1 /* 2 * Pressure stall information for CPU, memory and IO 3 * 4 * Copyright (c) 2018 Facebook, Inc. 5 * Author: Johannes Weiner <hannes@cmpxchg.org> 6 * 7 * Polling support by Suren Baghdasaryan <surenb@google.com> 8 * Copyright (c) 2018 Google, Inc. 9 * 10 * When CPU, memory and IO are contended, tasks experience delays that 11 * reduce throughput and introduce latencies into the workload. Memory 12 * and IO contention, in addition, can cause a full loss of forward 13 * progress in which the CPU goes idle. 14 * 15 * This code aggregates individual task delays into resource pressure 16 * metrics that indicate problems with both workload health and 17 * resource utilization. 18 * 19 * Model 20 * 21 * The time in which a task can execute on a CPU is our baseline for 22 * productivity. Pressure expresses the amount of time in which this 23 * potential cannot be realized due to resource contention. 24 * 25 * This concept of productivity has two components: the workload and 26 * the CPU. To measure the impact of pressure on both, we define two 27 * contention states for a resource: SOME and FULL. 28 * 29 * In the SOME state of a given resource, one or more tasks are 30 * delayed on that resource. This affects the workload's ability to 31 * perform work, but the CPU may still be executing other tasks. 32 * 33 * In the FULL state of a given resource, all non-idle tasks are 34 * delayed on that resource such that nobody is advancing and the CPU 35 * goes idle. This leaves both workload and CPU unproductive. 36 * 37 * (Naturally, the FULL state doesn't exist for the CPU resource.) 38 * 39 * SOME = nr_delayed_tasks != 0 40 * FULL = nr_delayed_tasks != 0 && nr_running_tasks == 0 41 * 42 * The percentage of wallclock time spent in those compound stall 43 * states gives pressure numbers between 0 and 100 for each resource, 44 * where the SOME percentage indicates workload slowdowns and the FULL 45 * percentage indicates reduced CPU utilization: 46 * 47 * %SOME = time(SOME) / period 48 * %FULL = time(FULL) / period 49 * 50 * Multiple CPUs 51 * 52 * The more tasks and available CPUs there are, the more work can be 53 * performed concurrently. This means that the potential that can go 54 * unrealized due to resource contention *also* scales with non-idle 55 * tasks and CPUs. 56 * 57 * Consider a scenario where 257 number crunching tasks are trying to 58 * run concurrently on 256 CPUs. If we simply aggregated the task 59 * states, we would have to conclude a CPU SOME pressure number of 60 * 100%, since *somebody* is waiting on a runqueue at all 61 * times. However, that is clearly not the amount of contention the 62 * workload is experiencing: only one out of 256 possible exceution 63 * threads will be contended at any given time, or about 0.4%. 64 * 65 * Conversely, consider a scenario of 4 tasks and 4 CPUs where at any 66 * given time *one* of the tasks is delayed due to a lack of memory. 67 * Again, looking purely at the task state would yield a memory FULL 68 * pressure number of 0%, since *somebody* is always making forward 69 * progress. But again this wouldn't capture the amount of execution 70 * potential lost, which is 1 out of 4 CPUs, or 25%. 71 * 72 * To calculate wasted potential (pressure) with multiple processors, 73 * we have to base our calculation on the number of non-idle tasks in 74 * conjunction with the number of available CPUs, which is the number 75 * of potential execution threads. SOME becomes then the proportion of 76 * delayed tasks to possibe threads, and FULL is the share of possible 77 * threads that are unproductive due to delays: 78 * 79 * threads = min(nr_nonidle_tasks, nr_cpus) 80 * SOME = min(nr_delayed_tasks / threads, 1) 81 * FULL = (threads - min(nr_running_tasks, threads)) / threads 82 * 83 * For the 257 number crunchers on 256 CPUs, this yields: 84 * 85 * threads = min(257, 256) 86 * SOME = min(1 / 256, 1) = 0.4% 87 * FULL = (256 - min(257, 256)) / 256 = 0% 88 * 89 * For the 1 out of 4 memory-delayed tasks, this yields: 90 * 91 * threads = min(4, 4) 92 * SOME = min(1 / 4, 1) = 25% 93 * FULL = (4 - min(3, 4)) / 4 = 25% 94 * 95 * [ Substitute nr_cpus with 1, and you can see that it's a natural 96 * extension of the single-CPU model. ] 97 * 98 * Implementation 99 * 100 * To assess the precise time spent in each such state, we would have 101 * to freeze the system on task changes and start/stop the state 102 * clocks accordingly. Obviously that doesn't scale in practice. 103 * 104 * Because the scheduler aims to distribute the compute load evenly 105 * among the available CPUs, we can track task state locally to each 106 * CPU and, at much lower frequency, extrapolate the global state for 107 * the cumulative stall times and the running averages. 