From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock Date: Mon, 19 Apr 2010 12:49:14 +0200 Message-ID: <1271674154.1674.771.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> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: Glauber Costa , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jeremy Fitzhardinge , Marcelo Tosatti , Zachary Amsden To: Avi Kivity Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:37739 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752281Ab0DSKtR (ORCPT ); Mon, 19 Apr 2010 06:49:17 -0400 Received: from f199130.upc-f.chello.nl ([80.56.199.130] helo=dyad.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.69 #1 (Red Hat Linux)) id 1O3oXV-00067N-Eu for kvm@vger.kernel.org; Mon, 19 Apr 2010 10:49:17 +0000 In-Reply-To: <1271673975.1674.763.camel@laptop> Sender: kvm-owner@vger.kernel.org List-ID: On Mon, 2010-04-19 at 12:46 +0200, 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. Fun, we also have: X86_FEATURE_NONSTOP_TSC, which states the thing doesn't stop in C states.