linux-kernel - Re: [lm-sensors] Could the k8temp driver be interfering with ACPI?

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Date:	Wed, 7 Mar 2007 10:36:44 +0100
From:	Pavel Machek <pavel@....cz>
To:	Jean Delvare <khali@...ux-fr.org>
Cc:	Bodo Eggert <7eggert@....de>,
	David Hubbard <david.c.hubbard@...il.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	lm-sensors@...sensors.org, linux-acpi@...r.kernel.org,
	Chuck Ebbert <cebbert@...hat.com>, Rudolf@...pms.net
Subject: Re: [lm-sensors] Could the k8temp driver be interfering with ACPI?

Hi!

> > > > 2) make ACPI take this lock whenever it touches ports not allocated by itself
> > > >    and release it on function return.
> > > 
> > > This is costly.
> > 
> > TANSTAAFL. You'll need to take some lock, and if you want port emulation 
> > or per-device-mutex, you'll have to pay the price.
> 
> True, but precisely, I wonder what will perform the best in practice, a
> single semaphore that is unconditionally taken by ACPI/AML, or your
> finer-grained approach and its many additional tests.

I'd say mutexes are not that bad. ... i/o accesses are expensive,
anyway, right?

> We may be able to workaround the inter-driver exclusion though, if we
> use a semaphore initialized to N, have ACPI take N, but other drivers
> take just one. This would let ACPI be exclusive with all the other
> drivers, but drivers themselves could otherwise run concurrently. That
> being said, we do not appear to have the required primitives to take
> more than 1 semaphore resource at once at the moment, so we'd need to
> do that first.

Hmm, nice hack. Yes, driver-driver serialization would be nasty.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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