108 * 109 * For each runqueue, we track: 110 * 111 * tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0) 112 * tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_running_tasks[cpu]) 113 * tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0) 114 * 115 * and then periodically aggregate: 116 * 117 * tNONIDLE = sum(tNONIDLE[i]) 118 * 119 * tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE 120 * tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE 121 * 122 * %SOME = tSOME / period 123 * %FULL = tFULL / period 124 * 125 * This gives us an approximation of pressure that is practical 126 * cost-wise, yet way more sensitive and accurate than periodic 127 * sampling of the aggregate task states would be. 128 */ 129 130 #include "../workqueue_internal.h" 131 #include <linux/sched/loadavg.h> 132 #include <linux/seq_file.h> 133 #include <linux/proc_fs.h> 134 #include <linux/seqlock.h> 135 #include <linux/uaccess.h> 136 #include <linux/cgroup.h> 137 #include <linux/module.h> 138 #include <linux/sched.h> 139 #include <linux/ctype.h> 140 #include <linux/file.h> 141 #include <linux/poll.h> 142 #include <linux/psi.h> 143 #include "sched.h" 144 145 static int psi_bug __read_mostly; 146 147 DEFINE_STATIC_KEY_FALSE(psi_disabled); 148 149 #ifdef CONFIG_PSI_DEFAULT_DISABLED 150 static bool psi_enable; 151 #else 152 static bool psi_enable = true; 153 #endif 154 static int __init setup_psi(char *str) 155 { 156 return kstrtobool(str, &psi_enable) == 0; 157 } 158 __setup("psi=", setup_psi); 159 160 /* Running averages - we need to be higher-res than loadavg */ 161 #define PSI_FREQ (2*HZ+1) /* 2 sec intervals */ 162 #define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */ 163 #define EXP_60s 1981 /* 1/exp(2s/60s) */ 164 #define EXP_300s 2034 /* 1/exp(2s/300s) */ 165 166 /* PSI trigger definitions */ 167 #define WINDOW_MIN_US 500000 /* Min window size is 500ms */ 168 #define WINDOW_MAX_US 10000000 /* Max window size is 10s */ 169 #define UPDATES_PER_WINDOW 10 /* 10 updates per window */ 170 171 /* Sampling frequency in nanoseconds */ 172 static u64 psi_period __read_mostly; 173 174 /* System-level pressure and stall tracking */ 175 static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu); 176 struct psi_group psi_system = { 177 .pcpu = &system_group_pcpu, 178 }; 179 180 static void psi_avgs_work(struct work_struct *work); 181 182 static void group_init(struct psi_group *group) 183 { 184 int cpu; 185 186 for_each_possible_cpu(cpu) 187 seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq); 188 group->avg_next_update = sched_clock() + psi_period; 189 INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work); 190 mutex_init(&group->avgs_lock); 191 /* Init trigger-related members */ 192 atomic_set(&group->poll_scheduled, 0); 193 mutex_init(&group->trigger_lock); 194 INIT_LIST_HEAD(&group->triggers); 195 memset(group->nr_triggers, 0, sizeof(group->nr_triggers)); 196 group->poll_states = 0; 197 group->poll_min_period = U32_MAX; 198 memset(group->polling_total, 0, sizeof(group->polling_total)); 199 group->polling_next_update = ULLONG_MAX; 200 group->polling_until = 0; 201 rcu_assign_pointer(group->poll_kworker, NULL); 202 } 203 204 void __init psi_init(void) 205 { 206 if (!psi_enable) { 207 static_branch_enable(&psi_disabled); 208 return; 209 } 210 211 psi_period = jiffies_to_nsecs(PSI_FREQ); 212 group_init(&psi_system); 213 } 214 215 static bool test_state(unsigned int *tasks, enum psi_states state) 216 { 217 switch (state) { 218 case PSI_IO_SOME: 219 return tasks[NR_IOWAIT]; 220 case PSI_IO_FULL: 221 return tasks[NR_IOWAIT] && !tasks[NR_RUNNING]; 222 case PSI_MEM_SOME: 223 return tasks[NR_MEMSTALL]; 224 case PSI_MEM_FULL: 225 return tasks[NR_MEMSTALL] && !tasks[NR_RUNNING]; 226 case PSI_CPU_SOME: 227 return tasks[NR_RUNNING] > 1; 228 case PSI_NONIDLE: 229 return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] || 230 tasks[NR_RUNNING]; 231 default: 232 return false; 233 } 234 } 235 236 static void get_recent_times(struct psi_group *group, int cpu, 237 enum psi_aggregators aggregator, u32 *times, 238 u32 *pchanged_states) 239 { 240 struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu); 241 u64 now, state_start; 242 enum psi_states s; 243 unsigned int seq; 244 u32 state_mask; 245 246 *pchanged_states = 0; 247 248 /* Snapshot a coherent view of the CPU state */ 249 do { 250 seq = read_seqcount_begin(&groupc->seq); 251 now = cpu_clock(cpu); 252 memcpy(times, groupc->times, sizeof(groupc->times)); 253 state_mask = groupc->state_mask; 254 state_start = groupc->state_start; 255 } while (read_seqcount_retry(&groupc->seq, seq)); 256 257 /* Calculate state time deltas against the previous snapshot */ 258 for (s = 0; s < NR_PSI_STATES; s++) { 259 u32 delta; 260 /* 261 * In addition to already concluded states, we also 262 * incorporate currently active states on the CPU, 263 * since states may last for many sampling periods. 264 * 265 * This way we keep our delta sampling buckets small 266 * (u32) and our reported pressure close to what's 267 * actually happening. 