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

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Message-ID: <20230907142923.GJ10955@noisy.programming.kicks-ass.net>
Date:   Thu, 7 Sep 2023 16:29:23 +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 02:57:26PM +0100, Lukasz Luba wrote:
> 
> 
> On 9/7/23 14:26, Peter Zijlstra wrote:
> > On Wed, Sep 06, 2023 at 10:18:50PM +0100, Qais Yousef wrote:
> > 
> > > This is probably controversial statement. But I am not in favour of util_est.
> > > I need to collect the data, but I think we're better with 16ms PELT HALFLIFE as
> > > default instead. But I will need to do a separate investigation on that.
> > 
> > I think util_est makes perfect sense, where PELT has to fundamentally
> > decay non-running / non-runnable tasks in order to provide a temporal
> > average, DVFS might be best served with a termporal max filter.
> > 
> > 
> 
> Since we are here...
> Would you allow to have a configuration for
> the util_est shifter: UTIL_EST_WEIGHT_SHIFT ?
> 
> I've found other values than '2' better in some scenarios. That helps
> to prevent a big task to 'down' migrate from a Big CPU (1024) to some
> Mid CPU (~500-700 capacity) or even Little (~120-300).

Larger values, I'm thinking you're after? Those would cause the new
contribution to weight less, making the function more smooth, right?

What task characteristic is tied to this? That is, this seems trivial to
modify per-task.