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

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Message-ID: <jhjftewvv5c.mognet@arm.com>
Date:   Thu, 27 Feb 2020 16:42:55 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Dietmar Eggemann <dietmar.eggemann@....com>
Cc:     Quentin Perret <qperret@...gle.com>, 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>,
        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 Thu, Feb 27 2020, Dietmar Eggemann wrote:
>>> +	/* EAS definitely does *not* handle SMT */
>>> +	if (sched_smt_active())
>
> Can you add a pr_warn() and use the current comment as the warning
> message? Since we have one for !Asym CPU capacity and !schedutil.
>
>>> +		goto free;
>>> +
>
> [...]
>
> There is this 'EAS can be used ...' list of currently 4 items in the
> build_perf_domains() function header. You could include 'X. No SMT
> support' there.
>  ;-)

Right, the rst doc says "EAS on SMT is not supported" but I think that can
be interpreted as "EAS on !asym SMT". I'll add the warning and update the
comment.