From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
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>
---
v2: modify the logic according to Suren's suggestion
v3: update commit message
v4: update variable name and comments
---
---
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 0a23300..e0ec129 100644
--- a/include/linux/psi_types.h
+++ b/include/linux/psi_types.h
@@ -132,6 +132,9 @@ 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 1652f2b..dd80bd2 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -515,7 +515,7 @@ 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];
/*
@@ -524,24 +524,35 @@ 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;
@@ -550,9 +561,11 @@ 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));
@@ -1152,6 +1165,7 @@ 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);
--
1.9.1
