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From: Valentin Schneider <valentin.schneider@arm.com>
To: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: linux-kernel@vger.kernel.org,
	Lai Jiangshan <laijs@linux.alibaba.com>,
	Qian Cai <cai@redhat.com>, Peter Zijlstra <peterz@infradead.org>,
	Vincent Donnefort <vincent.donnefort@arm.com>,
	Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 10/10] workqueue: Fix affinity of kworkers when attaching into pool
Date: Tue, 15 Dec 2020 15:03:20 +0000	[thread overview]
Message-ID: <jhjczzbt8lj.mognet@arm.com> (raw)
In-Reply-To: <20201214155457.3430-11-jiangshanlai@gmail.com>


On 14/12/20 15:54, Lai Jiangshan wrote:
> @@ -1848,11 +1848,11 @@ static void worker_attach_to_pool(struct worker *worker,
>  {
>       mutex_lock(&wq_pool_attach_mutex);
>
> -	/*
> -	 * set_cpus_allowed_ptr() will fail if the cpumask doesn't have any
> -	 * online CPUs.  It'll be re-applied when any of the CPUs come up.
> -	 */
> -	set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask);
> +	/* Is there any cpu in pool->attrs->cpumask online? */
> +	if (cpumask_any_and(pool->attrs->cpumask, wq_online_cpumask) < nr_cpu_ids)

  if (cpumask_intersects(pool->attrs->cpumask, wq_online_cpumask))

> +		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, pool->attrs->cpumask) < 0);
> +	else
> +		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);

So for that late-spawned per-CPU kworker case: the outgoing CPU should have
already been cleared from wq_online_cpumask, so it gets its affinity reset
to the possible mask and the subsequent wakeup will ensure it's put on an
active CPU.

Seems alright to me.

>
>       /*
>        * The wq_pool_attach_mutex ensures %POOL_DISASSOCIATED remains

  reply	other threads:[~2020-12-15 15:05 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-14 15:54 [PATCH 00/10] workqueue: break affinity initiatively Lai Jiangshan
2020-12-14 15:54 ` [PATCH 01/10] workqueue: restore unbound_workers' cpumask correctly Lai Jiangshan
2020-12-14 15:54 ` [PATCH 02/10] workqueue: use cpu_possible_mask instead of cpu_active_mask to break affinity Lai Jiangshan
2020-12-14 17:25   ` Peter Zijlstra
2020-12-15  8:33     ` Lai Jiangshan
2020-12-15  8:40     ` Peter Zijlstra
2020-12-16 14:32   ` Tejun Heo
2020-12-14 15:54 ` [PATCH 03/10] workqueue: Manually break affinity on pool detachment Lai Jiangshan
2020-12-14 15:54 ` [PATCH 04/10] workqueue: don't set the worker's cpumask when kthread_bind_mask() Lai Jiangshan
2020-12-16 14:39   ` Tejun Heo
2020-12-14 15:54 ` [PATCH 05/10] workqueue: introduce wq_online_cpumask Lai Jiangshan
2020-12-14 15:54 ` [PATCH 06/10] workqueue: use wq_online_cpumask in restore_unbound_workers_cpumask() Lai Jiangshan
2020-12-14 15:54 ` [PATCH 07/10] workqueue: Manually break affinity on hotplug for unbound pool Lai Jiangshan
2020-12-16 14:50   ` Tejun Heo
2020-12-14 15:54 ` [PATCH 08/10] workqueue: reorganize workqueue_online_cpu() Lai Jiangshan
2020-12-14 15:54 ` [PATCH 09/10] workqueue: reorganize workqueue_offline_cpu() unbind_workers() Lai Jiangshan
2020-12-14 15:54 ` [PATCH 10/10] workqueue: Fix affinity of kworkers when attaching into pool Lai Jiangshan
2020-12-15 15:03   ` Valentin Schneider [this message]
2020-12-14 17:36 ` [PATCH 00/10] workqueue: break affinity initiatively Peter Zijlstra
2020-12-15  5:44   ` Lai Jiangshan
2020-12-15  7:50     ` Peter Zijlstra
2020-12-15  8:14       ` Lai Jiangshan
2020-12-15  8:49         ` Peter Zijlstra
2020-12-15  9:46           ` Lai Jiangshan
2020-12-16 14:30 ` Tejun Heo

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