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 12:51:13 +0200
Message-ID: <1271674273.1674.777.camel@laptop>
References: <1271356648-5108-1-git-send-email-glommer@redhat.com>
	 <1271356648-5108-2-git-send-email-glommer@redhat.com>
	 <4BCA026D.3070309@redhat.com> <1271673975.1674.763.camel@laptop>
	 <4BCC3520.6090305@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 7bit
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>
Return-path: <kvm-owner@vger.kernel.org>
Received: from casper.infradead.org ([85.118.1.10]:60745 "EHLO
	casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754165Ab0DSKvQ (ORCPT <rfc822;kvm@vger.kernel.org>);
	Mon, 19 Apr 2010 06:51:16 -0400
Received: from f199130.upc-f.chello.nl ([80.56.199.130] helo=dyad.programming.kicks-ass.net)
	by casper.infradead.org with esmtpsa (Exim 4.69 #1 (Red Hat Linux))
	id 1O3oZP-0006pZ-Ql
	for kvm@vger.kernel.org; Mon, 19 Apr 2010 10:51:16 +0000
In-Reply-To: <4BCC3520.6090305@redhat.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Mon, 2010-04-19 at 13:49 +0300, Avi Kivity wrote:
> On 04/19/2010 01:46 PM, Peter Zijlstra wrote:
> > 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.
> >
> >    
> 
> Sockets and boards too?  (IOW, how reliable is TSC_RELIABLE)?

Not sure, IIRC we clear that when the TSC sync test fails, eg when we
mark the tsc clocksource unusable.