linux-kernel - Re: [update 2] Re: [RFC][PATCH] PM: Avoid losing wakeup events during suspend

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Date:	Fri, 25 Jun 2010 22:37:50 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Florian Mickler <florian@...kler.org>,
	"Linux-pm mailing list" <linux-pm@...ts.linux-foundation.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Arve Hjønnevåg <arve@...roid.com>,
	Neil Brown <neilb@...e.de>, mark gross <640e9920@...il.com>
Subject: Re: [update 2] Re: [RFC][PATCH] PM: Avoid losing wakeup events during suspend

On Friday, June 25, 2010, Alan Stern wrote:
> On Fri, 25 Jun 2010, Rafael J. Wysocki wrote:
> 
> > > That's not the point.  If a wakeup handler queues a work item (for
> > > example, by calling pm_request_resume) then it wouldn't need to guess a
> > > timeout.  The work item would be guaranteed to run before the system
> > > could suspend again.
> > 
> > You seem to be referring to the PM workqueue specifically.  Perhaps it would be
> > better to special-case it and stop it by adding a barrier work during suspend
> > instead of just freezing?  Then, it wouldn't need to be singlethread any more.
> 
> The barrier work would have to be queued to each CPU's thread.  That
> would be okay.

I guess we should stop the PM workqueue after the freezing of tasks, shouldn't we?

> Hmm, it looks like wait_event_freezable() and
> wait_event_freezable_timeout() could use similar changes: If the
> condition is true then they shouldn't try to freeze the caller.

Yes, but that should be a separate patch IMHO.

Rafael
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