Adding upstream version 6.1.76.upstream/6.1.76

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 1662 insertions, 0 deletions

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
new file mode 100644
index 000000000..80d8c10e9
--- /dev/null
+++ b/kernel/sched/psi.c
@@ -0,0 +1,1662 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 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.
+ *
+ *	SOME = nr_delayed_tasks != 0
+ *	FULL = nr_delayed_tasks != 0 && nr_productive_tasks == 0
+ *
+ * What it means for a task to be productive is defined differently
+ * for each resource. For IO, productive means a running task. For
+ * memory, productive means a running task that isn't a reclaimer. For
+ * CPU, productive means an oncpu task.
+ *
+ * Naturally, the FULL state doesn't exist for the CPU resource at the
+ * system level, but exist at the cgroup level. At the cgroup level,
+ * FULL means all non-idle tasks in the cgroup are delayed on the CPU
+ * resource which is being used by others outside of the cgroup or
+ * throttled by the cgroup cpu.max configuration.
+ *
+ * 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_productive_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(256, 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_productive_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.
+ */
+
+static int psi_bug __read_mostly;
+
+DEFINE_STATIC_KEY_FALSE(psi_disabled);
+DEFINE_STATIC_KEY_TRUE(psi_cgroups_enabled);
+
+#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 poll_timer_fn(struct timer_list *t);
+
+static void group_init(struct psi_group *group)
+{
+	int cpu;
+
+	group->enabled = true;
+	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;
+	mutex_init(&group->avgs_lock);
+
+	/* Init avg trigger-related members */
+	INIT_LIST_HEAD(&group->avg_triggers);
+	memset(group->avg_nr_triggers, 0, sizeof(group->avg_nr_triggers));
+	INIT_DELAYED_WORK(&group->avgs_work, psi_avgs_work);
+
+	/* Init rtpoll trigger-related members */
+	atomic_set(&group->rtpoll_scheduled, 0);
+	mutex_init(&group->rtpoll_trigger_lock);
+	INIT_LIST_HEAD(&group->rtpoll_triggers);
+	group->rtpoll_min_period = U32_MAX;
+	group->rtpoll_next_update = ULLONG_MAX;
+	init_waitqueue_head(&group->rtpoll_wait);
+	timer_setup(&group->rtpoll_timer, poll_timer_fn, 0);
+	rcu_assign_pointer(group->rtpoll_task, NULL);
+}
+
+void __init psi_init(void)
+{
+	if (!psi_enable) {
+		static_branch_enable(&psi_disabled);
+		static_branch_disable(&psi_cgroups_enabled);
+		return;
+	}
+
+	if (!cgroup_psi_enabled())
+		static_branch_disable(&psi_cgroups_enabled);
+
+	psi_period = jiffies_to_nsecs(PSI_FREQ);
+	group_init(&psi_system);
+}
+
+static bool test_state(unsigned int *tasks, enum psi_states state, bool oncpu)
+{
+	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] == tasks[NR_MEMSTALL_RUNNING]);
+	case PSI_CPU_SOME:
+		return unlikely(tasks[NR_RUNNING] > oncpu);
+	case PSI_CPU_FULL:
+		return unlikely(tasks[NR_RUNNING] && !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);
+	int current_cpu = raw_smp_processor_id();
+	unsigned int tasks[NR_PSI_TASK_COUNTS];
+	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;
+		if (cpu == current_cpu)
+			memcpy(tasks, groupc->tasks, sizeof(groupc->tasks));
+	} 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);
+	}
+
+	/*
+	 * When collect_percpu_times() from the avgs_work, we don't want to
+	 * re-arm avgs_work when all CPUs are IDLE. But the current CPU running
+	 * this avgs_work is never IDLE, cause avgs_work can't be shut off.
+	 * So for the current CPU, we need to re-arm avgs_work only when
+	 * (NR_RUNNING > 1 || NR_IOWAIT > 0 || NR_MEMSTALL > 0), for other CPUs
+	 * we can just check PSI_NONIDLE delta.
