From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760302Ab2DKOOs (ORCPT ); Wed, 11 Apr 2012 10:14:48 -0400 Received: from mail-pz0-f52.google.com ([209.85.210.52]:56697 "EHLO mail-pz0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754164Ab2DKOOr (ORCPT ); Wed, 11 Apr 2012 10:14:47 -0400 Date: Wed, 11 Apr 2012 23:14:41 +0900 From: Takuya Yoshikawa To: Xiao Guangrong Cc: Avi Kivity , Marcelo Tosatti , Xiao Guangrong , LKML , KVM Subject: Re: [PATCH 00/13] KVM: MMU: fast page fault Message-Id: <20120411231441.9d0984672dd252b806f99128@gmail.com> In-Reply-To: <4F857B61.9080602@linux.vnet.ibm.com> References: <4F742951.7080003@linux.vnet.ibm.com> <4F82E04E.6000900@redhat.com> <20120409175829.GB21894@amt.cnet> <4F8329D3.7000605@gmail.com> <20120409194614.GB23053@amt.cnet> <4F840DD2.3090101@redhat.com> <20120410204031.ffb5b976225ac9fe6dae474e@gmail.com> <4F842074.1050108@linux.vnet.ibm.com> <20120411211514.35db29c11460516e604059b6@gmail.com> <4F857B61.9080602@linux.vnet.ibm.com> X-Mailer: Sylpheed 3.2.0beta3 (GTK+ 2.24.6; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 11 Apr 2012 20:38:57 +0800 Xiao Guangrong wrote: > Well, my point is that live migration is so very useful that it is worth > to be improved, the description of your also proves this point. > > What is your really want to say but i missed? How to improve and what we should pay for that. Note that I am not objecting to O(1) itself. Do you remember that when we discussed O(1) issue last year, with Avi, the agreement was that we should take more time and look carefully with more measurements to confirm if it's really worthwhile. The point is whether we should do O(1) now, including near future. My opinion is that we should do what we can do now and wait for feedback from real users. Before making the current code stable, I do not want to see it replaced so dramatically. Otherwise when can we use live migration with enough confidence? There may be another subtle bugs we should fix now. In addition, XBRZLE and post-copy is now being developed in QEMU. What do you think about this Avi, Marcelo? I am testing the current live migration to see when and for what it can be used. I really want to see it become stable and usable for real services. > Okay, let us to compare the performance number after O(1) implemented. >>From my experience, I want to say that live migration is very difficult to say about performance. That is the problem I am now struggling with. I developed dirty-log-perf unit-test for that but that was not enough. Needless to say, checking the correctness is harder. So I really do not want to see drastic change now without any real need or feedback from real users -- this is my point. Thanks, Takuya