linux-kernel - Re: [PATCH v4 14/15] Remove the ext server BW before changing tasks to FAIR

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aFHTSJzanNYjIwJt@gpd4>
Date: Tue, 17 Jun 2025 22:42:48 +0200
From: Andrea Righi <arighi@...dia.com>
To: Joel Fernandes <joelagnelf@...dia.com>
Cc: linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
	David Vernet <void@...ifault.com>,
	Changwoo Min <changwoo@...lia.com>, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	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>
Subject: Re: [PATCH v4 14/15] Remove the ext server BW before changing tasks
 to FAIR

Hi Joel,

On Tue, Jun 17, 2025 at 04:05:17PM -0400, Joel Fernandes wrote:
> Signed-off-by: Joel Fernandes <joelagnelf@...dia.com>
> ---
>  kernel/sched/ext.c | 39 +++++++++++++++++++++++++--------------
>  1 file changed, 25 insertions(+), 14 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 84ccab8cb838..23e5711bc4fc 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -4960,6 +4960,31 @@ static void scx_disable_workfn(struct kthread_work *work)
>  
>  	scx_init_task_enabled = false;
>  
> +	for_each_possible_cpu(cpu) {
> +		struct rq *rq = cpu_rq(cpu);
> +		struct rq_flags rf;
> +
> +		/*
> +		 * Invalidate all the rq clocks to prevent getting outdated
> +		 * rq clocks from a previous scx scheduler.
> +		 */
> +		scx_rq_clock_invalidate(rq);

We're also calling scx_rq_clock_invalidate(rq) twice (see below).

> +
> +		/*
> +		 * We are unloading the sched_ext scheduler, we do not need its
> +		 * DL server bandwidth anymore, remove it for all CPUs. Whenever
> +		 * the first SCX task is enqueued (when scx is re-loaded), its DL
> +		 * server bandwidth will be re-initialized.
> +		 */
> +		rq_lock_irqsave(rq, &rf);
> +		update_rq_clock(rq);
> +		if (dl_server_active(&rq->ext_server))
> +			dl_server_stop(&rq->ext_server);
> +		dl_server_remove_params(&rq->ext_server);
> +		rq_unlock_irqrestore(rq, &rf);
> +	}
> +
> +
>  	scx_task_iter_start(&sti);
>  	while ((p = scx_task_iter_next_locked(&sti))) {
>  		const struct sched_class *old_class = p->sched_class;
> @@ -4985,26 +5010,12 @@ static void scx_disable_workfn(struct kthread_work *work)
>  
>  	for_each_possible_cpu(cpu) {
>  		struct rq *rq = cpu_rq(cpu);
> -		struct rq_flags rf;
>  
>  		/*
>  		 * Invalidate all the rq clocks to prevent getting outdated
>  		 * rq clocks from a previous scx scheduler.
>  		 */
>  		scx_rq_clock_invalidate(rq);
> -
> -		/*
> -		 * We are unloading the sched_ext scheduler, we do not need its
> -		 * DL server bandwidth anymore, remove it for all CPUs. Whenever
> -		 * the first SCX task is enqueued (when scx is re-loaded), its DL
> -		 * server bandwidth will be re-initialized.
> -		 */
> -		rq_lock_irqsave(rq, &rf);
> -		update_rq_clock(rq);
> -		if (dl_server_active(&rq->ext_server))
> -			dl_server_stop(&rq->ext_server);
> -		dl_server_remove_params(&rq->ext_server);
> -		rq_unlock_irqrestore(rq, &rf);
>  	}

We should probably remove this for_each_possible_cpu() completely.

>  
>  	/* no task is on scx, turn off all the switches and flush in-progress calls */
> -- 
> 2.43.0
> 

Thanks,
-Andrea