268 */ 269 if (state_mask & (1 << s)) 270 times[s] += now - state_start; 271 272 delta = times[s] - groupc->times_prev[aggregator][s]; 273 groupc->times_prev[aggregator][s] = times[s]; 274 275 times[s] = delta; 276 if (delta) 277 *pchanged_states |= (1 << s); 278 } 279 } 280 281 static void calc_avgs(unsigned long avg[3], int missed_periods, 282 u64 time, u64 period) 283 { 284 unsigned long pct; 285 286 /* Fill in zeroes for periods of no activity */ 287 if (missed_periods) { 288 avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods); 289 avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods); 290 avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods); 291 } 292 293 /* Sample the most recent active period */ 294 pct = div_u64(time * 100, period); 295 pct *= FIXED_1; 296 avg[0] = calc_load(avg[0], EXP_10s, pct); 297 avg[1] = calc_load(avg[1], EXP_60s, pct); 298 avg[2] = calc_load(avg[2], EXP_300s, pct); 299 } 300 301 static void collect_percpu_times(struct psi_group *group, 302 enum psi_aggregators aggregator, 303 u32 *pchanged_states) 304 { 305 u64 deltas[NR_PSI_STATES - 1] = { 0, }; 306 unsigned long nonidle_total = 0; 307 u32 changed_states = 0; 308 int cpu; 309 int s; 310 311 /* 312 * Collect the per-cpu time buckets and average them into a 313 * single time sample that is normalized to wallclock time. 314 * 315 * For averaging, each CPU is weighted by its non-idle time in 316 * the sampling period. This eliminates artifacts from uneven 317 * loading, or even entirely idle CPUs. 318 */ 319 for_each_possible_cpu(cpu) { 320 u32 times[NR_PSI_STATES]; 321 u32 nonidle; 322 u32 cpu_changed_states; 323 324 get_recent_times(group, cpu, aggregator, times, 325 &cpu_changed_states); 326 changed_states |= cpu_changed_states; 327 328 nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]); 329 nonidle_total += nonidle; 330 331 for (s = 0; s < PSI_NONIDLE; s++) 332 deltas[s] += (u64)times[s] * nonidle; 333 } 334 335 /* 336 * Integrate the sample into the running statistics that are 337 * reported to userspace: the cumulative stall times and the 338 * decaying averages. 339 * 340 * Pressure percentages are sampled at PSI_FREQ. We might be 341 * called more often when the user polls more frequently than 342 * that; we might be called less often when there is no task 343 * activity, thus no data, and clock ticks are sporadic. The 344 * below handles both. 345 */ 346 347 /* total= */ 348 for (s = 0; s < NR_PSI_STATES - 1; s++) 349 group->total[aggregator][s] += 350 div_u64(deltas[s], max(nonidle_total, 1UL)); 351 352 if (pchanged_states) 353 *pchanged_states = changed_states; 354 } 355 356 static u64 update_averages(struct psi_group *group, u64 now) 357 { 358 unsigned long missed_periods = 0; 359 u64 expires, period; 360 u64 avg_next_update; 361 int s; 362 363 /* avgX= */ 364 expires = group->avg_next_update; 365 if (now - expires >= psi_period) 366 missed_periods = div_u64(now - expires, psi_period); 367 368 /* 369 * The periodic clock tick can get delayed for various 370 * reasons, especially on loaded systems. To avoid clock 371 * drift, we schedule the clock in fixed psi_period intervals. 372 * But the deltas we sample out of the per-cpu buckets above 373 * are based on the actual time elapsing between clock ticks. 374 */ 375 avg_next_update = expires + ((1 + missed_periods) * psi_period); 376 period = now - (group->avg_last_update + (missed_periods * psi_period)); 377 group->avg_last_update = now; 378 379 for (s = 0; s < NR_PSI_STATES - 1; s++) { 380 u32 sample; 381 382 sample = group->total[PSI_AVGS][s] - group->avg_total[s]; 383 /* 384 * Due to the lockless sampling of the time buckets, 385 * recorded time deltas can slip into the next period, 386 * which under full pressure can result in samples in 387 * excess of the period length. 388 * 389 * We don't want to report non-sensical pressures in 390 * excess of 100%, nor do we want to drop such events 391 * on the floor. Instead we punt any overage into the 392 * future until pressure subsides. By doing this we 393 * don't underreport the occurring pressure curve, we 394 * just report it delayed by one period length. 395 * 396 * The error isn't cumulative. As soon as another 397 * delta slips from a period P to P+1, by definition 398 * it frees up its time T in P. 399 */ 400 if (sample > period) 401 sample = period; 402 group->avg_total[s] += sample; 403 calc_avgs(group->avg[s], missed_periods, sample, period); 404 } 405 406 return avg_next_update; 407 } 408 409 static void psi_avgs_work(struct work_struct *work) 410 { 411 struct delayed_work *dwork; 412 struct psi_group *group; 413 u32 changed_states; 414 bool nonidle; 415 u64 now; 416 417 dwork = to_delayed_work(work); 418 group = container_of(dwork, struct psi_group, avgs_work); 419 420 mutex_lock(&group->avgs_lock); 421 422 now = sched_clock(); 423 424 collect_percpu_times(group, PSI_AVGS, &changed_states); 425 nonidle = changed_states & (1 << PSI_NONIDLE); 426 /* 427 * If there is task activity, periodically fold the per-cpu 428 * times and feed samples into the running averages. If things 429 * are idle and there is no data to process, stop the clock. 