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 at the 38 * system level, but exist at the cgroup level, means all non-idle tasks 39 * in a cgroup are delayed on the CPU resource which used by others outside 40 * of the cgroup or throttled by the cgroup cpu.max configuration. 41 * 42 * SOME = nr_delayed_tasks != 0 43 * FULL = nr_delayed_tasks != 0 && nr_running_tasks == 0 44 * 45 * The percentage of wallclock time spent in those compound stall 46 * states gives pressure numbers between 0 and 100 for each resource, 47 * where the SOME percentage indicates workload slowdowns and the FULL 48 * percentage indicates reduced CPU utilization: 49 * 50 * %SOME = time(SOME) / period 51 * %FULL = time(FULL) / period 52 * 53 * Multiple CPUs 54 * 55 * The more tasks and available CPUs there are, the more work can be 56 * performed concurrently. This means that the potential that can go 57 * unrealized due to resource contention *also* scales with non-idle 58 * tasks and CPUs. 59 * 60 * Consider a scenario where 257 number crunching tasks are trying to 61 * run concurrently on 256 CPUs. If we simply aggregated the task 62 * states, we would have to conclude a CPU SOME pressure number of 63 * 100%, since *somebody* is waiting on a runqueue at all 64 * times. However, that is clearly not the amount of contention the 65 * workload is experiencing: only one out of 256 possible execution 66 * threads will be contended at any given time, or about 0.4%. 67 * 68 * Conversely, consider a scenario of 4 tasks and 4 CPUs where at any 69 * given time *one* of the tasks is delayed due to a lack of memory. 70 * Again, looking purely at the task state would yield a memory FULL 71 * pressure number of 0%, since *somebody* is always making forward 72 * progress. But again this wouldn't capture the amount of execution 73 * potential lost, which is 1 out of 4 CPUs, or 25%. 74 * 75 * To calculate wasted potential (pressure) with multiple processors, 76 * we have to base our calculation on the number of non-idle tasks in 77 * conjunction with the number of available CPUs, which is the number 78 * of potential execution threads. SOME becomes then the proportion of 79 * delayed tasks to possible threads, and FULL is the share of possible 80 * threads that are unproductive due to delays: 81 * 82 * threads = min(nr_nonidle_tasks, nr_cpus) 83 * SOME = min(nr_delayed_tasks / threads, 1) 84 * FULL = (threads - min(nr_running_tasks, threads)) / threads 85 * 86 * For the 257 number crunchers on 256 CPUs, this yields: 87 * 88 * threads = min(257, 256) 89 * SOME = min(1 / 256, 1) = 0.4% 90 * FULL = (256 - min(257, 256)) / 256 = 0% 91 * 92 * For the 1 out of 4 memory-delayed tasks, this yields: 93 * 94 * threads = min(4, 4) 95 * SOME = min(1 / 4, 1) = 25% 96 * FULL = (4 - min(3, 4)) / 4 = 25% 97 * 98 * [ Substitute nr_cpus with 1, and you can see that it's a natural 99 * extension of the single-CPU model. ] 100 * 101 * Implementation 102 * 103 * To assess the precise time spent in each such state, we would have 104 * to freeze the system on task changes and start/stop the state 105 * clocks accordingly. Obviously that doesn't scale in practice. 106 * 107 * Because the scheduler aims to distribute the compute load evenly 108 * among the available CPUs, we can track task state locally to each 109 * CPU and, at much lower frequency, extrapolate the global state for 110 * the cumulative stall times and the running averages. 111 * 112 * For each runqueue, we track: 113 * 114 * tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0) 115 * tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_running_tasks[cpu]) 116 * tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0) 117 * 118 * and then periodically aggregate: 119 * 120 * tNONIDLE = sum(tNONIDLE[i]) 121 * 122 * tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE 123 * tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE 124 * 125 * %SOME = tSOME / period 126 * %FULL = tFULL / period 127 * 128 * This gives us an approximation of pressure that is practical 129 * cost-wise, yet way more sensitive and accurate than periodic 130 * sampling of the aggregate task states would be. 131 */ 132 133 #include "../workqueue_internal.h" 134 #include <linux/sched/loadavg.h> 135 #include <linux/seq_file.h> 136 #include <linux/proc_fs.h> 137 #include <linux/seqlock.h> 138 #include <linux/uaccess.h> 139 #include <linux/cgroup.h> 140 #include <linux/module.h> 141 #include <linux/sched.h> 142 #include <linux/ctype.h> 143 #include <linux/file.h> 144 #include <linux/poll.h> 145 #include <linux/psi.h> 146 #include "sched.h" 147 148 static int psi_bug __read_mostly; 149 150 DEFINE_STATIC_KEY_FALSE(psi_disabled); 151 DEFINE_STATIC_KEY_TRUE(psi_cgroups_enabled); 152 153 #ifdef CONFIG_PSI_DEFAULT_DISABLED 154 static bool psi_enable; 155 #else 156 static bool psi_enable = true; 157 #endif 158 static int __init setup_psi(char *str) 159 { 160 return kstrtobool(str, &psi_enable) == 0; 161 } 162 __setup("psi=", setup_psi); 163 164 /* Running averages - we need to be higher-res than