sampling buckets small 305 * (u32) and our reported pressure close to what's 306 * actually happening. 307 */ 308 if (state_mask & (1 << s)) 309 times[s] += now - state_start; 310 311 delta = times[s] - groupc->times_prev[aggregator][s]; 312 groupc->times_prev[aggregator][s] = times[s]; 313 314 times[s] = delta; 315 if (delta) 316 *pchanged_states |= (1 << s); 317 } 318 319 /* 320 * When collect_percpu_times() from the avgs_work, we don't want to 321 * re-arm avgs_work when all CPUs are IDLE. But the current CPU running 322 * this avgs_work is never IDLE, cause avgs_work can't be shut off. 323 * So for the current CPU, we need to re-arm avgs_work only when 324 * (NR_RUNNING > 1 || NR_IOWAIT > 0 || NR_MEMSTALL > 0), for other CPUs 325 * we can just check PSI_NONIDLE delta. 326 */ 327 if (current_work() == &group->avgs_work.work) { 328 bool reschedule; 329 330 if (cpu == current_cpu) 331 reschedule = tasks[NR_RUNNING] + 332 tasks[NR_IOWAIT] + 333 tasks[NR_MEMSTALL] > 1; 334 else 335 reschedule = *pchanged_states & (1 << PSI_NONIDLE); 336 337 if (reschedule) 338 *pchanged_states |= PSI_STATE_RESCHEDULE; 339 } 340 } 341 342 static void calc_avgs(unsigned long avg[3], int missed_periods, 343 u64 time, u64 period) 344 { 345 unsigned long pct; 346 347 /* Fill in zeroes for periods of no activity */ 348 if (missed_periods) { 349 avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods); 350 avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods); 351 avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods); 352 } 353 354 /* Sample the most recent active period */ 355 pct = div_u64(time * 100, period); 356 pct *= FIXED_1; 357 avg[0] = calc_load(avg[0], EXP_10s, pct); 358 avg[1] = calc_load(avg[1], EXP_60s, pct); 359 avg[2] = calc_load(avg[2], EXP_300s, pct); 360 } 361 362 static void collect_percpu_times(struct psi_group *group, 363 enum psi_aggregators aggregator, 364 u32 *pchanged_states) 365 { 366 u64 deltas[NR_PSI_STATES - 1] = { 0, }; 367 unsigned long nonidle_total = 0; 368 u32 changed_states = 0; 369 int cpu; 370 int s; 371 372 /* 373 * Collect the per-cpu time buckets and average them into a 374 * single time sample that is normalized to wall clock time. 375 * 376 * For averaging, each CPU is weighted by its non-idle time in 377 * the sampling period. This eliminates artifacts from uneven 378 * loading, or even entirely idle CPUs. 379 */ 380 for_each_possible_cpu(cpu) { 381 u32 times[NR_PSI_STATES]; 382 u32 nonidle; 383 u32 cpu_changed_states; 384 385 get_recent_times(group, cpu, aggregator, times, 386 &cpu_changed_states); 387 changed_states |= cpu_changed_states; 388 389 nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]); 390 nonidle_total += nonidle; 391 392 for (s = 0; s < PSI_NONIDLE; s++) 393 deltas[s] += (u64)times[s] * nonidle; 394 } 395 396 /* 397 * Integrate the sample into the running statistics that are 398 * reported to userspace: the cumulative stall times and the 399 * decaying averages. 400 * 401 * Pressure percentages are sampled at PSI_FREQ. We might be 402 * called more often when the user polls more frequently than 403 * that; we might be called less often when there is no task 404 * activity, thus no data, and clock ticks are sporadic. The 405 * below handles both. 406 */ 407 408 /* total= */ 409 for (s = 0; s < NR_PSI_STATES - 1; s++) 410 group->total[aggregator][s] += 411 div_u64(deltas[s], max(nonidle_total, 1UL)); 412 413 if (pchanged_states) 414 *pchanged_states = changed_states; 415 } 416 417 /* Trigger tracking window manipulations */ 418 static void window_reset(struct psi_window *win, u64 now, u64 value, 419 u64 prev_growth) 420 { 421 win->start_time = now; 422 win->start_value = value; 423 win->prev_growth = prev_growth; 424 } 425 426 /* 427 * PSI growth tracking window update and growth calculation routine. 428 * 429 * This approximates a sliding tracking window by interpolating 430 * partially elapsed windows using historical growth data from the 431 * previous intervals. This minimizes memory requirements (by not storing 432 * all the intermediate values in the previous window) and simplifies 433 * the calculations. It works well because PSI signal changes only in 434 * positive direction and over relatively small window sizes the growth 435 * is close to linear. 436 */ 437 static u64 window_update(struct psi_window *win, u64 now, u64 value) 438 { 439 u64 elapsed; 440 u64 growth; 441 442 elapsed = now - win->start_time; 443 growth = value - win->start_value; 444 /* 445 * After each tracking window passes win->start_value and 446 * win->start_time get reset and win->prev_growth stores 447 * the average per-window growth of the previous window. 448 * win->prev_growth is then used to interpolate additional 449 * growth from the previous window assuming it was linear. 