/* * Pressure stall information for CPU, memory and IO * * Copyright (c) 2018 Facebook, Inc. * Author: Johannes Weiner * * Polling support by Suren Baghdasaryan * Copyright (c) 2018 Google, Inc. * * When CPU, memory and IO are contended, tasks experience delays that * reduce throughput and introduce latencies into the workload. Memory * and IO contention, in addition, can cause a full loss of forward * progress in which the CPU goes idle. * * This code aggregates individual task delays into resource pressure * metrics that indicate problems with both workload health and * resource utilization. * * Model * * The time in which a task can execute on a CPU is our baseline for * productivity. Pressure expresses the amount of time in which this * potential cannot be realized due to resource contention. * * This concept of productivity has two components: the workload and * the CPU. To measure the impact of pressure on both, we define two * contention states for a resource: SOME and FULL. * * In the SOME state of a given resource, one or more tasks are * delayed on that resource. This affects the workload's ability to * perform work, but the CPU may still be executing other tasks. * * In the FULL state of a given resource, all non-idle tasks are * delayed on that resource such that nobody is advancing and the CPU * goes idle. This leaves both workload and CPU unproductive. * * Naturally, the FULL state doesn't exist for the CPU resource at the * system level, but exist at the cgroup level, means all non-idle tasks * in a cgroup are delayed on the CPU resource which used by others outside * of the cgroup or throttled by the cgroup cpu.max configuration. * * SOME = nr_delayed_tasks != 0 * FULL = nr_delayed_tasks != 0 && nr_running_tasks == 0 * * The percentage of wallclock time spent in those compound stall * states gives pressure numbers between 0 and 100 for each resource, * where the SOME percentage indicates workload slowdowns and the FULL * percentage indicates reduced CPU utilization: * * %SOME = time(SOME) / period * %FULL = time(FULL) / period * * Multiple CPUs * * The more tasks and available CPUs there are, the more work can be * performed concurrently. This means that the potential that can go * unrealized due to resource contention *also* scales with non-idle * tasks and CPUs. * * Consider a scenario where 257 number crunching tasks are trying to * run concurrently on 256 CPUs. If we simply aggregated the task * states, we would have to conclude a CPU SOME pressure number of * 100%, since *somebody* is waiting on a runqueue at all * times. However, that is clearly not the amount of contention the * workload is experiencing: only one out of 256 possible execution * threads will be contended at any given time, or about 0.4%. * * Conversely, consider a scenario of 4 tasks and 4 CPUs where at any * given time *one* of the tasks is delayed due to a lack of memory. * Again, looking purely at the task state would yield a memory FULL * pressure number of 0%, since *somebody* is always making forward * progress. But again this wouldn't capture the amount of execution * potential lost, which is 1 out of 4 CPUs, or 25%. * * To calculate wasted potential (pressure) with multiple processors, * we have to base our calculation on the number of non-idle tasks in * conjunction with the number of available CPUs, which is the number * of potential execution threads. SOME becomes then the proportion of * delayed tasks to possible threads, and FULL is the share of possible * threads that are unproductive due to delays: * * threads = min(nr_nonidle_tasks, nr_cpus) * SOME = min(nr_delayed_tasks / threads, 1) * FULL = (threads - min(nr_running_tasks, threads)) / threads * * For the 257 number crunchers on 256 CPUs, this yields: * * threads = min(257, 256) * SOME = min(1 / 256, 1) = 0.4% * FULL = (256 - min(257, 256)) / 256 = 0% * * For the 1 out of 4 memory-delayed tasks, this yields: * * threads = min(4, 4) * SOME = min(1 / 4, 1) = 25% * FULL = (4 - min(3, 4)) / 4 = 25% * * [ Substitute nr_cpus with 1, and you can see that it's a natural * extension of the single-CPU model. ] * * Implementation * * To assess the precise time spent in each such state, we would have * to freeze the system on task changes and start/stop the state * clocks accordingly. Obviously that doesn't scale in practice. * * Because the scheduler aims to distribute the compute load evenly * among the available CPUs, we can track task state locally to each * CPU and, at much lower frequency, extrapolate the global state for * the cumulative stall times and the running averages. * * For each runqueue, we track: * * tSOME[cpu] = time(nr_delayed_tasks[cpu] != 0) * tFULL[cpu] = time(nr_delayed_tasks[cpu] && !nr_running_tasks[cpu]) * tNONIDLE[cpu] = time(nr_nonidle_tasks[cpu] != 0) * * and then periodically aggregate: * * tNONIDLE = sum(tNONIDLE[i]) * * tSOME = sum(tSOME[i] * tNONIDLE[i]) / tNONIDLE * tFULL = sum(tFULL[i] * tNONIDLE[i]) / tNONIDLE * * %SOME = tSOME / period * %FULL = tFULL / period * * This gives us an approximation of pressure that is practical * cost-wise, yet way more sensitive and accurate than periodic * sampling of the aggregate task states would be. */ #include "../workqueue_internal.h" #include #include #include #include #include #include #include #include #include #include #include #include #include "sched.h" static int psi_bug __read_mostly; DEFINE_STATIC_KEY_FALSE(psi_disabled); #ifdef CONFIG_PSI_DEFAULT_DISABLED static bool psi_enable; #else static bool psi_enable = true; #endif static int __init setup_psi(char *str) { return kstrtobool(str, &psi_enable) == 0; } __setup("psi=", setup_psi); /* Running averages - we need to be higher-res than loadavg */ #define PSI_FREQ (2*HZ+1) /* 2 sec intervals */ #define EXP_10s 1677 /* 1/exp(2s/10s) as fixed-point */ #define EXP_60s 1981 /* 1/exp(2s/60s) */ #define EXP_300s 2034 /* 1/exp(2s/300s) */ /* PSI trigger definitions */ #define WINDOW_MIN_US 500000 /* Min window size is 500ms */ #define WINDOW_MAX_US 10000000 /* Max window size is 10s */ #define UPDATES_PER_WINDOW 10 /* 10 updates per window */ /* Sampling frequency in nanoseconds */ static u64 psi_period __read_mostly; /* System-level pressure and stall tracking */ static DEFINE_PER_CPU(struct psi_group_cpu, system_group_pcpu); struct psi_group psi_system = { .pcpu = &system_group_pcpu, }; static void psi_avgs_work(struct work_struct *work); static void group_init(struct psi_group *group) { int cpu; for_each_possible_cpu(cpu) seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq); group->avg_last_update = sched_clock(); group->avg_next_update = group->avg_last_update + psi_period; INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work); mutex_init(&group->avgs_lock); /* Init trigger-related members */ mutex_init(&group->trigger_lock); INIT_LIST_HEAD(&group->triggers); memset(group->nr_triggers, 0, sizeof(group->nr_triggers)); group->poll_states = 0; group->poll_min_period = U32_MAX; memset(group->polling_total, 0, sizeof(group->polling_total)); group->polling_next_update = ULLONG_MAX; group->polling_until = 0; rcu_assign_pointer(group->poll_task, NULL); } void __init psi_init(void) { if (!psi_enable) { static_branch_enable(&psi_disabled); return; } psi_period = jiffies_to_nsecs(PSI_FREQ); group_init(&psi_system); } static bool test_state(unsigned int *tasks, enum psi_states state) { switch (state) { case PSI_IO_SOME: return unlikely(tasks[NR_IOWAIT]); case PSI_IO_FULL: return unlikely(tasks[NR_IOWAIT] && !tasks[NR_RUNNING]); case PSI_MEM_SOME: return unlikely(tasks[NR_MEMSTALL]); case PSI_MEM_FULL: return unlikely(tasks[NR_MEMSTALL] && !tasks[NR_RUNNING]); case PSI_CPU_SOME: return unlikely(tasks[NR_RUNNING] > tasks[NR_ONCPU]); case PSI_CPU_FULL: return unlikely(tasks[NR_RUNNING] && !tasks[NR_ONCPU]); case PSI_NONIDLE: return tasks[NR_IOWAIT] || tasks[NR_MEMSTALL] || tasks[NR_RUNNING]; default: return false; } } static void get_recent_times(struct psi_group *group, int cpu, enum psi_aggregators aggregator, u32 *times, u32 *pchanged_states) { struct psi_group_cpu *groupc = per_cpu_ptr(group->pcpu, cpu); u64 now, state_start; enum psi_states s; unsigned int seq; u32 state_mask; *pchanged_states = 0; /* Snapshot a coherent view of the CPU state */ do { seq = read_seqcount_begin(&groupc->seq); now = cpu_clock(cpu); memcpy(times, groupc->times, sizeof(groupc->times)); state_mask = groupc->state_mask; state_start = groupc->state_start; } while (read_seqcount_retry(&groupc->seq, seq)); /* Calculate state time deltas against the previous snapshot */ for (s = 0; s < NR_PSI_STATES; s++) { u32 delta; /* * In addition to already concluded states, we also * incorporate currently active states on the CPU, * since states may last for many sampling periods. * * This way we keep our delta sampling buckets small * (u32) and our reported pressure close to what's * actually happening. */ if (state_mask & (1 << s)) times[s] += now - state_start; delta = times[s] - groupc->times_prev[aggregator][s]; groupc->times_prev[aggregator][s] = times[s]; times[s] = delta; if (delta) *pchanged_states |= (1 << s); } } static void calc_avgs(unsigned long avg[3], int missed_periods, u64 time, u64 period) { unsigned long pct; /* Fill in zeroes for periods of no activity */ if (missed_periods) { avg[0] = calc_load_n(avg[0], EXP_10s, 0, missed_periods); avg[1] = calc_load_n(avg[1], EXP_60s, 0, missed_periods); avg[2] = calc_load_n(avg[2], EXP_300s, 0, missed_periods); } /* Sample the most recent active period */ pct = div_u64(time * 100, period); pct *= FIXED_1; avg[0] = calc_load(avg[0], EXP_10s, pct); avg[1] = calc_load(avg[1], EXP_60s, pct); avg[2] = calc_load(avg[2], EXP_300s, pct); } static void collect_percpu_times(struct psi_group *group, enum psi_aggregators aggregator, u32 *pchanged_states) { u64 deltas[NR_PSI_STATES - 1] = { 0, }; unsigned long nonidle_total = 0; u32 changed_states = 0; int cpu; int s; /* * Collect the per-cpu time buckets and average them into a * single time sample that is normalized to wallclock time. * * For averaging, each CPU is weighted by its non-idle time in * the sampling period. This eliminates artifacts from uneven * loading, or even entirely idle CPUs. */ for_each_possible_cpu(cpu) { u32 times[NR_PSI_STATES]; u32 nonidle; u32 cpu_changed_states; get_recent_times(group, cpu, aggregator, times, &cpu_changed_states); changed_states |= cpu_changed_states; nonidle = nsecs_to_jiffies(times[PSI_NONIDLE]); nonidle_total += nonidle; for (s = 0; s < PSI_NONIDLE; s++) deltas[s] += (u64)times[s] * nonidle; } /* * Integrate the sample into the running statistics that are * reported to userspace: the cumulative stall times and the * decaying averages. * * Pressure percentages are sampled at PSI_FREQ. We might be * called more often when the user polls more frequently than * that; we might be called less often when there is no task * activity, thus no data, and clock ticks are sporadic. The * below handles both. */ /* total= */ for (s = 0; s < NR_PSI_STATES - 1; s++) group->total[aggregator][s] += div_u64(deltas[s], max(nonidle_total, 1UL)); if (pchanged_states) *pchanged_states = changed_states; } static u64 update_averages(struct psi_group *group, u64 now) { unsigned long missed_periods = 0; u64 expires, period; u64 avg_next_update; int s; /* avgX= */ expires = group->avg_next_update; if (now - expires >= psi_period) missed_periods = div_u64(now - expires, psi_period); /* * The periodic clock tick can get delayed for various * reasons, especially on loaded systems. To avoid clock * drift, we schedule the clock in fixed psi_period intervals. * But the deltas we sample out of the per-cpu buckets above * are based on the actual time elapsing between clock ticks. */ avg_next_update = expires + ((1 + missed_periods) * psi_period); period = now - (group->avg_last_update + (missed_periods * psi_period)); group->avg_last_update = now; for (s = 0; s < NR_PSI_STATES - 1; s++) { u32 sample; sample = group->total[PSI_AVGS][s] - group->avg_total[s]; /* * Due to the lockless sampling of the time buckets, * recorded time deltas can slip into the next period, * which under full pressure can result in samples in * excess of the period length. * * We don't want to report non-sensical pressures in * excess of 100%, nor do we want to drop such events * on the floor. Instead we punt any overage into the * future until pressure subsides. By doing this we * don't underreport the occurring pressure curve, we * just report it delayed by one period length. * * The error isn't cumulative. As soon as another * delta slips from a period P to P+1, by definition * it frees up its time T in P. */ if (sample > period) sample = period; group->avg_total[s] += sample; calc_avgs(group->avg[s], missed_periods, sample, period); } return avg_next_update; } static void psi_avgs_work(struct work_struct *work) { struct delayed_work *dwork; struct psi_group *group; u32 changed_states; bool nonidle; u64 now; dwork = to_delayed_work(work); group = container_of(dwork, struct psi_group, avgs_work); mutex_lock(&group->avgs_lock); now = sched_clock(); collect_percpu_times(group, PSI_AVGS, &changed_states); nonidle = changed_states & (1 << PSI_NONIDLE); /* * If there is task activity, periodically fold the per-cpu * times and feed samples into the running averages. If things * are idle and there is no data to process, stop the clock. * Once restarted, we'll catch up the running averages