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

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Date:	Thu, 29 Mar 2007 14:16:54 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Andi Kleen <ak@...e.de>
cc:	Mark Langsdorf <mark.langsdorf@....com>,
	Len Brown <lenb@...nel.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"

On Thu, 29 Mar 2007, Andi Kleen wrote:
> 
> Here's a patch. I don't have a system with C1E, so i only tested that
> the apic timer still works on a older AMD box.

I think this looks better than what we have now, but it would look even 
better if the core CPUID stuff was in arch/i386/kernel/cpu/amd.c, and we 
simply had X86_FEATURE_BROKEN_C1_LAPIC etc..

And then the apic.c code would just check

	if (boot_cpu_has(X86_FEATURE_BROKEN_C1_LAPIC))
		return -1;

or similar.

Doing the same for C2 and C3 gives us a clean way to have all these 
per-vendor things in their relevant places, rather than having various 
vendor-specific checks sprinkled in random places..

That's *especially* true for something like this that can hit both on 
x86-64 and i386, where the cpuid logic is shared, but the APIC logic is 
*not* shared. If I read your patch correctly, this only fixes it on 32-bit 
platforms, and I don't think the problem is in any way 32-bit specific, is 
it?

		Linus
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