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

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Date:	Thu, 2 Aug 2007 00:18:02 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Daniel Walker <dwalker@...sta.com>
Cc:	Peter Zijlstra <peterz@...radead.org>, 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, Daniel Walker wrote:
>
> On Wed, 2007-08-01 at 22:12 +0400, Oleg Nesterov wrote:
> 
> > 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.
> 
> This change is more dynamic than than just setting a single priority ..
> There was some other work going on around this, so it's not totally
> clear what the benefits are ..

Yes, I see. But still I think the whole idea is broken, not just the
implementation.

What about delayed_work? insert_work() will use ->normal_prio of
the random interrupted process, while queue_work() uses current.

What if a niced thread queues the work? This work may have no chance
to run if workqueue is actively used.

And I don't understand why rt_mutex_setprio() is called just before
calling work->func(). This means that a high-priority work could
be delayed by the low-priority ->current_work.

> > > > @@ -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.
> 
> As the topic suggests , it's a Real Time kernel .. I can give you a link
> where to download it if you want.

Ok, thanks, I'll take a look. Still, we can't use raw_smp_processor_id()
unless we disabled cpu-hotplug.

Oleg.

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