+	 */
+	if (current_work() == &group->avgs_work.work) {
+		bool reschedule;
+
+		if (cpu == current_cpu)
+			reschedule = tasks[NR_RUNNING] +
+				     tasks[NR_IOWAIT] +
+				     tasks[NR_MEMSTALL] > 1;
+		else
+			reschedule = *pchanged_states & (1 << PSI_NONIDLE);
+
+		if (reschedule)
+			*pchanged_states |= PSI_STATE_RESCHEDULE;
+	}
+}
+
+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;
+}
+
+/* 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 u64 update_triggers(struct psi_group *group, u64 now, bool *update_total,
+						   enum psi_aggregators aggregator)
+{
+	struct psi_trigger *t;
+	u64 *total = group->total[aggregator];
+	struct list_head *triggers;
+	u64 *aggregator_total;
+	*update_total = false;
+
+	if (aggregator == PSI_AVGS) {
+		triggers = &group->avg_triggers;
+		aggregator_total = group->avg_total;
+	} else {
+		triggers = &group->rtpoll_triggers;
+		aggregator_total = group->rtpoll_total;
+	}
+
+	/*
+	 * On subsequent updates, calculate growth deltas and let
+	 * watchers know when their specified thresholds are exceeded.
+	 */
+	list_for_each_entry(t, triggers, node) {
+		u64 growth;
+		bool new_stall;
+
+		new_stall = aggregator_total[t->state] != total[t->state];
+
+		/* Check for stall activity or a previous threshold breach */
+		if (!new_stall && !t->pending_event)
+			continue;
+		/*
+		 * Check for new stall activity, as well as deferred
+		 * events that occurred in the last window after the
+		 * trigger had already fired (we want to ratelimit
+		 * events without dropping any).
+		 */
+		if (new_stall) {
+			/*
+			 * 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.
+			 */
+			*update_total = true;
+
+			/* Calculate growth since last update */
+			growth = window_update(&t->win, now, total[t->state]);
+			if (!t->pending_event) {
+				if (growth < t->threshold)
+					continue;
+
+				t->pending_event = true;
+			}
+		}
+		/* 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) {
+			if (t->of)
+				kernfs_notify(t->of->kn);
+			else
+				wake_up_interruptible(&t->event_wait);
+		}
+		t->last_event_time = now;
+		/* Reset threshold breach flag once event got generated */
+		t->pending_event = false;
+	}
+
+	return now + group->rtpoll_min_period;
+}
+
+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 update_total;
+	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);
+	/*
+	 * 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) {
+		update_triggers(group, now, &update_total, PSI_AVGS);
+		group->avg_next_update = update_averages(group, now);
+	}
+
+	if (changed_states & PSI_STATE_RESCHEDULE) {
+		schedule_delayed_work(dwork, nsecs_to_jiffies(
+				group->avg_next_update - now) + 1);
+	}
+
+	mutex_unlock(&group->avgs_lock);
+}
+
+static void init_rtpoll_triggers(struct psi_group *group, u64 now)
+{
+	struct psi_trigger *t;
+
+	list_for_each_entry(t, &group->rtpoll_triggers, node)
+		window_reset(&t->win, now,
+				group->total[PSI_POLL][t->state], 0);
+	memcpy(group->rtpoll_total, group->total[PSI_POLL],
+		   sizeof(group->rtpoll_total));
+	group->rtpoll_next_update = now + group->rtpoll_min_period;
+}
+
+/* Schedule polling if it's not already scheduled or forced. */
+static void psi_schedule_rtpoll_work(struct psi_group *group, unsigned long delay,
+				   bool force)
+{
+	struct task_struct *task;
+
+	/*
+	 * atomic_xchg should be called even when !force to provide a
+	 * full memory barrier (see the comment inside psi_rtpoll_work).
