| /* |
| * Pressure stall information for CPU, memory and IO |
| * |
| * Copyright (c) 2018 Facebook, Inc. |
| * Author: Johannes Weiner <hannes@cmpxchg.org> |
| * |
| * Polling support by Suren Baghdasaryan <surenb@google.com> |
| * 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.) |
| * |
| * 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 exceution |
| * 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 possibe 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 <linux/sched/loadavg.h> |
| #include <linux/seq_file.h> |
| #include <linux/proc_fs.h> |
| #include <linux/seqlock.h> |
| #include <linux/uaccess.h> |
| #include <linux/cgroup.h> |
| #include <linux/module.h> |
| #include <linux/sched.h> |
| #include <linux/ctype.h> |
| #include <linux/file.h> |
| #include <linux/poll.h> |
| #include <linux/psi.h> |
| #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_next_update = sched_clock() + psi_period; |
| INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work); |
| mutex_init(&group->avgs_lock); |
| /* Init trigger-related members */ |
| atomic_set(&group->poll_scheduled, 0); |
| 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_kworker, 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 tasks[NR_IOWAIT]; |
| case PSI_IO_FULL: |
| return tasks[NR_IOWAIT] && !tasks[NR_RUNNING]; |
| case PSI_MEM_SOME: |
| return tasks[NR_MEMSTALL]; |
| case PSI_MEM_FULL: |
| return tasks[NR_MEMSTALL] && !tasks[NR_RUNNING]; |
| case PSI_CPU_SOME: |
| return tasks[NR_RUNNING] > 1; |
| 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 manupulations */ |
| 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 += div_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. It's safe to call even from |
| * hotpath because even though kthread_queue_delayed_work takes worker->lock |
| * spinlock that spinlock is never contended due to poll_scheduled atomic |
| * preventing such competition. |
| */ |
| static void psi_schedule_poll_work(struct psi_group *group, unsigned long delay) |
| { |
| struct kthread_worker *kworker; |
| |
| /* Do not reschedule if already scheduled */ |
| if (atomic_cmpxchg(&group->poll_scheduled, 0, 1) != 0) |
| return; |
| |
| rcu_read_lock(); |
| |
| kworker = rcu_dereference(group->poll_kworker); |
| /* |
| * kworker might be NULL in case psi_trigger_destroy races with |
| * psi_task_change (hotpath) which can't use locks |
| */ |
| if (likely(kworker)) |
| kthread_queue_delayed_work(kworker, &group->poll_work, delay); |
| else |
| atomic_set(&group->poll_scheduled, 0); |
| |
| rcu_read_unlock(); |
| } |
| |
| static void psi_poll_work(struct kthread_work *work) |
| { |
| struct kthread_delayed_work *dwork; |
| struct psi_group *group; |
| u32 changed_states; |
| u64 now; |
| |
| dwork = container_of(work, struct kthread_delayed_work, work); |
| group = container_of(dwork, struct psi_group, poll_work); |
| |
| atomic_set(&group->poll_scheduled, 0); |
| |
| 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 void record_times(struct psi_group_cpu *groupc, int cpu, |
| bool memstall_tick) |
| { |
| u32 delta; |
| u64 now; |
| |
| now = cpu_clock(cpu); |
| 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; |
| else if (memstall_tick) { |
| u32 sample; |
| /* |
| * 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. |
| * |
| * When the timer tick sees a reclaiming CPU, |
| * regardless of runnable tasks, sample a FULL |
| * tick (or less if it hasn't been a full tick |
| * since the last state change). |
| */ |
| sample = min(delta, (u32)jiffies_to_nsecs(1)); |
| groupc->times[PSI_MEM_FULL] += sample; |
| } |
| } |
| |
| if (groupc->state_mask & (1 << PSI_CPU_SOME)) |
| groupc->times[PSI_CPU_SOME] += delta; |
| |
| if (groupc->state_mask & (1 << PSI_NONIDLE)) |
| groupc->times[PSI_NONIDLE] += delta; |
| } |
| |
| static u32 psi_group_change(struct psi_group *group, int cpu, |
| unsigned int clear, unsigned int set) |
| { |
| struct psi_group_cpu *groupc; |
| unsigned int t, m; |
| enum psi_states s; |
| u32 state_mask = 0; |
| |
| 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, cpu, false); |
| |
| 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] clear=%x set=%x\n", |
| cpu, t, groupc->tasks[0], |
| groupc->tasks[1], groupc->tasks[2], |
| 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); |
| } |
| groupc->state_mask = state_mask; |
| |
| write_seqcount_end(&groupc->seq); |
| |
| return state_mask; |
| } |
| |
