linux-kernel - Re: [PATCH] sched/isolation: Make CPU_ISOLATION depend on SMP or COMPILE

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Date:   Tue, 2 Jan 2018 18:25:10 -0500 (EST)
From:   Nicolas Pitre <nicolas.pitre@...aro.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
cc:     Frederic Weisbecker <frederic@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/isolation: Make CPU_ISOLATION depend on SMP or
 COMPILE_TEST

On Tue, 2 Jan 2018, Geert Uytterhoeven wrote:

> On uniprocessor systems, critical and non-critical tasks cannot be
> isolated, as there is only a single CPU core.  Hence enabling CPU
> isolation by default on such systems does not make much sense.
> 
> Instead of changing the default for !SMP, fix this by making the feature
> depend on SMP, with an override for compile-testing.  Note that its sole
> selector (NO_HZ_FULL) already depends on SMP.
> 
> This decreases kernel size for a default uniprocessor kernel by ca. 1
> KiB.
> 
> Fixes: 2c43838c99d9d23f ("sched/isolation: Enable CONFIG_CPU_ISOLATION=y by default")
> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>

Acked-by: Nicolas Pitre <nico@...aro.org>


> ---
>  init/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index 690a381adee0d164..c1221332e128c700 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -461,6 +461,7 @@ endmenu # "CPU/Task time and stats accounting"
>  
>  config CPU_ISOLATION
>  	bool "CPU isolation"
> +	depends on SMP || COMPILE_TEST
>  	default y
>  	help
>  	  Make sure that CPUs running critical tasks are not disturbed by
> -- 
> 2.7.4
> 
>