linux-kernel - Re: [PATCH V3] sched/deadline: Update rq_clock of later

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Message-ID: <20180720124615.GM2476@hirez.programming.kicks-ass.net>
Date:   Fri, 20 Jul 2018 14:46:15 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Daniel Bristot de Oliveira <bristot@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Clark Williams <williams@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Luca Abeni <luca.abeni@...tannapisa.it>,
        Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...nel.org>, stable@...r.kernel.org
Subject: Re: [PATCH V3] sched/deadline: Update rq_clock of later_rq when
 pushing a task

On Fri, Jul 20, 2018 at 11:16:30AM +0200, Daniel Bristot de Oliveira wrote:
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index fbfc3f1d368a..8b50eea4b607 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -2090,8 +2090,14 @@ static int push_dl_task(struct rq *rq)
>  	sub_rq_bw(&next_task->dl, &rq->dl);
>  	set_task_cpu(next_task, later_rq->cpu);
>  	add_rq_bw(&next_task->dl, &later_rq->dl);
> +
> +	/*
> +	 * Update the later_rq clock here, because the clock is used
> +	 * by the cpufreq_update_util() inside __add_running_bw().
> +	 */
> +	update_rq_clock(later_rq);
>  	add_running_bw(&next_task->dl, &later_rq->dl);
> -	activate_task(later_rq, next_task, 0);
> +	activate_task(later_rq, next_task, ENQUEUE_NOCLOCK);
>  	ret = 1;
>  
>  	resched_curr(later_rq);

Why isn't push_rt_task() affected by the very same issue?