linux-kernel - Re: [PATCH] RT: Add priority-queuing and priority-inheritance to workqueue infrastructure

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Date:	Wed, 1 Aug 2007 22:12:53 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Daniel Walker <dwalker@...sta.com>, Ingo Molnar <mingo@...e.hu>,
	Gregory Haskins <ghaskins@...ell.com>,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] RT: Add priority-queuing and priority-inheritance to workqueue infrastructure

On 08/01, Peter Zijlstra wrote:
>
> On Tue, 2007-07-31 at 20:52 -0700, Daniel Walker wrote:
> 
> >  static void insert_work(struct cpu_workqueue_struct *cwq,
> >  				struct work_struct *work, int tail)
> >  {
> > +	int prio = current->normal_prio;
> > +
> >  	set_wq_data(work, cwq);
> >  	/*
> >  	 * Ensure that we get the right work->data if we see the
> >  	 * result of list_add() below, see try_to_grab_pending().
> >  	 */
> >  	smp_wmb();
> > -	if (tail)
> > -		list_add_tail(&work->entry, &cwq->worklist);
> > -	else
> > -		list_add(&work->entry, &cwq->worklist);
> > +	plist_node_init(&work->entry, prio);
> > +	plist_add(&work->entry, &cwq->worklist);

Sorry, this patch is completely wrong. It immediately breaks
flush_workqueue/cancel_workqueue functions.

And I personally think it is not very useful, even if it was correct.
You can create your own workqueue and change the priority of cwq->thread.

> > @@ -168,7 +171,7 @@ int fastcall queue_work(struct workqueue
> >  	int ret = 0, cpu = raw_smp_processor_id();
> >  
> >  	if (!test_and_set_bit(WORK_STRUCT_PENDING, work_data_bits(work))) {
> > -		BUG_ON(!list_empty(&work->entry));
> > +		BUG_ON(!plist_node_empty(&work->entry));
> >  		__queue_work(wq_per_cpu(wq, cpu), work);
> >  		ret = 1;

Side note, looks like you use some strange kernel. This raw_smp_processor_id()
above is wrong.

Oleg.

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