450 */ 451 if (elapsed > win->size) 452 window_reset(win, now, value, growth); 453 else { 454 u32 remaining; 455 456 remaining = win->size - elapsed; 457 growth += div64_u64(win->prev_growth * remaining, win->size); 458 } 459 460 return growth; 461 } 462 463 static void update_triggers(struct psi_group *group, u64 now, 464 enum psi_aggregators aggregator) 465 { 466 struct psi_trigger *t; 467 u64 *total = group->total[aggregator]; 468 struct list_head *triggers; 469 u64 *aggregator_total; 470 471 if (aggregator == PSI_AVGS) { 472 triggers = &group->avg_triggers; 473 aggregator_total = group->avg_total; 474 } else { 475 triggers = &group->rtpoll_triggers; 476 aggregator_total = group->rtpoll_total; 477 } 478 479 /* 480 * On subsequent updates, calculate growth deltas and let 481 * watchers know when their specified thresholds are exceeded. 482 */ 483 list_for_each_entry(t, triggers, node) { 484 u64 growth; 485 bool new_stall; 486 487 new_stall = aggregator_total[t->state] != total[t->state]; 488 489 /* Check for stall activity or a previous threshold breach */ 490 if (!new_stall && !t->pending_event) 491 continue; 492 /* 493 * Check for new stall activity, as well as deferred 494 * events that occurred in the last window after the 495 * trigger had already fired (we want to ratelimit 496 * events without dropping any). 497 */ 498 if (new_stall) { 499 /* Calculate growth since last update */ 500 growth = window_update(&t->win, now, total[t->state]); 501 if (!t->pending_event) { 502 if (growth < t->threshold) 503 continue; 504 505 t->pending_event = true; 506 } 507 } 508 /* Limit event signaling to once per window */ 509 if (now < t->last_event_time + t->win.size) 510 continue; 511 512 /* Generate an event */ 513 if (cmpxchg(&t->event, 0, 1) == 0) { 514 if (t->of) 515 kernfs_notify(t->of->kn); 516 else 517 wake_up_interruptible(&t->event_wait); 518 } 519 t->last_event_time = now; 520 /* Reset threshold breach flag once event got generated */ 521 t->pending_event = false; 522 } 523 } 524 525 static u64 update_averages(struct psi_group *group, u64 now) 526 { 527 unsigned long missed_periods = 0; 528 u64 expires, period; 529 u64 avg_next_update; 530 int s; 531 532 /* avgX= */ 533 expires = group->avg_next_update; 534 if (now - expires >= psi_period) 535 missed_periods = div_u64(now - expires, psi_period); 536 537 /* 538 * The periodic clock tick can get delayed for various 539 * reasons, especially on loaded systems. To avoid clock 540 * drift, we schedule the clock in fixed psi_period intervals. 541 * But the deltas we sample out of the per-cpu buckets above 542 * are based on the actual time elapsing between clock ticks. 543 */ 544 avg_next_update = expires + ((1 + missed_periods) * psi_period); 545 period = now - (group->avg_last_update + (missed_periods * psi_period)); 546 group->avg_last_update = now; 547 548 for (s = 0; s < NR_PSI_STATES - 1; s++) { 549 u32 sample; 550 551 sample = group->total[PSI_AVGS][s] - group->avg_total[s]; 552 /* 553 * Due to the lockless sampling of the time buckets, 554 * recorded time deltas can slip into the next period, 555 * which under full pressure can result in samples in 556 * excess of the period length. 557 * 558 * We don't want to report non-sensical pressures in 559 * excess of 100%, nor do we want to drop such events 560 * on the floor. Instead we punt any overage into the 561 * future until pressure subsides. By doing this we 562 * don't underreport the occurring pressure curve, we 563 * just report it delayed by one period length. 564 * 565 * The error isn't cumulative. As soon as another 566 * delta slips from a period P to P+1, by definition 567 * it frees up its time T in P. 568 */ 569 if (sample > period) 570 sample = period; 571 group->avg_total[s] += sample; 572 calc_avgs(group->avg[s], missed_periods, sample, period); 573 } 574 575 return avg_next_update; 576 } 577 578 static void psi_avgs_work(struct work_struct *work) 579 { 580 struct delayed_work *dwork; 581 struct psi_group *group; 582 u32 changed_states; 583 u64 now; 584 585 dwork = to_delayed_work(work); 586 group = container_of(dwork, struct psi_group, avgs_work); 587 588 mutex_lock(&group->avgs_lock); 589 590 now = sched_clock(); 591 592 collect_percpu_times(group, PSI_AVGS, &changed_states); 593 /* 594 * If there is task activity, periodically fold the per-cpu 595 * times and feed samples into the running averages. If things 596 * are idle and there is no data to process, stop the clock. 597 * Once restarted, we'll catch up the running averages in one 598 * go - see calc_avgs() and missed_periods. 599 */ 600 if (now >= group->avg_next_update) { 601 update_triggers(group, now, PSI_AVGS); 602 group->avg_next_update = update_averages(group, now); 603 } 604 605 if (changed_states & PSI_STATE_RESCHEDULE) { 606 schedule_delayed_work(dwork, nsecs_to_jiffies( 607 group->avg_next_update - now) + 1); 608 } 609 610 mutex_unlock(&group->avgs_lock); 611 } 612 613 static void init_rtpoll_triggers(struct psi_group *group, u64 now) 614 { 615 struct psi_trigger *t; 616 617 list_for_each_entry(t, &group->rtpoll_triggers, node) 618 window_reset(&t->win, now, 619 group->total[PSI_POLL][t->state], 0); 620 memcpy(group->rtpoll_total, group->total[PSI_POLL], 621 sizeof(group->rtpoll_total)); 622 group->rtpoll_next_update = now + group->rtpoll_min_period; 623 } 624 625 /* Schedule rtpolling if it's not already scheduled or forced. */ 626 static void psi_schedule_rtpoll_work(struct psi_group *group, unsigned long delay, 627 bool force) 628 { 629 struct task_struct *task; 630 631 /* 632 * atomic_xchg should be called even when !force to provide a 633 * full memory barrier (see the comment inside psi_rtpoll_work). 