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psi: fix possible trigger missing in the window

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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: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Suren Baghdasaryan <surenb@google.com>
Link: https://lore.kernel.org/r/1643093818-19835-1-git-send-email-huangzhaoyang@gmail.com
This commit is contained in:
Zhaoyang Huang 2022-01-25 14:56:58 +08:00 committed by Peter Zijlstra
parent 5c7b1aaf13
commit e6df4ead85
2 changed files with 31 additions and 14 deletions
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3
include/linux/psi_types.h
View file

@ -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 {

42
kernel/sched/psi.c
View file

@ -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])
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;
/*
* 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.
* 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).
*/
new_stall = true;
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 (growth < t->threshold)
continue;
/* 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);