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

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Date:	Thu, 29 Mar 2007 15:02:35 -0500
From:	"Mark Langsdorf" <mark.langsdorf@....com>
To:	"Andi Kleen" <andi@...stfloor.org>
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"

Andi Kleen wrote:
> "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.

Yes.  The APIC timer still runs, but no longer has an HT link
to send the signal on.

>> 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.

Reviewed but not tested.  Needs to be wrapped in an AMD specific
call.

#define ENABLE_C1E_MASK		0x18000000
#define CPUID_PROCESSOR_SIGNATURE	1
#define CPUID_XFAM		0x0ff00000
#define CPUID_XFAM_K8		0x00000000
#define CPUID_XFAM_10H		0x00100000
#define CPUID_XFAM_11H		0x00200000
#define CPUID_XMOD		0x000f0000
#define CPUID_XMOD_REV_F	0x00040000

	int safe_c1 = 1;
	u32 eax, lo, hi;
	eax = cpuid_eax(CPUID_PROCESSOR_SIGNATURE)
	switch (eax & CPUID_XFAM) {
	case CPUID_XFAM_K8:
		if ((eax & CPUID_XMOD) < CPUID_XMOD_REV_F)
			break;
	case CPUID_XFAM_10H:
	case CPUID_XFAM_11H:
		rdmsr(MSR_ENABLE_C1E, lo, hi);
		if (lo & ENABLE_C1E_MASK)
			safe_c1 = 0;
		break;
	default:
		/* err on the side of caution */
		safe_c1 = 0;
	}

-Mark Langsdorf
Operating Systems Research Center
AMD, Inc.


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