loadavg */ 165 #define PSI_FREQ (2*HZ+1) /* 2 sec intervals */ 166 #define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */ 167 #define EXP_60s 1981 /* 1/exp(2s/60s) */ 168 #define EXP_300s 2034 /* 1/exp(2s/300s) */ 169 170 /* PSI trigger definitions */ 171 #define WINDOW_MIN_US 500000 /* Min window size is 500ms */ 172 #define WINDOW_MAX_US 10000000 /* Max window size is 10s */ 173 #define UPDATES_PER_WINDOW 10 /* 10 updates per window */ 174 175 /* Sampling frequency in nanoseconds */ 176 static u64 psi_period __read_mostly; 177 178 /* System-level pressure and stall tracking */ 179 static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu); 180 struct psi_group psi_system = { 181 .pcpu = &system_group_pcpu, 182 }; 183 184 static void psi_avgs_work(struct work_struct *work); 185 186 static void poll_timer_fn(struct timer_list *t); 187 188 static void group_init(struct psi_group *group) 189 { 190 int cpu; 191 192 for_each_possible_cpu(cpu) 193 seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq); 194 group->avg_last_update = sched_clock(); 195 group->avg_next_update = group->avg_last_update + psi_period; 196 INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work); 197 mutex_init(&group->avgs_lock); 198 /* Init trigger-related members */ 199 mutex_init(&group->trigger_lock); 200 INIT_LIST_HEAD(&group->triggers); 201 memset(group->nr_triggers, 0, sizeof(group->nr_triggers)); 202 group->poll_states = 0; 203 group->poll_min_period = U32_MAX; 204 memset(group->polling_total, 0, sizeof(group->polling_total)); 205 group->polling_next_update = ULLONG_MAX; 206 group->polling_until = 0; 207 init_waitqueue_head(&group->poll_wait); 208 timer_setup(&group->poll_timer, poll_timer_fn, 0); 209 rcu_assign_pointer(group->poll_task, NULL); 210 } 211 212 void __init psi_init(void) 213 { 214 if (!psi_enable) { 215 static_branch_enable(&psi_disabled); 216 return; 217 } 218 219 if (!cgroup_psi_enabled()) 220 static_branch_disable(&psi_cgroups_enabled); 221 222 psi_period = jiffies_to_nsecs(PSI_FREQ); 223 group_init(&psi_system); 224 } 225 226 static bool test_state(unsigned int *tasks, enum psi_states state) 227 { 228 switch (state) { 229 case PSI_IO_SOME: 230 return unlikely(tasks[NR_IOWAIT]); 231 case PSI_IO_FULL: 232 return unlikely(tasks[NR_IOWAIT] && !tasks[NR_RUNNING]); 233 case PSI_MEM_SOME: 234 return unlikely(tasks[NR_MEMSTALL]); 235 case PSI_MEM_FULL: 236 return unlikely(tasks[NR_MEMSTALL] && !tasks[NR_RUNNING]); 237 case PSI_CPU_SOME: 238 return unlikely(tasks[NR_RUNNING] > tasks[NR_ONCPU]); 239 case PSI_CPU_FULL: 240 return unlikely(tasks[NR_RUNNING] && !tasks[NR_ONCPU]); 241 case PSI_NONIDLE: 242 return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] || 243 tasks[NR_RUNNING]; 244 default: 245 return false; 246 } 247 } 248 249 static void get_recent_times(struct psi_group *group, int cpu, 250 enum psi_aggregators aggregator, u32 *times, 251 u32 *pchanged_states) 252 { 253 struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu); 254 u64 now, state_start; 255 enum psi_states s; 256 unsigned int seq; 257 u32 state_mask; 258 259 *pchanged_states = 0; 260 261 /* Snapshot a coherent view of the CPU state */ 262 do { 263 seq = read_seqcount_begin(&groupc->seq); 264 now = cpu_clock(cpu); 265 memcpy(times, groupc->times, sizeof(groupc->times)); 266 state_mask = groupc->state_mask; 267 state_start = groupc->state_start; 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 static void calc_avgs(unsigned long avg[3], int missed_periods, 295 u64 time, u64 period) 296 { 297 unsigned long pct; 298 299 /* Fill in zeroes for periods of no activity */ 300 if (missed_periods) { 301 avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods); 302 avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods); 303 avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods); 304 } 305 306 /* Sample the most recent active period */ 307 pct = div_u64(time * 100, period); 308 pct *= FIXED_1; 309 avg[0] = calc_load(avg[0], EXP_10s, pct); 310 avg[1] = calc_load(avg[1], EXP_60s, pct); 311 avg[2] = calc_load(avg[2], EXP_300s, pct); 312 } 313 314 static void collect_percpu_times(struct psi_group *group, 315 enum psi_aggregators aggregator, 316 u32 *pchanged_states) 317 { 318 u64 deltas[NR_PSI_STATES - 1] = { 0, }; 319 unsigned long nonidle_total = 0; 320 u32 changed_states = 0; 321 int cpu; 322 int s; 323 324 /* 325 * Collect the per-cpu time buckets and average them into a 326 * single time sample that is normalized to wallclock time. 327 * 328 * For averaging, each CPU is weighted by its non-idle time in 329 * the sampling period. This eliminates artifacts from uneven 330 * loading, or even entirely idle CPUs. 331 */ 332 for_each_possible_cpu(cpu) { 333 u32 times[NR_PSI_STATES]; 334 u32 nonidle; 335 u32 cpu_changed_states; 336 337 get_recent_times(group, cpu, aggregator, times, 338 &cpu_changed_states); 339 changed_states |= cpu_changed_states; 340 341 nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]); 342 nonidle_total += nonidle; 343 344 for (s = 0; s < PSI_NONIDLE; s++) 345 deltas[s] += (u64)times[s] * nonidle; 346 } 347 348 /* 349 * Integrate the sample into the running statistics that are 350 * reported to userspace: the cumulative stall times and the 351 * decaying averages. 