From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37025) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UlEVp-0001Hz-JM for qemu-devel@nongnu.org; Sat, 08 Jun 2013 04:28:39 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UlEVo-00065K-KY for qemu-devel@nongnu.org; Sat, 08 Jun 2013 04:28:37 -0400 Received: from e23smtp01.au.ibm.com ([202.81.31.143]:39527) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UlEVo-000655-2G for qemu-devel@nongnu.org; Sat, 08 Jun 2013 04:28:36 -0400 Received: from /spool/local by e23smtp01.au.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 8 Jun 2013 18:20:05 +1000 Message-ID: <51B2EA3D.8020905@linux.vnet.ibm.com> Date: Sat, 08 Jun 2013 16:24:29 +0800 From: Wenchao Xia MIME-Version: 1.0 References: <51A7036A.3050407@ozlabs.ru> <51A7049F.6040207@redhat.com> <51A70B3D.90609@ozlabs.ru> <51A71705.6060009@kamp.de> <51A74D79.7040204@redhat.com> In-Reply-To: <51A74D79.7040204@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Qemu-devel] broken incoming migration List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Paolo Bonzini Cc: Alexey Kardashevskiy , "qemu-ppc@nongnu.org" , Peter Lieven , "qemu-devel@nongnu.org" , David Gibson 于 2013-5-30 21:00, Paolo Bonzini 写道: > Il 30/05/2013 11:08, Peter Lieven ha scritto: >> Am 30.05.2013 10:18, schrieb Alexey Kardashevskiy: >>> On 05/30/2013 05:49 PM, Paolo Bonzini wrote: >>>> Il 30/05/2013 09:44, Alexey Kardashevskiy ha scritto: >>>>> Hi! >>>>> >>>>> I found the migration broken on pseries platform, specifically, this patch >>>>> broke it: >>>>> >>>>> f1c72795af573b24a7da5eb52375c9aba8a37972 >>>>> migration: do not sent zero pages in bulk stage >>>>> >>>>> The idea is not to send zero pages to the destination guest which is >>>>> expected to have 100% empty RAM. >>>>> >>>>> However on pseries plaftorm the guest always has some stuff in the RAM as a >>>>> part of initialization (device tree, system firmware and rtas (?)) so it is >>>>> not completely empty. As the source guest cannot detect this, it skips some >>>>> pages during migration and we get a broken destination guest. Bug. >>>>> >>>>> While the idea is ok in general, I do not see any easy way to fix it as >>>>> neither QEMUMachine::init nor QEMUMachine::reset callbacks has information >>>>> about whether we are about to receive a migration or not (-incoming >>>>> parameter) and we cannot move device-tree and system firmware >>>>> initialization anywhere else. >>>>> >>>>> ram_bulk_stage is static and cannot be disabled from the platform >>>>> initialization code. >>>>> >>>>> So what would the community suggest? >>>> Revert the patch. :) >>> I'll wait for 24 hours (forgot to cc: the author) and then post a revert >>> patch :) >>> >> does this problem only occur on pseries emulation? > > Probably not. On a PC, it would occur if you had 4K of zeros in the > source BIOS but not in the destination BIOS. When you reboot, the BIOS > image is wrong. > So one way is to migrate BIOS contents together? >> not sending zero pages is not only a performance benefit it also makes >> overcomitted memory usable. the madv_dontneed seems to kick in asynchronously >> and memory is not available immediately. > > You could also scan the page for nonzero values before writing it. > > Paolo > -- Best Regards Wenchao Xia