+	 */
+	if (atomic_xchg(&group->rtpoll_scheduled, 1) && !force)
+		return;
+
+	rcu_read_lock();
+
+	task = rcu_dereference(group->rtpoll_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->rtpoll_timer, jiffies + delay);
+	else
+		atomic_set(&group->rtpoll_scheduled, 0);
+
+	rcu_read_unlock();
+}
+
+static void psi_rtpoll_work(struct psi_group *group)
+{
+	bool force_reschedule = false;
+	u32 changed_states;
+	bool update_total;
+	u64 now;
+
+	mutex_lock(&group->rtpoll_trigger_lock);
+
+	now = sched_clock();
+
+	if (now > group->rtpoll_until) {
+		/*
+		 * We are either about to start or might stop polling if no
+		 * state change was recorded. Resetting poll_scheduled leaves
+		 * a small window for psi_group_change to sneak in and schedule
+		 * an immediate poll_work before we get to rescheduling. One
+		 * potential extra wakeup at the end of the polling window
+		 * should be negligible and polling_next_update still keeps
+		 * updates correctly on schedule.
+		 */
+		atomic_set(&group->rtpoll_scheduled, 0);
+		/*
+		 * A task change can race with the poll worker that is supposed to
+		 * report on it. To avoid missing events, ensure ordering between
+		 * poll_scheduled and the task state accesses, such that if the poll
+		 * worker misses the state update, the task change is guaranteed to
+		 * reschedule the poll worker:
+		 *
+		 * poll worker:
+		 *   atomic_set(poll_scheduled, 0)
+		 *   smp_mb()
+		 *   LOAD states
+		 *
+		 * task change:
+		 *   STORE states
+		 *   if atomic_xchg(poll_scheduled, 1) == 0:
+		 *     schedule poll worker
+		 *
+		 * The atomic_xchg() implies a full barrier.
+		 */
+		smp_mb();
+	} else {
+		/* Polling window is not over, keep rescheduling */
+		force_reschedule = true;
+	}
+
+
+	collect_percpu_times(group, PSI_POLL, &changed_states);
+
+	if (changed_states & group->rtpoll_states) {
+		/* Initialize trigger windows when entering polling mode */
+		if (now > group->rtpoll_until)
+			init_rtpoll_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->rtpoll_until = now +
+			group->rtpoll_min_period * UPDATES_PER_WINDOW;
+	}
+
+	if (now > group->rtpoll_until) {
+		group->rtpoll_next_update = ULLONG_MAX;
+		goto out;
+	}
+
+	if (now >= group->rtpoll_next_update) {
+		group->rtpoll_next_update = update_triggers(group, now, &update_total, PSI_POLL);
+		if (update_total)
+			memcpy(group->rtpoll_total, group->total[PSI_POLL],
+				   sizeof(group->rtpoll_total));
+	}
+
+	psi_schedule_rtpoll_work(group,
+		nsecs_to_jiffies(group->rtpoll_next_update - now) + 1,
+		force_reschedule);
+
+out:
+	mutex_unlock(&group->rtpoll_trigger_lock);
+}
+
+static int psi_rtpoll_worker(void *data)
+{
+	struct psi_group *group = (struct psi_group *)data;
+
+	sched_set_fifo_low(current);
+
+	while (true) {
+		wait_event_interruptible(group->rtpoll_wait,
+				atomic_cmpxchg(&group->rtpoll_wakeup, 1, 0) ||
+				kthread_should_stop());
+		if (kthread_should_stop())
+			break;
+
+		psi_rtpoll_work(group);
+	}
+	return 0;
+}
+
+static void poll_timer_fn(struct timer_list *t)
+{
+	struct psi_group *group = from_timer(group, t, rtpoll_timer);
+
+	atomic_set(&group->rtpoll_wakeup, 1);
+	wake_up_interruptible(&group->rtpoll_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;
+	unsigned int t, m;
+	enum psi_states s;
+	u32 state_mask;
+
+	groupc = per_cpu_ptr(group->pcpu, cpu);
+
+	/*
+	 * First we update the task counts according to the state
+	 * change requested through the @clear and @set bits.
