linux-kernel - Re: [PATCH] i386: add command line option "local_apic_timer_c2

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Date:	29 Mar 2007 18:50:09 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"Langsdorf, Mark" <mark.langsdorf@....com>
Cc:	"Len Brown" <lenb@...nel.org>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>,
	"Morrow, William" <William.Morrow@....com>,
	"Crouse, Jordan" <jordan.crouse@...mail.amd.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Pavel Machek" <pavel@....cz>, "Ingo Molnar" <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"Nick Piggin" <nickpiggin@...oo.com.au>,
	"Mingming Cao" <cmm@...ibm.com>, "Adrian Bunk" <bunk@...sta.de>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Michal Piotrowski" <michal.k.k.piotrowski@...il.com>,
	"Mariusz Kozlowski" <m.kozlowski@...land.pl>,
	"Oliver Pinter" <oliver.pntr@...il.com>,
	"Sid Boyce" <g3vbv@...eyonder.co.uk>,
	"Nick Piggin" <npiggin@...e.de>,
	"Jens Axboe" <jens.axboe@...cle.com>,
	"Thomas Renninger" <trenn@...e.de>
Subject: Re: [PATCH] i386: add command line option "local_apic_timer_c2_ok"

"Langsdorf, Mark" <mark.langsdorf@....com> writes:

> > > If we really care about using the LAPIC timer on systems with deeper
> > > than C1 support, the only alternative seems to be to test
> > > if it actually works or not at boot and run-time.
> > > Otherwise, we wait for future hardware with guaranteed
> > > not to break under any (BIOS) conditions ships, and check for that.
> > > 
> > > Based on what I read of the HP nx6325 where the LAPIC timer
> > > is breaking C1, AMD is in the same boat.
> > 
> > The nx6325 (Turion 64 X2) exports only C1.
> > I'm not sure how the conclusion was drawn that it has
> > a broken lapic timer as reflected in the "nolapic_timer" patch:
> 
> If both cores goes into C1 at the same time, the chipset
> can move the processor into a C3 like state called C1e.

... and that seems to break the local APIC timer.

> AMD can craft a patch to sort this out as soon as we have
> an idea what the framework is going to look like.

Just a snippet to detect it would be great. Then the dmi scan
could be removed and replaced with that. This would be a 2.6.21
candidate imho over the DMI hack.

-Andi
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