352 * 353 * Pressure percentages are sampled at PSI_FREQ. We might be 354 * called more often when the user polls more frequently than 355 * that; we might be called less often when there is no task 356 * activity, thus no data, and clock ticks are sporadic. The 357 * below handles both. 358 */ 359 360 /* total= */ 361 for (s = 0; s < NR_PSI_STATES - 1; s++) 362 group->total[aggregator][s] += 363 div_u64(deltas[s], max(nonidle_total, 1UL)); 364 365 if (pchanged_states) 366 *pchanged_states = changed_states; 367 } 368 369 static u64 update_averages(struct psi_group *group, u64 now) 370 { 371 unsigned long missed_periods = 0; 372 u64 expires, period; 373 u64 avg_next_update; 374 int s; 375 376 /* avgX= */ 377 expires = group->avg_next_update; 378 if (now - expires >= psi_period) 379 missed_periods = div_u64(now - expires, psi_period); 380 381 /* 382 * The periodic clock tick can get delayed for various 383 * reasons, especially on loaded systems. To avoid clock 384 * drift, we schedule the clock in fixed psi_period intervals. 385 * But the deltas we sample out of the per-cpu buckets above 386 * are based on the actual time elapsing between clock ticks. 387 */ 388 avg_next_update = expires + ((1 + missed_periods) * psi_period); 389 period = now - (group->avg_last_update + (missed_periods * psi_period)); 390 group->avg_last_update = now; 391 392 for (s = 0; s < NR_PSI_STATES - 1; s++) { 393 u32 sample; 394 395 sample = group->total[PSI_AVGS][s] - group->avg_total[s]; 396 /* 397 * Due to the lockless sampling of the time buckets, 398 * recorded time deltas can slip into the next period, 399 * which under full pressure can result in samples in 400 * excess of the period length. 401 * 402 * We don't want to report non-sensical pressures in 403 * excess of 100%, nor do we want to drop such events 404 * on the floor. Instead we punt any overage into the 405 * future until pressure subsides. By doing this we 406 * don't underreport the occurring pressure curve, we 407 * just report it delayed by one period length. 408 * 409 * The error isn't cumulative. As soon as another 410 * delta slips from a period P to P+1, by definition 411 * it frees up its time T in P. 412 */ 413 if (sample > period) 414 sample = period; 415 group->avg_total[s] += sample; 416 calc_avgs(group->avg[s], missed_periods, sample, period); 417 } 418 419 return avg_next_update; 420 } 421 422 static void psi_avgs_work(struct work_struct *work) 423 { 424 struct delayed_work *dwork; 425 struct psi_group *group; 426 u32 changed_states; 427 bool nonidle; 428 u64 now; 429 430 dwork = to_delayed_work(work); 431 group = container_of(dwork, struct psi_group, avgs_work); 432 433 mutex_lock(&group->avgs_lock); 434 435 now = sched_clock(); 436 437 collect_percpu_times(group, PSI_AVGS, &changed_states); 438 nonidle = changed_states & (1 << PSI_NONIDLE); 439 /* 440 * If there is task activity, periodically fold the per-cpu 441 * times and feed samples into the running averages. If things 442 * are idle and there is no data to process, stop the clock. 443 * Once restarted, we'll catch up the running averages in one 444 * go - see calc_avgs() and missed_periods. 445 */ 446 if (now >= group->avg_next_update) 447 group->avg_next_update = update_averages(group, now); 448 449 if (nonidle) { 450 schedule_delayed_work(dwork, nsecs_to_jiffies( 451 group->avg_next_update - now) + 1); 452 } 453 454 mutex_unlock(&group->avgs_lock); 455 } 456 457 /* Trigger tracking window manipulations */ 458 static void window_reset(struct psi_window *win, u64 now, u64 value, 459 u64 prev_growth) 460 { 461 win->start_time = now; 462 win->start_value = value; 463 win->prev_growth = prev_growth; 464 } 465 466 /* 467 * PSI growth tracking window update and growth calculation routine. 468 * 469 * This approximates a sliding tracking window by interpolating 470 * partially elapsed windows using historical growth data from the 471 * previous intervals. This minimizes memory requirements (by not storing 472 * all the intermediate values in the previous window) and simplifies 473 * the calculations. It works well because PSI signal changes only in 474 * positive direction and over relatively small window sizes the growth 475 * is close to linear. 476 */ 477 static u64 window_update(struct psi_window *win, u64 now, u64 value) 478 { 479 u64 elapsed; 480 u64 growth; 481 482 elapsed = now - win->start_time; 483 growth = value - win->start_value; 484 /* 485 * After each tracking window passes win->start_value and 486 * win->start_time get reset and win->prev_growth stores 487 * the average per-window growth of the previous window. 488 * win->prev_growth is then used to interpolate additional 489 * growth from the previous window assuming it was linear. 