634 */ 635 if (atomic_xchg(&group->rtpoll_scheduled, 1) && !force) 636 return; 637 638 rcu_read_lock(); 639 640 task = rcu_dereference(group->rtpoll_task); 641 /* 642 * kworker might be NULL in case psi_trigger_destroy races with 643 * psi_task_change (hotpath) which can't use locks 644 */ 645 if (likely(task)) 646 mod_timer(&group->rtpoll_timer, jiffies + delay); 647 else 648 atomic_set(&group->rtpoll_scheduled, 0); 649 650 rcu_read_unlock(); 651 } 652 653 static void psi_rtpoll_work(struct psi_group *group) 654 { 655 bool force_reschedule = false; 656 u32 changed_states; 657 u64 now; 658 659 mutex_lock(&group->rtpoll_trigger_lock); 660 661 now = sched_clock(); 662 663 if (now > group->rtpoll_until) { 664 /* 665 * We are either about to start or might stop rtpolling if no 666 * state change was recorded. Resetting rtpoll_scheduled leaves 667 * a small window for psi_group_change to sneak in and schedule 668 * an immediate rtpoll_work before we get to rescheduling. One 669 * potential extra wakeup at the end of the rtpolling window 670 * should be negligible and rtpoll_next_update still keeps 671 * updates correctly on schedule. 672 */ 673 atomic_set(&group->rtpoll_scheduled, 0); 674 /* 675 * A task change can race with the rtpoll worker that is supposed to 676 * report on it. To avoid missing events, ensure ordering between 677 * rtpoll_scheduled and the task state accesses, such that if the 678 * rtpoll worker misses the state update, the task change is 679 * guaranteed to reschedule the rtpoll worker: 680 * 681 * rtpoll worker: 682 * atomic_set(rtpoll_scheduled, 0) 683 * smp_mb() 684 * LOAD states 685 * 686 * task change: 687 * STORE states 688 * if atomic_xchg(rtpoll_scheduled, 1) == 0: 689 * schedule rtpoll worker 690 * 691 * The atomic_xchg() implies a full barrier. 692 */ 693 smp_mb(); 694 } else { 695 /* The rtpolling window is not over, keep rescheduling */ 696 force_reschedule = true; 697 } 698 699 700 collect_percpu_times(group, PSI_POLL, &changed_states); 701 702 if (changed_states & group->rtpoll_states) { 703 /* Initialize trigger windows when entering rtpolling mode */ 704 if (now > group->rtpoll_until) 705 init_rtpoll_triggers(group, now); 706 707 /* 708 * Keep the monitor active for at least the duration of the 709 * minimum tracking window as long as monitor states are 710 * changing. 711 */ 712 group->rtpoll_until = now + 713 group->rtpoll_min_period * UPDATES_PER_WINDOW; 714 } 715 716 if (now > group->rtpoll_until) { 717 group->rtpoll_next_update = ULLONG_MAX; 718 goto out; 719 } 720 721 if (now >= group->rtpoll_next_update) { 722 if (changed_states & group->rtpoll_states) { 723 update_triggers(group, now, PSI_POLL); 724 memcpy(group->rtpoll_total, group->total[PSI_POLL], 725 sizeof(group->rtpoll_total)); 726 } 727 group->rtpoll_next_update = now + group->rtpoll_min_period; 728 } 729 730 psi_schedule_rtpoll_work(group, 731 nsecs_to_jiffies(group->rtpoll_next_update - now) + 1, 732 force_reschedule); 733 734 out: 735 mutex_unlock(&group->rtpoll_trigger_lock); 736 } 737 738 static int psi_rtpoll_worker(void *data) 739 { 740 struct psi_group *group = (struct psi_group *)data; 741 742 sched_set_fifo_low(current); 743 744 while (true) { 745 wait_event_interruptible(group->rtpoll_wait, 746 atomic_cmpxchg(&group->rtpoll_wakeup, 1, 0) || 747 kthread_should_stop()); 748 if (kthread_should_stop()) 749 break; 750 751 psi_rtpoll_work(group); 752 } 753 return 0; 754 } 755 756 static void poll_timer_fn(struct timer_list *t) 757 { 758 struct psi_group *group = timer_container_of(group, t, rtpoll_timer); 759 760 atomic_set(&group->rtpoll_wakeup, 1); 761 wake_up_interruptible(&group->rtpoll_wait); 762 } 763 764 static void record_times(struct psi_group_cpu *groupc, u64 now) 765 { 766 u32 delta; 767 768 delta = now - groupc->state_start; 769 groupc->state_start = now; 770 771 if (groupc->state_mask & (1 << PSI_IO_SOME)) { 772 groupc->times[PSI_IO_SOME] += delta; 773 if (groupc->state_mask & (1 << PSI_IO_FULL)) 774 groupc->times[PSI_IO_FULL] += delta; 775 } 776 777 if (groupc->state_mask & (1 << PSI_MEM_SOME)) { 778 groupc->times[PSI_MEM_SOME] += delta; 779 if (groupc->state_mask & (1 << PSI_MEM_FULL)) 780 groupc->times[PSI_MEM_FULL] += delta; 781 } 782 783 if (groupc->state_mask & (1 << PSI_CPU_SOME)) { 784 groupc->times[PSI_CPU_SOME] += delta; 785 if (groupc->state_mask & (1 << PSI_CPU_FULL)) 786 groupc->times[PSI_CPU_FULL] += delta; 787 } 788 789 if (groupc->state_mask & (1 << PSI_NONIDLE)) 790 groupc->times[PSI_NONIDLE] += delta; 791 } 792 793 #define for_each_group(iter, group) \ 794 for (typeof(group) iter = group; iter; iter = iter->parent) 795 796 static void psi_group_change(struct psi_group *group, int cpu, 797 unsigned int clear, unsigned int set, 798 u64 now, bool wake_clock) 799 { 800 struct psi_group_cpu *groupc; 801 unsigned int t, m; 802 u32 state_mask; 803 804 lockdep_assert_rq_held(cpu_rq(cpu)); 805 groupc = per_cpu_ptr(group->pcpu, cpu); 806 807 /* 808 * Start with TSK_ONCPU, which doesn't have a corresponding 809 * task count - it's just a boolean flag directly encoded in 810 * the state mask. Clear, set, or carry the current state if 811 * no changes are requested. 