From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:58628) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zwur2-000862-Se for qemu-devel@nongnu.org; Thu, 12 Nov 2015 11:36:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Zwuqx-0008Ub-Tm for qemu-devel@nongnu.org; Thu, 12 Nov 2015 11:36:08 -0500 Received: from mx1.redhat.com ([209.132.183.28]:48266) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Zwuqx-0008UM-Ox for qemu-devel@nongnu.org; Thu, 12 Nov 2015 11:36:03 -0500 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) by mx1.redhat.com (Postfix) with ESMTPS id 53566C0D804B for ; Thu, 12 Nov 2015 16:36:03 +0000 (UTC) References: <56446FB8.8070701@redhat.com> <20151112152510.GM4180@thinpad.lan.raisama.net> <5644B72D.8080807@redhat.com> <20151112162748.GN4180@thinpad.lan.raisama.net> From: Paolo Bonzini Message-ID: <5644BFEF.8070909@redhat.com> Date: Thu, 12 Nov 2015 17:35:59 +0100 MIME-Version: 1.0 In-Reply-To: <20151112162748.GN4180@thinpad.lan.raisama.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] -cpu check, rdtscp and AMD KVM List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: qemu-devel On 12/11/2015 17:27, Eduardo Habkost wrote: >> > > To simply remove rdtscp from all Opteron_G* models? > > > > Not sure this is the right thing to do... Real hardware has it, and > > going forward KVM will provide it. > > Do you see any alternative? Live with the warning, and document it in the release notes. > We need AMD CPU models that can run > out of the box using today's kernels. As no existing VMs running > Opteron_G* on AMD CPUs have rdtscp, I believe it makes sense to > just define Opteron_G* without rdtscp. > > When we add SVM rdtscp support to KVM, we can add new > "Opteron_G[2-5]-rdtscp" CPU models. Makes sense too. However, I'm a bit afraid of the interaction with libvirt. Right now, libvirt has rdtscp in the description. If we remove it from libvirt, libvirt will start adding +rdtscp to the QEMU CPU command line option, so our change will be moot. And if we do not remove it from libvirt, libvirt will not be able to start a VM with rdtscp on a fixed kernel. Is this correct? Paolo