linux-kernel - Re: [PATCH RFC 5/5] sched/fair: remove impossible condition from find_idlest_group

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Date:   Mon, 30 Oct 2017 17:26:14 +0100
From:   Vincent Guittot <vincent.guittot@...aro.org>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Brendan Jackman <brendan.jackman@....com>,
        Dietmar <dietmar.eggemann@....com>,
        "Cc: Srinivas Pandruvada" <srinivas.pandruvada@...ux.intel.com>,
        "Cc: Len Brown" <lenb@...nel.org>,
        "Cc: Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Cc: Viresh Kumar" <viresh.kumar@...aro.org>,
        "Cc: Juri Lelli" <juri.lelli@....com>,
        "Cc: Patrick Bellasi" <patrick.bellasi@....com>,
        "Cc: Steve Muckle" <smuckle@...gle.com>,
        "Cc: Chris Redpath" <Chris.Redpath@....com>,
        "Cc: Atish Patra" <atish.patra@...cle.com>,
        "Cc: Morten Ramussen" <morten.rasmussen@....com>,
        "Cc: Frederic Weisbecker" <fweisbec@...il.com>,
        "Cc: Thomas Gleixner" <tglx@...utronix.de>,
        "Cc: EAS Dev" <eas-dev@...ts.linaro.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>
Subject: Re: [PATCH RFC 5/5] sched/fair: remove impossible condition from find_idlest_group_cpu

On 30 October 2017 at 17:19, Joel Fernandes <joelaf@...gle.com> wrote:
> Hi Vincent,
>
> On Mon, Oct 30, 2017 at 9:00 AM, Vincent Guittot
> <vincent.guittot@...aro.org> wrote:
>> On 28 October 2017 at 11:59, Joel Fernandes <joelaf@...gle.com> wrote:
>>> find_idlest_group_cpu goes through CPUs of a group previous selected by
>>> find_idlest_group. find_idlest_group returns NULL if the local group is the
>>> selected one and doesn't execute find_idlest_group_cpu if the group to which
>>> 'cpu' belongs to is chosen. So we're always guaranteed to call
>>> find_idlest_group_cpu with a group to which cpu is non-local. This makes one of
>>
>> Is this still true in case of overlapping topology ?
>
> Yes, I believe so. As per the code, find_idlest_group will only return
> a group to which this_cpu doesn't belong to. So incase an overlapping
> group was returned by find_idlest_group (instead of NULL), then none
> of the groups (among the set of overlapping groups) is local to
> this_cpu. Incase NULL is returned, then find_idlest_group_cpu doesn't
> execute at all.
>
> Do you agree?

Yes you're right. we skip of all groups to which this_cpu belong to

>
> thanks,
>
> - Joel
>
> [..]