linux-kernel - Re: [PATCH v2 1/1] wq: Avoid using isolated cpus' timers on queue_delayed

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Message-ID: <ZbhPWSWAZZo8gk-a@slm.duckdns.org>
Date: Mon, 29 Jan 2024 15:22:33 -1000
From: Tejun Heo <tj@...nel.org>
To: Leonardo Bras <leobras@...hat.com>
Cc: Lai Jiangshan <jiangshanlai@...il.com>, linux-kernel@...r.kernel.org,
	Junyao Zhao <junzhao@...hat.com>
Subject: Re: [PATCH v2 1/1] wq: Avoid using isolated cpus' timers on
 queue_delayed_work

On Mon, Jan 29, 2024 at 10:00:46PM -0300, Leonardo Bras wrote:
> When __queue_delayed_work() is called, it chooses a cpu for handling the
> timer interrupt. As of today, it will pick either the cpu passed as
> parameter or the last cpu used for this.
> 
> This is not good if a system does use CPU isolation, because it can take
> away some valuable cpu time to:
> 1 - deal with the timer interrupt,
> 2 - schedule-out the desired task,
> 3 - queue work on a random workqueue, and
> 4 - schedule the desired task back to the cpu.
> 
> So to fix this, during __queue_delayed_work(), if cpu isolation is in
> place, pick a random non-isolated cpu to handle the timer interrupt.
> 
> As an optimization, if the current cpu is not isolated, use it instead
> of looking for another candidate.
> 
> Signed-off-by: Leonardo Bras <leobras@...hat.com>

Applied to wq/for-6.9.

Thanks.

-- 
tejun