The following commit has been merged into the sched/core branch of tip:
Commit-ID: e6df4ead85d9da1b07dd40bd4c6d2182f3e210c4
Gitweb: https://git.kernel.org/tip/e6df4ead85d9da1b07dd40bd4c6d2182f3e210c4
Author: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
AuthorDate: Tue, 25 Jan 2022 14:56:58 +08:00
Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Wed, 16 Feb 2022 15:57:54 +01:00
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: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Acked-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Link: https://lore.kernel.org/r/1643093818-19835-1-git-send-email-huangzhaoyang@xxxxxxxxx
---
include/linux/psi_types.h | 3 ++-
kernel/sched/psi.c | 46 ++++++++++++++++++++++++--------------
2 files changed, 33 insertions(+), 16 deletions(-)
diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
index 516c0fe..dc3ec5e 100644
--- a/include/linux/psi_types.h
+++ b/include/linux/psi_types.h
@@ -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 {
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index cfe76f7..e9d623c 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -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;
/*
- * 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;
-
- /* Calculate growth since last update */
- growth = window_update(&t->win, now, total[t->state]);
- if (growth < t->threshold)
- continue;
-
+ 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;
+
+ 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);
|