From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: problem wit svm_get_msr on kvm-kmod-2.6.31.6 Date: Tue, 17 Nov 2009 18:00:01 +0100 Message-ID: <4B02D691.9050800@siemens.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> <4B029489.60302@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Joerg Roedel , Dietmar Maurer , kvm To: Avi Kivity Return-path: Received: from thoth.sbs.de ([192.35.17.2]:21673 "EHLO thoth.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751445AbZKQRAR (ORCPT ); Tue, 17 Nov 2009 12:00:17 -0500 In-Reply-To: <4B029489.60302@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > 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. > Right. So the kvm-kmod replacement is also fine. Dietmar, if you could confirm that your issue is fixed, I would roll out a kvm-kmod-2.6.31.6b, likely the last version of this series. The .32 series will be updated on 2.6.32-final or the next KVM-affecting -rc release. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux