From mboxrd@z Thu Jan  1 00:00:00 1970
From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock
Date: Mon, 19 Apr 2010 12:46:15 +0200
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Cc: Glauber Costa <glommer@redhat.com>, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Jeremy Fitzhardinge <jeremy@goop.org>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Zachary Amsden <zamsden@redhat.com>
To: Avi Kivity <avi@redhat.com>
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On Sat, 2010-04-17 at 21:48 +0300, Avi Kivity wrote:
> > After this patch is applied, I don't see a single warp in time during 5 days
> > of execution, in any of the machines I saw them before.
> >
> >    
> 
> Please define a cpuid bit that makes this optional.  When we eventually 
> enable it in the future, it will allow a wider range of guests to enjoy it.

Right, so on x86 we have:

X86_FEATURE_CONSTANT_TSC, which only states that TSC is frequency
independent, not that it doesn't stop in C states and similar fun stuff.

X86_FEATURE_TSC_RELIABLE, which IIRC should indicate the TSC is constant
and synced between cores.