490 */ 491 if (elapsed > win->size) 492 window_reset(win, now, value, growth); 493 else { 494 u32 remaining; 495 496 remaining = win->size - elapsed; 497 growth += div64_u64(win->prev_growth * remaining, win->size); 498 } 499 500 return growth; 501 } 502 503 static void init_triggers(struct psi_group *group, u64 now) 504 { 505 struct psi_trigger *t; 506 507 list_for_each_entry(t, &group->triggers, node) 508 window_reset(&t->win, now, 509 group->total[PSI_POLL][t->state], 0); 510 memcpy(group->polling_total, group->total[PSI_POLL], 511 sizeof(group->polling_total)); 512 group->polling_next_update = now + group->poll_min_period; 513 } 514 515 static u64 update_triggers(struct psi_group *group, u64 now) 516 { 517 struct psi_trigger *t; 518 bool new_stall = false; 519 u64 *total = group->total[PSI_POLL]; 520 521 /* 522 * On subsequent updates, calculate growth deltas and let 523 * watchers know when their specified thresholds are exceeded. 524 */ 525 list_for_each_entry(t, &group->triggers, node) { 526 u64 growth; 527 528 /* Check for stall activity */ 529 if (group->polling_total[t->state] == total[t->state]) 530 continue; 531 532 /* 533 * Multiple triggers might be looking at the same state, 534 * remember to update group->polling_total[] once we've 535 * been through all of them. Also remember to extend the 536 * polling time if we see new stall activity. 537 */ 538 new_stall = true; 539 540 /* Calculate growth since last update */ 541 growth = window_update(&t->win, now, total[t->state]); 542 if (growth < t->threshold) 543 continue; 544 545 /* Limit event signaling to once per window */ 546 if (now < t->last_event_time + t->win.size) 547 continue; 548 549 /* Generate an event */ 550 if (cmpxchg(&t->event, 0, 1) == 0) 551 wake_up_interruptible(&t->event_wait); 552 t->last_event_time = now; 553 } 554 555 if (new_stall) 556 memcpy(group->polling_total, total, 557 sizeof(group->polling_total)); 558 559 return now + group->poll_min_period; 560 } 561 562 /* Schedule polling if it's not already scheduled. */ 563 static void psi_schedule_poll_work(struct psi_group *group, unsigned long delay) 564 { 565 struct task_struct *task; 566 567 /* 568 * Do not reschedule if already scheduled. 569 * Possible race with a timer scheduled after this check but before 570 * mod_timer below can be tolerated because group->polling_next_update 571 * will keep updates on schedule. 572 */ 573 if (timer_pending(&group->poll_timer)) 574 return; 575 576 rcu_read_lock(); 577 578 task = rcu_dereference(group->poll_task); 579 /* 580 * kworker might be NULL in case psi_trigger_destroy races with 581 * psi_task_change (hotpath) which can't use locks 582 */ 583 if (likely(task)) 584 mod_timer(&group->poll_timer, jiffies + delay); 585 586 rcu_read_unlock(); 587 } 588 589 static void psi_poll_work(struct psi_group *group) 590 { 591 u32 changed_states; 592 u64 now; 593 594 mutex_lock(&group->trigger_lock); 595 596 now = sched_clock(); 597 598 collect_percpu_times(group, PSI_POLL, &changed_states); 599 600 if (changed_states & group->poll_states) { 601 /* Initialize trigger windows when entering polling mode */ 602 if (now > group->polling_until) 603 init_triggers(group, now); 604 605 /* 606 * Keep the monitor active for at least the duration of the 607 * minimum tracking window as long as monitor states are 608 * changing. 609 */ 610 group->polling_until = now + 611 group->poll_min_period * UPDATES_PER_WINDOW; 612 } 613 614 if (now > group->polling_until) { 615 group->polling_next_update = ULLONG_MAX; 616 goto out; 617 } 618 619 if (now >= group->polling_next_update) 620 group->polling_next_update = update_triggers(group, now); 621 622 psi_schedule_poll_work(group, 623 nsecs_to_jiffies(group->polling_next_update - now) + 1); 624 625 out: 626 mutex_unlock(&group->trigger_lock); 627 } 628 629 static int psi_poll_worker(void *data) 630 { 631 struct psi_group *group = (struct psi_group *)data; 632 633 sched_set_fifo_low(current); 634 635 while (true) { 636 wait_event_interruptible(group->poll_wait, 637 atomic_cmpxchg(&group->poll_wakeup, 1, 0) || 638 kthread_should_stop()); 639 if (kthread_should_stop()) 640 break; 641 642 psi_poll_work(group); 643 } 644 return 0; 645 } 646 647 static void poll_timer_fn(struct timer_list *t) 648 { 649 struct psi_group *group = from_timer(group, t, poll_timer); 650 651 atomic_set(&group->poll_wakeup, 1); 652 wake_up_interruptible(&group->poll_wait); 653 } 654 655 static void record_times(struct psi_group_cpu *groupc, u64 now) 656 { 657 u32 delta; 658 659 delta = now - groupc->state_start; 660 groupc->state_start = now; 661 662 if (groupc->state_mask & (1 << PSI_IO_SOME)) { 663 groupc->times[PSI_IO_SOME] += delta; 664 if (groupc->state_mask & (1 << PSI_IO_FULL)) 665 groupc->times[PSI_IO_FULL] += delta; 666 } 667 668 if (groupc->state_mask & (1 << PSI_MEM_SOME)) { 669 groupc->times[PSI_MEM_SOME] += delta; 670 if (groupc->state_mask & (1 << PSI_MEM_FULL)) 671 groupc->times[PSI_MEM_FULL] += delta; 672 } 673 674 if (groupc->state_mask & (1 << PSI_CPU_SOME)) { 675 groupc->times[PSI_CPU_SOME] += delta; 676 if (groupc->state_mask & (1 << PSI_CPU_FULL)) 677 groupc->times[PSI_CPU_FULL] += delta; 