From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH v4 06/10] KVM: MMU: fast path of handling guest page fault Date: Thu, 03 May 2012 15:13:47 +0300 Message-ID: <4FA2767B.5010707@redhat.com> References: <4F9776D2.7020506@linux.vnet.ibm.com> <4F9777A4.208@linux.vnet.ibm.com> <20120426234535.GA5057@amt.cnet> <4F9A3445.2060305@linux.vnet.ibm.com> <20120427145213.GB28796@amt.cnet> <20120429175004.b54d8c095a60d98c8cdbc942@gmail.com> <4FA0C8A7.9000001@linux.vnet.ibm.com> <20120502211031.GB12604@amt.cnet> <4FA27578.1010509@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti , Takuya Yoshikawa , LKML , KVM To: Xiao Guangrong Return-path: In-Reply-To: <4FA27578.1010509@linux.vnet.ibm.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 05/03/2012 03:09 PM, Xiao Guangrong wrote: > Actually, the improvement of lockless is that it can let vcpu to be parallel > as possible. > > From the test result, lockless gains little improvement for unix-migration, > in this case, the vcpus are almost idle (at least not busy). > > The large improvement is from dbench-migration, in this case, all vcpus are > busy accessing memory which is write-protected by dirty-log. If you enable > page-fault/fast-page-fault tracepoints, you can see huge number of page fault > from different vcpu during the migration. > We can kill the page faults completely by using A/D bits in shadow page tables. The latest version of the Intel SDM defines A/D bits for EPT, and NPT has had them from day one. Of course this comes at a cost, instead of traversing a bitmap we have to read all sptes, which are 64x as large. But it's probably worthwhile for large guests and perhaps also for smaller ones. -- error compiling committee.c: too many arguments to function