+	 *
+	 * Then if the cgroup PSI stats accounting enabled, 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.
+	 */
+	write_seqcount_begin(&groupc->seq);
+
+	/*
+	 * Start with TSK_ONCPU, which doesn't have a corresponding
+	 * task count - it's just a boolean flag directly encoded in
+	 * the state mask. Clear, set, or carry the current state if
+	 * no changes are requested.
+	 */
+	if (unlikely(clear & TSK_ONCPU)) {
+		state_mask = 0;
+		clear &= ~TSK_ONCPU;
+	} else if (unlikely(set & TSK_ONCPU)) {
+		state_mask = PSI_ONCPU;
+		set &= ~TSK_ONCPU;
+	} else {
+		state_mask = groupc->state_mask & PSI_ONCPU;
+	}
+
+	/*
+	 * The rest of the state mask is calculated based on the task
+	 * counts. Update those first, then construct the mask.
+	 */
+	for (t = 0, m = clear; m; m &= ~(1 << t), t++) {
+		if (!(m & (1 << t)))
+			continue;
+		if (groupc->tasks[t]) {
+			groupc->tasks[t]--;
+		} else if (!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;
+		}
+	}
+
+	for (t = 0; set; set &= ~(1 << t), t++)
+		if (set & (1 << t))
+			groupc->tasks[t]++;
+
+	if (!group->enabled) {
+		/*
+		 * On the first group change after disabling PSI, conclude
+		 * the current state and flush its time. This is unlikely
+		 * to matter to the user, but aggregation (get_recent_times)
+		 * may have already incorporated the live state into times_prev;
+		 * avoid a delta sample underflow when PSI is later re-enabled.
+		 */
+		if (unlikely(groupc->state_mask & (1 << PSI_NONIDLE)))
+			record_times(groupc, now);
+
+		groupc->state_mask = state_mask;
+
+		write_seqcount_end(&groupc->seq);
+		return;
+	}
+
+	for (s = 0; s < NR_PSI_STATES; s++) {
+		if (test_state(groupc->tasks, s, state_mask & PSI_ONCPU))
+			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((state_mask & PSI_ONCPU) && cpu_curr(cpu)->in_memstall))
+		state_mask |= (1 << PSI_MEM_FULL);
+
+	record_times(groupc, now);
+
+	groupc->state_mask = state_mask;
+
+	write_seqcount_end(&groupc->seq);
+
+	if (state_mask & group->rtpoll_states)
+		psi_schedule_rtpoll_work(group, 1, false);
+
+	if (wake_clock && !delayed_work_pending(&group->avgs_work))
+		schedule_delayed_work(&group->avgs_work, PSI_FREQ);
+}
+
+static inline struct psi_group *task_psi_group(struct task_struct *task)
+{
+#ifdef CONFIG_CGROUPS
+	if (static_branch_likely(&psi_cgroups_enabled))
+		return cgroup_psi(task_dfl_cgroup(task));
+#endif
+	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;
+	u64 now;
+
+	if (!task->pid)
+		return;
+
+	psi_flags_change(task, clear, set);
+
+	now = cpu_clock(cpu);
+
+	group = task_psi_group(task);
+	do {
+		psi_group_change(group, cpu, clear, set, now, true);
+	} while ((group = group->parent));
+}
+
+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);
+	u64 now = cpu_clock(cpu);
+
+	if (next->pid) {
+		psi_flags_change(next, 0, TSK_ONCPU);
+		/*
+		 * Set TSK_ONCPU on @next's cgroups. If @next shares any
+		 * ancestors with @prev, those will already have @prev's
+		 * TSK_ONCPU bit set, and we can stop the iteration there.