678 } 679 680 if (groupc->state_mask & (1 << PSI_NONIDLE)) 681 groupc->times[PSI_NONIDLE] += delta; 682 } 683 684 static void psi_group_change(struct psi_group *group, int cpu, 685 unsigned int clear, unsigned int set, u64 now, 686 bool wake_clock) 687 { 688 struct psi_group_cpu *groupc; 689 u32 state_mask = 0; 690 unsigned int t, m; 691 enum psi_states s; 692 693 groupc = per_cpu_ptr(group->pcpu, cpu); 694 695 /* 696 * First we assess the aggregate resource states this CPU's 697 * tasks have been in since the last change, and account any 698 * SOME and FULL time these may have resulted in. 699 * 700 * Then we update the task counts according to the state 701 * change requested through the @clear and @set bits. 702 */ 703 write_seqcount_begin(&groupc->seq); 704 705 record_times(groupc, now); 706 707 for (t = 0, m = clear; m; m &= ~(1 << t), t++) { 708 if (!(m & (1 << t))) 709 continue; 710 if (groupc->tasks[t]) { 711 groupc->tasks[t]--; 712 } else if (!psi_bug) { 713 printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u] clear=%x set=%x\n", 714 cpu, t, groupc->tasks[0], 715 groupc->tasks[1], groupc->tasks[2], 716 groupc->tasks[3], clear, set); 717 psi_bug = 1; 718 } 719 } 720 721 for (t = 0; set; set &= ~(1 << t), t++) 722 if (set & (1 << t)) 723 groupc->tasks[t]++; 724 725 /* Calculate state mask representing active states */ 726 for (s = 0; s < NR_PSI_STATES; s++) { 727 if (test_state(groupc->tasks, s)) 728 state_mask |= (1 << s); 729 } 730 731 /* 732 * Since we care about lost potential, a memstall is FULL 733 * when there are no other working tasks, but also when 734 * the CPU is actively reclaiming and nothing productive 735 * could run even if it were runnable. So when the current 736 * task in a cgroup is in_memstall, the corresponding groupc 737 * on that cpu is in PSI_MEM_FULL state. 738 */ 739 if (unlikely(groupc->tasks[NR_ONCPU] && cpu_curr(cpu)->in_memstall)) 740 state_mask |= (1 << PSI_MEM_FULL); 741 742 groupc->state_mask = state_mask; 743 744 write_seqcount_end(&groupc->seq); 745 746 if (state_mask & group->poll_states) 747 psi_schedule_poll_work(group, 1); 748 749 if (wake_clock && !delayed_work_pending(&group->avgs_work)) 750 schedule_delayed_work(&group->avgs_work, PSI_FREQ); 751 } 752 753 static struct psi_group *iterate_groups(struct task_struct *task, void **iter) 754 { 755 if (*iter == &psi_system) 756 return NULL; 757 758 #ifdef CONFIG_CGROUPS 759 if (static_branch_likely(&psi_cgroups_enabled)) { 760 struct cgroup *cgroup = NULL; 761 762 if (!*iter) 763 cgroup = task->cgroups->dfl_cgrp; 764 else 765 cgroup = cgroup_parent(*iter); 766 767 if (cgroup && cgroup_parent(cgroup)) { 768 *iter = cgroup; 769 return cgroup_psi(cgroup); 770 } 771 } 772 #endif 773 *iter = &psi_system; 774 return &psi_system; 775 } 776 777 static void psi_flags_change(struct task_struct *task, int clear, int set) 778 { 779 if (((task->psi_flags & set) || 780 (task->psi_flags & clear) != clear) && 781 !psi_bug) { 782 printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n", 783 task->pid, task->comm, task_cpu(task), 784 task->psi_flags, clear, set); 785 psi_bug = 1; 786 } 787 788 task->psi_flags &= ~clear; 789 task->psi_flags |= set; 790 } 791 792 void psi_task_change(struct task_struct *task, int clear, int set) 793 { 794 int cpu = task_cpu(task); 795 struct psi_group *group; 796 bool wake_clock = true; 797 void *iter = NULL; 798 u64 now; 799 800 if (!task->pid) 801 return; 802 803 psi_flags_change(task, clear, set); 804 805 now = cpu_clock(cpu); 806 /* 807 * Periodic aggregation shuts off if there is a period of no 808 * task changes, so we wake it back up if necessary. However, 809 * don't do this if the task change is the aggregation worker 810 * itself going to sleep, or we'll ping-pong forever. 811 */ 812 if (unlikely((clear & TSK_RUNNING) && 813 (task->flags & PF_WQ_WORKER) && 814 wq_worker_last_func(task) == psi_avgs_work)) 815 wake_clock = false; 816 817 while ((group = iterate_groups(task, &iter))) 818 psi_group_change(group, cpu, clear, set, now, wake_clock); 819 } 820 821 void psi_task_switch(struct task_struct *prev, struct task_struct *next, 822 bool sleep) 823 { 824 struct psi_group *group, *common = NULL; 825 int cpu = task_cpu(prev); 826 void *iter; 827 u64 now = cpu_clock(cpu); 828 829 if (next->pid) { 830 bool identical_state; 831 832 psi_flags_change(next, 0, TSK_ONCPU); 833 /* 834 * When switching between tasks that have an identical 835 * runtime state, the cgroup that contains both tasks 836 * runtime state, the cgroup that contains both tasks 837 * we reach the first common ancestor. Iterate @next's 838 * ancestors only until we encounter @prev's ONCPU. 839 */ 840 identical_state = prev->psi_flags == next->psi_flags; 841 iter = NULL; 842 while ((group = iterate_groups(next, &iter))) { 843 if (identical_state && 844 per_cpu_ptr(group->pcpu, cpu)->tasks[NR_ONCPU]) { 845 common = group; 846 break; 847 } 848 849 psi_group_change(group, cpu, 0, TSK_ONCPU, now, true); 850 } 851 } 852 853 if (prev->pid) { 854 int clear = TSK_ONCPU, set = 0; 855 856 /* 857 * When we're going to sleep, psi_dequeue() lets us handle 858 * TSK_RUNNING and TSK_IOWAIT here, where we can combine it 859 * with TSK_ONCPU and save walking common ancestors twice. 