linux-kernel - Re: [PATCH 03/13] workqueue: don't set work cwq until we queued it on pool

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Date:	Wed, 6 Feb 2013 19:35:24 +0800
From:	Lai Jiangshan <eag0628@...il.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/13] workqueue: don't set work cwq until we queued it on pool

On Wed, Feb 6, 2013 at 12:45 AM, Tejun Heo <tj@...nel.org> wrote:
> Hey, Lai.
>
> On Tue, Feb 05, 2013 at 11:00:42PM +0800, Lai Jiangshan wrote:
>> The @cpu can be WORK_CPU_UNBOUND, and the current code will delay
>> to determine on which cpu should this work be queued until timeout,
>> I didn't want to change this behavior when I wrote the patch.
>
> Hmmm?  The current code determines the CPU on queue_delayed_work().
>
>         /*
>          * If we cannot get the last pool from @work directly,
>          * select the last CPU such that it avoids unnecessarily
>          * triggering non-reentrancy check in __queue_work().
>          */
>         lcpu = cpu;
>         if (pool)
>                 lcpu = pool->cpu;
>         if (lcpu == WORK_CPU_UNBOUND)
>                 lcpu = raw_smp_processor_id();
>
> @lcpu is never WORK_CPU_UNBOUND for bound workqueues and for unbound
> workqueues we of course have cwq for WORK_CPU_UNBOUND.


Are you sure?
@lcpu is only used when it tries to set cwq to work data without
breaking nrt logic.

void delayed_work_timer_fn(unsigned long __data)
{
	struct delayed_work *dwork = (struct delayed_work *)__data;
	struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);

	/* should have been called from irqsafe timer with irq already off */
	__queue_work(dwork->cpu, cwq->wq, &dwork->work);
}

>
>> PS, again, @cpu and @wq can be saved/encoded in dwork.work.entry if needed.
>
> If possible, I'd much prefer to keep it inside delayed_work() proper.
>
> Thanks.
>
> --
> tejun
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