linux-kernel - Re: [PATCH] workqueue: Create kworker only for boot CPU pool prior SMP initialization

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Date:   Mon, 4 Apr 2022 07:40:04 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     jiangshanlai@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: Create kworker only for boot CPU pool prior
 SMP initialization

On Thu, Mar 31, 2022 at 09:14:35PM +0800, Zqiang wrote:
> The workqueue_init() is called before SMP initialization, which
> means only the boot CPU is online, just create kworker for boot
> CPU pool.
> 
> Signed-off-by: Zqiang <qiang1.zhang@...el.com>
> ---
>  kernel/workqueue.c | 8 +++-----
>  1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index abcc9a2ac319..3948babe02d5 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -6120,11 +6120,9 @@ void __init workqueue_init(void)
>  	mutex_unlock(&wq_pool_mutex);
>  
>  	/* create the initial workers */
> -	for_each_online_cpu(cpu) {
> -		for_each_cpu_worker_pool(pool, cpu) {
> -			pool->flags &= ~POOL_DISASSOCIATED;
> -			BUG_ON(!create_worker(pool));
> -		}
> +	for_each_cpu_worker_pool(pool, smp_processor_id()) {
> +		pool->flags &= ~POOL_DISASSOCIATED;
> +		BUG_ON(!create_worker(pool));

I mean, I guess this would work but what's the benefit? It doesn't make any
practical difference and the code is now more fragile to external changes.

Thanks.

-- 
tejun