860 */ 861 if (sleep) { 862 clear |= TSK_RUNNING; 863 if (prev->in_iowait) 864 set |= TSK_IOWAIT; 865 } 866 867 psi_flags_change(prev, clear, set); 868 869 iter = NULL; 870 while ((group = iterate_groups(prev, &iter)) && group != common) 871 psi_group_change(group, cpu, clear, set, now, true); 872 873 /* 874 * TSK_ONCPU is handled up to the common ancestor. If we're tasked 875 * with dequeuing too, finish that for the rest of the hierarchy. 876 */ 877 if (sleep) { 878 clear &= ~TSK_ONCPU; 879 for (; group; group = iterate_groups(prev, &iter)) 880 psi_group_change(group, cpu, clear, set, now, true); 881 } 882 } 883 } 884 885 /** 886 * psi_memstall_enter - mark the beginning of a memory stall section 887 * @flags: flags to handle nested sections 888 * 889 * Marks the calling task as being stalled due to a lack of memory, 890 * such as waiting for a refault or performing reclaim. 891 */ 892 void psi_memstall_enter(unsigned long *flags) 893 { 894 struct rq_flags rf; 895 struct rq *rq; 896 897 if (static_branch_likely(&psi_disabled)) 898 return; 899 900 *flags = current->in_memstall; 901 if (*flags) 902 return; 903 /* 904 * in_memstall setting & accounting needs to be atomic wrt 905 * changes to the task's scheduling state, otherwise we can 906 * race with CPU migration. 907 */ 908 rq = this_rq_lock_irq(&rf); 909 910 current->in_memstall = 1; 911 psi_task_change(current, 0, TSK_MEMSTALL); 912 913 rq_unlock_irq(rq, &rf); 914 } 915 916 /** 917 * psi_memstall_leave - mark the end of an memory stall section 918 * @flags: flags to handle nested memdelay sections 919 * 920 * Marks the calling task as no longer stalled due to lack of memory. 921 */ 922 void psi_memstall_leave(unsigned long *flags) 923 { 924 struct rq_flags rf; 925 struct rq *rq; 926 927 if (static_branch_likely(&psi_disabled)) 928 return; 929 930 if (*flags) 931 return; 932 /* 933 * in_memstall clearing & accounting needs to be atomic wrt 934 * changes to the task's scheduling state, otherwise we could 935 * race with CPU migration. 936 */ 937 rq = this_rq_lock_irq(&rf); 938 939 current->in_memstall = 0; 940 psi_task_change(current, TSK_MEMSTALL, 0); 941 942 rq_unlock_irq(rq, &rf); 943 } 944 945 #ifdef CONFIG_CGROUPS 946 int psi_cgroup_alloc(struct cgroup *cgroup) 947 { 948 if (static_branch_likely(&psi_disabled)) 949 return 0; 950 951 cgroup->psi.pcpu = alloc_percpu(struct psi_group_cpu); 952 if (!cgroup->psi.pcpu) 953 return -ENOMEM; 954 group_init(&cgroup->psi); 955 return 0; 956 } 957 958 void psi_cgroup_free(struct cgroup *cgroup) 959 { 960 if (static_branch_likely(&psi_disabled)) 961 return; 962 963 cancel_delayed_work_sync(&cgroup->psi.avgs_work); 964 free_percpu(cgroup->psi.pcpu); 965 /* All triggers must be removed by now */ 966 WARN_ONCE(cgroup->psi.poll_states, "psi: trigger leak\n"); 967 } 968 969 /** 970 * cgroup_move_task - move task to a different cgroup 971 * @task: the task 972 * @to: the target css_set 973 * 974 * Move task to a new cgroup and safely migrate its associated stall 975 * state between the different groups. 976 * 977 * This function acquires the task's rq lock to lock out concurrent 978 * changes to the task's scheduling state and - in case the task is 979 * running - concurrent changes to its stall state. 980 */ 981 void cgroup_move_task(struct task_struct *task, struct css_set *to) 982 { 983 unsigned int task_flags; 984 struct rq_flags rf; 985 struct rq *rq; 986 987 if (static_branch_likely(&psi_disabled)) { 988 /* 989 * Lame to do this here, but the scheduler cannot be locked 990 * from the outside, so we move cgroups from inside sched/. 991 */ 992 rcu_assign_pointer(task->cgroups, to); 993 return; 994 } 995 996 rq = task_rq_lock(task, &rf); 997 998 /* 999 * We may race with schedule() dropping the rq lock between 1000 * deactivating prev and switching to next. Because the psi 1001 * updates from the deactivation are deferred to the switch 1002 * callback to save cgroup tree updates, the task's scheduling 1003 * state here is not coherent with its psi state: 1004 * 1005 * schedule() cgroup_move_task() 1006 * rq_lock() 1007 * deactivate_task() 1008 * p->on_rq = 0 1009 * psi_dequeue() // defers TSK_RUNNING & TSK_IOWAIT updates 1010 * pick_next_task() 1011 * rq_unlock() 1012 * rq_lock() 1013 * psi_task_change() // old cgroup 1014 * task->cgroups = to 1015 * psi_task_change() // new cgroup 1016 * rq_unlock() 1017 * rq_lock() 1018 * psi_sched_switch() // does deferred updates in new cgroup 1019 * 1020 * Don't rely on the scheduling state. Use psi_flags instead. 