linux-kernel - Re: [PATCH 1/2] sched/topology: Don't enable EAS on SMT systems

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Message-ID: <20200227130001.GA107011@google.com>
Date:   Thu, 27 Feb 2020 13:00:01 +0000
From:   Quentin Perret <qperret@...gle.com>
To:     Valentin Schneider <valentin.schneider@....com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        morten.rasmussen@....com,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>, kernel-team@...roid.com
Subject: Re: [PATCH 1/2] sched/topology: Don't enable EAS on SMT systems

On Wednesday 26 Feb 2020 at 16:41:17 (+0000), Valentin Schneider wrote:
> EAS already requires asymmetric CPU capacities to be enabled, and mixing
> this with SMT is an aberration, but better be safe than sorry.
> 
> Signed-off-by: Valentin Schneider <valentin.schneider@....com>

Acked-by: Quentin Perret <qperret@...gle.com>

Thanks,
Quentin

> ---
>  kernel/sched/topology.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
> index 00911884b7e7..76cd0a370b9a 100644
> --- a/kernel/sched/topology.c
> +++ b/kernel/sched/topology.c
> @@ -360,6 +360,10 @@ static bool build_perf_domains(const struct cpumask *cpu_map)
>  		goto free;
>  	}
>  
> +	/* EAS definitely does *not* handle SMT */
> +	if (sched_smt_active())
> +		goto free;
> +
>  	for_each_cpu(i, cpu_map) {
>  		/* Skip already covered CPUs. */
>  		if (find_pd(pd, i))
> -- 
> 2.24.0
>