Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753175Ab0DSLfu (ORCPT ); Mon, 19 Apr 2010 07:35:50 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38248 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750706Ab0DSLfs (ORCPT ); Mon, 19 Apr 2010 07:35:48 -0400 Message-ID: <4BCC4006.8000501@redhat.com> Date: Mon, 19 Apr 2010 14:35:34 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Peter Zijlstra CC: Glauber Costa , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Jeremy Fitzhardinge , Marcelo Tosatti , Zachary Amsden Subject: Re: [PATCH 1/5] Add a global synchronization point for pvclock 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> <1271674745.1674.802.camel@laptop> In-Reply-To: <1271674745.1674.802.camel@laptop> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1295 Lines: 37 On 04/19/2010 01:59 PM, Peter Zijlstra wrote: > >> 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. > The manual says: > 16.11.1 Invariant TSC > > The time stamp counter in newer processors may support an enhancement, > referred > to as invariant TSC. Processor’s support for invariant TSC is indicated by > CPUID.80000007H:EDX[8]. > The invariant TSC will run at a constant rate in all ACPI P-, C-. and > T-states. This is > the architectural behavior moving forward. On processors with > invariant TSC > support, the OS may use the TSC for wall clock timer services (instead > of ACPI or > HPET timers). TSC reads are much more efficient and do not incur the > overhead > associated with a ring transition or access to a platform resource. and this maps to NONSTOP, so I think we're fine. -- error compiling committee.c: too many arguments to function -- 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/