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

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Message-ID: <87tvygk5h5.fsf@arm.com>
Date:   Mon, 30 Oct 2017 15:41:58 +0000
From:   Brendan Jackman <brendan.jackman@....com>
To:     Joel Fernandes <joelaf@...gle.com>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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\: Vincent Guittot" <vincent.guittot@...aro.org>,
        "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 Sat, Oct 28 2017 at 09:59, Joel Fernandes 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
> the conditions in find_idlest_group_cpu an impossible one, which we can get rid
> off.
>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Brendan Jackman <brendan.jackman@....com>
> Cc: Dietmar <dietmar.eggemann@....com>
> Signed-off-by: Joel Fernandes <joelaf@...gle.com>

FWIW:

Reviewed-by: Brendan Jackman <brendan.jackman@....com>

> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 5c49fdb4c508..740602ce799f 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5922,7 +5922,7 @@ find_idlest_group_cpu(struct sched_group *group, struct task_struct *p, int this
>  			}
>  		} else if (shallowest_idle_cpu == -1) {
>  			load = weighted_cpuload(cpu_rq(i));
> -			if (load < min_load || (load == min_load && i == this_cpu)) {
> +			if (load < min_load) {
>  				min_load = load;
>  				least_loaded_cpu = i;
>  			}