Subject: Re: [PATCH] RT: Add priority-queuing and priority-inheritance to
	workqueue infrastructure
From: Daniel Walker <dwalker@mvista.com>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@elte.hu>,
       Gregory Haskins <ghaskins@novell.com>, linux-rt-users@vger.kernel.org,
       linux-kernel@vger.kernel.org
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Date: Wed, 01 Aug 2007 14:02:25 -0700
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On Thu, 2007-08-02 at 00:50 +0400, Oleg Nesterov wrote:
> On 08/01, Daniel Walker wrote:
> >
> > On Thu, 2007-08-02 at 00:18 +0400, Oleg Nesterov wrote:
> > > 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.
> > 
> > It's translating priorities through the work queues, which doesn't seem
> > to happen with the current implementation. A high priority, say
> > SCHED_FIFO priority 99, task may have to wait for a nice -5 work queue
> > to finish..
> 
> Why should that task wait?

If the high priority tasks is waiting for the work to complete..
Assuming the scenario happens which your more likely to know than me.. 

I suppose in the flush_workqueue situation a thread could be waiting on
the lower priority work queue ..

> > > What about delayed_work? insert_work() will use ->normal_prio of
> > > the random interrupted process, while queue_work() uses current.
> > 
> > Actually it would be the priority of the timer softirq .. I think what
> > is desired here would be saving the priority of the task calling
> > delayed_work then using that..
> 
> But mainline calls  __do_softirq() from interrupt (irq_exit).

Yeah, I suppose your right in that case .. In -rt softirq's are all in
threads so it would be the timer softirq thread..

Daniel

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