Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754345Ab0DSK7P (ORCPT ); Mon, 19 Apr 2010 06:59:15 -0400 Received: from bombadil.infradead.org ([18.85.46.34]:49385 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752988Ab0DSK7O (ORCPT ); Mon, 19 Apr 2010 06:59:14 -0400 Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock From: Peter Zijlstra To: Avi Kivity Cc: Glauber Costa , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jeremy Fitzhardinge , Marcelo Tosatti , Zachary Amsden In-Reply-To: <4BCC3617.6050106@redhat.com> 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> <1271674154.1674.771.camel@laptop> <4BCC3617.6050106@redhat.com> Content-Type: text/plain; charset="UTF-8" Date: Mon, 19 Apr 2010 12:59:05 +0200 Message-ID: <1271674745.1674.802.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1211 Lines: 35 On Mon, 2010-04-19 at 13:53 +0300, Avi Kivity wrote: > On 04/19/2010 01:49 PM, Peter Zijlstra wrote: > > > >> 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. > > > > All of them? I though tsc stops in some mwait deep REM sleep thing. The idea is that TSC will not stop ever (except s2r like stuff), not sure about the actual implementation of the NONSTOP_TSC bit though. > So what do we need? test for both TSC_RELIABLE and NONSTOP_TSC? IMO > TSC_RELIABLE should imply NONSTOP_TSC. Yeah, I think RELIABLE does imply NONSTOP and CONSTANT, but NONSTOP && CONSTANT does not make RELIABLE. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/