Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756005AbZJ1J3s (ORCPT ); Wed, 28 Oct 2009 05:29:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754421AbZJ1J3r (ORCPT ); Wed, 28 Oct 2009 05:29:47 -0400 Received: from mx1.redhat.com ([209.132.183.28]:23066 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752197AbZJ1J3q (ORCPT ); Wed, 28 Oct 2009 05:29:46 -0400 Date: Wed, 28 Oct 2009 10:29:01 +0100 From: Glauber Costa To: Avi Kivity Cc: Jeremy Fitzhardinge , 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 Message-ID: <20091028092900.GG3627@mothafucka.localdomain> References: <4f079cd6-0872-4cb5-832b-ee6a46841192@default> <4AE739DA.20601@goop.org> <4AE7DC04.7080706@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4AE7DC04.7080706@redhat.com> X-ChuckNorris: True User-Agent: Jack Bauer Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1149 Lines: 25 On Wed, Oct 28, 2009 at 07:52:04AM +0200, Avi Kivity wrote: > 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? If we loop gettimeofday(), I would expect the vsyscall-based version not to show up in strace, right? -- 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/