Update Linux to v5.4.2
Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
new file mode 100644
index 0000000..517e371
--- /dev/null
+++ b/kernel/sched/psi.c
@@ -0,0 +1,1288 @@
+/*
+ * 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));
+ 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);