linux-kernel - Re: [PATCH 2/8] Add interface for queuing work on a specific CPU

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Date:	Mon, 11 Feb 2008 13:51:15 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jens Axboe <jens.axboe@...cle.com>, linux-kernel@...r.kernel.org,
	Alan.Brunelle@...com, arjan@...ux.intel.com, dgc@....com,
	npiggin@...e.de
Subject: Re: [PATCH 2/8] Add interface for queuing work on a specific CPU

Sorry for delay,

On 02/07, Andrew Morton wrote:
>
> On Thu,  7 Feb 2008 10:18:59 +0100 Jens Axboe <jens.axboe@...cle.com> wrote:
> 
> > --- a/kernel/workqueue.c
> > +++ b/kernel/workqueue.c
> > @@ -175,6 +175,21 @@ int fastcall queue_work(struct workqueue_struct *wq, struct work_struct *work)
> >  }
> >  EXPORT_SYMBOL_GPL(queue_work);
> >  
> > +int fastcall queue_work_on_cpu(struct workqueue_struct *wq,
> > +			       struct work_struct *work, int cpu)
> > +{
> > +	int ret = 0;
> > +
> > +	if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
> > +		BUG_ON(!list_empty(&work->entry));
> > +		__queue_work(per_cpu_ptr(wq->cpu_wq, cpu), work);
> > +		ret = 1;
> > +	}
> > +
> > +	return ret;
> > +}
> > +EXPORT_SYMBOL_GPL(queue_work_on_cpu);
> 
> Might as well change queue_work() to call this?

This is possible, but in that case queue_work_on_cpu() should use wq_per_cpu(),
not per_cpu_ptr(). (otherwise queue_work(single_threaded_wq) won't work).


A bit off-topic, the comment near queue_work() says

	* We queue the work to the CPU it was submitted, but there is no
	* guarantee that it will be processed by that CPU.

This is wrong. Unless cpu_down() happens, we do guarantee it will be processed
by that CPU. Perhaps it makes sense to fix the comment as well?

Oleg.

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