linux-kernel - Re: [PATCH 03/10] freezer: add new freezable helpers using freezer_do_not

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Message-ID: <20130502134646.GA24576@amd.pavel.ucw.cz>
Date:	Thu, 2 May 2013 15:46:46 +0200
From:	Pavel Machek <pavel@....cz>
To:	Oliver Neukum <oneukum@...e.de>
Cc:	Colin Cross <ccross@...roid.com>, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	arve@...roid.com, Len Brown <len.brown@...el.com>
Subject: Re: [PATCH 03/10] freezer: add new freezable helpers using
 freezer_do_not_count()

On Thu 2013-05-02 15:05:13, Oliver Neukum wrote:
> On Thursday 02 May 2013 14:48:26 Pavel Machek wrote:
> > On Mon 2013-04-29 14:45:39, Colin Cross wrote:
> > > Freezing tasks will wake up almost every userspace task from
> > > where it is blocking and force it to run until it hits a
> > > call to try_to_sleep(), generally on the exit path from the syscall
> > > it is blocking in.  On resume each task will run again, usually
> > > restarting the syscall and running until it hits the same
> > > blocking call as it was originally blocked in.
> > 
> > Ok, so you are optimizing suspend at the cost of runtime operations,
> > right?
> > 
> > Would it make sense to do suspends entirely without freezer in your
> > configurations? With the right drivers, it should work ok.
> 
> Right now drivers now that they will not be busy when runtime
> suspend happens. The freezer has the same effect for system PM.
> If you remove that certainty it becomes impossible for simple drivers
> to declare their devices busy upon open and do no synchronization
> between IO and PM.

I know. Drivers can mostly ignore suspend.

But android people do suspend multiple times a second, and are
optimizing freezer. I'm suggesting they should take a look at their
drivers, and perhaps they can optimize freezer out totally.

(Or perhaps switch to n900-like solution, and avoid suspend
entirely. They keep machines functioning in suspend mode. That aint no
suspend.)
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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