1 files changed, 556 insertions, 61 deletions

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 0e97ca9306ef..7acc632c3b82 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -4,6 +4,9 @@
  * 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
@@ -129,9 +132,13 @@
 #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"
 
@@ -140,9 +147,9 @@ static int psi_bug __read_mostly;
 DEFINE_STATIC_KEY_FALSE(psi_disabled);
 
 #ifdef CONFIG_PSI_DEFAULT_DISABLED
-bool psi_enable;
+static bool psi_enable;
 #else
-bool psi_enable = true;
+static bool psi_enable = true;
 #endif
 static int __init setup_psi(char *str)
 {
@@ -156,16 +163,21 @@ __setup("psi=", setup_psi);
 #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);
-static struct psi_group psi_system = {
+struct psi_group psi_system = {
 	.pcpu = &system_group_pcpu,
 };
 
-static void psi_update_work(struct work_struct *work);
+static void psi_avgs_work(struct work_struct *work);
 
 static void group_init(struct psi_group *group)
 {
@@ -173,9 +185,20 @@ static void group_init(struct psi_group *group)
 
 	for_each_possible_cpu(cpu)
 		seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq);
-	group->next_update = sched_clock() + psi_period;
-	INIT_DELAYED_WORK(&group->clock_work, psi_update_work);
-	mutex_init(&group->stat_lock);
+	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)
@@ -210,20 +233,24 @@ static bool test_state(unsigned int *tasks, enum psi_states state)
 	}
 }
 
-static void get_recent_times(struct psi_group *group, int cpu, u32 *times)
+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);
-	unsigned int tasks[NR_PSI_TASK_COUNTS];
 	u64 now, state_start;
+	enum psi_states s;
 	unsigned int seq;
-	int s;
+	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));
-		memcpy(tasks, groupc->tasks, sizeof(groupc->tasks));
+		state_mask = groupc->state_mask;
 		state_start = groupc->state_start;
 	} while (read_seqcount_retry(&groupc->seq, seq));
 
@@ -239,13 +266,15 @@ static void get_recent_times(struct psi_group *group, int cpu, u32 *times)
 		 * (u32) and our reported pressure close to what's
 		 * actually happening.
 		 */
-		if (test_state(tasks, s))
+		if (state_mask & (1 << s))
 			times[s] += now - state_start;
 
-		delta = times[s] - groupc->times_prev[s];
-		groupc->times_prev[s] = times[s];
+		delta = times[s] - groupc->times_prev[aggregator][s];
+		groupc->times_prev[aggregator][s] = times[s];
 
 		times[s] = delta;
+		if (delta)
+			*pchanged_states |= (1 << s);
 	}
 }
 
@@ -269,17 +298,16 @@ static void calc_avgs(unsigned long avg[3], int missed_periods,
 	avg[2] = calc_load(avg[2], EXP_300s, pct);
 }
 
-static bool update_stats(struct psi_group *group)
+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 missed_periods = 0;
 	unsigned long nonidle_total = 0;
-	u64 now, expires, period;
+	u32 changed_states = 0;
 	int cpu;
 	int s;
 
-	mutex_lock(&group->stat_lock);
-
 	/*
 	 * Collect the per-cpu time buckets and average them into a
 	 * single time sample that is normalized to wallclock time.
@@ -291,8 +319,11 @@ static bool update_stats(struct psi_group *group)
 	for_each_possible_cpu(cpu) {
 		u32 times[NR_PSI_STATES];
 		u32 nonidle;
+		u32 cpu_changed_states;
 
-		get_recent_times(group, cpu, times);
+		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;
@@ -315,13 +346,22 @@ static bool update_stats(struct psi_group *group)
 
 	/* total= */
 	for (s = 0; s < NR_PSI_STATES - 1; s++)
-		group->total[s] += div_u64(deltas[s], max(nonidle_total, 1UL));
+		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= */
-	now = sched_clock();
-	expires = group->next_update;
-	if (now < expires)
-		goto out;
+	expires = group->avg_next_update;
 	if (now - expires >= psi_period)
 		missed_periods = div_u64(now - expires, psi_period);
 
@@ -332,14 +372,14 @@ static bool update_stats(struct psi_group *group)
 	 * But the deltas we sample out of the per-cpu buckets above
 	 * are based on the actual time elapsing between clock ticks.
 	 */
-	group->next_update = expires + ((1 + missed_periods) * psi_period);
-	period = now - (group->last_update + (missed_periods * psi_period));
-	group->last_update = now;
+	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[s] - group->total_prev[s];
+		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,
@@ -359,23 +399,30 @@ static bool update_stats(struct psi_group *group)
 		 */
 		if (sample > period)
 			sample = period;
-		group->total_prev[s] += sample;
+		group->avg_total[s] += sample;
 		calc_avgs(group->avg[s], missed_periods, sample, period);
 	}
-out:
-	mutex_unlock(&group->stat_lock);
-	return nonidle_total;
+
+	return avg_next_update;
 }
 
