Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932117AbZJ1Fwz (ORCPT ); Wed, 28 Oct 2009 01:52:55 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756700AbZJ1Fwy (ORCPT ); Wed, 28 Oct 2009 01:52:54 -0400 Received: from mx1.redhat.com ([209.132.183.28]:15215 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756684AbZJ1Fwy (ORCPT ); Wed, 28 Oct 2009 01:52:54 -0400 Message-ID: <4AE7DC04.7080706@redhat.com> Date: Wed, 28 Oct 2009 07:52:04 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.4pre) Gecko/20091014 Fedora/3.0-2.8.b4.fc11 Thunderbird/3.0b4 MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: Dan Magenheimer , Jeremy Fitzhardinge , kurt.hackel@oracle.com, the arch/x86 maintainers , Linux Kernel Mailing List , Glauber de Oliveira Costa , Xen-devel , Keir Fraser , zach.brown@oracle.com, chris.mason@oracle.com, Ingo Molnar Subject: Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation References: <4f079cd6-0872-4cb5-832b-ee6a46841192@default> <4AE739DA.20601@goop.org> In-Reply-To: <4AE739DA.20601@goop.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1057 Lines: 26 On 10/27/2009 08:20 PM, Jeremy Fitzhardinge wrote: > On 10/27/09 10:29, Dan Magenheimer wrote: > >> Is there any way for an application to conclusively determine >> programmatically if the "fast vsyscall" pvclock is functional >> vs the much much slower gettimeofday/clock_gettime equivalents? >> >> If not, might it be possible to implement some (sysfs?) >> way to determine this, that would also be backwards compatible >> to existing OS's that don't have pvclock+vsyscall supported? >> >> > It would probably be simplest and most portable for the app to just > measure the performance of gettimeofday and see if it meets its needs. > How can you reliably measure performance in a virtualized environment? -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. -- 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/