linux-kernel - Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core

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Message-ID: <1790766.jaFeG3T87Z@kreacher>
Date:   Thu, 22 Oct 2020 14:19:29 +0200
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Julia Lawall <julia.lawall@...ia.fr>,
        Mel Gorman <mgorman@...e.de>, Ingo Molnar <mingo@...hat.com>,
        kernel-janitors@...r.kernel.org,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-kernel@...r.kernel.org,
        Valentin Schneider <valentin.schneider@....com>,
        Gilles Muller <Gilles.Muller@...ia.fr>,
        srinivas.pandruvada@...ux.intel.com,
        Linux PM <linux-pm@...r.kernel.org>,
        Len Brown <len.brown@...el.com>
Subject: Re: default cpufreq gov, was: [PATCH] sched/fair: check for idle core

[CC linux-pm and Len]

On Thursday, October 22, 2020 2:02:13 PM CEST Peter Zijlstra wrote:
> On Thu, Oct 22, 2020 at 01:45:25PM +0200, Rafael J. Wysocki wrote:
> > On Thursday, October 22, 2020 12:47:03 PM CEST Viresh Kumar wrote:
> > > On 22-10-20, 09:11, Peter Zijlstra wrote:
> > > > Well, but we need to do something to force people onto schedutil,
> > > > otherwise we'll get more crap like this thread.
> > > > 
> > > > Can we take the choice away? Only let Kconfig select which governors are
> > > > available and then set the default ourselves? I mean, the end goal being
> > > > to not have selectable governors at all, this seems like a good step
> > > > anyway.
> > > 
> > > Just to clarify and complete the point a bit here, the users can still
> > > pass the default governor from cmdline using
> > > cpufreq.default_governor=, which will take precedence over the one the
> > > below code is playing with. And later once the kernel is up, they can
> > > still choose a different governor from userspace.
> > 
> > Right.
> > 
> > Also some people simply set "performance" as the default governor and then
> > don't touch cpufreq otherwise (the idea is to get everything to the max
> > freq right away and stay in that mode forever).  This still needs to be
> > possible IMO.
> 
> Performance/powersave make sense to keep.
> 
> However I do want to retire ondemand, conservative and also very much
> intel_pstate/active mode.

I agree in general, but IMO it would not be prudent to do that without making
schedutil provide the same level of performance in all of the relevant use
cases.

> I also have very little sympathy for userspace.

That I completely agree with.

> We should start by making it hard to use them and eventually just delete
> them outright.

Right, but see above: IMO step 0 should be to ensure that schedutil is a viable
replacement for all users.