in one * go - see calc_avgs() and missed_periods. */ if (now >= group->avg_next_update) group->avg_next_update = update_averages(group, now); if (nonidle) { schedule_delayed_work(dwork, nsecs_to_jiffies( group->avg_next_update - now) + 1); } mutex_unlock(&group->avgs_lock); } /* Trigger tracking window manipulations */ static void window_reset(struct psi_window *win, u64 now, u64 value, u64 prev_growth) { win->start_time = now; win->start_value = value; win->prev_growth = prev_growth; } /* * PSI growth tracking window update and growth calculation routine. * * This approximates a sliding tracking window by interpolating * partially elapsed windows using historical growth data from the * previous intervals. This minimizes memory requirements (by not storing * all the intermediate values in the previous window) and simplifies * the calculations. It works well because PSI signal changes only in * positive direction and over relatively small window sizes the growth * is close to linear. */ static u64 window_update(struct psi_window *win, u64 now, u64 value) { u64 elapsed; u64 growth; elapsed = now - win->start_time; growth = value - win->start_value; /* * After each tracking window passes win->start_value and * win->start_time get reset and win->prev_growth stores * the average per-window growth of the previous window. * win->prev_growth is then used to interpolate additional * growth from the previous window assuming it was linear. */ if (elapsed > win->size) window_reset(win, now, value, growth); else { u32 remaining; remaining = win->size - elapsed; growth += div64_u64(win->prev_growth * remaining, win->size); } return growth; } static void init_triggers(struct psi_group *group, u64 now) { struct psi_trigger *t; list_for_each_entry(t, &group->triggers, node) window_reset(&t->win, now, group->total[PSI_POLL][t->state], 0); memcpy(group->polling_total, group->total[PSI_POLL], sizeof(group->polling_total)); group->polling_next_update = now + group->poll_min_period; } static u64 update_triggers(struct psi_group *group, u64 now) { struct psi_trigger *t; bool new_stall = false; u64 *total = group->total[PSI_POLL]; /* * On subsequent updates, calculate growth deltas and let * watchers know when their specified thresholds are exceeded. */ list_for_each_entry(t, &group->triggers, node) { u64 growth; /* Check for stall activity */ if (group->polling_total[t->state] == total[t->state]) continue; /* * Multiple triggers might be looking at the same state, * remember to update group->polling_total[] once we've * been through all of them. Also remember to extend the * polling time if we see new stall activity. */ new_stall = true; /* Calculate growth since last update */ growth = window_update(&t->win, now, total[t->state]); if (growth < t->threshold) continue; /* Limit event signaling to once per window */ if (now < t->last_event_time + t->win.size) continue; /* Generate an event */ if (cmpxchg(&t->event, 0, 1) == 0) wake_up_interruptible(&t->event_wait); t->last_event_time = now; } if (new_stall) memcpy(group->polling_total, total, sizeof(group->polling_total)); return now + group->poll_min_period; } /* Schedule polling if it's not already scheduled. */ static void psi_schedule_poll_work(struct psi_group *group, unsigned long delay) { struct task_struct *task; /* * Do not reschedule if already scheduled. * Possible race with a timer scheduled after this check but before * mod_timer below can be tolerated because group->polling_next_update * will keep updates on schedule. */ if (timer_pending(&group->poll_timer)) return; rcu_read_lock(); task = rcu_dereference(group->poll_task); /* * kworker might be NULL in case psi_trigger_destroy races with * psi_task_change (hotpath) which can't use locks */ if (likely(task)) mod_timer(&group->poll_timer, jiffies + delay); rcu_read_unlock(); } static void psi_poll_work(struct psi_group *group) { u32 changed_states; u64 now; mutex_lock(&group->trigger_lock); now = sched_clock(); collect_percpu_times(group, PSI_POLL, &changed_states); if (changed_states & group->poll_states) { /* Initialize trigger windows when entering polling mode */ if (now > group->polling_until) init_triggers(group, now); /* * Keep the monitor active for at least the duration of the * minimum tracking window as long as monitor states are * changing. */ group->polling_until = now + group->poll_min_period * UPDATES_PER_WINDOW; } if (now > group->polling_until) { group->polling_next_update = ULLONG_MAX; goto