linux-kernel - Re: [PATCH 2/2 wq/for-3.9] workqueue: reimplement is_chained_work() using current_wq

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Message-ID: <511FBCA0.9020205@gmail.com>
Date:	Sun, 17 Feb 2013 01:06:40 +0800
From:	Lai Jiangshan <eag0628@...il.com>
To:	Tejun Heo <tj@...nel.org>
CC:	linux-kernel@...r.kernel.org, Lai Jiangshan <laijs@...fujitsu.com>
Subject: Re: [PATCH 2/2 wq/for-3.9] workqueue: reimplement is_chained_work()
 using current_wq_worker()

Hi, tj

Thank you for adding this one.

Would you deffer "workqueue: rename cpu_workqueue to pool_workqueue" a 
little? I don't want to rebase my almost-ready work again(not a good 
reason... but please...)

I will answer your other emails soon and sent the patches.

Thanks,
Lai

On 14/02/13 11:27, Tejun Heo wrote:
> is_chained_work() was added before current_wq_worker() and implemented
> its own ham-fisted way of finding out whether %current is a workqueue
> worker - it iterates through all possible workers.
>
> Drop the custom implementation and reimplement using
> current_wq_worker().
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> ---
>   kernel/workqueue.c |   33 ++++++++-------------------------
>   1 file changed, 8 insertions(+), 25 deletions(-)
>
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1159,35 +1159,18 @@ static void insert_work(struct cpu_workq
>
>   /*
>    * Test whether @work is being queued from another work executing on the
> - * same workqueue.  This is rather expensive and should only be used from
> - * cold paths.
> + * same workqueue.
>    */
>   static bool is_chained_work(struct workqueue_struct *wq)
>   {
> -	unsigned long flags;
> -	unsigned int cpu;
> +	struct worker *worker;
>
> -	for_each_cwq_cpu(cpu, wq) {
> -		struct cpu_workqueue_struct *cwq = get_cwq(cpu, wq);
> -		struct worker_pool *pool = cwq->pool;
> -		struct worker *worker;
> -		struct hlist_node *pos;
> -		int i;
> -
> -		spin_lock_irqsave(&pool->lock, flags);
> -		for_each_busy_worker(worker, i, pos, pool) {
> -			if (worker->task != current)
> -				continue;
> -			spin_unlock_irqrestore(&pool->lock, flags);
> -			/*
> -			 * I'm @worker, no locking necessary.  See if @work
> -			 * is headed to the same workqueue.
> -			 */
> -			return worker->current_cwq->wq == wq;
> -		}
> -		spin_unlock_irqrestore(&pool->lock, flags);
> -	}
> -	return false;
> +	worker = current_wq_worker();
> +	/*
> +	 * Return %true iff I'm a worker execuing a work item on @wq.  If
> +	 * I'm @worker, it's safe to dereference it without locking.
> +	 */
> +	return worker && worker->current_cwq->wq == wq;
>   }
>
>   static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
> --
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