linux-kernel - Re: [PATCH 06/10] sched: server: Don't start hrtick for DL server tasks

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Date: Wed, 21 Feb 2024 09:39:59 +0100
From: Daniel Bristot de Oliveira <bristot@...hat.com>
To: "Joel Fernandes (Google)" <joel@...lfernandes.org>,
 linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>,
 Vincent Guittot <vincent.guittot@...aro.org>
Cc: Suleiman Souhlal <suleiman@...gle.com>,
 Youssef Esmat <youssefesmat@...gle.com>, David Vernet <void@...ifault.com>,
 Thomas Gleixner <tglx@...utronix.de>, "Paul E . McKenney"
 <paulmck@...nel.org>, joseph.salisbury@...onical.com,
 Luca Abeni <luca.abeni@...tannapisa.it>,
 Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
 Vineeth Pillai <vineeth@...byteword.org>,
 Shuah Khan <skhan@...uxfoundation.org>, Phil Auld <pauld@...hat.com>,
 Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
 Valentin Schneider <vschneid@...hat.com>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH 06/10] sched: server: Don't start hrtick for DL server
 tasks

On 2/16/24 19:31, Joel Fernandes (Google) wrote:
> From: Suleiman Souhlal <suleiman@...gle.com>
> 
> Otherwise, we might start it even for tasks in a sched class that should
> have it off.

If the task is fair, but it is running inside a DL reservation, we want the
hrtick for the dl reservation.

This is one of the reasons why we are moving to the DL server, having microseconds
granularity for the boost duration (runtime).

-- Daniel

> 
> Signed-off-by: Suleiman Souhlal <suleiman@...gle.com>
> ---
>  kernel/sched/deadline.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 8fafe3f8b59c..5adfc15803c3 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -2325,11 +2325,12 @@ static struct task_struct *pick_next_task_dl(struct rq *rq)
>  	if (!p)
>  		return p;
>  
> -	if (!p->dl_server)
> +	if (!p->dl_server) {
>  		set_next_task_dl(rq, p, true);
>  
> -	if (hrtick_enabled(rq))
> -		start_hrtick_dl(rq, &p->dl);
> +		if (hrtick_enabled(rq))
> +			start_hrtick_dl(rq, &p->dl);
> +	}
>  
>  	return p;
>  }