linux-kernel - Re: [patch 6/6] x86: add c1e aware idle function

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Message-ID: <20080618192148.GA4243@ucw.cz>
Date:	Wed, 18 Jun 2008 21:21:48 +0200
From:	Pavel Machek <pavel@...e.cz>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Arjan van de Veen <arjan@...radead.org>,
	Andreas Herrmann <andreas.herrmann3@....com>
Subject: Re: [patch 6/6] x86: add c1e aware idle function

On Thu 2008-06-12 10:29:00, Thomas Gleixner wrote:
> C1E on AMD machines is like C3 but without control from the OS. Up to
> now we disabled the local apic timer for those machines as it stops
> when the CPU goes into C1E. This excludes those machines from high
> resolution timers / dynamic ticks, which hurts especially the X2 based
> laptops.
> 
> The current boot time C1E detection has another more serious flaw:
> some BIOSes do not enable C1E until the ACPI processor module is
> loaded. This causes systems to stop working after that point.
> 
> To work nicely with C1E enabled machines we use a separate idle
> function, which checks on idle entry whether C1E was enabled in the
> Interrupt Pending Message MSR. This allows us to do timer broadcasting

Entering idle is quite a common operation, and reading MSR is quite
slow. Is it possible to do better here?

What happens if ACPI BIOS toggles MSR on all cpus *while* we are
entering idle? This seems inherently racy...
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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