linux-kernel - Re: [PATCH 10/10 V2] workqueue: use generic attach/detach routine for rescuers

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Message-ID: <20140512220505.GI18959@mtj.dyndns.org>
Date:	Mon, 12 May 2014 18:05:05 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/10 V2] workqueue: use generic attach/detach routine
 for rescuers

On Mon, May 12, 2014 at 02:56:22PM +0800, Lai Jiangshan wrote:
> There are several problems with the code that rescuers bind itself to the pool'
> cpumask
>   1) It uses a way different from the normal workers to bind to the cpumask
>      So we can't maintain the normal/rescuer workers under the same framework.
>   2) The the code of cpu-binding for rescuer is complicated
>   3) If one or more cpuhotplugs happen while the rescuer processes the
>      scheduled works, the rescuer may not be correctly bound to the cpumask of
>      the pool. This is allowed behavior, but is not good. It will be better
>      if the cpumask of the rescuer is always kept coordination with the pool
>      across any cpuhotplugs.
> 
> Using generic attach/detach routine will solve the above problems,
> and result much more simple code.
> 
> Signed-off-by: Lai Jiangshan <laijs@...fujitsu.com>
>  static struct worker *alloc_worker(void)
>  {
>  	struct worker *worker;
> @@ -2343,8 +2279,9 @@ repeat:
>  
>  		spin_unlock_irq(&wq_mayday_lock);
>  
> -		/* migrate to the target cpu if possible */
> -		worker_maybe_bind_and_lock(pool);
> +		worker_attach_to_pool(rescuer, pool);
> +
> +		spin_lock_irq(&pool->lock);
>  		rescuer->pool = pool;
>  
>  		/*
> @@ -2357,6 +2294,11 @@ repeat:
>  				move_linked_works(work, scheduled, &n);
>  
>  		process_scheduled_works(rescuer);
> +		spin_unlock_irq(&pool->lock);
> +
> +		worker_detach_from_pool(rescuer, pool);
> +
> +		spin_lock_irq(&pool->lock);

Ah, right, this is how it's used.  Yeah, it makes sense.  In a long
patchset, it usually helps to mention your intentions when structuring
functions tho.  When you're separating out detach_from_pool, just
mention that the function will later be used to make rescuers use the
same attach/detach framework as normal workers.

How has this been tested?

Thanks.

-- 
tejun
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