From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:47186) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UCqfB-0004aG-2l for qemu-devel@nongnu.org; Tue, 05 Mar 2013 07:08:13 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1UCqf7-0007ZR-9T for qemu-devel@nongnu.org; Tue, 05 Mar 2013 07:08:09 -0500 Received: from mx1.redhat.com ([209.132.183.28]:34269) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1UCqf7-0007ZH-1q for qemu-devel@nongnu.org; Tue, 05 Mar 2013 07:08:05 -0500 Message-ID: <5135DF34.8060508@redhat.com> Date: Tue, 05 Mar 2013 13:04:04 +0100 From: Pavel Hrdina MIME-Version: 1.0 References: <1362038985-19008-1-git-send-email-xiawenc@linux.vnet.ibm.com> <20130228105035.GE2429@dhcp-200-207.str.redhat.com> <513013F0.2030007@linux.vnet.ibm.com> <5134B7F0.5020008@linux.vnet.ibm.com> In-Reply-To: <5134B7F0.5020008@linux.vnet.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC PATCH 0/4] savevm: save vmsate with fixed size List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wenchao Xia Cc: Kevin Wolf , aliguori@us.ibm.com, quintela@redhat.com, stefanha@gmail.com, qemu-devel@nongnu.org, pbonzini@redhat.com On 03/04/2013 04:04 PM, Wenchao Xia wrote: > >>> You probably get some improvements of the file size when the migration >>> takes a while, depending on how much of the memory actually has to be >>> saved. You might however end up with a lot more small writes instead of >>> some big ones before, which might hurt performance. >>> >>> Do you have any data about the resulting performance and file size? >>> >> ah, an important issue I haven't test, thanks for tipping it, let >> me add code for migration to file, and have a test. It also >> can be optimized a bit in qemu_fseek(), but IMHO the optimization >> for small writes would better goto block layer either in qemu >> or underling components in system. >> > Hi,Juan > talking about performance, in migration there are two buffer used, > one in qemu_file as static array, and one in migration as dynamic > allocated buffer, > should they be merged to avoid extra memcpy? > Hi Wenchao, This is already posted on qemu-devel list, http://lists.gnu.org/archive/html/qemu-devel/2013-02/msg04119.html http://lists.gnu.org/archive/html/qemu-devel/2013-02/msg04222.html Pavel