From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57346) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XbfKN-0007lX-Kd for qemu-devel@nongnu.org; Tue, 07 Oct 2014 20:42:09 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XbfKH-0006ED-41 for qemu-devel@nongnu.org; Tue, 07 Oct 2014 20:42:03 -0400 Received: from mx1.redhat.com ([209.132.183.28]:24813) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XbfKG-0006E7-SW for qemu-devel@nongnu.org; Tue, 07 Oct 2014 20:41:57 -0400 Message-ID: <54348850.9080808@redhat.com> Date: Tue, 07 Oct 2014 19:41:52 -0500 From: Wei Huang MIME-Version: 1.0 References: <1412711059-12524-1-git-send-email-wei@redhat.com> <543453D9.8020706@redhat.com> <54345843.8070703@redhat.com> <54345CC8.8050806@redhat.com> In-Reply-To: <54345CC8.8050806@redhat.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 1/1] target-i386: prevent users from setting threads>1 for AMD CPUs List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini , afaerber@suse.de Cc: qemu-devel@nongnu.org On 10/07/2014 04:36 PM, Paolo Bonzini wrote: > Il 07/10/2014 23:16, Wei Huang ha scritto: >> It isn't a bug IMO. I tested various combinations; and current QEMU >> handles it very well. It converts threads=n to proper >> CPUID_0000_0001_EBX[LogicalProcCount] and CPUID_8000_0008_ECX[NC] >> accordingly for AMD. > > So if it ain't broken, don't fix it. :) > >>> I am worried that the default CPU is an AMD one when KVM is disabled, >>> and thus "qemu-system-x86_64 -smp threads=2" will likely be broken. >> >> "-smp threads=2" will be rejected by the patch. > > Yeah, I am afraid that is an incompatible change, and one more reason > not to do this. AMD not selling hyperthreaded processors does not mean > that they could not be represented properly with the CPUID leaves that > AMD processors support. I am OK with either way. The key question is: should QEMU presents CPUIDs strictly as specified by the command line or QEMU can tweak a little bit on behalf of end-users? For instance, if end-users say "-smp 8,cores=2,threads=2,sockets=2", they meant "two socket, each has two 2-hyperthread cores". Current QEMU will convert CPUID as "two socket, each has 4 cores". My patch will forbid the tweaking... -Wei > > Paolo > >> Unless the meaning of >> threads is not limited to threads-per-core, shouldn't end users use >> "-smp 2" in this case or something like "-smp 2,cores=2,sockets=1"? >