1021 */ 1022 task_flags = task->psi_flags; 1023 1024 if (task_flags) 1025 psi_task_change(task, task_flags, 0); 1026 1027 /* See comment above */ 1028 rcu_assign_pointer(task->cgroups, to); 1029 1030 if (task_flags) 1031 psi_task_change(task, 0, task_flags); 1032 1033 task_rq_unlock(rq, task, &rf); 1034 } 1035 #endif /* CONFIG_CGROUPS */ 1036 1037 int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res) 1038 { 1039 int full; 1040 u64 now; 1041 1042 if (static_branch_likely(&psi_disabled)) 1043 return -EOPNOTSUPP; 1044 1045 /* Update averages before reporting them */ 1046 mutex_lock(&group->avgs_lock); 1047 now = sched_clock(); 1048 collect_percpu_times(group, PSI_AVGS, NULL); 1049 if (now >= group->avg_next_update) 1050 group->avg_next_update = update_averages(group, now); 1051 mutex_unlock(&group->avgs_lock); 1052 1053 for (full = 0; full < 2; full++) { 1054 unsigned long avg[3]; 1055 u64 total; 1056 int w; 1057 1058 for (w = 0; w < 3; w++) 1059 avg[w] = group->avg[res * 2 + full][w]; 1060 total = div_u64(group->total[PSI_AVGS][res * 2 + full], 1061 NSEC_PER_USEC); 1062 1063 seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n", 1064 full ? "full" : "some", 1065 LOAD_INT(avg[0]), LOAD_FRAC(avg[0]), 1066 LOAD_INT(avg[1]), LOAD_FRAC(avg[1]), 1067 LOAD_INT(avg[2]), LOAD_FRAC(avg[2]), 1068 total); 1069 } 1070 1071 return 0; 1072 } 1073 1074 static int psi_io_show(struct seq_file *m, void *v) 1075 { 1076 return psi_show(m, &psi_system, PSI_IO); 1077 } 1078 1079 static int psi_memory_show(struct seq_file *m, void *v) 1080 { 1081 return psi_show(m, &psi_system, PSI_MEM); 1082 } 1083 1084 static int psi_cpu_show(struct seq_file *m, void *v) 1085 { 1086 return psi_show(m, &psi_system, PSI_CPU); 1087 } 1088 1089 static int psi_open(struct file *file, int (*psi_show)(struct seq_file *, void *)) 1090 { 1091 if (file->f_mode & FMODE_WRITE && !capable(CAP_SYS_RESOURCE)) 1092 return -EPERM; 1093 1094 return single_open(file, psi_show, NULL); 1095 } 1096 1097 static int psi_io_open(struct inode *inode, struct file *file) 1098 { 1099 return psi_open(file, psi_io_show); 1100 } 1101 1102 static int psi_memory_open(struct inode *inode, struct file *file) 1103 { 1104 return psi_open(file, psi_memory_show); 1105 } 1106 1107 static int psi_cpu_open(struct inode *inode, struct file *file) 1108 { 1109 return psi_open(file, psi_cpu_show); 1110 } 1111 1112 struct psi_trigger *psi_trigger_create(struct psi_group *group, 1113 char *buf, size_t nbytes, enum psi_res res) 1114 { 1115 struct psi_trigger *t; 1116 enum psi_states state; 1117 u32 threshold_us; 1118 u32 window_us; 1119 1120 if (static_branch_likely(&psi_disabled)) 1121 return ERR_PTR(-EOPNOTSUPP); 1122 1123 if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2) 1124 state = PSI_IO_SOME + res * 2; 1125 else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2) 1126 state = PSI_IO_FULL + res * 2; 1127 else 1128 return ERR_PTR(-EINVAL); 1129 1130 if (state >= PSI_NONIDLE) 1131 return ERR_PTR(-EINVAL); 1132 1133 if (window_us < WINDOW_MIN_US || 1134 window_us > WINDOW_MAX_US) 1135 return ERR_PTR(-EINVAL); 1136 1137 /* Check threshold */ 1138 if (threshold_us == 0 || threshold_us > window_us) 1139 return ERR_PTR(-EINVAL); 1140 1141 t = kmalloc(sizeof(*t), GFP_KERNEL); 1142 if (!t) 1143 return ERR_PTR(-ENOMEM); 1144 1145 t->group = group; 1146 t->state = state; 1147 t->threshold = threshold_us * NSEC_PER_USEC; 1148 t->win.size = window_us * NSEC_PER_USEC; 1149 window_reset(&t->win, 0, 0, 0); 1150 1151 t->event = 0; 1152 t->last_event_time = 0; 1153 init_waitqueue_head(&t->event_wait); 1154 kref_init(&t->refcount); 1155 1156 mutex_lock(&group->trigger_lock); 1157 1158 if (!rcu_access_pointer(group->poll_task)) { 1159 struct task_struct *task; 1160 1161 task = kthread_create(psi_poll_worker, group, "psimon"); 1162 if (IS_ERR(task)) { 1163 kfree(t); 1164 mutex_unlock(&group->trigger_lock); 1165 return ERR_CAST(task); 1166 } 1167 atomic_set(&group->poll_wakeup, 0); 1168 wake_up_process(task); 1169 rcu_assign_pointer(group->poll_task, task); 1170 } 1171 1172 list_add(&t->node, &group->triggers); 1173 group->poll_min_period = min(group->poll_min_period, 1174 div_u64(t->win.size, UPDATES_PER_WINDOW)); 1175 group->nr_triggers[t->state]++; 1176 group->poll_states |= (1 << t->state); 1177 1178 mutex_unlock(&group->trigger_lock); 1179 1180 return t; 1181 } 1182 1183 static void psi_trigger_destroy(struct kref *ref) 1184 { 1185 struct psi_trigger *t = container_of(ref, struct psi_trigger, refcount); 1186 struct psi_group *group = t->group; 1187 struct task_struct *task_to_destroy = NULL; 1188 1189 if (static_branch_likely(&psi_disabled)) 1190 return; 1191 1192 /* 1193 * Wakeup waiters to stop polling. Can happen if cgroup is deleted 1194 * from under a polling process. 