linux-kernel - Re: [RFC PATCH 0/7] sched: cpufreq: Remove magic margins

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Message-ID: <20230907201609.GC14243@noisy.programming.kicks-ass.net>
Date:   Thu, 7 Sep 2023 22:16:09 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Lukasz Luba <lukasz.luba@....com>
Cc:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Qais Yousef <qyousef@...alina.io>
Subject: Re: [RFC PATCH 0/7] sched: cpufreq: Remove magic margins

On Thu, Sep 07, 2023 at 03:42:13PM +0100, Lukasz Luba wrote:

> > What task characteristic is tied to this? That is, this seems trivial to
> > modify per-task.
> 
> In particular Speedometer test and the main browser task, which reaches
> ~900util, but sometimes vanish and waits for other background tasks
> to do something. In the meantime it can decay and wake-up on
> Mid/Little (which can cause a penalty to score up to 5-10% vs. if
> we pin the task to big CPUs). So, a longer util_est helps to avoid
> at least very bad down migration to Littles...

Do they do a few short activations (wakeup/sleeps) while waiting? That
would indeed completely ruin things since the EWMA thing is activation
based.

I wonder if there's anything sane we can do here...