out; } if (now >= group->polling_next_update) group->polling_next_update = update_triggers(group, now); psi_schedule_poll_work(group, nsecs_to_jiffies(group->polling_next_update - now) + 1); out: mutex_unlock(&group->trigger_lock); } static int psi_poll_worker(void *data) { struct psi_group *group = (struct psi_group *)data; sched_set_fifo_low(current); while (true) { wait_event_interruptible(group->poll_wait, atomic_cmpxchg(&group->poll_wakeup, 1, 0) || kthread_should_stop()); if (kthread_should_stop()) break; psi_poll_work(group); } return 0; } static void poll_timer_fn(struct timer_list *t) { struct psi_group *group = from_timer(group, t, poll_timer); atomic_set(&group->poll_wakeup, 1); wake_up_interruptible(&group->poll_wait); } static void record_times(struct psi_group_cpu *groupc, u64 now) { u32 delta; delta = now - groupc->state_start; groupc->state_start = now; if (groupc->state_mask & (1 << PSI_IO_SOME)) { groupc->times[PSI_IO_SOME] += delta; if (groupc->state_mask & (1 << PSI_IO_FULL)) groupc->times[PSI_IO_FULL] += delta; } if (groupc->state_mask & (1 << PSI_MEM_SOME)) { groupc->times[PSI_MEM_SOME] += delta; if (groupc->state_mask & (1 << PSI_MEM_FULL)) groupc->times[PSI_MEM_FULL] += delta; } if (groupc->state_mask & (1 << PSI_CPU_SOME)) { groupc->times[PSI_CPU_SOME] += delta; if (groupc->state_mask & (1 << PSI_CPU_FULL)) groupc->times[PSI_CPU_FULL] += delta; } if (groupc->state_mask & (1 << PSI_NONIDLE)) groupc->times[PSI_NONIDLE] += delta; } static void psi_group_change(struct psi_group *group, int cpu, unsigned int clear, unsigned int set, u64 now, bool wake_clock) { struct psi_group_cpu *groupc; u32 state_mask = 0; unsigned int t, m; enum psi_states s; groupc = per_cpu_ptr(group->pcpu, cpu); /* * First we assess the aggregate resource states this CPU's * tasks have been in since the last change, and account any * SOME and FULL time these may have resulted in. * * Then we update the task counts according to the state * change requested through the @clear and @set bits. */ write_seqcount_begin(&groupc->seq); record_times(groupc, now); for (t = 0, m = clear; m; m &= ~(1 << t), t++) { if (!(m & (1 << t))) continue; if (groupc->tasks[t] == 0 && !psi_bug) { printk_deferred(KERN_ERR "psi: task underflow! cpu=%d t=%d tasks=[%u %u %u %u] clear=%x set=%x\n", cpu, t, groupc->tasks[0], groupc->tasks[1], groupc->tasks[2], groupc->tasks[3], clear, set); psi_bug = 1; } groupc->tasks[t]--; } for (t = 0; set; set &= ~(1 << t), t++) if (set & (1 << t)) groupc->tasks[t]++; /* Calculate state mask representing active states */ for (s = 0; s < NR_PSI_STATES; s++) { if (test_state(groupc->tasks, s)) state_mask |= (1 << s); } /* * Since we care about lost potential, a memstall is FULL * when there are no other working tasks, but also when * the CPU is actively reclaiming and nothing productive * could run even if it were runnable. So when the current * task in a cgroup is in_memstall, the corresponding groupc * on that cpu is in PSI_MEM_FULL state. */ if (unlikely(groupc->tasks[NR_ONCPU] && cpu_curr(cpu)->in_memstall)) state_mask |= (1 << PSI_MEM_FULL); groupc->state_mask = state_mask; write_seqcount_end(&groupc->seq); if (state_mask & group->poll_states) psi_schedule_poll_work(group, 1); if (wake_clock && !delayed_work_pending(&group->avgs_work)) schedule_delayed_work(&group->avgs_work, PSI_FREQ); } static struct psi_group *iterate_groups(struct task_struct *task, void **iter) { #ifdef CONFIG_CGROUPS struct cgroup *cgroup = NULL; if (!*iter) cgroup = task->cgroups->dfl_cgrp; else if (*iter == &psi_system) return NULL; else cgroup = cgroup_parent(*iter); if (cgroup && cgroup_parent(cgroup)) { *iter = cgroup; return cgroup_psi(cgroup); } #else if (*iter) return NULL; #endif *iter = &psi_system; return &psi_system; } static void psi_flags_change(struct task_struct *task, int clear, int set) { if (((task->psi_flags & set) || (task->psi_flags & clear) != clear) && !psi_bug) { printk_deferred(KERN_ERR "psi: inconsistent task state! task=%d:%s cpu=%d psi_flags=%x clear=%x set=%x\n", task->pid, task->comm, task_cpu(task), task->psi_flags, clear, set); psi_bug = 1; } task->psi_flags &= ~clear; task->psi_flags |= set; } void psi_task_change(struct task_struct *task, int clear, int set) { int cpu = task_cpu(task); struct psi_group *group; bool wake_clock = true; void *iter = NULL; u64 now; if (!task->pid) return; psi_flags_change(task, clear, set); now = cpu_clock(cpu); /* * Periodic aggregation shuts off if there is a period