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From: Suren Baghdasaryan <surenb@google.com>
To: Hillf Danton <hdanton@sina.com>
Cc: Pavan Kondeti <quic_pkondeti@quicinc.com>,
	Johannes Weiner <hannes@cmpxchg.org>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	quic_charante@quicinc.com
Subject: Re: PSI idle-shutoff
Date: Wed, 12 Oct 2022 08:40:17 -0700	[thread overview]
Message-ID: <CAJuCfpFsx6C1tRnAXVPz3Nn=odqDuQwgrEr5qVWWYh7t6Tpukw@mail.gmail.com> (raw)
In-Reply-To: <20221012062034.486-1-hdanton@sina.com>

On Tue, Oct 11, 2022 at 11:20 PM Hillf Danton <hdanton@sina.com> wrote:
>
> On 11 Oct 2022 10:11:58 -0700 Suren Baghdasaryan <surenb@google.com>
> >On Tue, Oct 11, 2022 at 4:38 AM Hillf Danton <hdanton@sina.com> wrote:
> >>
> >> Given activities on remote CPUs, can you specify what prevents psi_avgs_work
> >> from being scheduled on remote CPUs if for example the local CPU has been
> >> idle for a second?
> >
> > I'm not a scheduler expert but I can imagine some work that finished
> > running on a big core A and generated some activity since the last
> > time psi_avgs_work executed.  With no other activity the next
> > psi_avgs_work could be scheduled on a small core B to conserve power.
>
> Given core A and B, nothing prevents.
>
> > There might be other cases involving cpuset limitation changes or cpu
> > offlining but I didn't think too hard about these. The bottom line, I
> > don't think we should be designing mechanisms which rely on
> > assumptions about how tasks will be scheduled. Even if these
>
> The tasks here makes me guess that we are on different pages - scheduling
> work has little to do with how tasks are scheduled, and is no more than
> queuing work on the system_wq in the case of psi_avgs_work,

I must have misunderstood your question then. My original concern was
that in the above example your suggested patch would not reschedule
psi_avgs_work to aggregate the activity recorded from core A. Easily
fixable but looks like a simpler approach is possible.

>
> > assumptions are correct today they might change in the future and
> > things will break in unexpected places.
>
> with nothing assumed.
>

      reply	other threads:[~2022-10-12 15:40 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-13 14:08 PSI idle-shutoff Pavan Kondeti
2022-09-15  6:20 ` Pavan Kondeti
2022-09-17  5:45   ` Suren Baghdasaryan
2022-10-03  6:11     ` Suren Baghdasaryan
2022-10-05 16:32       ` Suren Baghdasaryan
2022-10-09 12:41         ` Chengming Zhou
2022-10-09 13:17           ` Chengming Zhou
2022-10-10  6:18             ` Pavan Kondeti
2022-10-10  6:43               ` Pavan Kondeti
2022-10-10  6:57                 ` [External] " Chengming Zhou
2022-10-10  8:30                   ` Chengming Zhou
2022-10-10  9:09                     ` Pavan Kondeti
2022-10-10  9:22                       ` Chengming Zhou
2022-10-10 20:59             ` Suren Baghdasaryan
2022-10-10 20:33           ` Suren Baghdasaryan
2022-10-10  5:57         ` Pavan Kondeti
2022-10-10  9:01           ` Pavan Kondeti
2022-10-10  6:25         ` Pavan Kondeti
2022-10-10 10:42 ` [PATCH] sched/psi: Fix avgs_work re-arm in psi_avgs_work() Chengming Zhou
2022-10-10 21:21   ` Suren Baghdasaryan
2022-10-11  0:07     ` Chengming Zhou
2022-10-11 17:00       ` Suren Baghdasaryan
2022-10-12  2:10         ` Chengming Zhou
2022-10-12 18:24           ` Suren Baghdasaryan
2022-10-13  2:23             ` Chengming Zhou
2022-10-13 11:06             ` Chengming Zhou
2022-10-13 15:52               ` Johannes Weiner
2022-10-13 16:10                 ` Suren Baghdasaryan
2022-10-14  2:03                   ` Chengming Zhou
2022-10-14  2:02                 ` Chengming Zhou
2022-10-28  6:42   ` [tip: sched/core] " tip-bot2 for Chengming Zhou
2022-10-28  6:50     ` [External] " Chengming Zhou
2022-10-28 15:58       ` Suren Baghdasaryan
2022-10-28 16:05         ` Chengming Zhou
2022-10-28 19:53         ` [External] " Peter Zijlstra
2022-10-29 11:55           ` Peter Zijlstra
2022-10-29 12:40             ` Chengming Zhou
2022-10-29 18:46               ` Suren Baghdasaryan
2022-10-10 10:57 ` PSI idle-shutoff Hillf Danton
2022-10-10 21:16   ` Suren Baghdasaryan
2022-10-11 11:38     ` Hillf Danton
2022-10-11 17:11       ` Suren Baghdasaryan
2022-10-12  6:20         ` Hillf Danton
2022-10-12 15:40           ` Suren Baghdasaryan [this message]

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