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

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Message-ID: <8919ed14-8d19-d964-2278-3303a5bda8ee@arm.com>
Date:   Thu, 7 Sep 2023 14:57:26 +0100
From:   Lukasz Luba <lukasz.luba@....com>
To:     Peter Zijlstra <peterz@...radead.org>
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 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).