430 * Once restarted, we'll catch up the running averages in one 431 * go - see calc_avgs() and missed_periods. 432 */ 433 if (now >= group->avg_next_update) 434 group->avg_next_update = update_averages(group, now); 435 436 if (nonidle) { 437 schedule_delayed_work(dwork, nsecs_to_jiffies( 438 group->avg_next_update - now) + 1); 439 } 440 441 mutex_unlock(&group->avgs_lock); 442 } 443 444 /* Trigger tracking window manupulations */ 445 static void window_reset(struct psi_window *win, u64 now, u64 value, 446 u64 prev_growth) 447 { 448 win->start_time = now; 449 win->start_value = value; 450 win->prev_growth = prev_growth; 451 } 452 453 /* 454 * PSI growth tracking window update and growth calculation routine. 455 * 456 * This approximates a sliding tracking window by interpolating 457 * partially elapsed windows using historical growth data from the 458 * previous intervals. This minimizes memory requirements (by not storing 459 * all the intermediate values in the previous window) and simplifies 460 * the calculations. It works well because PSI signal changes only in 461 * positive direction and over relatively small window sizes the growth 462 * is close to linear. 463 */ 464 static u64 window_update(struct psi_window *win, u64 now, u64 value) 465 { 466 u64 elapsed; 467 u64 growth; 468 469 elapsed = now - win->start_time; 470 growth = value - win->start_value; 471 /* 472 * After each tracking window passes win->start_value and 473 * win->start_time get reset and win->prev_growth stores 474 * the average per-window growth of the previous window. 475 * win->prev_growth is then used to interpolate additional 476 * growth from the previous window assuming it was linear. 477 */ 478 if (elapsed > win->size) 479 window_reset(win, now, value, growth); 480 else { 481 u32 remaining; 482 483 remaining = win->size - elapsed; 484 growth += div_u64(win->prev_growth * remaining, win->size); 485 } 486 487 return growth; 488 } 489 490 static void init_triggers(struct psi_group *group, u64 now) 491 { 492 struct psi_trigger *t; 493 494 list_for_each_entry(t, &group->triggers, node) 495 window_reset(&t->win, now, 496 group->total[PSI_POLL][t->state], 0); 497 memcpy(group->polling_total, group->total[PSI_POLL], 498 sizeof(group->polling_total)); 499 group->polling_next_update = now + group->poll_min_period; 500 } 501 502 static u64 update_triggers(struct psi_group *group, u64 now) 503 { 504 struct psi_trigger *t; 505 bool new_stall = false; 506 u64 *total = group->total[PSI_POLL]; 507 508 /* 509 * On subsequent updates, calculate growth deltas and let 510 * watchers know when their specified thresholds are exceeded. 511 */ 512 list_for_each_entry(t, &group->triggers, node) { 513 u64 growth; 514 515 /* Check for stall activity */ 516 if (group->polling_total[t->state] == total[t->state]) 517 continue; 518 519 /* 520 * Multiple triggers might be looking at the same state, 521 * remember to update group->polling_total[] once we've 522 * been through all of them. Also remember to extend the 523 * polling time if we see new stall activity. 524 */ 525 new_stall = true; 526 527 /* Calculate growth since last update */ 528 growth = window_update(&t->win, now, total[t->state]); 529 if (growth < t->threshold) 530 continue; 531 532 /* Limit event signaling to once per window */ 533 if (now < t->last_event_time + t->win.size) 534 continue; 535 536 /* Generate an event */ 537 if (cmpxchg(&t->event, 0, 1) == 0) 538 wake_up_interruptible(&t->event_wait); 539 t->last_event_time = now; 540 } 541 542 if (new_stall) 543 memcpy(group->polling_total, total, 544 sizeof(group->polling_total)); 545 546 return now + group->poll_min_period; 547 } 548 549 /* 550 * Schedule polling if it's not already scheduled. It's safe to call even from 551 * hotpath because even though kthread_queue_delayed_work takes worker->lock 552 * spinlock that spinlock is never contended due to poll_scheduled atomic 553 * preventing such competition. 