linux-kernel - Re: [PATCH] sched/fair: use RETRY_TASK in idle

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Message-ID: <20180426114956.GJ4064@hirez.programming.kicks-ass.net>
Date:   Thu, 26 Apr 2018 13:49:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>
Cc:     mingo@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: use RETRY_TASK in idle_balance

On Thu, Apr 26, 2018 at 12:37:02PM +0200, Vincent Guittot wrote:
> Use RETRY_TASK in idle_balance when we want select_task_rq() function to 
> rerun the complete task selection path
> 
> Signed-off-by: Vincent Guittot <vincent.guittot@...aro.org>
> ---
>  kernel/sched/fair.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 0951d1c..ba49f83 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -9862,7 +9862,7 @@ static int idle_balance(struct rq *this_rq, struct rq_flags *rf)
>  
>  	/* Is there a task of a high priority class? */
>  	if (this_rq->nr_running != this_rq->cfs.h_nr_running)
> -		pulled_task = -1;
> +		pulled_task = RETRY_TASK;

This doesn't make sense, pulled_task is an integer, not a task pointer.
Also see how the caller in select_task_rq_fair() converts a negative
into RETRY_TASK.