linux-kernel - Re: [PATCH 1/2] sched: Add default dynamic preempt mode Kconfig

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Date:   Tue, 8 Jun 2021 15:55:59 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Frederic Weisbecker <frederic@...nel.org>
Cc:     Ingo Molnar <mingo@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] sched: Add default dynamic preempt mode Kconfig

On Tue, Jun 08, 2021 at 02:04:41PM +0200, Frederic Weisbecker wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 9e9a5be35cde..df47a8275c37 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6238,6 +6238,14 @@ enum {
>  
>  int preempt_dynamic_mode = preempt_dynamic_full;
>  
> +#if defined(CONFIG_PREEMPT_DYNAMIC_FULL)
> +static __initdata int preempt_dynamic_mode_init = preempt_dynamic_full;
> +#elif defined(CONFIG_PREEMPT_DYNAMIC_VOLUNTARY)
> +static __initdata int preempt_dynamic_mode_init = preempt_dynamic_voluntary;
> +#elif defined(CONFIG_PREEMPT_DYNAMIC_NONE)
> +static __initdata int preempt_dynamic_mode_init = preempt_dynamic_none;
> +#endif

Why does preempt_dynamic_mode_init exist? Why can't we simply set
preempt_dynamic_mode?