From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756632AbZETJSL (ORCPT ); Wed, 20 May 2009 05:18:11 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755385AbZETJR6 (ORCPT ); Wed, 20 May 2009 05:17:58 -0400 Received: from mx2.redhat.com ([66.187.237.31]:57106 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755025AbZETJR5 (ORCPT ); Wed, 20 May 2009 05:17:57 -0400 Message-ID: <4A13CABB.9010000@redhat.com> Date: Wed, 20 May 2009 12:17:47 +0300 From: Avi Kivity User-Agent: Thunderbird 2.0.0.21 (X11/20090320) MIME-Version: 1.0 To: Peter Zijlstra CC: Mark Langsdorf , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH][KVM][retry 3] Add support for Pause Filtering to AMD SVM References: <200905050909.58583.mark.langsdorf@amd.com> <200905071000.14038.mark.langsdorf@amd.com> <200905081203.55484.mark.langsdorf@amd.com> <200905191356.37071.mark.langsdorf@amd.com> <1242806386.26820.549.camel@twins> <4A13C199.5020400@redhat.com> <1242808954.26820.556.camel@twins> <4A13C40B.8080608@redhat.com> <1242809657.26820.559.camel@twins> <4A13C7B0.10507@redhat.com> <1242810616.26820.562.camel@twins> In-Reply-To: <1242810616.26820.562.camel@twins> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Peter Zijlstra wrote: >>>> It's a fully virtualized guest. There's no way to get this without >>>> patching the guest kernel. >>>> >>>> >>> Yes there is.. virtualized monitor-wait stuff coupled with a >>> monitor-wait based spinlock implementation. >>> >>> >> That only works if the guest uses monitor/mwait. Not all of the guests >> are under our control. I don't know whether Windows uses >> monitor/mwait. Further, we don't have timed exits on mwait like we do >> with pause. >> > > Ugh, you really care about crap like windows? > Yes, it is used by my users. Either we convince them not to use Windows, or we find a way to support it well. >> I've also heard that monitor/mwait are very slow and only usable on idle >> loop stuff. >> > > Yeah, current implementations suck, doesn't mean it has to stay that > way. > Well, I'm not speculating on future cpu changes. I'd like to support current and near-future software and hardware, not how it should have been done software running on how it should have been done hardware. >>> Once we go change silicon, you might as well do it right. >>> >>> >> None of the major x86 vendors are under my control. >> > > I thought this patch came from AMD, who changed their silicon so 'solve' > one of these virt problems. > They changed the silicon to support existing guests. For both Linux and Windows, the pause instruction is the only indication the guest is spinning. > /me goes hide again, and pretend all of virt doesn't exist :-) Think > happy thoughts. > You'll end up running permanently in a guest, with no way out. -- error compiling committee.c: too many arguments to function