Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757677Ab0FOLpO (ORCPT ); Tue, 15 Jun 2010 07:45:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:1222 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752841Ab0FOLpM (ORCPT ); Tue, 15 Jun 2010 07:45:12 -0400 Message-ID: <4C1767C4.7020506@redhat.com> Date: Tue, 15 Jun 2010 14:45:08 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100430 Fedora/3.0.4-3.fc13 Thunderbird/3.0.4 MIME-Version: 1.0 To: Xiao Guangrong CC: Marcelo Tosatti , LKML , KVM list Subject: Re: [PATCH 0/6] KVM: MMU: support pte prefetch when intercepted guest #PF References: <4C16E974.8000304@cn.fujitsu.com> In-Reply-To: <4C16E974.8000304@cn.fujitsu.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1304 Lines: 36 On 06/15/2010 05:46 AM, Xiao Guangrong wrote: > Hi Avi, Marcelo, > > This patchset support pte prefetch when intercepted guest #PF, > the aim is to reduce guest #PF which can be intercepted by VMM. > > If we meet any failure in the prefetch path, we will exit it > and not try other ptes to avoid become heavy path. > > During my performance test, under EPT enabled case, unixbench > shows the performance improved ~1.2%, Once the guest has faulted in all memory, we shouldn't see much improvement, yes? > user EPT disable case, > unixbench shows the performance improved ~3.6% > I'm a little worried about this. In some workloads, prefetch can often fail due to gpte.a=0 so we spend effort doing nothing. There is also the issue of marking pages as accessed or even dirty when in fact the guest did not access them. We should map those pages with pte.a=pte.d=0 so we don't confuse host memory management. On EPT (which lacks a/d bits) we can't enable it (but we can on NPT). -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/