From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: KVM Processor cache size Date: Mon, 02 Aug 2010 16:08:35 +0300 Message-ID: <4C56C353.7020607@redhat.com> References: <4C56BF6F.9040402@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Andre Przywara , Ricardo Martins , "kvm@vger.kernel.org" To: Anthony Liguori Return-path: Received: from mx1.redhat.com ([209.132.183.28]:54585 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751306Ab0HBNIl (ORCPT ); Mon, 2 Aug 2010 09:08:41 -0400 In-Reply-To: <4C56BF6F.9040402@amd.com> Sender: kvm-owner@vger.kernel.org List-ID: On 08/02/2010 03:51 PM, Andre Przywara wrote: > Ricardo Martins wrote: >> Hi guys, >> >> I'm having a problem with kvm, my physical machine have 2 processor >> Xeon E5520, with 8 mb cache size, when i run "cat /proc/cpuinfo" the >> linux shows 16 processors equal. >> >> processor : 15 >> vendor_id : GenuineIntel >> cpu family : 6 >> model : 26 >> model name : Intel(R) Xeon(R) CPU E5520 @ 2.27GHz >> stepping : 5 >> cpu MHz : 1596.000 >> cache size : 8192 KB > > .... >> The problem is that when I run the same command on the virtual >> machine, Linux shows the processors with only 32 kb, I believe that >> anything is wrong. >> >> processor : 0 >> vendor_id : GenuineIntel >> cpu family : 6 >> model : 6 >> model name : QEMU Virtual CPU version 0.9.1 >> stepping : 3 >> cpu MHz : 2266.575 >> cache size : 32 KB > > .... >> On virtual Machine: >> linea:/# x86info >> x86info v1.21. Dave Jones 2001-2007 >> >> >> Found 1 CPU, but found 16d CPUs in MPTable. >> -------------------------------------------------------------------------- >> >> Family: 6 Model: 6 Stepping: 3 Type: 0 Brand: 0 >> CPU Model: Celeron / Mobile Pentium II Original OEM >> Feature flags: >> fpu de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 >> clflsh mmx fxsr sse sse2 >> Extended feature flags: >> sse3 [31] >> [0] [2] [3] [4] [5] [6] [7] [8] [9] SYSCALL [13] [15] [16] xd [23] >> [24] em64t >> Cache info >> L1 Instruction cache: 32KB, 8-way associative. 64 byte line size. >> L1 Data cache: 32KB, 8-way associative. 64 byte line size. >> L2 unified cache: 2MB, sectored, 8-way associative. 64 byte line size. >> TLB info > > KVM (or better: the QEMU part) injects a bogus CPU model (compare > family/model/name), which is the same on all host CPUs. This helps > with migration, because the CPU does not change. > The cache size is also the same, as it is part of the "cpuid" command > output. > You can use other CPU models (like kvm64) for better base models, but > the cache size will likely not match your host processor's one. > For that purpose exists the "host" CPU model, which will (to some > degree) simply push your host CPU model to the guest. For now this > only affects the family/model/stepping/name values and the feature flags. > I sent a patch to include the cache size when using -cpu host, but > this has been n'acked because the benefit is not clear. Anthony, why was this NACKed? First, there are programs which query the cache size. That's why it's exposed! Second, -cpu host is for exposing as many host cpu features as we can, not just those we have an immediate use for. It's like 'cp -a' dropping attributes the author didn't care about. -- error compiling committee.c: too many arguments to function