From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35046) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bFd0j-0004RL-55 for qemu-devel@nongnu.org; Wed, 22 Jun 2016 03:55:46 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bFd0e-0005LL-UF for qemu-devel@nongnu.org; Wed, 22 Jun 2016 03:55:44 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:9903) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bFd0e-0005LF-II for qemu-devel@nongnu.org; Wed, 22 Jun 2016 03:55:40 -0400 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.11/8.16.0.11) with SMTP id u5M7tY9R145156 for ; Wed, 22 Jun 2016 03:55:39 -0400 Received: from e06smtp05.uk.ibm.com (e06smtp05.uk.ibm.com [195.75.94.101]) by mx0a-001b2d01.pphosted.com with ESMTP id 23qcxdyx74-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 22 Jun 2016 03:55:36 -0400 Received: from localhost by e06smtp05.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 22 Jun 2016 08:54:59 +0100 Received: from b06cxnps3074.portsmouth.uk.ibm.com (d06relay09.portsmouth.uk.ibm.com [9.149.109.194]) by d06dlp01.portsmouth.uk.ibm.com (Postfix) with ESMTP id 2DD5C17D8062 for ; Wed, 22 Jun 2016 08:56:13 +0100 (BST) Received: from d06av04.portsmouth.uk.ibm.com (d06av04.portsmouth.uk.ibm.com [9.149.37.216]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u5M7suM964290938 for ; Wed, 22 Jun 2016 07:54:56 GMT Received: from d06av04.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av04.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u5M7ssbF012814 for ; Wed, 22 Jun 2016 01:54:55 -0600 Date: Wed, 22 Jun 2016 09:54:51 +0200 From: David Hildenbrand In-Reply-To: <20160622075327.GI2450045@orkuz.home> References: <1466514153-85777-1-git-send-email-dahi@linux.vnet.ibm.com> <20160621164431.GI2048@thinpad.lan.raisama.net> <20160621190144.174c93cd@thinkpad-w530> <20160621203309.GK2048@thinpad.lan.raisama.net> <20160621210949.GH4783@orkuz.home> <20160622085140.06984206@thinkpad-w530> <20160622072621.GH2450045@orkuz.home> <20160622093449.6084d7d8@thinkpad-w530> <20160622075327.GI2450045@orkuz.home> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-Id: <20160622095451.11a00cac@thinkpad-w530> Subject: Re: [Qemu-devel] [RFC 00/28] s390x CPU models: exposing features List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jiri Denemark Cc: Eduardo Habkost , qemu-devel@nongnu.org, imammedo@redhat.com, cornelia.huck@de.ibm.com, borntraeger@de.ibm.com, fiuczy@linux.vnet.ibm.com, mimu@linux.vnet.ibm.com, libvir-list@redhat.com > On Wed, Jun 22, 2016 at 09:34:49 +0200, David Hildenbrand wrote: > > I think the coffee didn't do its work already :) . I wanted to write that we can > > _with_ this additional query. Meaning the involved overhead would be ok - in my > > opinion for s390x. > > > > What we could do to avoid one compare operation would be: > > > > a) Expand the host model > > b) Expand the target model (because on s390x we could have migration unsafe > > model) > > c) Work with the runnability information returned via query-cpu-definitions > > > > But as we have to do b) either way on s390x, we can directly do a compare > > operation. (which makes implementation a lot simpler, because libvirt then > > doesn't have to deal with any feature/model names). > > But why do you even need to do any comparison? Isn't it possible to let > QEMU do it when a domain starts? The thing is we should avoid doing > completely different things on each architecture. > Sure, QEMU will of course double check when starting the guest! So trying to start and failing is of course an option! So no check is needed if that is acceptable. David