Commit e6df4ead authored by Zhaoyang Huang's avatar Zhaoyang Huang Committed by Peter Zijlstra
Browse files

psi: fix possible trigger missing in the window 



When a new threshold breaching stall happens after a psi event was
generated and within the window duration, the new event is not
generated because the events are rate-limited to one per window. If
after that no new stall is recorded then the event will not be
generated even after rate-limiting duration has passed. This is
happening because with no new stall, window_update will not be called
even though threshold was previously breached. To fix this, record
threshold breaching occurrence and generate the event once window
duration is passed.

Suggested-by: default avatarSuren Baghdasaryan <surenb@google.com>
Signed-off-by: default avatarZhaoyang Huang <zhaoyang.huang@unisoc.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Acked-by: default avatarSuren Baghdasaryan <surenb@google.com>
Link: https://lore.kernel.org/r/1643093818-19835-1-git-send-email-huangzhaoyang@gmail.com
parent 5c7b1aaf

include/linux/psi_types.h

+3 −0
Original line number Diff line number Diff line
@@ -144,6 +144,9 @@ struct psi_trigger { 


	/* Refcounting to prevent premature destruction */

	struct kref refcount;



	/* Deferred event(s) from previous ratelimit window */

	bool pending_event;

};



struct psi_group {

kernel/sched/psi.c

+30 −16
Original line number Diff line number Diff line
@@ -523,7 +523,7 @@ static void init_triggers(struct psi_group *group, u64 now) 
static u64 update_triggers(struct psi_group *group, u64 now)

{

	struct psi_trigger *t;

	bool new_stall = false;

	bool update_total = false;

	u64 *total = group->total[PSI_POLL];



	/*
@@ -532,24 +532,35 @@ static u64 update_triggers(struct psi_group *group, u64 now) 
	 */

	list_for_each_entry(t, &group->triggers, node) {

		u64 growth;

		bool new_stall;



		/* Check for stall activity */

		if (group->polling_total[t->state] == total[t->state])

			continue;

		new_stall = group->polling_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.

			 */

		new_stall = true;

			update_total = true;



			/* Calculate growth since last update */

			growth = window_update(&t->win, now, total[t->state]);

			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;
@@ -558,9 +569,11 @@ static u64 update_triggers(struct psi_group *group, u64 now) 
		if (cmpxchg(&t->event, 0, 1) == 0)

			wake_up_interruptible(&t->event_wait);

		t->last_event_time = now;

		/* Reset threshold breach flag once event got generated */

		t->pending_event = false;

	}



	if (new_stall)

	if (update_total)

		memcpy(group->polling_total, total,

				sizeof(group->polling_total));
@@ -1125,6 +1138,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group, 
	t->last_event_time = 0;

	init_waitqueue_head(&t->event_wait);

	kref_init(&t->refcount);

	t->pending_event = false;



	mutex_lock(&group->trigger_lock);