+		 */
+		group = task_psi_group(next);
+		do {
+			if (per_cpu_ptr(group->pcpu, cpu)->state_mask &
+			    PSI_ONCPU) {
+				common = group;
+				break;
+			}
+
+			psi_group_change(group, cpu, 0, TSK_ONCPU, now, true);
+		} while ((group = group->parent));
+	}
+
+	if (prev->pid) {
+		int clear = TSK_ONCPU, set = 0;
+		bool wake_clock = true;
+
+		/*
+		 * When we're going to sleep, psi_dequeue() lets us
+		 * handle TSK_RUNNING, TSK_MEMSTALL_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_memstall)
+				clear |= TSK_MEMSTALL_RUNNING;
+			if (prev->in_iowait)
+				set |= TSK_IOWAIT;
+
+			/*
+			 * 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((prev->flags & PF_WQ_WORKER) &&
+				     wq_worker_last_func(prev) == psi_avgs_work))
+				wake_clock = false;
+		}
+
+		psi_flags_change(prev, clear, set);
+
+		group = task_psi_group(prev);
+		do {
+			if (group == common)
+				break;
+			psi_group_change(group, cpu, clear, set, now, wake_clock);
+		} while ((group = group->parent));
+
+		/*
+		 * TSK_ONCPU is handled up to the common ancestor. If there are
+		 * any other differences between the two tasks (e.g. prev goes
+		 * to sleep, or only one task is memstall), finish propagating
+		 * those differences all the way up to the root.
+		 */
+		if ((prev->psi_flags ^ next->psi_flags) & ~TSK_ONCPU) {
+			clear &= ~TSK_ONCPU;
+			for (; group; group = group->parent)
+				psi_group_change(group, cpu, clear, set, now, wake_clock);
+		}
+	}
+}
+
+#ifdef CONFIG_IRQ_TIME_ACCOUNTING
+void psi_account_irqtime(struct task_struct *task, u32 delta)
+{
+	int cpu = task_cpu(task);
+	struct psi_group *group;
+	struct psi_group_cpu *groupc;
+	u64 now;
+
+	if (!task->pid)
+		return;
+
+	now = cpu_clock(cpu);
+
+	group = task_psi_group(task);
+	do {
+		if (!group->enabled)
+			continue;
+
+		groupc = per_cpu_ptr(group->pcpu, cpu);
+
+		write_seqcount_begin(&groupc->seq);
+
+		record_times(groupc, now);
+		groupc->times[PSI_IRQ_FULL] += delta;
+
+		write_seqcount_end(&groupc->seq);
+
+		if (group->rtpoll_states & (1 << PSI_IRQ_FULL))
+			psi_schedule_rtpoll_work(group, 1, false);
+	} while ((group = group->parent));
+}
+#endif
+
+/**
+ * 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 | TSK_MEMSTALL_RUNNING);
+
+	rq_unlock_irq(rq, &rf);
+}
+EXPORT_SYMBOL_GPL(psi_memstall_enter);
+
+/**
+ * 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 | TSK_MEMSTALL_RUNNING, 0);
+
+	rq_unlock_irq(rq, &rf);
+}
+EXPORT_SYMBOL_GPL(psi_memstall_leave);
+
+#ifdef CONFIG_CGROUPS
+int psi_cgroup_alloc(struct cgroup *cgroup)
+{
+	if (!static_branch_likely(&psi_cgroups_enabled))
+		return 0;
+
+	cgroup->psi = kzalloc(sizeof(struct psi_group), GFP_KERNEL);
+	if (!cgroup->psi)
+		return -ENOMEM;
+
+	cgroup->psi->pcpu = alloc_percpu(struct psi_group_cpu);
+	if (!cgroup->psi->pcpu) {
+		kfree(cgroup->psi);
+		return -ENOMEM;
+	}
+	group_init(cgroup->psi);
+	cgroup->psi->parent = cgroup_psi(cgroup_parent(cgroup));
+	return 0;
+}
+
+void psi_cgroup_free(struct cgroup *cgroup)
+{
+	if (!static_branch_likely(&psi_cgroups_enabled))
+		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->rtpoll_states, "psi: trigger leak\n");
+	kfree(cgroup->psi);
+}
+
+/**
+ * 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;
+	struct rq_flags rf;
+	struct rq *rq;
+
+	if (!static_branch_likely(&psi_cgroups_enabled)) {
+		/*
+		 * 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);
+
+	/*
+	 * We may race with schedule() dropping the rq lock between
+	 * deactivating prev and switching to next. Because the psi
+	 * updates from the deactivation are deferred to the switch
+	 * callback to save cgroup tree updates, the task's scheduling
+	 * state here is not coherent with its psi state:
+	 *
+	 * schedule()                   cgroup_move_task()
+	 *   rq_lock()
+	 *   deactivate_task()
+	 *     p->on_rq = 0
+	 *     psi_dequeue() // defers TSK_RUNNING & TSK_IOWAIT updates
+	 *   pick_next_task()
+	 *     rq_unlock()
+	 *                                rq_lock()
+	 *                                psi_task_change() // old cgroup
+	 *                                task->cgroups = to
+	 *                                psi_task_change() // new cgroup
+	 *                                rq_unlock()
+	 *     rq_lock()
+	 *   psi_sched_switch() // does deferred updates in new cgroup
+	 *
+	 * Don't rely on the scheduling state. Use psi_flags instead.
