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References: <20190830174944.21741-1-subhra.mazumdar@oracle.com> <20190830174944.21741-5-subhra.mazumdar@oracle.com>
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From:   Patrick Bellasi <patrick.bellasi@arm.com>
To:     subhra mazumdar <subhra.mazumdar@oracle.com>
Cc:     linux-kernel@vger.kernel.org, peterz@infradead.org,
        mingo@redhat.com, tglx@linutronix.de, steven.sistare@oracle.com,
        dhaval.giani@oracle.com, daniel.lezcano@linaro.org,
        vincent.guittot@linaro.org, viresh.kumar@linaro.org,
        tim.c.chen@linux.intel.com, mgorman@techsingularity.net,
        parth@linux.ibm.com
Subject: Re: [RFC PATCH 4/9] sched: SIS_CORE to disable idle core search
In-reply-to: <20190830174944.21741-5-subhra.mazumdar@oracle.com>
Date:   Thu, 05 Sep 2019 11:19:57 +0100
Message-ID: <87lfv32gfm.fsf@arm.com>
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Sender: linux-kernel-owner@vger.kernel.org
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On Fri, Aug 30, 2019 at 18:49:39 +0100, subhra mazumdar wrote...

> Use SIS_CORE to disable idle core search. For some workloads
> select_idle_core becomes a scalability bottleneck, removing it improves
> throughput. Also there are workloads where disabling it can hurt latency,
> so need to have an option.
>
> Signed-off-by: subhra mazumdar <subhra.mazumdar@oracle.com>
> ---
>  kernel/sched/fair.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index c31082d..23ec9c6 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -6268,9 +6268,11 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target)
>  	if (!sd)
>  		return target;
>  
> -	i = select_idle_core(p, sd, target);
> -	if ((unsigned)i < nr_cpumask_bits)
> -		return i;
> +	if (sched_feat(SIS_CORE)) {
> +		i = select_idle_core(p, sd, target);
> +		if ((unsigned)i < nr_cpumask_bits)
> +			return i;
> +	}
>  
>  	i = select_idle_cpu(p, sd, target);
>  	if ((unsigned)i < nr_cpumask_bits)

This looks like should be squashed with the previous one, or whatever
code you'll add to define when this "biasing" is to be used or not.

Best,
Patrick

-- 
#include <best/regards.h>

Patrick Bellasi