812 */ 813 if (unlikely(clear & TSK_ONCPU)) { 814 state_mask = 0; 815 clear &= ~TSK_ONCPU; 816 } else if (unlikely(set & TSK_ONCPU)) { 817 state_mask = PSI_ONCPU; 818 set &= ~TSK_ONCPU; 819 } else { 820 state_mask = groupc->state_mask & PSI_ONCPU; 821 } 822 823 /* 824 * The rest of the state mask is calculated based on the task 825 * counts. Update those first, then construct the mask. 826 */ 827 for (t = 0, m = clear; m; m &= ~(1 << t), t++) { 828 if (!(m & (1 << t))) 829 continue; 830 if (groupc->tasks[t]) { 831 groupc->tasks[t]--; 832 } else if (!psi_bug) { 833 printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u] clear=%x set=%x\n", 834 cpu, t, groupc->tasks[0], 835 groupc->tasks[1], groupc->tasks[2], 836 groupc->tasks[3], clear, set); 837 psi_bug = 1; 838 } 839 } 840 841 for (t = 0; set; set &= ~(1 << t), t++) 842 if (set & (1 << t)) 843 groupc->tasks[t]++; 844 845 if (!group->enabled) { 846 /* 847 * On the first group change after disabling PSI, conclude 848 * the current state and flush its time. This is unlikely 849 * to matter to the user, but aggregation (get_recent_times) 850 * may have already incorporated the live state into times_prev; 851 * avoid a delta sample underflow when PSI is later re-enabled. 852 */ 853 if (unlikely(groupc->state_mask & (1 << PSI_NONIDLE))) 854 record_times(groupc, now); 855 856 groupc->state_mask = state_mask; 857 858 return; 859 } 860 861 state_mask = test_states(groupc->tasks, state_mask); 862 863 /* 864 * Since we care about lost potential, a memstall is FULL 865 * when there are no other working tasks, but also when 866 * the CPU is actively reclaiming and nothing productive 867 * could run even if it were runnable. So when the current 868 * task in a cgroup is in_memstall, the corresponding groupc 869 * on that cpu is in PSI_MEM_FULL state. 870 */ 871 if (unlikely((state_mask & PSI_ONCPU) && cpu_curr(cpu)->in_memstall)) 872 state_mask |= (1 << PSI_MEM_FULL); 873 874 record_times(groupc, now); 875 876 groupc->state_mask = state_mask; 877 878 if (state_mask & group->rtpoll_states) 879 psi_schedule_rtpoll_work(group, 1, false); 880 881 if (wake_clock && !delayed_work_pending(&group->avgs_work)) 882 schedule_delayed_work(&group->avgs_work, PSI_FREQ); 883 } 884 885 static inline struct psi_group *task_psi_group(struct task_struct *task) 886 { 887 #ifdef CONFIG_CGROUPS 888 if (static_branch_likely(&psi_cgroups_enabled)) 889 return cgroup_psi(task_dfl_cgroup(task)); 890 #endif 891 return &psi_system; 892 } 893 894 static void psi_flags_change(struct task_struct *task, int clear, int set) 895 { 896 if (((task->psi_flags & set) || 897 (task->psi_flags & clear) != clear) && 898 !psi_bug) { 899 printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n", 900 task->pid, task->comm, task_cpu(task), 901 task->psi_flags, clear, set); 902 psi_bug = 1; 903 } 904 905 task->psi_flags &= ~clear; 906 task->psi_flags |= set; 907 } 908 909 void psi_task_change(struct task_struct *task, int clear, int set) 910 { 911 int cpu = task_cpu(task); 912 u64 now; 913 914 if (!task->pid) 915 return; 916 917 psi_flags_change(task, clear, set); 918 919 psi_write_begin(cpu); 920 now = cpu_clock(cpu); 921 for_each_group(group, task_psi_group(task)) 922 psi_group_change(group, cpu, clear, set, now, true); 923 psi_write_end(cpu); 924 } 925 926 void psi_task_switch(struct task_struct *prev, struct task_struct *next, 927 bool sleep) 928 { 929 struct psi_group *common = NULL; 930 int cpu = task_cpu(prev); 931 u64 now; 932 933 psi_write_begin(cpu); 934 now = cpu_clock(cpu); 935 936 if (next->pid) { 937 psi_flags_change(next, 0, TSK_ONCPU); 938 /* 939 * Set TSK_ONCPU on @next's cgroups. If @next shares any 940 * ancestors with @prev, those will already have @prev's 941 * TSK_ONCPU bit set, and we can stop the iteration there. 942 */ 943 for_each_group(group, task_psi_group(next)) { 944 struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu); 945 946 if (groupc->state_mask & PSI_ONCPU) { 947 common = group; 948 break; 949 } 950 psi_group_change(group, cpu, 0, TSK_ONCPU, now, true); 951 } 952 } 953 954 if (prev->pid) { 955 int clear = TSK_ONCPU, set = 0; 956 bool wake_clock = true; 957 958 /* 959 * When we're going to sleep, psi_dequeue() lets us 960 * handle TSK_RUNNING, TSK_MEMSTALL_RUNNING and 961 * TSK_IOWAIT here, where we can combine it with 962 * TSK_ONCPU and save walking common ancestors twice. 963 */ 964 if (sleep) { 965 clear |= TSK_RUNNING; 966 if (prev->in_memstall) 967 clear |= TSK_MEMSTALL_RUNNING; 968 if (prev->in_iowait) 969 set |= TSK_IOWAIT; 970 971 /* 972 * Periodic aggregation shuts off if there is a period of no 973 * task changes, so we wake it back up if necessary. However, 974 * don't do this if the task change is the aggregation worker 975 * itself going to sleep, or we'll ping-pong forever. 