+	 */
+	task_flags = task->psi_flags;
+
+	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);
+}
+
+void psi_cgroup_restart(struct psi_group *group)
+{
+	int cpu;
+
+	/*
+	 * After we disable psi_group->enabled, we don't actually
+	 * stop percpu tasks accounting in each psi_group_cpu,
+	 * instead only stop test_state() loop, record_times()
+	 * and averaging worker, see psi_group_change() for details.
+	 *
+	 * When disable cgroup PSI, this function has nothing to sync
+	 * since cgroup pressure files are hidden and percpu psi_group_cpu
+	 * would see !psi_group->enabled and only do task accounting.
+	 *
+	 * When re-enable cgroup PSI, this function use psi_group_change()
+	 * to get correct state mask from test_state() loop on tasks[],
+	 * and restart groupc->state_start from now, use .clear = .set = 0
+	 * here since no task status really changed.
+	 */
+	if (!group->enabled)
+		return;
+
+	for_each_possible_cpu(cpu) {
+		struct rq *rq = cpu_rq(cpu);
+		struct rq_flags rf;
+		u64 now;
+
+		rq_lock_irq(rq, &rf);
+		now = cpu_clock(cpu);
+		psi_group_change(group, cpu, 0, 0, now, true);
+		rq_unlock_irq(rq, &rf);
+	}
+}
+#endif /* CONFIG_CGROUPS */
+
+int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
+{
+	bool only_full = false;
+	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);
+
+#ifdef CONFIG_IRQ_TIME_ACCOUNTING
+	only_full = res == PSI_IRQ;
+#endif
+
+	for (full = 0; full < 2 - only_full; full++) {
+		unsigned long avg[3] = { 0, };
+		u64 total = 0;
+		int w;
+
+		/* CPU FULL is undefined at the system level */
+		if (!(group == &psi_system && res == PSI_CPU && full)) {
+			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 || only_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;
+}
+
+struct psi_trigger *psi_trigger_create(struct psi_group *group, char *buf,
+				       enum psi_res res, struct file *file,
+				       struct kernfs_open_file *of)
+{
+	struct psi_trigger *t;
+	enum psi_states state;
+	u32 threshold_us;
+	bool privileged;
+	u32 window_us;
+
+	if (static_branch_likely(&psi_disabled))
+		return ERR_PTR(-EOPNOTSUPP);
+
+	/*
+	 * Checking the privilege here on file->f_cred implies that a privileged user
+	 * could open the file and delegate the write to an unprivileged one.
