From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41537) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V1fN4-00058I-4q for qemu-devel@nongnu.org; Tue, 23 Jul 2013 12:23:31 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1V1fN3-0006qX-11 for qemu-devel@nongnu.org; Tue, 23 Jul 2013 12:23:30 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40339) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1V1fN2-0006qJ-Pd for qemu-devel@nongnu.org; Tue, 23 Jul 2013 12:23:28 -0400 Message-ID: <51EEADEC.7090700@redhat.com> Date: Tue, 23 Jul 2013 18:23:08 +0200 From: Paolo Bonzini MIME-Version: 1.0 References: <1374521135-30404-1-git-send-email-ehabkost@redhat.com> <1374521135-30404-3-git-send-email-ehabkost@redhat.com> <51EE4A4B.1040500@redhat.com> <20130723141304.GA3222@otherpad.lan.raisama.net> <51EE9C8E.9030805@redhat.com> <20130723154051.GC3222@otherpad.lan.raisama.net> In-Reply-To: <20130723154051.GC3222@otherpad.lan.raisama.net> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [qom-cpu PATCH 2/2] i386: disable PMU passthrough mode by default List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: Igor Mammedov , qemu-devel@nongnu.org, Gleb Natapov , =?ISO-8859-1?Q?Andreas_F=E4rber?= Il 23/07/2013 17:40, Eduardo Habkost ha scritto: > On Tue, Jul 23, 2013 at 05:09:02PM +0200, Paolo Bonzini wrote: >> Il 23/07/2013 16:13, Eduardo Habkost ha scritto: >>> On Tue, Jul 23, 2013 at 11:18:03AM +0200, Paolo Bonzini wrote: >>>> Il 22/07/2013 21:25, Eduardo Habkost ha scritto: >>>>> Bug description: QEMU currently gets all bits from GET_SUPPORTED_CPUID >>>>> for CPUID leaf 0xA and passes them directly to the guest. This makes >>>>> the guest ABI depend on host kernel and host CPU capabilities, and >>>>> breaks live migration if we migrate between host with different >>>>> capabilities (e.g. different number of PMU counters). >>>>> >>>>> This patch adds a "pmu-passthrough" property to X86CPU, and set it to >>>>> true only on "-cpu host", or on pc-*-1.5 and older machine-types. >>>> >>>> Can we just call the property "pmu"? It doesn't have to be passthough. >>> >>> Yes, but the only options we have today are "no PMU" and "passthrough >>> PMU". I wouldn't like to make "pmu=on" enable the passthrough behavior >>> implicitly (I don't want things that break live-migration to be enabled >>> without making it explicit that it is a host-dependent/passthrough >>> mode). >> >> I think "passthrough PMU" should be considered a bug except of course >> with "-cpu host". >> >> If "-cpu Nehalem,pmu=on" goes from passthrough to Nehalem-compatible in >> a future QEMU release, that'll be a bugfix. > > Exactly. But then I don't understand your suggestion. We still need a > property to enable pasthrough behavior on old machine-types (not > perfect, but a best-effort way to try to keep compatibility), Do we? We only need "pmu=on"---which right now is buggy on old machine types because it will always passthrough. Paolo > and I > named that option "pmu-passthrough". How do you think we should name it?