976 */ 977 if (unlikely((prev->flags & PF_WQ_WORKER) && 978 wq_worker_last_func(prev) == psi_avgs_work)) 979 wake_clock = false; 980 } 981 982 psi_flags_change(prev, clear, set); 983 984 for_each_group(group, task_psi_group(prev)) { 985 if (group == common) 986 break; 987 psi_group_change(group, cpu, clear, set, now, wake_clock); 988 } 989 990 /* 991 * TSK_ONCPU is handled up to the common ancestor. If there are 992 * any other differences between the two tasks (e.g. prev goes 993 * to sleep, or only one task is memstall), finish propagating 994 * those differences all the way up to the root. 995 */ 996 if ((prev->psi_flags ^ next->psi_flags) & ~TSK_ONCPU) { 997 clear &= ~TSK_ONCPU; 998 for_each_group(group, common) 999 psi_group_change(group, cpu, clear, set, now, wake_clock); 1000 } 1001 } 1002 psi_write_end(cpu); 1003 } 1004 1005 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 1006 void psi_account_irqtime(struct rq *rq, struct task_struct *curr, struct task_struct *prev) 1007 { 1008 int cpu = task_cpu(curr); 1009 struct psi_group_cpu *groupc; 1010 s64 delta; 1011 u64 irq; 1012 u64 now; 1013 1014 if (static_branch_likely(&psi_disabled) || !irqtime_enabled()) 1015 return; 1016 1017 if (!curr->pid) 1018 return; 1019 1020 lockdep_assert_rq_held(rq); 1021 if (prev && task_psi_group(prev) == task_psi_group(curr)) 1022 return; 1023 1024 irq = irq_time_read(cpu); 1025 delta = (s64)(irq - rq->psi_irq_time); 1026 if (delta < 0) 1027 return; 1028 rq->psi_irq_time = irq; 1029 1030 psi_write_begin(cpu); 1031 now = cpu_clock(cpu); 1032 1033 for_each_group(group, task_psi_group(curr)) { 1034 if (!group->enabled) 1035 continue; 1036 1037 groupc = per_cpu_ptr(group->pcpu, cpu); 1038 1039 record_times(groupc, now); 1040 groupc->times[PSI_IRQ_FULL] += delta; 1041 1042 if (group->rtpoll_states & (1 << PSI_IRQ_FULL)) 1043 psi_schedule_rtpoll_work(group, 1, false); 1044 } 1045 psi_write_end(cpu); 1046 } 1047 #endif /* CONFIG_IRQ_TIME_ACCOUNTING */ 1048 1049 /** 1050 * psi_memstall_enter - mark the beginning of a memory stall section 1051 * @flags: flags to handle nested sections 1052 * 1053 * Marks the calling task as being stalled due to a lack of memory, 1054 * such as waiting for a refault or performing reclaim. 1055 */ 1056 void psi_memstall_enter(unsigned long *flags) 1057 { 1058 struct rq_flags rf; 1059 struct rq *rq; 1060 1061 if (static_branch_likely(&psi_disabled)) 1062 return; 1063 1064 *flags = current->in_memstall; 1065 if (*flags) 1066 return; 1067 /* 1068 * in_memstall setting & accounting needs to be atomic wrt 1069 * changes to the task's scheduling state, otherwise we can 1070 * race with CPU migration. 1071 */ 1072 rq = this_rq_lock_irq(&rf); 1073 1074 current->in_memstall = 1; 1075 psi_task_change(current, 0, TSK_MEMSTALL | TSK_MEMSTALL_RUNNING); 1076 1077 rq_unlock_irq(rq, &rf); 1078 } 1079 EXPORT_SYMBOL_GPL(psi_memstall_enter); 1080 1081 /** 1082 * psi_memstall_leave - mark the end of an memory stall section 1083 * @flags: flags to handle nested memdelay sections 1084 * 1085 * Marks the calling task as no longer stalled due to lack of memory. 1086 */ 1087 void psi_memstall_leave(unsigned long *flags) 1088 { 1089 struct rq_flags rf; 1090 struct rq *rq; 1091 1092 if (static_branch_likely(&psi_disabled)) 1093 return; 1094 1095 if (*flags) 1096 return; 1097 /* 1098 * in_memstall clearing & accounting needs to be atomic wrt 1099 * changes to the task's scheduling state, otherwise we could 1100 * race with CPU migration. 1101 */ 1102 rq = this_rq_lock_irq(&rf); 1103 1104 current->in_memstall = 0; 1105 psi_task_change(current, TSK_MEMSTALL | TSK_MEMSTALL_RUNNING, 0); 1106 1107 rq_unlock_irq(rq, &rf); 1108 } 1109 EXPORT_SYMBOL_GPL(psi_memstall_leave); 1110 1111 #ifdef CONFIG_CGROUPS 1112 int psi_cgroup_alloc(struct cgroup *cgroup) 1113 { 1114 if (!static_branch_likely(&psi_cgroups_enabled)) 1115 return 0; 1116 1117 cgroup->psi = kzalloc(sizeof(struct psi_group), GFP_KERNEL); 1118 if (!cgroup->psi) 1119 return -ENOMEM; 1120 1121 cgroup->psi->pcpu = alloc_percpu(struct psi_group_cpu); 1122 if (!cgroup->psi->pcpu) { 1123 kfree(cgroup->psi); 1124 return -ENOMEM; 1125 } 1126 group_init(cgroup->psi); 1127 cgroup->psi->parent = cgroup_psi(cgroup_parent(cgroup)); 1128 return 0; 1129 } 1130 1131 void psi_cgroup_free(struct cgroup *cgroup) 1132 { 1133 if (!static_branch_likely(&psi_cgroups_enabled)) 1134 return; 1135 1136 cancel_delayed_work_sync(&cgroup->psi->avgs_work); 1137 free_percpu(cgroup->psi->pcpu); 1138 /* All triggers must be removed by now */ 1139 WARN_ONCE(cgroup->psi->rtpoll_states, "psi: trigger leak\n"); 1140 kfree(cgroup->psi); 1141 } 1142 1143 /** 1144 * cgroup_move_task - move task to a different cgroup 1145 * @task: the task 1146 * @to: the target css_set 1147 * 1148 * Move task to a new cgroup and safely migrate its associated stall 1149 * state between the different groups. 1150 * 1151 * This function acquires the task's rq lock to lock out concurrent 1152 * changes to the task's scheduling state and - in case the task is 1153 * running - concurrent changes to its stall state. 