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Date:   Tue, 25 May 2021 15:17:22 -0700 (PDT)
From:   Hugh Dickins <hughd@google.com>
To:     Peter Zijlstra <peterz@infradead.org>
cc:     Hugh Dickins <hughd@google.com>, linux-kernel@vger.kernel.org,
        rdunlap@infradead.org, joel@joelfernandes.org,
        Ingo Molnar <mingo@kernel.org>, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
        bristot@redhat.com, Valentin Schneider <valentin.schneider@arm.com>
Subject: Re: [PATCH] sched: Add CONFIG_SCHED_CORE help text
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On Tue, 25 May 2021, Peter Zijlstra wrote:

> Subject: sched: Add CONFIG_SCHED_CORE help text
> From: Peter Zijlstra <peterz@infradead.org>
> Date: Tue May 25 08:53:28 CEST 2021
> 
> Hugh noted that the SCHED_CORE Kconfig option could do with a help
> text.
> 
> Requested-by: Hugh Dickins <hughd@google.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>

Thanks,
Acked-by: Hugh Dickins <hughd@google.com>
if necessary (but there's more than enough of me there already).

> ---
>  kernel/Kconfig.preempt |   14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> --- a/kernel/Kconfig.preempt
> +++ b/kernel/Kconfig.preempt
> @@ -104,4 +104,18 @@ config SCHED_CORE
>  	bool "Core Scheduling for SMT"
>  	default y
>  	depends on SCHED_SMT
> +	help
> +	  This option permits Core Scheduling, a means of coordinated task
> +	  selection across SMT siblings. When enabled -- see
> +	  prctl(PR_SCHED_CORE) -- task selection ensures that all SMT siblings
> +	  will execute a task from the same 'core group', forcing idle when no
> +	  matching task is found.
> +
> +	  Use of this feature includes:
> +	   - mitigation of some (not all) SMT side channels;
> +	   - limiting SMT interference to improve determinism and/or performance.
> +
> +	  SCHED_CORE is default enabled when SCHED_SMT is enabled -- when
> +	  unused there should be no impact on performance.
> +