linux-kernel - Re: [PATCH 07/14] sched/debug: Add support to change sched

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Message-ID: <aPYu_obVO4QjbqUL@jlelli-thinkpadt14gen4.remote.csb>
Date: Mon, 20 Oct 2025 14:45:50 +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 07/14] sched/debug: Add support to change sched_ext
 server params

Hi!

On 17/10/25 11:25, Andrea Righi wrote:
> From: Joel Fernandes <joelagnelf@...dia.com>
> 
> When a sched_ext server is loaded, tasks in CFS are converted to run in
> sched_ext class. Add support to modify the ext server parameters similar
> to how the fair server parameters are modified.
> 
> Re-use common code between ext and fair servers as needed.
> 
> [ arighi: Use dl_se->dl_server to determine if dl_se is a DL server, as
>           suggested by PeterZ. ]
> 
> Co-developed-by: Andrea Righi <arighi@...dia.com>
> Signed-off-by: Andrea Righi <arighi@...dia.com>
> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
> ---

...

> @@ -373,25 +375,25 @@ static ssize_t sched_fair_server_write(struct file *filp, const char __user *ubu
>  		}
>  
>  		if (runtime > period ||
> -		    period > fair_server_period_max ||
> -		    period < fair_server_period_min) {
> +		    period > dl_server_period_max ||
> +		    period < dl_server_period_min) {
>  			return  -EINVAL;
>  		}
>  
> -		is_active = dl_server_active(&rq->fair_server);
> +		is_active = dl_server_active(dl_se);
>  		if (is_active) {
>  			update_rq_clock(rq);
> -			dl_server_stop(&rq->fair_server);
> +			dl_server_stop(dl_se);
>  		}
>  
> -		retval = dl_server_apply_params(&rq->fair_server, runtime, period, 0);
> +		retval = dl_server_apply_params(dl_se, runtime, period, 0);
>  
>  		if (!runtime)
> -			printk_deferred("Fair server disabled in CPU %d, system may crash due to starvation.\n",
> -					cpu_of(rq));
> +			printk_deferred("%s server disabled on CPU %d, system may crash due to starvation.\n",
> +					server == &rq->fair_server ? "Fair" : "Ext", cpu_of(rq));

Guess this might get convoluted if are ever going to add an additional
dl-server, but I fail to see that happening atm (to service what?).

Reviewed-by: Juri Lelli <juri.lelli@...hat.com>

Thanks,
Juri