linux-kernel - Re: [PATCH 1/10] PM: Rework handling of interrupts during suspend-resume (rev. 5)

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Message-ID: <alpine.LFD.2.00.0903112342440.29264@localhost.localdomain>
Date:	Wed, 11 Mar 2009 23:45:48 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Ingo Molnar <mingo@...e.hu>,
	pm list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Len Brown <lenb@...nel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Frans Pop <elendil@...net.nl>,
	Arve Hjønnevåg <arve@...roid.com>
Subject: Re: [PATCH 1/10] PM: Rework handling of interrupts during suspend-resume
 (rev. 5)

On Wed, 11 Mar 2009, Thomas Gleixner wrote:
> On Wed, 11 Mar 2009, Rafael J. Wysocki wrote:
> > On Wednesday 11 March 2009, Thomas Gleixner wrote:
> > > > +EXPORT_SYMBOL_GPL(suspend_device_irqs);
> > > 
> > >   I'm not too enthusiastic about this open coded implementation of
> > >   disable_irq() with slightly different semantics.
> > 
> > The difference in semantics is important IMO, otherwise I woulndn't have
> > done that.  In particular, IMO, the condition should be under the spinlock IMO
> > and I'd rather not synchronize all interrupts we don't really disable here.
> 
> I don't say that the difference is not relevant. But the code is
> almost the same and disable_irq() could have the sync_irq optimization
> as well.

Thought more about that. Avoiding the sync_irq() for irqs which have
no action associated is fine, but you need to catch the following case
as well:

   driver code calls disable_irq_nosyc() from the handler (which is
   still running)

   suspend code skips the sync due to depth > 0

The sync operation is not that expensive.

Thanks,

	tglx
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