From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH 05/16] KVM-HDR: Implement wallclock over KVM - KVM Virtual Memory Date: Wed, 26 Jan 2011 17:17:02 +0200 Message-ID: <4D403AEE.6010208@redhat.com> References: <1295892397-11354-1-git-send-email-glommer@redhat.com> <1295892397-11354-6-git-send-email-glommer@redhat.com> <4D4001D6.9030909@redhat.com> <1296044403.15920.54.camel@mothafucka.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, aliguori@us.ibm.com To: Glauber Costa Return-path: In-Reply-To: <1296044403.15920.54.camel@mothafucka.localdomain> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 01/26/2011 02:20 PM, Glauber Costa wrote: > On Wed, 2011-01-26 at 13:13 +0200, Avi Kivity wrote: > > On 01/24/2011 08:06 PM, Glauber Costa wrote: > > > As a proof of concept to KVM - Kernel Virtual Memory, this patch > > > implements wallclock grabbing on top of it. At first, it may seem > > > as a waste of work to just redo it, since it is working well. But over the > > > time, other MSRs were added - think ASYNC_PF - and more will probably come. > > > After this patch, we won't need to ever add another virtual MSR to KVM. > > > > > > > So instead of adding MSRs, we're adding area identifiers. What did we gain? > > * No risk of namespace clashes of any kind, > * less need for userspace coordination for feature enablement, That's a bug, not a feature. > * more robust mechanism that can do discovery even on early boot, cpuid/wrmsr should be robust enough. > * more informative result values can be passed on to guest kernel, True. > * more flexibility, since we go back to userspace if we can't handle > some request. Also, some requests are better handled by userspace > anyway. But again, maybe this is a separate issue here... Yes. > * size information goes together with base, allowing for extending > structures (well, maybe I should add versioning explicitly?) > We could do that as well with wrmsr, by having the size as the first field of the structure. Usually the size isn't really interesting, though, since you need to discover/enable the new features independently. -- error compiling committee.c: too many arguments to function