@Peter Zijlstra @Johannes Weiner
Would you please review this patch? We would like to have it be merged
ASAP. Thanks.

On Wed, Dec 22, 2021 at 8:31 AM Suren Baghdasaryan [off-list ref] wrote:

On Tue, Dec 21, 2021 at 4:24 PM Huangzhaoyang [off-list ref] wrote:

quoted

From: Zhaoyang Huang <redacted>

Please remember to CC Peter.

quoted

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 <redacted>
---
v2: modify the logic according to Suren's suggestion
v3: update commit message
---
---
 include/linux/psi_types.h |  2 ++
 kernel/sched/psi.c        | 38 +++++++++++++++++++++++---------------
 2 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/include/linux/psi_types.h b/include/linux/psi_types.h
index 0a23300..87b694a 100644
--- a/include/linux/psi_types.h
+++ b/include/linux/psi_types.h

@@ -132,6 +132,8 @@ struct psi_trigger {

        /* Refcounting to prevent premature destruction */
        struct kref refcount;
+
+       bool threshold_breach;
 };

 struct psi_group {

diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 1652f2b..5c67ab9 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c

@@ -524,24 +524,29 @@ static u64 update_triggers(struct psi_group *group, u64 now)
         */
        list_for_each_entry(t, &group->triggers, node) {
                u64 growth;
+               bool trigger_stalled =
+                       group->polling_total[t->state] != total[t->state];

-               /* 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)
+               /* Check for stall activity or a previous threshold breach */
+               if (!trigger_stalled && !t->threshold_breach)
                        continue;

+               if (trigger_stalled) {
+                       /*
+                        * 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;
+
+                       t->threshold_breach = true;
+               }
                /* Limit event signaling to once per window */
                if (now < t->last_event_time + t->win.size)
                        continue;

@@ -550,6 +555,8 @@ 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->threshold_breach = false;
        }

        if (new_stall)

@@ -1152,6 +1159,7 @@ 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->threshold_breach = false;

        mutex_lock(&group->trigger_lock);

--

1.9.1