of no * task changes, so we wake it back up if necessary. However, * don't do this if the task change is the aggregation worker * itself going to sleep, or we'll ping-pong forever. */ if (unlikely((clear & TSK_RUNNING) && (task->flags & PF_WQ_WORKER) && wq_worker_last_func(task) == psi_avgs_work)) wake_clock = false; while ((group = iterate_groups(task, &iter))) psi_group_change(group, cpu, clear, set, now, wake_clock); } void psi_task_switch(struct task_struct *prev, struct task_struct *next, bool sleep) { struct psi_group *group, *common = NULL; int cpu = task_cpu(prev); void *iter; u64 now = cpu_clock(cpu); if (next->pid) { bool identical_state; psi_flags_change(next, 0, TSK_ONCPU); /* * When switching between tasks that have an identical * runtime state, the cgroup that contains both tasks * runtime state, the cgroup that contains both tasks * we reach the first common ancestor. Iterate @next's * ancestors only until we encounter @prev's ONCPU. */ identical_state = prev->psi_flags == next->psi_flags; iter = NULL; while ((group = iterate_groups(next, &iter))) { if (identical_state && per_cpu_ptr(group->pcpu, cpu)->tasks[NR_ONCPU]) { common = group; break; } psi_group_change(group, cpu, 0, TSK_ONCPU, now, true); } } if (prev->pid) { int clear = TSK_ONCPU, set = 0; /* * When we're going to sleep, psi_dequeue() lets us handle * TSK_RUNNING and TSK_IOWAIT here, where we can combine it * with TSK_ONCPU and save walking common ancestors twice. */ if (sleep) { clear |= TSK_RUNNING; if (prev->in_iowait) set |= TSK_IOWAIT; } psi_flags_change(prev, clear, set); iter = NULL; while ((group = iterate_groups(prev, &iter)) && group != common) psi_group_change(group, cpu, clear, set, now, true); /* * TSK_ONCPU is handled up to the common ancestor. If we're tasked * with dequeuing too, finish that for the rest of the hierarchy. */ if (sleep) { clear &= ~TSK_ONCPU; for (; group; group = iterate_groups(prev, &iter)) psi_group_change(group, cpu, clear, set, now, true); } } } /** * psi_memstall_enter - mark the beginning of a memory stall section * @flags: flags to handle nested sections * * Marks the calling task as being stalled due to a lack of memory, * such as waiting for a refault or performing reclaim. */ void psi_memstall_enter(unsigned long *flags) { struct rq_flags rf; struct rq *rq; if (static_branch_likely(&psi_disabled)) return; *flags = current->in_memstall; if (*flags) return; /* * in_memstall setting & accounting needs to be atomic wrt * changes to the task's scheduling state, otherwise we can * race with CPU migration. */ rq = this_rq_lock_irq(&rf); current->in_memstall = 1; psi_task_change(current, 0, TSK_MEMSTALL); rq_unlock_irq(rq, &rf); } /** * psi_memstall_leave - mark the end of an memory stall section * @flags: flags to handle nested memdelay sections * * Marks the calling task as no longer stalled due to lack of memory. */ void psi_memstall_leave(unsigned long *flags) { struct rq_flags rf; struct rq *rq; if (static_branch_likely(&psi_disabled)) return; if (*flags) return; /* * in_memstall clearing & accounting needs to be atomic wrt * changes to the task's scheduling state, otherwise we could * race with CPU migration. */ rq = this_rq_lock_irq(&rf); current->in_memstall = 0; psi_task_change(current, TSK_MEMSTALL, 0); rq_unlock_irq(rq, &rf); } #ifdef CONFIG_CGROUPS int psi_cgroup_alloc(struct cgroup *cgroup) { if (static_branch_likely(&psi_disabled)) return 0; cgroup->psi.pcpu = alloc_percpu(struct psi_group_cpu); if (!cgroup->psi.pcpu) return -ENOMEM; group_init(&cgroup->psi); return 0; } void psi_cgroup_free(struct cgroup *cgroup) { if (static_branch_likely(&psi_disabled)) return; cancel_delayed_work_sync(&cgroup->psi.avgs_work); free_percpu(cgroup->psi.pcpu); /* All triggers must be removed by now */ WARN_ONCE(cgroup->psi.poll_states, "psi: trigger leak\n"); } /** * cgroup_move_task - move task to a different cgroup * @task: the task * @to: the target css_set * * Move task to a new cgroup and safely migrate its associated stall * state between the different groups. * * This function acquires the task's rq lock to lock out concurrent * changes to the task's scheduling state and - in case the task is * running - concurrent changes to its stall state. */ void cgroup_move_task(struct task_struct *task, struct css_set *to) { unsigned int task_flags = 0; struct rq_flags rf; struct rq *rq; if (static_branch_likely(&psi_disabled)) { /* * Lame to do this here, but the scheduler cannot be locked * from