From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id A4513C48BD4 for ; Tue, 25 Jun 2019 16:13:52 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 3860D2080C for ; Tue, 25 Jun 2019 16:13:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3860D2080C Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:33598 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hfo4t-0002Rk-9e for qemu-devel@archiver.kernel.org; Tue, 25 Jun 2019 12:13:51 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:41416) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hfnx1-00043g-Uh for qemu-devel@nongnu.org; Tue, 25 Jun 2019 12:05:44 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hfnwz-0006De-TP for qemu-devel@nongnu.org; Tue, 25 Jun 2019 12:05:43 -0400 Received: from mx1.redhat.com ([209.132.183.28]:19082) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hfnwy-0005PY-2V for qemu-devel@nongnu.org; Tue, 25 Jun 2019 12:05:41 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 94DC67FD6C; Tue, 25 Jun 2019 16:05:06 +0000 (UTC) Received: from localhost (ovpn-116-76.gru2.redhat.com [10.97.116.76]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1F80F608A4; Tue, 25 Jun 2019 16:05:05 +0000 (UTC) Date: Tue, 25 Jun 2019 13:05:04 -0300 From: Eduardo Habkost To: "Dr. David Alan Gilbert" Message-ID: <20190625160504.GS1862@habkost.net> References: <20190625050008.12789-1-ehabkost@redhat.com> <20190625050008.12789-5-ehabkost@redhat.com> <20190625093201.GF3226@work-vm> <20190625134029.GP1862@habkost.net> <20190625143216.GL3226@work-vm> <20190625145309.GQ1862@habkost.net> <20190625145651.GM3226@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190625145651.GM3226@work-vm> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Tue, 25 Jun 2019 16:05:06 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH 4/6] i386: Infrastructure for versioned CPU models X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "Daniel P. Berrange" , qemu-devel@nongnu.org, Paolo Bonzini , Igor Mammedov , Jiri Denemark , Richard Henderson Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jun 25, 2019 at 03:56:51PM +0100, Dr. David Alan Gilbert wrote: > * Eduardo Habkost (ehabkost@redhat.com) wrote: > > On Tue, Jun 25, 2019 at 03:32:16PM +0100, Dr. David Alan Gilbert wrote: > > > * Eduardo Habkost (ehabkost@redhat.com) wrote: > > > > On Tue, Jun 25, 2019 at 10:32:01AM +0100, Dr. David Alan Gilbert wrote: > > > > > * Eduardo Habkost (ehabkost@redhat.com) wrote: > > > > > > Base code for versioned CPU models. This will register a "-4.1" > > > > > > version of all existing CPU models, and make the unversioned CPU > > > > > > models be an alias for the -4.1 versions on the pc-*-4.1 machine > > > > > > types. > > > > > > > > > > > > On older machine types, the unversioned CPU models will keep the > > > > > > old behavior. This way, management software can use old machine > > > > > > types while resolving aliases if compatibility with older QEMU > > > > > > versions is required. > > > > > > > > > > > > Using "-machine none", the unversioned CPU models will be aliases > > > > > > to the latest CPU model version. > > > > > > > > > > > > Includes a test case to ensure that: > > > > > > old machine types won't report any alias to versioned CPU models; > > > > > > "pc-*-4.1" will return aliases to -4.1 CPU models; > > > > > > and "-machine none" will report aliases to some versioned CPU model. > > > > > > > > > > > > Signed-off-by: Eduardo Habkost > > > > > > > > > > What happens when we add the next new CPU model? So say in 4.2 we add > > > > > a new CPU, does that default to being newcpu-4.2 ? > > > > > > > > We can choose between providing old versions of the CPU model > > > > retroactively ("NewModel-4.1" and "NewModel-4.2"), or providing > > > > only "NewModel-4.2". > > > > > > > > The question is: if we provide only "NewModel-4.2", what should > > > > be the behavior of "-machine pc-i440fx-4.1 -cpu NewModel"? > > > > > > Perhaps the existing CPUs and the first instance of a new CPU > > > we should use something non-numeric, e.g. 'orig' rather than 4.1; > > > we only go numeric when we cause a divergence. > > > > What would be the advantage of a non-numeric version identifier? > > I believe it would be more confusing to have (e.g.) > > ["NewModel-orig", "NewModel-4.3"] in QEMU 4.3 instead of > > ["NewModel-4.2", "NewModel-4.3"]. > > To my mind it answers your question: > > > > The question is: if we provide only "NewModel-4.2", what should > > > > be the behavior of "-machine pc-i440fx-4.1 -cpu NewModel"? > > NewModel-orig doesn't look weird in pc-i440fx-4.1 It doesn't look weird in the surface, but it doesn't change the fact that "NewModel-orig" is the version of NewModel that was shipped in in QEMU 4.2. Why would we want to hide that fact? What's the advantage of: "-machine pc-i440fx-4.1 -cpu NewModel" will use "NewModel-orig", which is the version of NewModel added in QEMU 4.2. in relation to: "-machine pc-i440fx-4.1 -cpu NewModel" will use "NewModel-4.2", which is the version of NewModel added in QEMU 4.2. -- Eduardo