From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamie Lokier Subject: Re: [PATCH] introduce kvm64 CPU Date: Sun, 23 Aug 2009 13:47:18 +0100 Message-ID: <20090823124718.GB30789@shareable.org> References: <1250804057-29681-1-git-send-email-andre.przywara@amd.com> <4A8EC03D.4000202@redhat.com> <4A8F18CB.6000200@amd.com> <4A910649.5000600@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andre Przywara , anthony@codemonkey.ws, qemu-devel@nongnu.org, kvm@vger.kernel.org To: Avi Kivity Return-path: Received: from mail2.shareable.org ([80.68.89.115]:60068 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755992AbZHWMrW (ORCPT ); Sun, 23 Aug 2009 08:47:22 -0400 Content-Disposition: inline In-Reply-To: <4A910649.5000600@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > On 08/22/2009 12:59 AM, Andre Przywara wrote: > >>Typically users will want more specialized greatest common denomiator > >>cpu types; if a site has standardized on recent hardware they will > >>want the features of that hardware exposed. > >Sure, but this was not the purpose of this patch. Currently KVM guests > >see a CPU type which is TCG dependent, so I just wanted to get rid of > >this. Features of TCG and features of the host processor are totally > >uncorrelated. This new type should be KVM's default, leaving -cpu host > >as the alternative for the non-migration case. > > That does make sense. Note we can call it '-cpu kvm' since qemu will > strip away long mode if it is not supported by the cpu or by the kernel. I thought the point was to provide a "lowest common denominator" for migration, while acknowledging that 64-bit is too useful to exclude? So if you start running on a 64-bit host, but know you have 32-bit hosts in your pool, you'll need '-cpu kvm32'. And if you start on a 32-bit host, but want to migrate to a 64-bit host, will that work if the destination has different cpuid than the source? -- Jamie