554 */ 555 static void psi_schedule_poll_work(struct psi_group *group, unsigned long delay) 556 { 557 struct kthread_worker *kworker; 558 559 /* Do not reschedule if already scheduled */ 560 if (atomic_cmpxchg(&group->poll_scheduled, 0, 1) != 0) 561 return; 562 563 rcu_read_lock(); 564 565 kworker = rcu_dereference(group->poll_kworker); 566 /* 567 * kworker might be NULL in case psi_trigger_destroy races with 568 * psi_task_change (hotpath) which can't use locks 569 */ 570 if (likely(kworker)) 571 kthread_queue_delayed_work(kworker, &group->poll_work, delay); 572 else 573 atomic_set(&group->poll_scheduled, 0); 574 575 rcu_read_unlock(); 576 } 577 578 static void psi_poll_work(struct kthread_work *work) 579 { 580 struct kthread_delayed_work *dwork; 581 struct psi_group *group; 582 u32 changed_states; 583 u64 now; 584 585 dwork = container_of(work, struct kthread_delayed_work, work); 586 group = container_of(dwork, struct psi_group, poll_work); 587 588 atomic_set(&group->poll_scheduled, 0); 589 590 mutex_lock(&group->trigger_lock); 591 592 now = sched_clock(); 593 594 collect_percpu_times(group, PSI_POLL, &changed_states); 595 596 if (changed_states & group->poll_states) { 597 /* Initialize trigger windows when entering polling mode */ 598 if (now > group->polling_until) 599 init_triggers(group, now); 600 601 /* 602 * Keep the monitor active for at least the duration of the 603 * minimum tracking window as long as monitor states are 604 * changing. 605 */ 606 group->polling_until = now + 607 group->poll_min_period * UPDATES_PER_WINDOW; 608 } 609 610 if (now > group->polling_until) { 611 group->polling_next_update = ULLONG_MAX; 612 goto out; 613 } 614 615 if (now >= group->polling_next_update) 616 group->polling_next_update = update_triggers(group, now); 617 618 psi_schedule_poll_work(group, 619 nsecs_to_jiffies(group->polling_next_update - now) + 1); 620 621 out: 622 mutex_unlock(&group->trigger_lock); 623 } 624 625 static void record_times(struct psi_group_cpu *groupc, int cpu, 626 bool memstall_tick) 627 { 628 u32 delta; 629 u64 now; 630 631 now = cpu_clock(cpu); 632 delta = now - groupc->state_start; 633 groupc->state_start = now; 634 635 if (groupc->state_mask & (1 << PSI_IO_SOME)) { 636 groupc->times[PSI_IO_SOME] += delta; 637 if (groupc->state_mask & (1 << PSI_IO_FULL)) 638 groupc->times[PSI_IO_FULL] += delta; 639 } 640 641 if (groupc->state_mask & (1 << PSI_MEM_SOME)) { 642 groupc->times[PSI_MEM_SOME] += delta; 643 if (groupc->state_mask & (1 << PSI_MEM_FULL)) 644 groupc->times[PSI_MEM_FULL] += delta; 645 else if (memstall_tick) { 646 u32 sample; 647 /* 648 * Since we care about lost potential, a 649 * memstall is FULL when there are no other 650 * working tasks, but also when the CPU is 651 * actively reclaiming and nothing productive 652 * could run even if it were runnable. 653 * 654 * When the timer tick sees a reclaiming CPU, 655 * regardless of runnable tasks, sample a FULL 656 * tick (or less if it hasn't been a full tick 657 * since the last state change). 658 */ 659 sample = min(delta, (u32)jiffies_to_nsecs(1)); 660 groupc->times[PSI_MEM_FULL] += sample; 661 } 662 } 663 664 if (groupc->state_mask & (1 << PSI_CPU_SOME)) 665 groupc->times[PSI_CPU_SOME] += delta; 666 667 if (groupc->state_mask & (1 << PSI_NONIDLE)) 668 groupc->times[PSI_NONIDLE] += delta; 669 } 670 671 static u32 psi_group_change(struct psi_group *group, int cpu, 672 unsigned int clear, unsigned int set) 673 { 674 struct psi_group_cpu *groupc; 675 unsigned int t, m; 676 enum psi_states s; 677 u32 state_mask = 0; 678 679 groupc = per_cpu_ptr(group->pcpu, cpu); 680 681 /* 682 * First we assess the aggregate resource states this CPU's 683 * tasks have been in since the last change, and account any 684 * SOME and FULL time these may have resulted in. 685 * 686 * Then we update the task counts according to the state 687 * change requested through the @clear and @set bits. 688 */ 689 write_seqcount_begin(&groupc->seq); 690 691 record_times(groupc, cpu, false); 692 693 for (t = 0, m = clear; m; m &= ~(1 << t), t++) { 694 if (!(m & (1 << t))) 695 continue; 696 if (groupc->tasks[t] == 0 && !psi_bug) { 697 printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u] clear=%x set=%x\n", 698 cpu, t, groupc->tasks[0], 699 groupc->tasks[1], groupc->tasks[2], 700 clear, set); 701 psi_bug = 1; 702 } 703 groupc->tasks[t]--; 704 } 705 706 for (t = 0; set; set &= ~(1 << t), t++) 707 if (set & (1 << t)) 708 groupc->tasks[t]++; 709 710 /* Calculate state mask representing active states */ 711 for (s = 0; s < NR_PSI_STATES; s++) { 712 if (test_state(groupc->tasks, s)) 713 state_mask |= (1 << s); 714 } 715 groupc->state_mask = state_mask; 716 717 write_seqcount_end(&groupc->seq); 718 719 return state_mask; 720 } 721 722 static struct psi_group *iterate_groups(struct task_struct *task, void **iter) 723 { 724 #ifdef CONFIG_CGROUPS 725 struct cgroup *cgroup = NULL; 726 727 if (!*iter) 728 cgroup = task->cgroups->dfl_cgrp; 729 else if (*iter == &psi_system) 730 return NULL; 731 else 732 cgroup = cgroup_parent(*iter); 733 734 if (cgroup && cgroup_parent(cgroup)) { 735 *iter = cgroup; 736 return cgroup_psi(cgroup); 737 } 738 #else 739 if (*iter) 740 return NULL; 741 #endif 742 *iter = &psi_system; 743 return &psi_system; 744 } 745 746 void psi_task_change(struct task_struct *task, int clear, int set) 747 { 748 int cpu = task_cpu(task); 749 struct psi_group *group; 750 bool wake_clock = true; 751 void *iter = NULL; 752 753 if (!task->pid) 754 return; 755 756 if (((task->psi_flags & set) || 757 (task->psi_flags & clear) != clear) && 758 !psi_bug) { 759 printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n", 760 task->pid, task->comm, cpu, 761 task->psi_flags, clear, set); 762 psi_bug = 1; 763 } 764 765 task->psi_flags &= ~clear; 766 task->psi_flags |= set; 767 768 /* 769 * Periodic aggregation shuts off if there is a period of no 770 * task changes, so we wake it back up if necessary. However, 771 * don't do this if the task change is the aggregation worker 772 * itself going to sleep, or we'll ping-pong forever. 