@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 <surenb@xxxxxxxxxx> wrote:
>
> On Tue, Dec 21, 2021 at 4:24 PM Huangzhaoyang <huangzhaoyang@xxxxxxxxx> wrote:
> >
> > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
>
> 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@xxxxxxxxxx>
> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> > ---
> > 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
> >
