From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57751) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WAenD-0005U8-PX for qemu-devel@nongnu.org; Tue, 04 Feb 2014 07:08:02 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WAen7-0005L1-PI for qemu-devel@nongnu.org; Tue, 04 Feb 2014 07:07:55 -0500 Received: from mx1.redhat.com ([209.132.183.28]:54846) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WAen7-0005Kv-Fr for qemu-devel@nongnu.org; Tue, 04 Feb 2014 07:07:49 -0500 Message-ID: <52F0D810.4070806@redhat.com> Date: Tue, 04 Feb 2014 13:07:44 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <52F0938F.2040102@ozlabs.ru> <52F0C523.30102@redhat.com> <52F0D611.7070105@ozlabs.ru> In-Reply-To: <52F0D611.7070105@ozlabs.ru> Content-Type: text/plain; charset=KOI8-R; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] migration: broken ram_save_pending List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey Kardashevskiy , "qemu-devel@nongnu.org" Cc: Alex Graf Il 04/02/2014 12:59, Alexey Kardashevskiy ha scritto: >> > With the default throttling of 32 MiB/s, bandwidth must be something like >> > 33000 (expressed in bytes/ms) with the default settings, and then max_size >> > should be 33000*3*10^9 / 10^6 = 6000000. Where is my computation wrong? > > migrate_max_downtime() = 30000000 = 3*10^7. Oops, that's the mistake. > When the migration is in iterating stage, bandwidth is a speed in last > 100ms which is usually 5 blocks 250KB each so it is > 1250000/100=12500bytes/s and max_size=12500*30000000/10^6=375000 which is > less than the last chunk is. > > Perhaps our default maximum downtime is too low. 30 ms doesn't seem achievable in practice with 32 MiB/s bandwidth. Just making it 300 ms or so should fix your problem. Paolo