linux-kernel - Re: [PATCH v2 5/7] sched/preempt: add PREEMPT

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Message-ID: <20220207115708.GA514319@lothringen>
Date:   Mon, 7 Feb 2022 12:57:08 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, ardb@...nel.org,
        bp@...en8.de, catalin.marinas@....com, dave.hansen@...ux.intel.com,
        james.morse@....com, joey.gouly@....com, juri.lelli@...hat.com,
        linux-kernel@...r.kernel.org, luto@...nel.org, mingo@...hat.com,
        peterz@...radead.org, tglx@...utronix.de,
        valentin.schneider@....com, will@...nel.org
Subject: Re: [PATCH v2 5/7] sched/preempt: add PREEMPT_DYNAMIC using static
 keys

On Fri, Feb 04, 2022 at 03:05:55PM +0000, Mark Rutland wrote:
> diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
> index dfd84c59b144..141952f4fee8 100644
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -456,13 +456,19 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
>   */
>  void raw_irqentry_exit_cond_resched(void);
>  #ifdef CONFIG_PREEMPT_DYNAMIC
> +#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
>  #define irqentry_exit_cond_resched_dynamic_enabled	raw_irqentry_exit_cond_resched
>  #define irqentry_exit_cond_resched_dynamic_disabled	NULL
>  DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
>  #define irqentry_exit_cond_resched()	static_call(irqentry_exit_cond_resched)()
> -#else
> -#define irqentry_exit_cond_resched()	raw_irqentry_exit_cond_resched()
> +#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
> +DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);

If CONFIG_PREEMPT && CONFIG_PREEMPT_DYNAMIC and no "preempt=" parameter is
passed, nothing is overriden on boot. So you need to either have cond_resched
and might_resched initially disabled (STATIC_KEY_FALSE?) or call
sched_dynamic_update() from preempt_dynamic_init() also when CONFIG_PREEMPT=y.

Thanks.