1154 */ 1155 void cgroup_move_task(struct task_struct *task, struct css_set *to) 1156 { 1157 unsigned int task_flags; 1158 struct rq_flags rf; 1159 struct rq *rq; 1160 1161 if (!static_branch_likely(&psi_cgroups_enabled)) { 1162 /* 1163 * Lame to do this here, but the scheduler cannot be locked 1164 * from the outside, so we move cgroups from inside sched/. 1165 */ 1166 rcu_assign_pointer(task->cgroups, to); 1167 return; 1168 } 1169 1170 rq = task_rq_lock(task, &rf); 1171 1172 /* 1173 * We may race with schedule() dropping the rq lock between 1174 * deactivating prev and switching to next. Because the psi 1175 * updates from the deactivation are deferred to the switch 1176 * callback to save cgroup tree updates, the task's scheduling 1177 * state here is not coherent with its psi state: 1178 * 1179 * schedule() cgroup_move_task() 1180 * rq_lock() 1181 * deactivate_task() 1182 * p->on_rq = 0 1183 * psi_dequeue() // defers TSK_RUNNING & TSK_IOWAIT updates 1184 * pick_next_task() 1185 * rq_unlock() 1186 * rq_lock() 1187 * psi_task_change() // old cgroup 1188 * task->cgroups = to 1189 * psi_task_change() // new cgroup 1190 * rq_unlock() 1191 * rq_lock() 1192 * psi_sched_switch() // does deferred updates in new cgroup 1193 * 1194 * Don't rely on the scheduling state. Use psi_flags instead. 1195 */ 1196 task_flags = task->psi_flags; 1197 1198 if (task_flags) 1199 psi_task_change(task, task_flags, 0); 1200 1201 /* See comment above */ 1202 rcu_assign_pointer(task->cgroups, to); 1203 1204 if (task_flags) 1205 psi_task_change(task, 0, task_flags); 1206 1207 task_rq_unlock(rq, task, &rf); 1208 } 1209 1210 void psi_cgroup_restart(struct psi_group *group) 1211 { 1212 int cpu; 1213 1214 /* 1215 * After we disable psi_group->enabled, we don't actually 1216 * stop percpu tasks accounting in each psi_group_cpu, 1217 * instead only stop test_states() loop, record_times() 1218 * and averaging worker, see psi_group_change() for details. 1219 * 1220 * When disable cgroup PSI, this function has nothing to sync 1221 * since cgroup pressure files are hidden and percpu psi_group_cpu 1222 * would see !psi_group->enabled and only do task accounting. 1223 * 1224 * When re-enable cgroup PSI, this function use psi_group_change() 1225 * to get correct state mask from test_states() loop on tasks[], 1226 * and restart groupc->state_start from now, use .clear = .set = 0 1227 * here since no task status really changed. 1228 */ 1229 if (!group->enabled) 1230 return; 1231 1232 for_each_possible_cpu(cpu) { 1233 u64 now; 1234 1235 guard(rq_lock_irq)(cpu_rq(cpu)); 1236 1237 psi_write_begin(cpu); 1238 now = cpu_clock(cpu); 1239 psi_group_change(group, cpu, 0, 0, now, true); 1240 psi_write_end(cpu); 1241 } 1242 } 1243 #endif /* CONFIG_CGROUPS */ 1244 1245 int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res) 1246 { 1247 bool only_full = false; 1248 int full; 1249 u64 now; 1250 1251 if (static_branch_likely(&psi_disabled)) 1252 return -EOPNOTSUPP; 1253 1254 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 1255 if (!irqtime_enabled() && res == PSI_IRQ) 1256 return -EOPNOTSUPP; 1257 #endif 1258 1259 /* Update averages before reporting them */ 1260 mutex_lock(&group->avgs_lock); 1261 now = sched_clock(); 1262 collect_percpu_times(group, PSI_AVGS, NULL); 1263 if (now >= group->avg_next_update) 1264 group->avg_next_update = update_averages(group, now); 1265 mutex_unlock(&group->avgs_lock); 1266 1267 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 1268 only_full = res == PSI_IRQ; 1269 #endif 1270 1271 for (full = 0; full < 2 - only_full; full++) { 1272 unsigned long avg[3] = { 0, }; 1273 u64 total = 0; 1274 int w; 1275 1276 /* CPU FULL is undefined at the system level */ 1277 if (!(group == &psi_system && res == PSI_CPU && full)) { 1278 for (w = 0; w < 3; w++) 1279 avg[w] = group->avg[res * 2 + full][w]; 1280 total = div_u64(group->total[PSI_AVGS][res * 2 + full], 1281 NSEC_PER_USEC); 1282 } 1283 1284 seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n", 1285 full || only_full ? "full" : "some", 1286 LOAD_INT(avg[0]), LOAD_FRAC(avg[0]), 1287 LOAD_INT(avg[1]), LOAD_FRAC(avg[1]), 1288 LOAD_INT(avg[2]), LOAD_FRAC(avg[2]), 1289 total); 1290 } 1291 1292 return 0; 1293 } 1294 1295 struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf, 1296 enum psi_res res, struct file *file, 1297 struct kernfs_open_file *of) 1298 { 1299 struct psi_trigger *t; 1300 enum psi_states state; 1301 u32 threshold_us; 1302 bool privileged; 1303 u32 window_us; 1304 1305 if (static_branch_likely(&psi_disabled)) 1306 return ERR_PTR(-EOPNOTSUPP); 1307 1308 /* 1309 * Checking the privilege here on file->f_cred implies that a privileged user 1310 * could open the file and delegate the write to an unprivileged one. 1311 */ 1312 privileged = cap_raised(file->f_cred->cap_effective, CAP_SYS_RESOURCE); 1313 1314 if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2) 1315 state = PSI_IO_SOME + res * 2; 1316 else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2) 1317 state = PSI_IO_FULL + res * 2; 1318 else 1319 return ERR_PTR(-EINVAL); 1320 1321 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 1322 if (res == PSI_IRQ && --state != PSI_IRQ_FULL) 1323 return ERR_PTR(-EINVAL); 1324 #endif 1325 1326 if (state >= PSI_NONIDLE) 1327 return ERR_PTR(-EINVAL); 1328 1329 if (window_us == 0 || window_us > WINDOW_MAX_US) 1330 return ERR_PTR(-EINVAL); 1331 1332 /* 1333 * Unprivileged users can only use 2s windows so that averages aggregation 1334 * work is used, and no RT threads need to be spawned. 