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[2001:4830:134:3::11]) by mx.google.com with ESMTPS id g76si127095qke.10.2018.04.10.00.42.13 for (version=TLS1 cipher=AES128-SHA bits=128/128); Tue, 10 Apr 2018 00:42:13 -0700 (PDT) Received-SPF: pass (google.com: domain of qemu-arm-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-arm-bounces+alex.bennee=linaro.org@nongnu.org designates 2001:4830:134:3::11 as permitted sender) smtp.mailfrom=qemu-arm-bounces+alex.bennee=linaro.org@nongnu.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from localhost ([::1]:49893 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f5nuu-0007h3-O3 for alex.bennee@linaro.org; Tue, 10 Apr 2018 03:42:12 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55995) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f5nuh-0007fK-FH for qemu-arm@nongnu.org; Tue, 10 Apr 2018 03:42:00 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f5nud-0001nM-Ej for qemu-arm@nongnu.org; Tue, 10 Apr 2018 03:41:59 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:54764 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f5nud-0001mt-AD; Tue, 10 Apr 2018 03:41:55 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.rdu2.redhat.com [10.11.54.5]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 42ECD8011462; Tue, 10 Apr 2018 07:41:44 +0000 (UTC) Received: from inaba.usersys.redhat.com (unknown [10.43.2.44]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 37CD56353F; Tue, 10 Apr 2018 07:41:34 +0000 (UTC) Message-ID: <1523346093.16671.23.camel@redhat.com> From: Andrea Bolognani To: Wei Huang , "Daniel P." =?ISO-8859-1?Q?Berrang=E9?= Date: Tue, 10 Apr 2018 09:41:33 +0200 In-Reply-To: <6bb12858-3b4e-e92f-93ea-b8708c8be870@redhat.com> References: <20180409154921.29906-1-wei@redhat.com> <20180409155634.GO18283@redhat.com> <6bb12858-3b4e-e92f-93ea-b8708c8be870@redhat.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.11.54.5 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Tue, 10 Apr 2018 07:41:44 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Tue, 10 Apr 2018 07:41:44 +0000 (UTC) for IP:'10.11.54.5' DOMAIN:'int-mx05.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'abologna@redhat.com' RCPT:'' X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 66.187.233.73 Subject: Re: [Qemu-arm] [Qemu-devel] [PATCH 1/1] mach-virt: Change default cpu and gic-version setting to "max" X-BeenThere: qemu-arm@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@linaro.org, drjones@redhat.com, qemu-arm@nongnu.org, qemu-devel@nongnu.org Errors-To: qemu-arm-bounces+alex.bennee=linaro.org@nongnu.org Sender: "Qemu-arm" X-TUID: cfeE5K4ETrSh On Mon, 2018-04-09 at 11:29 -0500, Wei Huang wrote: > > > Running mach-virt machine types (i.e. "-M virt") on different systems can > > > result in various misleading warnings if -cpu and/or gic-version not specified. > > > For KVM, this can be solved mostly by using "host" type. But the "host" type > > > doesn't work for TCG. Compared with "host", the "max" type not only supports > > > auto detection under KVM mode, but also works with TCG. So this patch set > > > "max" as the default types for both -cpu and gic-version. > > > > Hmm, generally we aim for the config provided by a machine type to be stable > > across QEMU versions. > > I understand this principle. But in reality, under KVM mode, the default > config most time doesn't work. If end users specify cpu type manually, > it still doesn't work because the host CPU is vendor-specific design > (e.g. "cortex-a57" doesn't work on QCOM's machine). So we end up with > using "-cpu host" all the time. My argument for this patch is that "-cpu > max" isn't worse than "-cpu host". I figure the people not explicitly specifying a CPU model on the command line will probably also use '-M virt' instead of versioned machine types, which means they will get a different guest behavior after upgrading QEMU regardless. Defaulting to 'max' for '-cpu' and 'gic-version' makes it convenient to quickly and concisely start a guest; if you care about guest ABI at all, then you are already specifying everything explicitly on the command line instead of relying on defaults - or using libvirt ;) -- Andrea Bolognani / Red Hat / Virtualization From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:56048) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f5num-0007jd-Kw for qemu-devel@nongnu.org; Tue, 10 Apr 2018 03:42:05 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f5nui-0001qa-OQ for qemu-devel@nongnu.org; Tue, 10 Apr 2018 03:42:04 -0400 Message-ID: <1523346093.16671.23.camel@redhat.com> From: Andrea Bolognani Date: Tue, 10 Apr 2018 09:41:33 +0200 In-Reply-To: <6bb12858-3b4e-e92f-93ea-b8708c8be870@redhat.com> References: <20180409154921.29906-1-wei@redhat.com> <20180409155634.GO18283@redhat.com> <6bb12858-3b4e-e92f-93ea-b8708c8be870@redhat.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/1] mach-virt: Change default cpu and gic-version setting to "max" List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wei Huang , "Daniel P. =?ISO-8859-1?Q?Berrang=E9?=" Cc: qemu-devel@nongnu.org, peter.maydell@linaro.org, drjones@redhat.com, qemu-arm@nongnu.org On Mon, 2018-04-09 at 11:29 -0500, Wei Huang wrote: > > > Running mach-virt machine types (i.e. "-M virt") on different systems can > > > result in various misleading warnings if -cpu and/or gic-version not specified. > > > For KVM, this can be solved mostly by using "host" type. But the "host" type > > > doesn't work for TCG. Compared with "host", the "max" type not only supports > > > auto detection under KVM mode, but also works with TCG. So this patch set > > > "max" as the default types for both -cpu and gic-version. > > > > Hmm, generally we aim for the config provided by a machine type to be stable > > across QEMU versions. > > I understand this principle. But in reality, under KVM mode, the default > config most time doesn't work. If end users specify cpu type manually, > it still doesn't work because the host CPU is vendor-specific design > (e.g. "cortex-a57" doesn't work on QCOM's machine). So we end up with > using "-cpu host" all the time. My argument for this patch is that "-cpu > max" isn't worse than "-cpu host". I figure the people not explicitly specifying a CPU model on the command line will probably also use '-M virt' instead of versioned machine types, which means they will get a different guest behavior after upgrading QEMU regardless. Defaulting to 'max' for '-cpu' and 'gic-version' makes it convenient to quickly and concisely start a guest; if you care about guest ABI at all, then you are already specifying everything explicitly on the command line instead of relying on defaults - or using libvirt ;) -- Andrea Bolognani / Red Hat / Virtualization