From mboxrd@z Thu Jan 1 00:00:00 1970 Received: by 10.25.21.96 with SMTP id l93csp2419781lfi; Wed, 22 Jun 2016 04:37:12 -0700 (PDT) X-Received: by 10.55.65.81 with SMTP id o78mr37739387qka.127.1466595432050; Wed, 22 Jun 2016 04:37:12 -0700 (PDT) Return-Path: Received: from lists.gnu.org (lists.gnu.org. [2001:4830:134:3::11]) by mx.google.com with ESMTPS id q8si60050854qta.40.2016.06.22.04.37.11 for (version=TLS1 cipher=AES128-SHA bits=128/128); Wed, 22 Jun 2016 04:37:12 -0700 (PDT) Received-SPF: pass (google.com: domain of qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org designates 2001:4830:134:3::11 as permitted sender) client-ip=2001:4830:134:3::11; Authentication-Results: mx.google.com; spf=pass (google.com: domain of qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org designates 2001:4830:134:3::11 as permitted sender) smtp.mailfrom=qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org Received: from localhost ([::1]:57357 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bFgT1-0001gX-In for alex.bennee@linaro.org; Wed, 22 Jun 2016 07:37:11 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37718) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bFgS4-0001Mc-3d for qemu-devel@nongnu.org; Wed, 22 Jun 2016 07:36:14 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bFgS1-0007Ps-Vu for qemu-devel@nongnu.org; Wed, 22 Jun 2016 07:36:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42569) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bFgRw-0007N9-6U; Wed, 22 Jun 2016 07:36:04 -0400 Received: from int-mx14.intmail.prod.int.phx2.redhat.com (int-mx14.intmail.prod.int.phx2.redhat.com [10.5.11.27]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 81AA160C1; Wed, 22 Jun 2016 11:36:03 +0000 (UTC) Received: from work-vm (ovpn-116-97.ams2.redhat.com [10.36.116.97]) by int-mx14.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id u5MBZxLG017011 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 22 Jun 2016 07:36:01 -0400 Date: Wed, 22 Jun 2016 12:35:59 +0100 From: "Dr. David Alan Gilbert" To: Andrew Jones Message-ID: <20160622113558.GF2274@work-vm> References: <1466528974-12183-1-git-send-email-peter.maydell@linaro.org> <1466528974-12183-7-git-send-email-peter.maydell@linaro.org> <20160621184552.p7trf4zpqnrmwruu@hawk.localdomain> <20160622080234.f57jjn43tcwmvmcd@hawk.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160622080234.f57jjn43tcwmvmcd@hawk.localdomain> User-Agent: Mutt/1.6.1 (2016-04-27) X-Scanned-By: MIMEDefang 2.68 on 10.5.11.27 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 22 Jun 2016 11:36:03 +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 v2 6/6] hw/arm/virt: Set minimum_page_bits to 12 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Patch Tracking , Vijaya Kumar K , QEMU Developers , qemu-arm , Paolo Bonzini Errors-To: qemu-devel-bounces+alex.bennee=linaro.org@nongnu.org Sender: "Qemu-devel" X-TUID: f5ubJPkJhAMh * Andrew Jones (drjones@redhat.com) wrote: > On Tue, Jun 21, 2016 at 08:47:39PM +0100, Peter Maydell wrote: > > On 21 June 2016 at 19:45, Andrew Jones wrote: > > > On Tue, Jun 21, 2016 at 06:09:34PM +0100, Peter Maydell wrote: > > >> Since the virt board model will never create a CPU which is > > >> pre-ARMv7, we know that our minimum page size is 4K and can > > >> set minimum_page_bits accordingly, for improved performance. > > >> > > >> Note that this is a migration compatibility break. > > >> > > >> Signed-off-by: Peter Maydell > > >> --- > > >> hw/arm/virt.c | 2 ++ > > >> 1 file changed, 2 insertions(+) > > >> > > >> diff --git a/hw/arm/virt.c b/hw/arm/virt.c > > >> index c5c125e..f9b51aa 100644 > > >> --- a/hw/arm/virt.c > > >> +++ b/hw/arm/virt.c > > >> @@ -1440,6 +1440,8 @@ static void virt_machine_class_init(ObjectClass *oc, void *data) > > >> mc->block_default_type = IF_VIRTIO; > > >> mc->no_cdrom = 1; > > >> mc->pci_allow_0_address = true; > > >> + /* We know we will never create a pre-ARMv7 CPU which needs 1K pages */ > > >> + mc->minimum_page_bits = 12; > > >> } > > > > > > As this breaks migration, then I guess we also need > > > > > > @@ -1507,5 +1510,6 @@ static void virt_machine_2_6_options(MachineClass *mc) > > > { > > > virt_machine_2_7_options(mc); > > > SET_MACHINE_COMPAT(mc, VIRT_COMPAT_2_6); > > > + mc->minimum_page_bits = 10; > > > } > > > DEFINE_VIRT_MACHINE(2, 6) > > > > Doesn't hurt, but are we trying to claim migration > > compat between different QEMU versions with the > > versioned-machine names ? > > I'm still learning how best to approach compat/migration concerns. > I've CC'ed David to help. > > Up until now my main concern has been keeping the RHEL-x.y mach-virt > (and now upstream versioned mach-virt) type from changing as new > features are added. In which case, I think the above makes sense > regardless. With respect to migration I'm unsure of the claims we > can/should make. IMO, we'd ideally be able to always migrate a > versioned-machine (obviously running with a QEMU that supports that > version) to a host with a later QEMU (which, being later, means it > also supports that version) Yes, my hope is that any versioned machine type should migrate to a newer qemu with the same machine type set. There are really two separate things that we state with the machine versioning: a) that the guest view is the same b) that the migration format is the same Dave > Thanks, > drew > -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK