Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:4 as permitted sender) client-ip=2620:137:e000::3:4;
MIME-Version: 1.0
References: <cover.1696345700.git.Hongyan.Xia2@arm.com> <20231203002544.d4zx3oyvjugohh22@airbuntu>
 <7f1f7dd0-e3b5-4e16-a44e-c08fca567f97@arm.com> <CAKfTPtBZ+7STLsRH7h+WeitcH1i4623J4xb0XQKTzsp=XNV_-w@mail.gmail.com>
 <cf221099-31f4-4de1-9418-a354f002e26e@arm.com>
In-Reply-To: <cf221099-31f4-4de1-9418-a354f002e26e@arm.com>
From:   Vincent Guittot <vincent.guittot@linaro.org>
Date:   Tue, 5 Dec 2023 17:26:46 +0100
Message-ID: <CAKfTPtD10c4Uif6EATJ2SiAPdnEzXkC78nZE=q23dLM7fszvEQ@mail.gmail.com>
Subject: Re: [RFC PATCH 0/6] sched: uclamp sum aggregation
To:     Hongyan Xia <hongyan.xia2@arm.com>
Cc:     Qais Yousef <qyousef@layalina.io>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Morten Rasmussen <morten.rasmussen@arm.com>,
        Lukasz Luba <lukasz.luba@arm.com>,
        Christian Loehle <christian.loehle@arm.com>,
        linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Tue, 5 Dec 2023 at 16:19, Hongyan Xia <hongyan.xia2@arm.com> wrote:
>
> On 04/12/2023 16:12, Vincent Guittot wrote:
> > On Mon, 4 Dec 2023 at 02:48, Hongyan Xia <hongyan.xia2@arm.com> wrote:
> >>
> >> [...]
> >>
> >> Other shortcomings are not that critical, but the fact that uclamp_min's
> >> effectiveness is divided by N under max aggregation I think is not
> >> acceptable.
> >
> > Change EAS task placement policy in this case to take into account
> > actual utilization and uclamp_min/max
>
> Thank you. I agree. I want to emphasize this specifically because this
> is exactly what I'm trying to do. The whole series can be rephrased in a
> different way:
>
> - The PELT signal is distorted when uclamp is active.

Sorry but no it's not

> - Let's consider the [PELT, uclamp_min, uclamp_max] tuple.

That's what we are already doing with effective_cpu_util. We might
want to improve how we use them in EAS but that's another story than
your proposal

> - Always carrying all three variables is too much, but [PELT,
> clamped(PELT)] is an approximation that works really well.

As said before. It's a no go for this mix

>
> Of course, I'll explore if there's a way to make things less messy. I
> just realized why I didn't do things util_est way but instead directly
> clamping on PELT, it's because util_est boosts util_avg and can't work
> for uclamp_max. I'll keep exploring options.
>
> >> [...]