773 */ 774 if (unlikely((clear & TSK_RUNNING) && 775 (task->flags & PF_WQ_WORKER) && 776 wq_worker_last_func(task) == psi_avgs_work)) 777 wake_clock = false; 778 779 while ((group = iterate_groups(task, &iter))) { 780 u32 state_mask = psi_group_change(group, cpu, clear, set); 781 782 if (state_mask & group->poll_states) 783 psi_schedule_poll_work(group, 1); 784 785 if (wake_clock && !delayed_work_pending(&group->avgs_work)) 786 schedule_delayed_work(&group->avgs_work, PSI_FREQ); 787 } 788 } 789 790 void psi_memstall_tick(struct task_struct *task, int cpu) 791 { 792 struct psi_group *group; 793 void *iter = NULL; 794 795 while ((group = iterate_groups(task, &iter))) { 796 struct psi_group_cpu *groupc; 797 798 groupc = per_cpu_ptr(group->pcpu, cpu); 799 write_seqcount_begin(&groupc->seq); 800 record_times(groupc, cpu, true); 801 write_seqcount_end(&groupc->seq); 802 } 803 } 804 805 /** 806 * psi_memstall_enter - mark the beginning of a memory stall section 807 * @flags: flags to handle nested sections 808 * 809 * Marks the calling task as being stalled due to a lack of memory, 810 * such as waiting for a refault or performing reclaim. 811 */ 812 void psi_memstall_enter(unsigned long *flags) 813 { 814 struct rq_flags rf; 815 struct rq *rq; 816 817 if (static_branch_likely(&psi_disabled)) 818 return; 819 820 *flags = current->flags & PF_MEMSTALL; 821 if (*flags) 822 return; 823 /* 824 * PF_MEMSTALL setting & accounting needs to be atomic wrt 825 * changes to the task's scheduling state, otherwise we can 826 * race with CPU migration. 827 */ 828 rq = this_rq_lock_irq(&rf); 829 830 current->flags |= PF_MEMSTALL; 831 psi_task_change(current, 0, TSK_MEMSTALL); 832 833 rq_unlock_irq(rq, &rf); 834 } 835 836 /** 837 * psi_memstall_leave - mark the end of an memory stall section 838 * @flags: flags to handle nested memdelay sections 839 * 840 * Marks the calling task as no longer stalled due to lack of memory. 841 */ 842 void psi_memstall_leave(unsigned long *flags) 843 { 844 struct rq_flags rf; 845 struct rq *rq; 846 847 if (static_branch_likely(&psi_disabled)) 848 return; 849 850 if (*flags) 851 return; 852 /* 853 * PF_MEMSTALL clearing & accounting needs to be atomic wrt 854 * changes to the task's scheduling state, otherwise we could 855 * race with CPU migration. 856 */ 857 rq = this_rq_lock_irq(&rf); 858 859 current->flags &= ~PF_MEMSTALL; 860 psi_task_change(current, TSK_MEMSTALL, 0); 861 862 rq_unlock_irq(rq, &rf); 863 } 864 865 #ifdef CONFIG_CGROUPS 866 int psi_cgroup_alloc(struct cgroup *cgroup) 867 { 868 if (static_branch_likely(&psi_disabled)) 869 return 0; 870 871 cgroup->psi.pcpu = alloc_percpu(struct psi_group_cpu); 872 if (!cgroup->psi.pcpu) 873 return -ENOMEM; 874 group_init(&cgroup->psi); 875 return 0; 876 } 877 878 void psi_cgroup_free(struct cgroup *cgroup) 879 { 880 if (static_branch_likely(&psi_disabled)) 881 return; 882 883 cancel_delayed_work_sync(&cgroup->psi.avgs_work); 884 free_percpu(cgroup->psi.pcpu); 885 /* All triggers must be removed by now */ 886 WARN_ONCE(cgroup->psi.poll_states, "psi: trigger leak\n"); 887 } 888 889 /** 890 * cgroup_move_task - move task to a different cgroup 891 * @task: the task 892 * @to: the target css_set 893 * 894 * Move task to a new cgroup and safely migrate its associated stall 895 * state between the different groups. 896 * 897 * This function acquires the task's rq lock to lock out concurrent 898 * changes to the task's scheduling state and - in case the task is 899 * running - concurrent changes to its stall state. 900 */ 901 void cgroup_move_task(struct task_struct *task, struct css_set *to) 902 { 903 unsigned int task_flags = 0; 904 struct rq_flags rf; 905 struct rq *rq; 906 907 if (static_branch_likely(&psi_disabled)) { 908 /* 909 * Lame to do this here, but the scheduler cannot be locked 910 * from the outside, so we move cgroups from inside sched/. 