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    SubjectRe: [PATCH v3] psi: fix possible trigger missing in the window
    On Wed, Dec 22, 2021 at 4:50 PM Zhaoyang Huang <huangzhaoyang@gmail.com> wrote:
    >
    > @Peter Zijlstra @Johannes Weiner
    > Would you please review this patch? We would like to have it be merged
    > ASAP. Thanks.

    It's the holiday season, so I would not expect a quick turnaround.

    >
    > On Wed, Dec 22, 2021 at 8:31 AM Suren Baghdasaryan <surenb@google.com> wrote:
    > >
    > > On Tue, Dec 21, 2021 at 4:24 PM Huangzhaoyang <huangzhaoyang@gmail.com> wrote:
    > > >
    > > > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
    > >
    > > Please remember to CC Peter.
    > >
    > > >
    > > > 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>
    > > > ---
    > > > 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
    > > >

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