linux-kernel - Re: [Resend PATCH] psi : calc cfs task memstall time more precisely

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Message-ID: <YYuEoftqXxOhStJ7@hirez.programming.kicks-ass.net>
Date:   Wed, 10 Nov 2021 09:36:49 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ke Wang <ke.wang@...soc.com>, xuewen.yan@...soc.com,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [Resend PATCH] psi : calc cfs task memstall time more precisely

On Wed, Nov 10, 2021 at 09:37:00AM +0800, Zhaoyang Huang wrote:
> On Tue, Nov 9, 2021 at 10:56 PM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Tue, Nov 02, 2021 at 03:47:33PM -0400, Johannes Weiner wrote:
> > > CC peterz as well for rt and timekeeping magic
> > >
> > > On Fri, Oct 15, 2021 at 02:16:52PM +0800, Huangzhaoyang wrote:
> > > > From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > > >
> > > > In an EAS enabled system, there are two scenarios discordant to current design,
> > > >
> > > > 1. workload used to be heavy uneven among cores for sake of scheduler policy.
> > > > RT task usually preempts CFS task in little core.
> > > > 2. CFS task's memstall time is counted as simple as exit - entry so far, which
> > > > ignore the preempted time by RT, DL and Irqs.
> >
> > It ignores preemption full-stop. I don't see why RT/IRQ should be
> > special cased here.
> As Johannes comments, what we are trying to solve is mainly the
> preempted time of the CFS task by RT/IRQ, NOT the RT/IRQ themselves.
> Could you please catch up the recent reply of Dietmar, which maybe
> provide more information.

In that case NAK.