+	 */
+	privileged = cap_raised(file->f_cred->cap_effective, CAP_SYS_RESOURCE);
+
+	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);
+
+#ifdef CONFIG_IRQ_TIME_ACCOUNTING
+	if (res == PSI_IRQ && --state != PSI_IRQ_FULL)
+		return ERR_PTR(-EINVAL);
+#endif
+
+	if (state >= PSI_NONIDLE)
+		return ERR_PTR(-EINVAL);
+
+	if (window_us < WINDOW_MIN_US ||
+		window_us > WINDOW_MAX_US)
+		return ERR_PTR(-EINVAL);
+
+	/*
+	 * Unprivileged users can only use 2s windows so that averages aggregation
+	 * work is used, and no RT threads need to be spawned.
+	 */
+	if (!privileged && window_us % 2000000)
+		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, sched_clock(),
+			group->total[PSI_POLL][t->state], 0);
+
+	t->event = 0;
+	t->last_event_time = 0;
+	t->of = of;
+	if (!of)
+		init_waitqueue_head(&t->event_wait);
+	t->pending_event = false;
+	t->aggregator = privileged ? PSI_POLL : PSI_AVGS;
+
+	if (privileged) {
+		mutex_lock(&group->rtpoll_trigger_lock);
+
+		if (!rcu_access_pointer(group->rtpoll_task)) {
+			struct task_struct *task;
+
+			task = kthread_create(psi_rtpoll_worker, group, "psimon");
+			if (IS_ERR(task)) {
+				kfree(t);
+				mutex_unlock(&group->rtpoll_trigger_lock);
+				return ERR_CAST(task);
+			}
+			atomic_set(&group->rtpoll_wakeup, 0);
+			wake_up_process(task);
+			rcu_assign_pointer(group->rtpoll_task, task);
+		}
+
+		list_add(&t->node, &group->rtpoll_triggers);
+		group->rtpoll_min_period = min(group->rtpoll_min_period,
+			div_u64(t->win.size, UPDATES_PER_WINDOW));
+		group->rtpoll_nr_triggers[t->state]++;
+		group->rtpoll_states |= (1 << t->state);
+
+		mutex_unlock(&group->rtpoll_trigger_lock);
+	} else {
+		mutex_lock(&group->avgs_lock);
+
+		list_add(&t->node, &group->avg_triggers);
+		group->avg_nr_triggers[t->state]++;
+
+		mutex_unlock(&group->avgs_lock);
+	}
+	return t;
+}
+
+void psi_trigger_destroy(struct psi_trigger *t)
+{
+	struct psi_group *group;
+	struct task_struct *task_to_destroy = NULL;
+
+	/*
+	 * We do not check psi_disabled since it might have been disabled after
+	 * the trigger got created.
+	 */
+	if (!t)
+		return;
+
+	group = t->group;
+	/*
+	 * Wakeup waiters to stop polling and clear the queue to prevent it from
+	 * being accessed later. Can happen if cgroup is deleted from under a
+	 * polling process.
+	 */
+	if (t->of)
+		kernfs_notify(t->of->kn);
+	else
+		wake_up_interruptible(&t->event_wait);
+
+	if (t->aggregator == PSI_AVGS) {
+		mutex_lock(&group->avgs_lock);
+		if (!list_empty(&t->node)) {
+			list_del(&t->node);
+			group->avg_nr_triggers[t->state]--;
+		}
+		mutex_unlock(&group->avgs_lock);
+	} else {
+		mutex_lock(&group->rtpoll_trigger_lock);
+		if (!list_empty(&t->node)) {
+			struct psi_trigger *tmp;
+			u64 period = ULLONG_MAX;
+
+			list_del(&t->node);
+			group->rtpoll_nr_triggers[t->state]--;
+			if (!group->rtpoll_nr_triggers[t->state])
+				group->rtpoll_states &= ~(1 << t->state);
+			/* reset min update period for the remaining triggers */
+			list_for_each_entry(tmp, &group->rtpoll_triggers, node)
+				period = min(period, div_u64(tmp->win.size,
+						UPDATES_PER_WINDOW));
+			group->rtpoll_min_period = period;
+			/* Destroy rtpoll_task when the last trigger is destroyed */
+			if (group->rtpoll_states == 0) {
+				group->rtpoll_until = 0;
+				task_to_destroy = rcu_dereference_protected(
+						group->rtpoll_task,
+						lockdep_is_held(&group->rtpoll_trigger_lock));
+				rcu_assign_pointer(group->rtpoll_task, NULL);
+				del_timer(&group->rtpoll_timer);
+			}
+		}
+		mutex_unlock(&group->rtpoll_trigger_lock);
+	}
+
+	/*
+	 * Wait for psi_schedule_rtpoll_work RCU to complete its read-side
+	 * critical section before destroying the trigger and optionally the
+	 * rtpoll_task.
