From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v4] kvm/fpu: Enable fully eager restore kvm FPU Date: Tue, 25 Sep 2012 10:16:25 +0200 Message-ID: <50616859.60804@redhat.com> References: <1348457323-22616-1-git-send-email-xudong.hao@intel.com> <50606B4F.5080600@redhat.com> <403610A45A2B5242BD291EDAE8B37D300FEC6747@SHSMSX102.ccr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "kvm@vger.kernel.org" , "Zhang, Xiantao" To: "Hao, Xudong" Return-path: Received: from mx1.redhat.com ([209.132.183.28]:50887 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753657Ab2IYIQa (ORCPT ); Tue, 25 Sep 2012 04:16:30 -0400 In-Reply-To: <403610A45A2B5242BD291EDAE8B37D300FEC6747@SHSMSX102.ccr.corp.intel.com> Sender: kvm-owner@vger.kernel.org List-ID: On 09/25/2012 04:32 AM, Hao, Xudong wrote: > > > > btw, it is clear that long term the fpu will always be eagerly loaded, > > as hosts and guests (and hardware) are updated. At that time it will > > make sense to remove the lazy fpu code entirely. But maybe that time is > > here already, since exits are rare and so the guest has a lot of chance > > to use the fpu, so eager fpu saves the #NM vmexit. > > > > Can you check a kernel compile on a westmere system? If eager fpu is > > faster there than lazy fpu, we can just make the fpu always eager and > > remove quite a bit of code. > > > I remember westmere does not support Xsave, do you want performance of fxsave/fresotr ? Yes. If a westmere is fast enough then we can probably justify it. If you can run tests on Sandy/Ivy Bridge, even better. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.