1335 */ 1336 if (!privileged && window_us % 2000000) 1337 return ERR_PTR(-EINVAL); 1338 1339 /* Check threshold */ 1340 if (threshold_us == 0 || threshold_us > window_us) 1341 return ERR_PTR(-EINVAL); 1342 1343 t = kmalloc(sizeof(*t), GFP_KERNEL); 1344 if (!t) 1345 return ERR_PTR(-ENOMEM); 1346 1347 t->group = group; 1348 t->state = state; 1349 t->threshold = threshold_us * NSEC_PER_USEC; 1350 t->win.size = window_us * NSEC_PER_USEC; 1351 window_reset(&t->win, sched_clock(), 1352 group->total[PSI_POLL][t->state], 0); 1353 1354 t->event = 0; 1355 t->last_event_time = 0; 1356 t->of = of; 1357 if (!of) 1358 init_waitqueue_head(&t->event_wait); 1359 t->pending_event = false; 1360 t->aggregator = privileged ? PSI_POLL : PSI_AVGS; 1361 1362 if (privileged) { 1363 mutex_lock(&group->rtpoll_trigger_lock); 1364 1365 if (!rcu_access_pointer(group->rtpoll_task)) { 1366 struct task_struct *task; 1367 1368 task = kthread_create(psi_rtpoll_worker, group, "psimon"); 1369 if (IS_ERR(task)) { 1370 kfree(t); 1371 mutex_unlock(&group->rtpoll_trigger_lock); 1372 return ERR_CAST(task); 1373 } 1374 atomic_set(&group->rtpoll_wakeup, 0); 1375 wake_up_process(task); 1376 rcu_assign_pointer(group->rtpoll_task, task); 1377 } 1378 1379 list_add(&t->node, &group->rtpoll_triggers); 1380 group->rtpoll_min_period = min(group->rtpoll_min_period, 1381 div_u64(t->win.size, UPDATES_PER_WINDOW)); 1382 group->rtpoll_nr_triggers[t->state]++; 1383 group->rtpoll_states |= (1 << t->state); 1384 1385 mutex_unlock(&group->rtpoll_trigger_lock); 1386 } else { 1387 mutex_lock(&group->avgs_lock); 1388 1389 list_add(&t->node, &group->avg_triggers); 1390 group->avg_nr_triggers[t->state]++; 1391 1392 mutex_unlock(&group->avgs_lock); 1393 } 1394 return t; 1395 } 1396 1397 void psi_trigger_destroy(struct psi_trigger *t) 1398 { 1399 struct psi_group *group; 1400 struct task_struct *task_to_destroy = NULL; 1401 1402 /* 1403 * We do not check psi_disabled since it might have been disabled after 1404 * the trigger got created. 1405 */ 1406 if (!t) 1407 return; 1408 1409 group = t->group; 1410 /* 1411 * Wakeup waiters to stop polling and clear the queue to prevent it from 1412 * being accessed later. Can happen if cgroup is deleted from under a 1413 * polling process. 1414 */ 1415 if (t->of) 1416 kernfs_notify(t->of->kn); 1417 else 1418 wake_up_interruptible(&t->event_wait); 1419 1420 if (t->aggregator == PSI_AVGS) { 1421 mutex_lock(&group->avgs_lock); 1422 if (!list_empty(&t->node)) { 1423 list_del(&t->node); 1424 group->avg_nr_triggers[t->state]--; 1425 } 1426 mutex_unlock(&group->avgs_lock); 1427 } else { 1428 mutex_lock(&group->rtpoll_trigger_lock); 1429 if (!list_empty(&t->node)) { 1430 struct psi_trigger *tmp; 1431 u64 period = ULLONG_MAX; 1432 1433 list_del(&t->node); 1434 group->rtpoll_nr_triggers[t->state]--; 1435 if (!group->rtpoll_nr_triggers[t->state]) 1436 group->rtpoll_states &= ~(1 << t->state); 1437 /* 1438 * Reset min update period for the remaining triggers 1439 * iff the destroying trigger had the min window size. 1440 */ 1441 if (group->rtpoll_min_period == div_u64(t->win.size, UPDATES_PER_WINDOW)) { 1442 list_for_each_entry(tmp, &group->rtpoll_triggers, node) 1443 period = min(period, div_u64(tmp->win.size, 1444 UPDATES_PER_WINDOW)); 1445 group->rtpoll_min_period = period; 1446 } 1447 /* Destroy rtpoll_task when the last trigger is destroyed */ 1448 if (group->rtpoll_states == 0) { 1449 group->rtpoll_until = 0; 1450 task_to_destroy = rcu_dereference_protected( 1451 group->rtpoll_task, 1452 lockdep_is_held(&group->rtpoll_trigger_lock)); 1453 rcu_assign_pointer(group->rtpoll_task, NULL); 1454 timer_delete(&group->rtpoll_timer); 1455 } 1456 } 1457 mutex_unlock(&group->rtpoll_trigger_lock); 1458 } 1459 1460 /* 1461 * Wait for psi_schedule_rtpoll_work RCU to complete its read-side 1462 * critical section before destroying the trigger and optionally the 1463 * rtpoll_task. 1464 */ 1465 synchronize_rcu(); 1466 /* 1467 * Stop kthread 'psimon' after releasing rtpoll_trigger_lock to prevent 1468 * a deadlock while waiting for psi_rtpoll_work to acquire 1469 * rtpoll_trigger_lock 1470 */ 1471 if (task_to_destroy) { 1472 /* 1473 * After the RCU grace period has expired, the worker 1474 * can no longer be found through group->rtpoll_task. 1475 */ 1476 kthread_stop(task_to_destroy); 1477 atomic_set(&group->rtpoll_scheduled, 0); 1478 } 1479 kfree(t); 1480 } 1481 1482 __poll_t psi_trigger_poll(void **trigger_ptr, 1483 struct file *file, poll_table *wait) 1484 { 1485 __poll_t ret = DEFAULT_POLLMASK; 1486 struct psi_trigger *t; 1487 1488 if (static_branch_likely(&psi_disabled)) 1489 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; 1490 1491 t = smp_load_acquire(trigger_ptr); 1492 if (!t) 1493 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; 1494 1495 if (t->of) 1496 kernfs_generic_poll(t->of, wait); 1497 else 1498 