linux-kernel - Re: [PATCH 20/23] sched,rcutorture: Convert to sched_set_fifo

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Message-ID: <20200422155158.GV17661@paulmck-ThinkPad-P72>
Date:   Wed, 22 Apr 2020 08:51:58 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
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
Subject: Re: [PATCH 20/23] sched,rcutorture: Convert to sched_set_fifo_low()

On Wed, Apr 22, 2020 at 01:27:39PM +0200, 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.
> 
> Effectively no change.
> 
> Cc: paulmck@...nel.org
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Reviewed-by: Ingo Molnar <mingo@...nel.org>

Reviewed-by: Paul E. McKenney <paulmck@...nel.org>

> ---
>  kernel/rcu/rcutorture.c |    4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -802,13 +802,11 @@ static int rcu_torture_boost(void *arg)
>  	unsigned long endtime;
>  	unsigned long oldstarttime;
>  	struct rcu_boost_inflight rbi = { .inflight = 0 };
> -	struct sched_param sp;
>  
>  	VERBOSE_TOROUT_STRING("rcu_torture_boost started");
>  
>  	/* Set real-time priority. */
> -	sp.sched_priority = 1;
> -	if (sched_setscheduler(current, SCHED_FIFO, &sp) < 0) {
> +	if (sched_set_fifo_low(current) < 0) {
>  		VERBOSE_TOROUT_STRING("rcu_torture_boost RT prio failed!");
>  		n_rcu_torture_boost_rterror++;
>  	}
> 
>