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Date: Wed, 22 Dec 2021 17:11:40 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Zhaoyang Huang <huangzhaoyang@...il.com>
Cc: Johannes Weiner <hannes@...xchg.org>,
Zhaoyang Huang <zhaoyang.huang@...soc.com>,
"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
LKML <linux-kernel@...r.kernel.org>,
Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v3] psi: fix possible trigger missing in the window
On Wed, Dec 22, 2021 at 4:50 PM Zhaoyang Huang <huangzhaoyang@...il.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@...gle.com> wrote:
> >
> > On Tue, Dec 21, 2021 at 4:24 PM Huangzhaoyang <huangzhaoyang@...il.com> wrote:
> > >
> > > From: Zhaoyang Huang <zhaoyang.huang@...soc.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@...gle.com>
> > > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.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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