| 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; |
| } |
| |
| 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; |
| |
| if (!task->pid) |
| return; |
| |
| 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, cpu, |
| task->psi_flags, clear, set); |
| psi_bug = 1; |
| } |
| |
| task->psi_flags &= ~clear; |
| task->psi_flags |= set; |
| |
| /* |
| * 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))) { |
| u32 state_mask = psi_group_change(group, cpu, clear, set); |
| |
| 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); |
| } |
| } |
| |
| void psi_memstall_tick(struct task_struct *task, int cpu) |
| { |
| struct psi_group *group; |
| void *iter = NULL; |
| |
| while ((group = iterate_groups(task, &iter))) { |
| struct psi_group_cpu *groupc; |
| |
| groupc = per_cpu_ptr(group->pcpu, cpu); |
| write_seqcount_begin(&groupc->seq); |
| record_times(groupc, cpu, true); |
| write_seqcount_end(&groupc->seq); |
| } |
| } |
| |
| /** |
| * 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->flags & PF_MEMSTALL; |
| if (*flags) |
| return; |
| /* |
| * PF_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->flags |= PF_MEMSTALL; |
| 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; |
| /* |
| * PF_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->flags &= ~PF_MEMSTALL; |
| 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; |
| else if (task->in_iowait) |
| task_flags = TSK_IOWAIT; |
| |
| if (task->flags & PF_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 - (res == PSI_CPU); 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_kworker)) { |
| struct sched_param param = { |
| .sched_priority = 1, |
| }; |
| struct kthread_worker *kworker; |
| |
| kworker = kthread_create_worker(0, "psimon"); |
| if (IS_ERR(kworker)) { |
| kfree(t); |
| mutex_unlock(&group->trigger_lock); |
| return ERR_CAST(kworker); |
| } |
| sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, ¶m); |
| kthread_init_delayed_work(&group->poll_work, |
| psi_poll_work); |
| rcu_assign_pointer(group->poll_kworker, kworker); |
| } |
| |
| 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 kthread_worker *kworker_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_kworker when the last trigger is destroyed */ |
| if (group->poll_states == 0) { |
| group->polling_until = 0; |
| kworker_to_destroy = rcu_dereference_protected( |
| group->poll_kworker, |
| lockdep_is_held(&group->trigger_lock)); |
| rcu_assign_pointer(group->poll_kworker, NULL); |
| } |
| } |
| |
| mutex_unlock(&group->trigger_lock); |
| |
| /* |
| * Wait for both *trigger_ptr from psi_trigger_replace and |
| * poll_kworker RCUs to complete their read-side critical sections |
| * before destroying the trigger and optionally the poll_kworker |
| */ |
| synchronize_rcu(); |
| /* |
| * Destroy the kworker after releasing trigger_lock to prevent a |
| * deadlock while waiting for psi_poll_work to acquire trigger_lock |
| */ |
| if (kworker_to_destroy) { |
| /* |
| * After the RCU grace period has expired, the worker |
| * can no longer be found through group->poll_kworker. |
| * But it might have been already scheduled before |
| * that - deschedule it cleanly before destroying it. |
| */ |
| kthread_cancel_delayed_work_sync(&group->poll_work); |
| atomic_set(&group->poll_scheduled, 0); |
| |
| kthread_destroy_worker(kworker_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; |
| |
| buf_size = min(nbytes, (sizeof(buf) - 1)); |
| 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 file_operations psi_io_fops = { |
| .open = psi_io_open, |
| .read = seq_read, |
| .llseek = seq_lseek, |
| .write = psi_io_write, |
| .poll = psi_fop_poll, |
| .release = psi_fop_release, |
| }; |
| |
| static const struct file_operations psi_memory_fops = { |
| .open = psi_memory_open, |
| .read = seq_read, |
| .llseek = seq_lseek, |
| .write = psi_memory_write, |
| .poll = psi_fop_poll, |
| .release = psi_fop_release, |
| }; |
| |
| static const struct file_operations psi_cpu_fops = { |
| .open = psi_cpu_open, |
| .read = seq_read, |
| .llseek = seq_lseek, |
| .write = psi_cpu_write, |
| .poll = psi_fop_poll, |
| .release = psi_fop_release, |
| }; |
| |
| static int __init psi_proc_init(void) |
| { |
| proc_mkdir("pressure", NULL); |
| proc_create("pressure/io", 0, NULL, &psi_io_fops); |
| proc_create("pressure/memory", 0, NULL, &psi_memory_fops); |
| proc_create("pressure/cpu", 0, NULL, &psi_cpu_fops); |
| return 0; |
| } |
| module_init(psi_proc_init); |