the outside, so we move cgroups from inside sched/. */ rcu_assign_pointer(task->cgroups, to); return; } rq = task_rq_lock(task, &rf); if (task_on_rq_queued(task)) { task_flags = TSK_RUNNING; if (task_current(rq, task)) task_flags |= TSK_ONCPU; } else if (task->in_iowait) task_flags = TSK_IOWAIT; if (task->in_memstall) task_flags |= TSK_MEMSTALL; if (task_flags) psi_task_change(task, task_flags, 0); /* See comment above */ rcu_assign_pointer(task->cgroups, to); if (task_flags) psi_task_change(task, 0, task_flags); task_rq_unlock(rq, task, &rf); } #endif /* CONFIG_CGROUPS */ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res) { int full; u64 now; if (static_branch_likely(&psi_disabled)) return -EOPNOTSUPP; /* Update averages before reporting them */ mutex_lock(&group->avgs_lock); now = sched_clock(); collect_percpu_times(group, PSI_AVGS, NULL); if (now >= group->avg_next_update) group->avg_next_update = update_averages(group, now); mutex_unlock(&group->avgs_lock); for (full = 0; full < 2; full++) { unsigned long avg[3]; u64 total; int w; for (w = 0; w < 3; w++) avg[w] = group->avg[res * 2 + full][w]; total = div_u64(group->total[PSI_AVGS][res * 2 + full], NSEC_PER_USEC); seq_printf(m, "%s avg10=%lu.%02lu avg60=%lu.%02lu avg300=%lu.%02lu total=%llu\n", full ? "full" : "some", LOAD_INT(avg[0]), LOAD_FRAC(avg[0]), LOAD_INT(avg[1]), LOAD_FRAC(avg[1]), LOAD_INT(avg[2]), LOAD_FRAC(avg[2]), total); } return 0; } static int psi_io_show(struct seq_file *m, void *v) { return psi_show(m, &psi_system, PSI_IO); } static int psi_memory_show(struct seq_file *m, void *v) { return psi_show(m, &psi_system, PSI_MEM); } static int psi_cpu_show(struct seq_file *m, void *v) { return psi_show(m, &psi_system, PSI_CPU); } static int psi_io_open(struct inode *inode, struct file *file) { return single_open(file, psi_io_show, NULL); } static int psi_memory_open(struct inode *inode, struct file *file) { return single_open(file, psi_memory_show, NULL); } static int psi_cpu_open(struct inode *inode, struct file *file) { return single_open(file, psi_cpu_show, NULL); } struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf, size_t nbytes, enum psi_res res) { struct psi_trigger *t; enum psi_states state; u32 threshold_us; u32 window_us; if (static_branch_likely(&psi_disabled)) return ERR_PTR(-EOPNOTSUPP); if (sscanf(buf, "some %u %u", &threshold_us, &window_us) == 2) state = PSI_IO_SOME + res * 2; else if (sscanf(buf, "full %u %u", &threshold_us, &window_us) == 2) state = PSI_IO_FULL + res * 2; else return ERR_PTR(-EINVAL); if (state >= PSI_NONIDLE) return ERR_PTR(-EINVAL); if (window_us < WINDOW_MIN_US || window_us > WINDOW_MAX_US) return ERR_PTR(-EINVAL); /* Check threshold */ if (threshold_us == 0 || threshold_us > window_us) return ERR_PTR(-EINVAL); t = kmalloc(sizeof(*t), GFP_KERNEL); if (!t) return ERR_PTR(-ENOMEM); t->group = group; t->state = state; t->threshold = threshold_us * NSEC_PER_USEC; t->win.size = window_us * NSEC_PER_USEC; window_reset(&t->win, 0, 0, 0); t->event = 0; t->last_event_time = 0; init_waitqueue_head(&t->event_wait); kref_init(&t->refcount); mutex_lock(&group->trigger_lock); if (!rcu_access_pointer(group->poll_task)) { struct task_struct *task; task = kthread_create(psi_poll_worker, group, "psimon"); if (IS_ERR(task)) { kfree(t); mutex_unlock(&group->trigger_lock); return ERR_CAST(task); } atomic_set(&group->poll_wakeup, 0); init_waitqueue_head(&group->poll_wait); wake_up_process(task); timer_setup(&group->poll_timer, poll_timer_fn, 0); rcu_assign_pointer(group->poll_task, task); } list_add(&t->node, &group->triggers); group->poll_min_period = min(group->poll_min_period, div_u64(t->win.size, UPDATES_PER_WINDOW)); group->nr_triggers[t->state]++; group->poll_states |= (1 << t->state); mutex_unlock(&group->trigger_lock); return t; } static void psi_trigger_destroy(struct kref *ref) { struct psi_trigger *t = container_of(ref, struct psi_trigger, refcount); struct psi_group *group = t->group; struct task_struct *task_to_destroy = NULL; if (static_branch_likely(&psi_disabled)) return; /* * Wakeup waiters to stop polling. Can happen if cgroup is deleted * from under a polling process. */ wake_up_interruptible(&t->event_wait); mutex_lock(&group->trigger_lock); if (!list_empty(&t->node)) { struct psi_trigger *tmp; u64 period = ULLONG_MAX; list_del(&t->node); group->nr_triggers[t->state]--; if (!group->nr_triggers[t->state]) group->poll_states &= ~(1 << t->state); /* reset min update period for the remaining