911 */ 912 rcu_assign_pointer(task->cgroups, to); 913 return; 914 } 915 916 rq = task_rq_lock(task, &rf); 917 918 if (task_on_rq_queued(task)) 919 task_flags = TSK_RUNNING; 920 else if (task->in_iowait) 921 task_flags = TSK_IOWAIT; 922 923 if (task->flags & PF_MEMSTALL) 924 task_flags |= TSK_MEMSTALL; 925 926 if (task_flags) 927 psi_task_change(task, task_flags, 0); 928 929 /* See comment above */ 930 rcu_assign_pointer(task->cgroups, to); 931 932 if (task_flags) 933 psi_task_change(task, 0, task_flags); 934 935 task_rq_unlock(rq, task, &rf); 936 } 937 #endif /* CONFIG_CGROUPS */ 938 939 int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res) 940 { 941 int full; 942 u64 now; 943 944 if (static_branch_likely(&psi_disabled)) 945 return -EOPNOTSUPP; 946 947 /* Update averages before reporting them */ 948 mutex_lock(&group->avgs_lock); 949 now = sched_clock(); 950 collect_percpu_times(group, PSI_AVGS, NULL); 951 if (now >= group->avg_next_update) 952 group->avg_next_update = update_averages(group, now); 953 mutex_unlock(&group->avgs_lock); 954 955 for (full = 0; full < 2 - (res == PSI_CPU); full++) { 956 unsigned long avg[3]; 957 u64 total; 958 int w; 959 960 for (w = 0; w < 3; w++) 961 avg[w] = group->avg[res * 2 + full][w]; 962 total = div_u64(group->total[PSI_AVGS][res * 2 + full], 963 NSEC_PER_USEC); 964 965 seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n", 966 full ? "full" : "some", 967 LOAD_INT(avg[0]), LOAD_FRAC(avg[0]), 968 LOAD_INT(avg[1]), LOAD_FRAC(avg[1]), 969 LOAD_INT(avg[2]), LOAD_FRAC(avg[2]), 970 total); 971 } 972 973 return 0; 974 } 975 976 static int psi_io_show(struct seq_file *m, void *v) 977 { 978 return psi_show(m, &psi_system, PSI_IO); 979 } 980 981 static int psi_memory_show(struct seq_file *m, void *v) 982 { 983 return psi_show(m, &psi_system, PSI_MEM); 984 } 985 986 static int psi_cpu_show(struct seq_file *m, void *v) 987 { 988 return psi_show(m, &psi_system, PSI_CPU); 989 } 990 991 static int psi_io_open(struct inode *inode, struct file *file) 992 { 993 return single_open(file, psi_io_show, NULL); 994 } 995 996 static int psi_memory_open(struct inode *inode, struct file *file) 997 { 998 return single_open(file, psi_memory_show, NULL); 999 } 1000 1001 static int psi_cpu_open(struct inode *inode, struct file *file) 1002 { 1003 return single_open(file, psi_cpu_show, NULL); 1004 } 1005 1006 struct psi_trigger *psi_trigger_create(struct psi_group *group, 1007 char *buf, size_t nbytes, enum psi_res res) 1008 { 1009 struct psi_trigger *t; 1010 enum psi_states state; 1011 u32 threshold_us; 1012 u32 window_us; 1013 1014 if (static_branch_likely(&psi_disabled)) 1015 return ERR_PTR(-EOPNOTSUPP); 1016 1017 if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2) 1018 state = PSI_IO_SOME + res * 2; 1019 else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2) 1020 state = PSI_IO_FULL + res * 2; 1021 else 1022 return ERR_PTR(-EINVAL); 1023 1024 if (state >= PSI_NONIDLE) 1025 return ERR_PTR(-EINVAL); 1026 1027 if (window_us < WINDOW_MIN_US || 1028 window_us > WINDOW_MAX_US) 1029 return ERR_PTR(-EINVAL); 1030 1031 /* Check threshold */ 1032 if (threshold_us == 0 || threshold_us > window_us) 1033 return ERR_PTR(-EINVAL); 1034 1035 t = kmalloc(sizeof(*t), GFP_KERNEL); 1036 if (!t) 1037 return ERR_PTR(-ENOMEM); 1038 1039 t->group = group; 1040 t->state = state; 1041 t->threshold = threshold_us * NSEC_PER_USEC; 1042 t->win.size = window_us * NSEC_PER_USEC; 1043 window_reset(&t->win, 0, 0, 0); 1044 1045 t->event = 0; 1046 t->last_event_time = 0; 1047 init_waitqueue_head(&t->event_wait); 1048 kref_init(&t->refcount); 1049 1050 mutex_lock(&group->trigger_lock); 1051 1052 if (!rcu_access_pointer(group->poll_kworker)) { 1053 struct sched_param param = { 1054 .sched_priority = 1, 1055 }; 1056 struct kthread_worker *kworker; 1057 1058 kworker = kthread_create_worker(0, "psimon"); 1059 if (IS_ERR(kworker)) { 1060 kfree(t); 1061 mutex_unlock(&group->trigger_lock); 1062 return ERR_CAST(kworker); 1063 } 1064 sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, ¶m); 1065 kthread_init_delayed_work(&group->poll_work, 1066 psi_poll_work); 1067 rcu_assign_pointer(group->poll_kworker, kworker); 1068 } 1069 1070 list_add(&t->node, &group->triggers); 1071 group->poll_min_period = min(group->poll_min_period, 1072 div_u64(t->win.size, UPDATES_PER_WINDOW)); 1073 group->nr_triggers[t->state]++; 1074 group->poll_states |= (1 << t->state); 1075 1076 mutex_unlock(&group->trigger_lock); 1077 1078 return t; 1079 } 1080 1081 static void psi_trigger_destroy(struct kref *ref) 1082 { 1083 struct psi_trigger *t = container_of(ref, struct psi_trigger, refcount); 1084 struct psi_group *group = t->group; 1085 struct kthread_worker *kworker_to_destroy = NULL; 1086 1087 if (static_branch_likely(&psi_disabled)) 1088 return; 1089 1090 /* 1091 * Wakeup waiters to stop polling. Can happen if cgroup is deleted 1092 * from under a polling process. 