linux-kernel - Re: [PATCH 04/10] workqueue: don't set the worker's cpumask when kthread_bind

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Date:   Wed, 16 Dec 2020 09:39:06 -0500
From:   Tejun Heo <tj@...nel.org>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 04/10] workqueue: don't set the worker's cpumask when
 kthread_bind_mask()

On Mon, Dec 14, 2020 at 11:54:51PM +0800, Lai Jiangshan wrote:
> @@ -1945,7 +1945,15 @@ static struct worker *create_worker(struct worker_pool *pool)
>  		goto fail;
>  
>  	set_user_nice(worker->task, pool->attrs->nice);
> -	kthread_bind_mask(worker->task, pool->attrs->cpumask);
> +
> +	/*
> +	 * Set PF_NO_SETAFFINITY via kthread_bind_mask().  We use
> +	 * cpu_possible_mask other than pool->attrs->cpumask, because
                             ^
                             instead of

> +	 * there might be no online cpu in the pool->attrs->cpumask.
                 ^
                 might not be any

> +	 * The cpumask of the worker will be set properly later in
> +	 * worker_attach_to_pool().
> +	 */
> +	kthread_bind_mask(worker->task, cpu_possible_mask);

This is a bit ugly but not the end of the world. Maybe we can move it to the
start of worker_thread() but that'd require an extra handshake. Oh well...

Thanks.

-- 
tejun