+	 */
+	synchronize_rcu();
+	/*
+	 * Stop kthread 'psimon' after releasing rtpoll_trigger_lock to prevent
+	 * a deadlock while waiting for psi_rtpoll_work to acquire
+	 * rtpoll_trigger_lock
+	 */
+	if (task_to_destroy) {
+		/*
+		 * After the RCU grace period has expired, the worker
+		 * can no longer be found through group->rtpoll_task.
+		 */
+		kthread_stop(task_to_destroy);
+		atomic_set(&group->rtpoll_scheduled, 0);
+	}
+	kfree(t);
+}
+
+__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;
+
+	t = smp_load_acquire(trigger_ptr);
+	if (!t)
+		return DEFAULT_POLLMASK | EPOLLERR | EPOLLPRI;
+
+	if (t->of)
+		kernfs_generic_poll(t->of, wait);
+	else
+		poll_wait(file, &t->event_wait, wait);
+
+	if (cmpxchg(&t->event, 1, 0) == 1)
+		ret |= EPOLLPRI;
+
+	return ret;
+}
+
+#ifdef CONFIG_PROC_FS
+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);
+}
+
+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';
+
+	seq = file->private_data;
+
+	/* Take seq->lock to protect seq->private from concurrent writes */
+	mutex_lock(&seq->lock);
+
+	/* Allow only one trigger per file descriptor */
+	if (seq->private) {
+		mutex_unlock(&seq->lock);
+		return -EBUSY;
+	}
+
+	new = psi_trigger_create(&psi_system, buf, res, file, NULL);
+	if (IS_ERR(new)) {
+		mutex_unlock(&seq->lock);
+		return PTR_ERR(new);
+	}
+
+	smp_store_release(&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_destroy(seq->private);
+	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,
+};
+
+#ifdef CONFIG_IRQ_TIME_ACCOUNTING
+static int psi_irq_show(struct seq_file *m, void *v)
+{
+	return psi_show(m, &psi_system, PSI_IRQ);
+}
+
+static int psi_irq_open(struct inode *inode, struct file *file)
+{
+	return single_open(file, psi_irq_show, NULL);
+}
+
+static ssize_t psi_irq_write(struct file *file, const char __user *user_buf,
+			     size_t nbytes, loff_t *ppos)
+{
+	return psi_write(file, user_buf, nbytes, PSI_IRQ);
+}
+
+static const struct proc_ops psi_irq_proc_ops = {
+	.proc_open	= psi_irq_open,
+	.proc_read	= seq_read,
+	.proc_lseek	= seq_lseek,
+	.proc_write	= psi_irq_write,
+	.proc_poll	= psi_fop_poll,
+	.proc_release	= psi_fop_release,
+};
+#endif
+
+static int __init psi_proc_init(void)
+{
+	if (psi_enable) {
+		proc_mkdir("pressure", NULL);
+		proc_create("pressure/io", 0666, NULL, &psi_io_proc_ops);
+		proc_create("pressure/memory", 0666, NULL, &psi_memory_proc_ops);
+		proc_create("pressure/cpu", 0666, NULL, &psi_cpu_proc_ops);
+#ifdef CONFIG_IRQ_TIME_ACCOUNTING
+		proc_create("pressure/irq", 0666, NULL, &psi_irq_proc_ops);
+#endif
+	}
+	return 0;
+}
+module_init(psi_proc_init);
+
+#endif /* CONFIG_PROC_FS */