poll_wait(file, &t->event_wait, wait); 1499 1500 if (cmpxchg(&t->event, 1, 0) == 1) 1501 ret |= EPOLLPRI; 1502 1503 return ret; 1504 } 1505 1506 #ifdef CONFIG_PROC_FS 1507 static int psi_io_show(struct seq_file *m, void *v) 1508 { 1509 return psi_show(m, &psi_system, PSI_IO); 1510 } 1511 1512 static int psi_memory_show(struct seq_file *m, void *v) 1513 { 1514 return psi_show(m, &psi_system, PSI_MEM); 1515 } 1516 1517 static int psi_cpu_show(struct seq_file *m, void *v) 1518 { 1519 return psi_show(m, &psi_system, PSI_CPU); 1520 } 1521 1522 static int psi_io_open(struct inode *inode, struct file *file) 1523 { 1524 return single_open(file, psi_io_show, NULL); 1525 } 1526 1527 static int psi_memory_open(struct inode *inode, struct file *file) 1528 { 1529 return single_open(file, psi_memory_show, NULL); 1530 } 1531 1532 static int psi_cpu_open(struct inode *inode, struct file *file) 1533 { 1534 return single_open(file, psi_cpu_show, NULL); 1535 } 1536 1537 static ssize_t psi_write(struct file *file, const char __user *user_buf, 1538 size_t nbytes, enum psi_res res) 1539 { 1540 char buf[32]; 1541 size_t buf_size; 1542 struct seq_file *seq; 1543 struct psi_trigger *new; 1544 1545 if (static_branch_likely(&psi_disabled)) 1546 return -EOPNOTSUPP; 1547 1548 if (!nbytes) 1549 return -EINVAL; 1550 1551 buf_size = min(nbytes, sizeof(buf)); 1552 if (copy_from_user(buf, user_buf, buf_size)) 1553 return -EFAULT; 1554 1555 buf[buf_size - 1] = '\0'; 1556 1557 seq = file->private_data; 1558 1559 /* Take seq->lock to protect seq->private from concurrent writes */ 1560 mutex_lock(&seq->lock); 1561 1562 /* Allow only one trigger per file descriptor */ 1563 if (seq->private) { 1564 mutex_unlock(&seq->lock); 1565 return -EBUSY; 1566 } 1567 1568 new = psi_trigger_create(&psi_system, buf, res, file, NULL); 1569 if (IS_ERR(new)) { 1570 mutex_unlock(&seq->lock); 1571 return PTR_ERR(new); 1572 } 1573 1574 smp_store_release(&seq->private, new); 1575 mutex_unlock(&seq->lock); 1576 1577 return nbytes; 1578 } 1579 1580 static ssize_t psi_io_write(struct file *file, const char __user *user_buf, 1581 size_t nbytes, loff_t *ppos) 1582 { 1583 return psi_write(file, user_buf, nbytes, PSI_IO); 1584 } 1585 1586 static ssize_t psi_memory_write(struct file *file, const char __user *user_buf, 1587 size_t nbytes, loff_t *ppos) 1588 { 1589 return psi_write(file, user_buf, nbytes, PSI_MEM); 1590 } 1591 1592 static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf, 1593 size_t nbytes, loff_t *ppos) 1594 { 1595 return psi_write(file, user_buf, nbytes, PSI_CPU); 1596 } 1597 1598 static __poll_t psi_fop_poll(struct file *file, poll_table *wait) 1599 { 1600 struct seq_file *seq = file->private_data; 1601 1602 return psi_trigger_poll(&seq->private, file, wait); 1603 } 1604 1605 static int psi_fop_release(struct inode *inode, struct file *file) 1606 { 1607 struct seq_file *seq = file->private_data; 1608 1609 psi_trigger_destroy(seq->private); 1610 return single_release(inode, file); 1611 } 1612 1613 static const struct proc_ops psi_io_proc_ops = { 1614 .proc_open = psi_io_open, 1615 .proc_read = seq_read, 1616 .proc_lseek = seq_lseek, 1617 .proc_write = psi_io_write, 1618 .proc_poll = psi_fop_poll, 1619 .proc_release = psi_fop_release, 1620 }; 1621 1622 static const struct proc_ops psi_memory_proc_ops = { 1623 .proc_open = psi_memory_open, 1624 .proc_read = seq_read, 1625 .proc_lseek = seq_lseek, 1626 .proc_write = psi_memory_write, 1627 .proc_poll = psi_fop_poll, 1628 .proc_release = psi_fop_release, 1629 }; 1630 1631 static const struct proc_ops psi_cpu_proc_ops = { 1632 .proc_open = psi_cpu_open, 1633 .proc_read = seq_read, 1634 .proc_lseek = seq_lseek, 1635 .proc_write = psi_cpu_write, 1636 .proc_poll = psi_fop_poll, 1637 .proc_release = psi_fop_release, 1638 }; 1639 1640 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 1641 static int psi_irq_show(struct seq_file *m, void *v) 1642 { 1643 return psi_show(m, &psi_system, PSI_IRQ); 1644 } 1645 1646 static int psi_irq_open(struct inode *inode, struct file *file) 1647 { 1648 return single_open(file, psi_irq_show, NULL); 1649 } 1650 1651 static ssize_t psi_irq_write(struct file *file, const char __user *user_buf, 1652 size_t nbytes, loff_t *ppos) 1653 { 1654 return psi_write(file, user_buf, nbytes, PSI_IRQ); 1655 } 1656 1657 static const struct proc_ops psi_irq_proc_ops = { 1658 .proc_open = psi_irq_open, 1659 .proc_read = seq_read, 1660 .proc_lseek = seq_lseek, 1661 .proc_write = psi_irq_write, 1662 .proc_poll = psi_fop_poll, 1663 .proc_release = psi_fop_release, 1664 }; 1665 #endif /* CONFIG_IRQ_TIME_ACCOUNTING */ 1666 1667 static int __init psi_proc_init(void) 1668 { 1669 if (psi_enable) { 1670 proc_mkdir("pressure", NULL); 1671 proc_create("pressure/io", 0666, NULL, &psi_io_proc_ops); 1672 proc_create("pressure/memory", 0666, NULL, &psi_memory_proc_ops); 1673 proc_create("pressure/cpu", 0666, NULL, &psi_cpu_proc_ops); 1674 #ifdef CONFIG_IRQ_TIME_ACCOUNTING 1675 proc_create("pressure/irq", 0666, NULL, &psi_irq_proc_ops); 1676 #endif 1677 } 1678 return 0; 1679 } 1680 module_init(psi_proc_init); 1681 1682 #endif /* CONFIG_PROC_FS */ 1683