1195 */ 1196 wake_up_interruptible(&t->event_wait); 1197 1198 mutex_lock(&group->trigger_lock); 1199 1200 if (!list_empty(&t->node)) { 1201 struct psi_trigger *tmp; 1202 u64 period = ULLONG_MAX; 1203 1204 list_del(&t->node); 1205 group->nr_triggers[t->state]--; 1206 if (!group->nr_triggers[t->state]) 1207 group->poll_states &= ~(1 << t->state); 1208 /* reset min update period for the remaining triggers */ 1209 list_for_each_entry(tmp, &group->triggers, node) 1210 period = min(period, div_u64(tmp->win.size, 1211 UPDATES_PER_WINDOW)); 1212 group->poll_min_period = period; 1213 /* Destroy poll_task when the last trigger is destroyed */ 1214 if (group->poll_states == 0) { 1215 group->polling_until = 0; 1216 task_to_destroy = rcu_dereference_protected( 1217 group->poll_task, 1218 lockdep_is_held(&group->trigger_lock)); 1219 rcu_assign_pointer(group->poll_task, NULL); 1220 del_timer(&group->poll_timer); 1221 } 1222 } 1223 1224 mutex_unlock(&group->trigger_lock); 1225 1226 /* 1227 * Wait for both *trigger_ptr from psi_trigger_replace and 1228 * poll_task RCUs to complete their read-side critical sections 1229 * before destroying the trigger and optionally the poll_task 1230 */ 1231 synchronize_rcu(); 1232 /* 1233 * Stop kthread 'psimon' after releasing trigger_lock to prevent a 1234 * deadlock while waiting for psi_poll_work to acquire trigger_lock 1235 */ 1236 if (task_to_destroy) { 1237 /* 1238 * After the RCU grace period has expired, the worker 1239 * can no longer be found through group->poll_task. 1240 */ 1241 kthread_stop(task_to_destroy); 1242 } 1243 kfree(t); 1244 } 1245 1246 void psi_trigger_replace(void **trigger_ptr, struct psi_trigger *new) 1247 { 1248 struct psi_trigger *old = *trigger_ptr; 1249 1250 if (static_branch_likely(&psi_disabled)) 1251 return; 1252 1253 rcu_assign_pointer(*trigger_ptr, new); 1254 if (old) 1255 kref_put(&old->refcount, psi_trigger_destroy); 1256 } 1257 1258 __poll_t psi_trigger_poll(void **trigger_ptr, 1259 struct file *file, poll_table *wait) 1260 { 1261 __poll_t ret = DEFAULT_POLLMASK; 1262 struct psi_trigger *t; 1263 1264 if (static_branch_likely(&psi_disabled)) 1265 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; 1266 1267 rcu_read_lock(); 1268 1269 t = rcu_dereference(*(void __rcu __force **)trigger_ptr); 1270 if (!t) { 1271 rcu_read_unlock(); 1272 return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; 1273 } 1274 kref_get(&t->refcount); 1275 1276 rcu_read_unlock(); 1277 1278 poll_wait(file, &t->event_wait, wait); 1279 1280 if (cmpxchg(&t->event, 1, 0) == 1) 1281 ret |= EPOLLPRI; 1282 1283 kref_put(&t->refcount, psi_trigger_destroy); 1284 1285 return ret; 1286 } 1287 1288 static ssize_t psi_write(struct file *file, const char __user *user_buf, 1289 size_t nbytes, enum psi_res res) 1290 { 1291 char buf[32]; 1292 size_t buf_size; 1293 struct seq_file *seq; 1294 struct psi_trigger *new; 1295 1296 if (static_branch_likely(&psi_disabled)) 1297 return -EOPNOTSUPP; 1298 1299 if (!nbytes) 1300 return -EINVAL; 1301 1302 buf_size = min(nbytes, sizeof(buf)); 1303 if (copy_from_user(buf, user_buf, buf_size)) 1304 return -EFAULT; 1305 1306 buf[buf_size - 1] = '\0'; 1307 1308 new = psi_trigger_create(&psi_system, buf, nbytes, res); 1309 if (IS_ERR(new)) 1310 return PTR_ERR(new); 1311 1312 seq = file->private_data; 1313 /* Take seq->lock to protect seq->private from concurrent writes */ 1314 mutex_lock(&seq->lock); 1315 psi_trigger_replace(&seq->private, new); 1316 mutex_unlock(&seq->lock); 1317 1318 return nbytes; 1319 } 1320 1321 static ssize_t psi_io_write(struct file *file, const char __user *user_buf, 1322 size_t nbytes, loff_t *ppos) 1323 { 1324 return psi_write(file, user_buf, nbytes, PSI_IO); 1325 } 1326 1327 static ssize_t psi_memory_write(struct file *file, const char __user *user_buf, 1328 size_t nbytes, loff_t *ppos) 1329 { 1330 return psi_write(file, user_buf, nbytes, PSI_MEM); 1331 } 1332 1333 static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf, 1334 size_t nbytes, loff_t *ppos) 1335 { 1336 return psi_write(file, user_buf, nbytes, PSI_CPU); 1337 } 1338 1339 static __poll_t psi_fop_poll(struct file *file, poll_table *wait) 1340 { 1341 struct seq_file *seq = file->private_data; 1342 1343 return psi_trigger_poll(&seq->private, file, wait); 1344 } 1345 1346 static int psi_fop_release(struct inode *inode, struct file *file) 1347 { 1348 struct seq_file *seq = file->private_data; 1349 1350 psi_trigger_replace(&seq->private, NULL); 1351 return single_release(inode, file); 1352 } 1353 1354 static const struct proc_ops psi_io_proc_ops = { 1355 .proc_open = psi_io_open, 1356 .proc_read = seq_read, 1357 .proc_lseek = seq_lseek, 1358 .proc_write = psi_io_write, 1359 .proc_poll = psi_fop_poll, 1360 .proc_release = psi_fop_release, 1361 }; 1362 1363 static const struct proc_ops psi_memory_proc_ops = { 1364 .proc_open = psi_memory_open, 1365 .proc_read = seq_read, 1366 .proc_lseek = seq_lseek, 1367 .proc_write = psi_memory_write, 1368 .proc_poll = psi_fop_poll, 1369 .proc_release = psi_fop_release, 1370 }; 1371 1372 static const struct proc_ops psi_cpu_proc_ops = { 1373 .proc_open = psi_cpu_open, 1374 .proc_read = seq_read, 1375 .proc_lseek = seq_lseek, 1376 .proc_write = psi_cpu_write, 1377 .proc_poll = psi_fop_poll, 1378 .proc_release = psi_fop_release, 1379 }; 1380 1381 static int __init psi_proc_init(void) 1382 { 1383 if (psi_enable) { 1384 proc_mkdir("pressure", NULL); 1385 proc_create("pressure/io", 0666, NULL, &psi_io_proc_ops); 1386 proc_create("pressure/memory", 0666, NULL, &psi_memory_proc_ops); 1387 proc_create("pressure/cpu", 0666, NULL, &psi_cpu_proc_ops); 1388 } 1389 return 0; 1390 } 1391 module_init(psi_proc_init); 1392