linux-kernel - Re: [PATCH 02/14] sched/debug: Stop and start server based on if it was active

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Message-ID: <aPX86h9lSEZh0YP2@jlelli-thinkpadt14gen4.remote.csb>
Date: Mon, 20 Oct 2025 11:12:10 +0200
From: Juri Lelli <juri.lelli@...hat.com>
To: Andrea Righi <arighi@...dia.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Joel Fernandes <joelagnelf@...dia.com>, Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Shuah Khan <shuah@...nel.org>,
	sched-ext@...ts.linux.dev, bpf@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/14] sched/debug: Stop and start server based on if it
 was active

Hi!

On 17/10/25 11:25, Andrea Righi wrote:
> From: Joel Fernandes <joelagnelf@...dia.com>
> 
> Currently the DL server interface for applying parameters checks
> CFS-internals to identify if the server is active. This is error-prone
> and makes it difficult when adding new servers in the future.
> 
> Fix it, by using dl_server_active() which is also used by the DL server
> code to determine if the DL server was started.
> 
> Acked-by: Tejun Heo <tj@...nel.org>
> Reviewed-by: Andrea Righi <arighi@...dia.com>
> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
> ---
>  kernel/sched/debug.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
> index 6cf9be6eea49a..e71f6618c1a6a 100644
> --- a/kernel/sched/debug.c
> +++ b/kernel/sched/debug.c
> @@ -354,6 +354,8 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
>  		return err;
>  
>  	scoped_guard (rq_lock_irqsave, rq) {
> +		bool is_active;
> +
>  		runtime  = rq->fair_server.dl_runtime;
>  		period = rq->fair_server.dl_period;
>  
> @@ -376,8 +378,11 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
>  			return  -EINVAL;
>  		}
>  
> -		update_rq_clock(rq);
> -		dl_server_stop(&rq->fair_server);
> +		is_active = dl_server_active(&rq->fair_server);
> +		if (is_active) {
> +			update_rq_clock(rq);
> +			dl_server_stop(&rq->fair_server);
> +		}

Won't this reintroduce what bb4700adc3abe ("sched/deadline: Always stop
dl-server before changing parameters") fixed?

Thanks,
Juri