linux-kernel - Re: [Patch] Skip cpu_calibrate for kernel running under hypervisors.

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Message-ID: <20100817070520.GD32714@liondog.tnic>
Date:	Tue, 17 Aug 2010 09:05:20 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	akataria@...are.com, the arch/x86 maintainers <x86@...nel.org>,
	Greg KH <gregkh@...e.de>, "greg@...ah.com" <greg@...ah.com>,
	"ksrinivasan@...ell.com" <ksrinivasan@...ell.com>,
	LKML <linux-kernel@...r.kernel.org>, borislav.petkov@....com
Subject: Re: [Patch] Skip cpu_calibrate for kernel running under
 hypervisors.

From: "H. Peter Anvin" <hpa@...or.com>
Date: Mon, Aug 16, 2010 at 11:30:48PM -0700

> On 08/16/2010 10:51 PM, Alok Kataria wrote:
> >>
> >> I'm somewhat reluctant to take this one, since it assumes all the
> >> hypervisors act the same.  This seems rather inherently wrong.  In fact,
> >> the whole statement is fishy as heck... instead of being dependent on
> >> AMD and so on, 
> > 
> > The check about being on AMD is something that was already there. 
> > 
> 
> I know it was... and calibrate_cpu() seems to be an AMD-specific
> function, but that's rather crappy.  I'm thinking that perhaps we should
> make it an x86_init function, then the AMD CPU detection can install it
> and the vmware hypervisor detection can uninstall it.

Btw, can we revisit this AMD-specific issue? IIUC, Alok you're seeing
a mismatch between the calibrated TSC value and the cpu frequency even
on cpus which have the CONSTANT_TSC bit set, i.e. their TSC is counting
with P0 frequency. Can you please elaborate more on what systems you're
seeing this (cpu family, chipset, etc)?

Thanks.

-- 
Regards/Gruss,
    Boris.
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