1093 */ 1094 wake_up_interruptible(&t->event_wait); 1095 1096 mutex_lock(&group->trigger_lock); 1097 1098 if (!list_empty(&t->node)) { 1099 struct psi_trigger *tmp; 1100 u64 period = ULLONG_MAX; 1101 1102 list_del(&t->node); 1103 group->nr_triggers[t->state]--; 1104 if (!group->nr_triggers[t->state]) 1105 group->poll_states &= ~(1 << t->state); 1106 /* reset min update period for the remaining triggers */ 1107 list_for_each_entry(tmp, &group->triggers, node) 1108 period = min(period, div_u64(tmp->win.size, 1109 UPDATES_PER_WINDOW)); 1110 group->poll_min_period = period; 1111 /* Destroy poll_kworker when the last trigger is destroyed */ 1112 if (group->poll_states == 0) { 1113 group->polling_until = 0; 1114 kworker_to_destroy = rcu_dereference_protected( 1115 group->poll_kworker, 1116 lockdep_is_held(&group->trigger_lock)); 1117 rcu_assign_pointer(group->poll_kworker, NULL); 1118 } 1119 } 1120 1121 mutex_unlock(&group->trigger_lock); 1122 1123 /* 1124 * Wait for both *trigger_ptr from psi_trigger_replace and 1125 * poll_kworker RCUs to complete their read-side critical sections 1126 * before destroying the trigger and optionally the poll_kworker 1127 */ 1128 synchronize_rcu(); 1129 /* 1130 * Destroy the kworker after releasing trigger_lock to prevent a 1131 * deadlock while waiting for psi_poll_work to acquire trigger_lock 1132 */ 1133 if (kworker_to_destroy) { 1134 kthread_cancel_delayed_work_sync(&group->poll_work); 1135 kthread_destroy_worker(kworker_to_destroy); 1136 } 1137 kfree(t); 1138 } 1139 1140 void psi_trigger_replace(void **trigger_ptr, struct psi_trigger *new) 1141 { 1142 struct psi_trigger *old = *trigger_ptr; 1143 1144 if (static_branch_likely(&psi_disabled)) 1145 return; 1146 1147 rcu_assign_pointer(*trigger_ptr, new); 1148 if (old) 1149 kref_put(&old->refcount, psi_trigger_destroy); 1150 } 1151 1152 __poll_t psi_trigger_poll(void **trigger_ptr, 1153 struct file *file, poll_table *wait) 1154 { 1155 __poll_t ret = DEFAULT_POLLMASK; 1156 struct psi_trigger *t; 1157 1158 if (static_branch_likely(&psi_disabled)) 1159 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; 1160 1161 rcu_read_lock(); 1162 1163 t = rcu_dereference(*(void __rcu __force **)trigger_ptr); 1164 if (!t) { 1165 rcu_read_unlock(); 1166 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; 1167 } 1168 kref_get(&t->refcount); 1169 1170 rcu_read_unlock(); 1171 1172 poll_wait(file, &t->event_wait, wait); 1173 1174 if (cmpxchg(&t->event, 1, 0) == 1) 1175 ret |= EPOLLPRI; 1176 1177 kref_put(&t->refcount, psi_trigger_destroy); 1178 1179 return ret; 1180 } 1181 1182 static ssize_t psi_write(struct file *file, const char __user *user_buf, 1183 size_t nbytes, enum psi_res res) 1184 { 1185 char buf[32]; 1186 size_t buf_size; 1187 struct seq_file *seq; 1188 struct psi_trigger *new; 1189 1190 if (static_branch_likely(&psi_disabled)) 1191 return -EOPNOTSUPP; 1192 1193 buf_size = min(nbytes, (sizeof(buf) - 1)); 1194 if (copy_from_user(buf, user_buf, buf_size)) 1195 return -EFAULT; 1196 1197 buf[buf_size - 1] = '\0'; 1198 1199 new = psi_trigger_create(&psi_system, buf, nbytes, res); 1200 if (IS_ERR(new)) 1201 return PTR_ERR(new); 1202 1203 seq = file->private_data; 1204 /* Take seq->lock to protect seq->private from concurrent writes */ 1205 mutex_lock(&seq->lock); 1206 psi_trigger_replace(&seq->private, new); 1207 mutex_unlock(&seq->lock); 1208 1209 return nbytes; 1210 } 1211 1212 static ssize_t psi_io_write(struct file *file, const char __user *user_buf, 1213 size_t nbytes, loff_t *ppos) 1214 { 1215 return psi_write(file, user_buf, nbytes, PSI_IO); 1216 } 1217 1218 static ssize_t psi_memory_write(struct file *file, const char __user *user_buf, 1219 size_t nbytes, loff_t *ppos) 1220 { 1221 return psi_write(file, user_buf, nbytes, PSI_MEM); 1222 } 1223 1224 static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf, 1225 size_t nbytes, loff_t *ppos) 1226 { 1227 return psi_write(file, user_buf, nbytes, PSI_CPU); 1228 } 1229 1230 static __poll_t psi_fop_poll(struct file *file, poll_table *wait) 1231 { 1232 struct seq_file *seq = file->private_data; 1233 1234 return psi_trigger_poll(&seq->private, file, wait); 1235 } 1236 1237 static int psi_fop_release(struct inode *inode, struct file *file) 1238 { 1239 struct seq_file *seq = file->private_data; 1240 1241 psi_trigger_replace(&seq->private, NULL); 1242 return single_release(inode, file); 1243 } 1244 1245 static const struct file_operations psi_io_fops = { 1246 .open = psi_io_open, 1247 .read = seq_read, 1248 .llseek = seq_lseek, 1249 .write = psi_io_write, 1250 .poll = psi_fop_poll, 1251 .release = psi_fop_release, 1252 }; 1253 1254 static const struct file_operations psi_memory_fops = { 1255 .open = psi_memory_open, 1256 .read = seq_read, 1257 .llseek = seq_lseek, 1258 .write = psi_memory_write, 1259 .poll = psi_fop_poll, 1260 .release = psi_fop_release, 1261 }; 1262 1263 static const struct file_operations psi_cpu_fops = { 1264 .open = psi_cpu_open, 1265 .read = seq_read, 1266 .llseek = seq_lseek, 1267 .write = psi_cpu_write, 1268 .poll = psi_fop_poll, 1269 .release = psi_fop_release, 1270 }; 1271 1272 static int __init psi_proc_init(void) 1273 { 1274 proc_mkdir("pressure", NULL); 1275 proc_create("pressure/io", 0, NULL, &psi_io_fops); 1276 proc_create("pressure/memory", 0, NULL, &psi_memory_fops); 1277 proc_create("pressure/cpu", 0, NULL, &psi_cpu_fops); 1278 return 0; 1279 } 1280 module_init(psi_proc_init); 1281