From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:56518) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S79FD-0008Kz-IC for qemu-devel@nongnu.org; Mon, 12 Mar 2012 13:41:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1S79F6-0000km-VK for qemu-devel@nongnu.org; Mon, 12 Mar 2012 13:41:15 -0400 Received: from cantor2.suse.de ([195.135.220.15]:49483 helo=mx2.suse.de) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S79F6-0000kI-LR for qemu-devel@nongnu.org; Mon, 12 Mar 2012 13:41:08 -0400 Message-ID: <4F5E3532.4060003@suse.de> Date: Mon, 12 Mar 2012 18:41:06 +0100 From: =?ISO-8859-1?Q?Andreas_F=E4rber?= MIME-Version: 1.0 References: <20120309210403.GA2319@redhat.com> <20120310124246.GA4408@redhat.com> <20120310155843.GJ2914@otherpad.lan.raisama.net> <4F5B9C6F.3050705@codemonkey.ws> <20120311132755.GJ17882@redhat.com> <4F5CB2EA.10000@codemonkey.ws> <20120311145655.GK17882@redhat.com> <4F5CC5BB.3070000@codemonkey.ws> <20120311161625.GN17882@redhat.com> <4F5E1B1B.1040606@suse.de> <20120312165014.GA25451@otherpad.lan.raisama.net> In-Reply-To: <20120312165014.GA25451@otherpad.lan.raisama.net> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [libvirt] Modern CPU models cannot be used with libvirt List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: "Liu, Jinsong" , Gleb Natapov , libvir-list@redhat.com, Jan Kiszka , qemu-devel@nongnu.org, Avi Kivity , Anthony Liguori , Igor Mammedov , Jiri Denemark , "arch@ovirt.org" Am 12.03.2012 17:50, schrieb Eduardo Habkost: > On Mon, Mar 12, 2012 at 04:49:47PM +0100, Andreas F=E4rber wrote: >> Am 11.03.2012 17:16, schrieb Gleb Natapov: >>> On Sun, Mar 11, 2012 at 10:33:15AM -0500, Anthony Liguori wrote: >>>> On 03/11/2012 09:56 AM, Gleb Natapov wrote: >>>>> On Sun, Mar 11, 2012 at 09:12:58AM -0500, Anthony Liguori wrote: >>>>>> -cpu best wouldn't solve this. You need a read/write configuratio= n >>>>>> file where QEMU probes the available CPU and records it to be used >>>>>> for the lifetime of the VM. >>>>> That what I thought too, but this shouldn't be the case (Avi's idea= ). >>>>> We need two things: 1) CPU model config should be per machine type. >>>>> 2) QEMU should refuse to start if it cannot create cpu exactly as >>>>> specified by model config. >>>> >>>> This would either mean: >>>> >>>> A. pc-1.1 uses -cpu best with a fixed mask for 1.1 >>>> >>>> B. pc-1.1 hardcodes Westmere or some other family >>>> >>> This would mean neither A nor B. May be it wasn't clear but I didn't = talk >>> about -cpu best above. I am talking about any CPU model with fixed me= aning >>> (not host or best which are host cpu dependant). Lets take Nehalem fo= r >>> example (just to move from Westmere :)). Currently it has level=3D2. = Eduardo >>> wants to fix it to be 11, but old guests, installed with -cpu Nehalem= , >>> should see the same CPU exactly. How do you do it? Have different >>> Nehalem definition for pc-1.0 (which level=3D2) and pc-1.1 (with leve= l=3D11). >>> Lets get back to Westmere. It actually has level=3D11, but that's onl= y >>> expose another problem. Kernel 3.3 and qemu-1.1 combo will support >>> architectural PMU which is exposed in cpuid leaf 10. We do not want >>> guests installed with -cpu Westmere and qemu-1.0 to see architectural >>> PMU after upgrade. How do you do it? Have different Westmere definiti= ons >>> for pc-1.0 (does not report PMU) and pc-1.1 (reports PMU). What happe= ns >>> if you'll try to run qemu-1.1 -cpu Westmere on Kernel < 3.3 (without >>> PMU support)? Qemu will fail to start. [...] >> IMO interpreting an explicit -cpu parameter depending on -M would be >> wrong. Changing the default CPU based on -M is fine with me. For an >> explicit argument we would need Westmere-1.0 analog to pc-1.0. Then th= e >> user gets what the user asks for, without unexpected magic. >=20 > It is not unexpected magic. It would be a documented mechanism: > "-cpu Nehalem-1.0" and "-cpu Nehalem-1.1" would have the same meaning > every time, with any machine-type, but "-cpu Nehalem" would be an alias= , > whose meaning depends on the machine-type. >=20 > Otherwise we would be stuck with a broken "Nehalem" model forever, and > we don't want that. Not quite what I meant: In light of QOM we should be able to instantiate a CPU based on its name and optional parameters IMO. No dependency on the machine, please. An alias sure, but if the user explicitly says -cpu Nehalem then on 1.1 it should always be an alias to Nehalem-1.1 whether the machine is -M pc-0.15 or pc. If no -cpu was specified by the user, then choosing a default of Nehalem-1.0 for pc-1.0 is fine. Just trying to keep separate things separate here. Also keep in mind linux-user. There's no concept of a machine there, but there's a cpu_copy() function used for forking that tries to re-create the CPU based on its model. So currently cpu_*_init(env->cpu_model_str) needs to be able to recreate an identical CPU through the central code path, without access to a QEMUMachine. (I'd really like to fix this "reentrancy" but we can't just trivially memcpy().) Andreas --=20 SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N=FCrnberg, Germany GF: Jeff Hawn, Jennifer Guild, Felix Imend=F6rffer; HRB 16746 AG N=FCrnbe= rg