linux-kernel - Re: [PATCH] x86: c1e_idle: don't mark TSC unstable if CPU has invariant TSC

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Date:	Sat, 20 Sep 2008 08:14:57 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Andreas Herrmann <andreas.herrmann3@....com>
Cc:	Valdis.Kletnieks@...edu, Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86: c1e_idle: don't mark TSC unstable if CPU has
	invariant TSC


* Andreas Herrmann <andreas.herrmann3@....com> wrote:

> Currently the kernel assumes TSC is stable and there are various 
> places where Linux might spot when TSC is unstable. c1e_idle is one 
> such place. But it's wrong to mark TSC unstable for all AMD CPUs in 
> this function as newer CPU families have TSC's that are P- and C-state 
> invariant.

i agree with the purpose of the patch (as it flags the first really sane 
TSC implementation on x86!!!) - but it would be nice to indicate this in 
a different CPU feature bit other than X86_FEATURE_CONSTANT_TSC, to 
reduce confusion. Perhaps introduce a virtual CPU feature bit for that?

	Ingo
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