From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: problem wit svm_get_msr on kvm-kmod-2.6.31.6 Date: Tue, 17 Nov 2009 14:18:17 +0200 Message-ID: <4B029489.60302@redhat.com> References: <90D306BE6EBC8D428A824FBBA7A3113D014275E0F0@ronja.maurer-it.com> <4B012709.20508@redhat.com> <90D306BE6EBC8D428A824FBBA7A3113D014275E0F2@ronja.maurer-it.com> <4B012EDF.7030109@redhat.com> <90D306BE6EBC8D428A824FBBA7A3113D014275E0F5@ronja.maurer-it.com> <4B013F2A.2040900@redhat.com> <4B013FA1.4050003@siemens.com> <90D306BE6EBC8D428A824FBBA7A3113D014275E101@ronja.maurer-it.com> <4B0271DC.7090708@siemens.com> <4B0273F4.8030204@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Joerg Roedel , Dietmar Maurer , kvm To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:36614 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755468AbZKQMSY (ORCPT ); Tue, 17 Nov 2009 07:18:24 -0500 In-Reply-To: <4B0273F4.8030204@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On 11/17/2009 11:59 AM, Jan Kiszka wrote: > Jan Kiszka wrote: > >> Dietmar Maurer wrote: >> >>> Hi Jan, >>> >>> The ubuntu code puts some barrier around the read. >>> >>> http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-hardy.git;a=commitdiff;h=198b348d96c9769153e72ca2461f8d841ddff1cc >>> >>> You simply override this with your own code - without barrier. Do you think this is correct? >>> >> Unless I messed it up again, I "overwrote" it with what is in latest >> mainline regarding native_read_tsc. But I will check once more. >> > The removal of those barriers came with > 0d12cdd5f883f508d33b85c1bae98fa28987c8c7 (sched: improve sched_clock() > performance). So this is now an upstream question: > > Do we bother about the precision of native_read_tsc in svm or not? > > I doubt it matters. rdtsc will be followed by a return to the guest or userspace, either of which is expensive enough to swamp any speculation. -- error compiling committee.c: too many arguments to function