-static void psi_update_work(struct work_struct *work)
+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, clock_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
@@ -383,18 +430,196 @@ static void psi_update_work(struct work_struct *work)
 	 * Once restarted, we'll catch up the running averages in one
 	 * go - see calc_avgs() and missed_periods.
 	 */
-
-	nonidle = update_stats(group);
+	if (now >= group->avg_next_update)
+		group->avg_next_update = update_averages(group, now);
 
 	if (nonidle) {
-		unsigned long delay = 0;
-		u64 now;
+		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();
 
-		now = sched_clock();
-		if (group->next_update > now)
-			delay = nsecs_to_jiffies(group->next_update - now) + 1;
-		schedule_delayed_work(dwork, delay);
+	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,
@@ -407,15 +632,15 @@ static void record_times(struct psi_group_cpu *groupc, int cpu,
 	delta = now - groupc->state_start;
 	groupc->state_start = now;
 
-	if (test_state(groupc->tasks, PSI_IO_SOME)) {
+	if (groupc->state_mask & (1 << PSI_IO_SOME)) {
 		groupc->times[PSI_IO_SOME] += delta;
-		if (test_state(groupc->tasks, PSI_IO_FULL))
+		if (groupc->state_mask & (1 << PSI_IO_FULL))
 			groupc->times[PSI_IO_FULL] += delta;
 	}
 
-	if (test_state(groupc->tasks, PSI_MEM_SOME)) {
+	if (groupc->state_mask & (1 << PSI_MEM_SOME)) {
 		groupc->times[PSI_MEM_SOME] += delta;
-		if (test_state(groupc->tasks, PSI_MEM_FULL))
+		if (groupc->state_mask & (1 << PSI_MEM_FULL))
 			groupc->times[PSI_MEM_FULL] += delta;
 		else if (memstall_tick) {
 			u32 sample;
@@ -436,18 +661,20 @@ static void record_times(struct psi_group_cpu *groupc, int cpu,
 		}
 	}
 
-	if (test_state(groupc->tasks, PSI_CPU_SOME))
+	if (groupc->state_mask & (1 << PSI_CPU_SOME))
 		groupc->times[PSI_CPU_SOME] += delta;
 
-	if (test_state(groupc->tasks, PSI_NONIDLE))
+	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)
+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);
 
@@ -480,7 +707,16 @@ static void psi_group_change(struct psi_group *group, int cpu,
 		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)
@@ -537,13 +773,17 @@ void psi_task_change(struct task_struct *task, int clear, int set)
 	 */
 	if (unlikely((clear & TSK_RUNNING) &&
 		     (task->flags & PF_WQ_WORKER) &&
-		     wq_worker_last_func(task) == psi_update_work))
+		     wq_worker_last_func(task) == psi_avgs_work))
 		wake_clock = false;
 
 	while ((group = iterate_groups(task, &iter))) {
-		psi_group_change(group, cpu, clear, set);
-		if (wake_clock && !delayed_work_pending(&group->clock_work))
-			schedule_delayed_work(&group->clock_work, PSI_FREQ);
+		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);
 	}
 }
 
@@ -640,8 +880,10 @@ void psi_cgroup_free(struct cgroup *cgroup)
 	if (static_branch_likely(&psi_disabled))
 		return;
 
-	cancel_delayed_work_sync(&cgroup->psi.clock_work);
+	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");
 }
 
 /**
@@ -697,11 +939,18 @@ void cgroup_move_task(struct task_struct *task, struct css_set *to)
 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_stats(group);
+	/* 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];
@@ -710,7 +959,8 @@ int psi_show(struct seq_file *m, struct psi_group *group, enum psi_res res)
 
 		for (w = 0; w < 3; w++)
 			avg[w] = group->avg[res * 2 + full][w];
-		total = div_u64(group->total[res * 2 + full], NSEC_PER_USEC);
+		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",
@@ -753,25 +1003,270 @@ 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 = MAX_RT_PRIO - 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(kworker->task, SCHED_FIFO, &param);
+		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) {
+		kthread_cancel_delayed_work_sync(&group->poll_work);
+		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,
-	.release        = single_release,
+	.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,
-	.release        = single_release,
+	.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,
-	.release        = single_release,
+	.write          = psi_cpu_write,
+	.poll           = psi_fop_poll,
+	.release        = psi_fop_release,
 };
 
 static int __init psi_proc_init(void)