triggers */ list_for_each_entry(tmp, &group->triggers, node) period = min(period, div_u64(tmp->win.size, UPDATES_PER_WINDOW)); group->poll_min_period = period; /* Destroy poll_task when the last trigger is destroyed */ if (group->poll_states == 0) { group->polling_until = 0; task_to_destroy = rcu_dereference_protected( group->poll_task, lockdep_is_held(&group->trigger_lock)); rcu_assign_pointer(group->poll_task, NULL); } } mutex_unlock(&group->trigger_lock); /* * Wait for both *trigger_ptr from psi_trigger_replace and * poll_task RCUs to complete their read-side critical sections * before destroying the trigger and optionally the poll_task */ synchronize_rcu(); /* * Destroy the kworker after releasing trigger_lock to prevent a * deadlock while waiting for psi_poll_work to acquire trigger_lock */ if (task_to_destroy) { /* * After the RCU grace period has expired, the worker * can no longer be found through group->poll_task. * But it might have been already scheduled before * that - deschedule it cleanly before destroying it. */ del_timer_sync(&group->poll_timer); kthread_stop(task_to_destroy); } kfree(t); } void psi_trigger_replace(void **trigger_ptr, struct psi_trigger *new) { struct psi_trigger *old = *trigger_ptr; if (static_branch_likely(&psi_disabled)) return; rcu_assign_pointer(*trigger_ptr, new); if (old) kref_put(&old->refcount, psi_trigger_destroy); } __poll_t psi_trigger_poll(void **trigger_ptr, struct file *file, poll_table *wait) { __poll_t ret = DEFAULT_POLLMASK; struct psi_trigger *t; if (static_branch_likely(&psi_disabled)) return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; rcu_read_lock(); t = rcu_dereference(*(void __rcu __force **)trigger_ptr); if (!t) { rcu_read_unlock(); return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI; } kref_get(&t->refcount); rcu_read_unlock(); poll_wait(file, &t->event_wait, wait); if (cmpxchg(&t->event, 1, 0) == 1) ret |= EPOLLPRI; kref_put(&t->refcount, psi_trigger_destroy); return ret; } static ssize_t psi_write(struct file *file, const char __user *user_buf, size_t nbytes, enum psi_res res) { char buf[32]; size_t buf_size; struct seq_file *seq; struct psi_trigger *new; if (static_branch_likely(&psi_disabled)) return -EOPNOTSUPP; if (!nbytes) return -EINVAL; buf_size = min(nbytes, sizeof(buf)); if (copy_from_user(buf, user_buf, buf_size)) return -EFAULT; buf[buf_size - 1] = '\0'; new = psi_trigger_create(&psi_system, buf, nbytes, res); if (IS_ERR(new)) return PTR_ERR(new); seq = file->private_data; /* Take seq->lock to protect seq->private from concurrent writes */ mutex_lock(&seq->lock); psi_trigger_replace(&seq->private, new); mutex_unlock(&seq->lock); return nbytes; } static ssize_t psi_io_write(struct file *file, const char __user *user_buf, size_t nbytes, loff_t *ppos) { return psi_write(file, user_buf, nbytes, PSI_IO); } static ssize_t psi_memory_write(struct file *file, const char __user *user_buf, size_t nbytes, loff_t *ppos) { return psi_write(file, user_buf, nbytes, PSI_MEM); } static ssize_t psi_cpu_write(struct file *file, const char __user *user_buf, size_t nbytes, loff_t *ppos) { return psi_write(file, user_buf, nbytes, PSI_CPU); } static __poll_t psi_fop_poll(struct file *file, poll_table *wait) { struct seq_file *seq = file->private_data; return psi_trigger_poll(&seq->private, file, wait); } static int psi_fop_release(struct inode *inode, struct file *file) { struct seq_file *seq = file->private_data; psi_trigger_replace(&seq->private, NULL); return single_release(inode, file); } static const struct proc_ops psi_io_proc_ops = { .proc_open = psi_io_open, .proc_read = seq_read, .proc_lseek = seq_lseek, .proc_write = psi_io_write, .proc_poll = psi_fop_poll, .proc_release = psi_fop_release, }; static const struct proc_ops psi_memory_proc_ops = { .proc_open = psi_memory_open, .proc_read = seq_read, .proc_lseek = seq_lseek, .proc_write = psi_memory_write, .proc_poll = psi_fop_poll, .proc_release = psi_fop_release, }; static const struct proc_ops psi_cpu_proc_ops = { .proc_open = psi_cpu_open, .proc_read = seq_read, .proc_lseek = seq_lseek, .proc_write = psi_cpu_write, .proc_poll = psi_fop_poll, .proc_release = psi_fop_release, }; static int __init psi_proc_init(void) { if (psi_enable) { proc_mkdir("pressure", NULL); proc_create("pressure/io", 0, NULL, &psi_io_proc_ops); proc_create("pressure/memory", 0, NULL, &psi_memory_proc_ops); proc_create("pressure/cpu", 0, NULL, &psi_cpu_proc_ops); } return 0; } module_init(psi_proc_init);