linux-kernel - Re: [PATCH] Revert "cpufreq: schedutil: Don't restrict kthread to related

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Message-ID: <20180508112424.GA463@e108498-lin.cambridge.arm.com>
Date:   Tue, 8 May 2018 12:24:25 +0100
From:   Quentin Perret <quentin.perret@....com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Dietmar Eggemann <dietmar.eggemann@....com>,
        linux-kernel@...r.kernel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, linux-pm@...r.kernel.org,
        Pavan Kondeti <pkondeti@...eaurora.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Patrick Bellasi <patrick.bellasi@....com>
Subject: Re: [PATCH] Revert "cpufreq: schedutil: Don't restrict kthread to
 related_cpus unnecessarily"

On Tuesday 08 May 2018 at 16:44:51 (+0530), Viresh Kumar wrote:
> On 08-05-18, 12:00, Quentin Perret wrote:
> > Right, I see your point. Now, with the current implementation, why should
> > we randomly force a CPU to manage the kthread of another ? IIUC deadline
> > should assign the kthreads to CPUs depending on the state of the system
> > when the task is created. So, from one boot to another, you could
> > theoretically end up with varying configurations, and varying power/perf
> > numbers.
> 
> Yeah, if it is fixed at boot then there is no good reason to push it
> to any other CPU. I agree.
> 

To be fair, I think that DL tasks _can_ migrate, but only in special
conditions (hotplug, or if a DL task wakes up when another DL task is
running and things like that IIRC) but that probably doesn't matter much
for our discussion here.

Thanks,
Quentin