linux-kernel - Re: [PATCH 02/23] sched,bL_switcher: Convert to sched_set

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Message-ID: <nycvar.YSQ.7.76.2004220926280.2671@knanqh.ubzr>
Date:   Wed, 22 Apr 2020 09:27:04 -0400 (EDT)
From:   Nicolas Pitre <nico@...xnic.net>
To:     Peter Zijlstra <peterz@...radead.org>
cc:     mingo@...nel.org, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        rostedt@...dmis.org, qais.yousef@....com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, rmk+kernel@....linux.org.uk
Subject: Re: [PATCH 02/23] sched,bL_switcher: Convert to sched_set_fifo*()

On Wed, 22 Apr 2020, Peter Zijlstra wrote:

> Because SCHED_FIFO is a broken scheduler model (see previous patches)
> take away the priority field, the kernel can't possibly make an
> informed decision.
> 
> In this case, use fifo_low, because it only cares about being above
> SCHED_NORMAL. Effectively no change in behaviour.
> 
> Cc: nico@...xnic.net
> Cc: rmk+kernel@....linux.org.uk
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Reviewed-by: Ingo Molnar <mingo@...nel.org>

Acked-by: Nicolas Pitre <nico@...xnic.net>

> ---
>  arch/arm/common/bL_switcher.c |    3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> --- a/arch/arm/common/bL_switcher.c
> +++ b/arch/arm/common/bL_switcher.c
> @@ -270,12 +270,11 @@ static struct bL_thread bL_threads[NR_CP
>  static int bL_switcher_thread(void *arg)
>  {
>  	struct bL_thread *t = arg;
> -	struct sched_param param = { .sched_priority = 1 };
>  	int cluster;
>  	bL_switch_completion_handler completer;
>  	void *completer_cookie;
>  
> -	sched_setscheduler_nocheck(current, SCHED_FIFO, &param);
> +	sched_set_fifo_low(current);
>  	complete(&t->started);
>  
>  	do {
> 
> 
>