From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:51744) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WB5S9-0007IZ-47 for qemu-devel@nongnu.org; Wed, 05 Feb 2014 11:36:05 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WB5Ry-0003Sc-5m for qemu-devel@nongnu.org; Wed, 05 Feb 2014 11:35:57 -0500 Received: from mail-qa0-x231.google.com ([2607:f8b0:400d:c00::231]:63806) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WB5Ry-0003SS-1U for qemu-devel@nongnu.org; Wed, 05 Feb 2014 11:35:46 -0500 Received: by mail-qa0-f49.google.com with SMTP id w8so879447qac.8 for ; Wed, 05 Feb 2014 08:35:45 -0800 (PST) Sender: Paolo Bonzini Message-ID: <52F2685D.2050405@redhat.com> Date: Wed, 05 Feb 2014 17:35:41 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <52F0938F.2040102@ozlabs.ru> <52F0C523.30102@redhat.com> <52F0D611.7070105@ozlabs.ru> <52F0D810.4070806@redhat.com> <52F0DA04.9040003@ozlabs.ru> <52F0F26A.5020304@redhat.com> <52F16708.8060902@ozlabs.ru> <52F1E5BA.60902@redhat.com> <20140205090912.GA2398@work-vm> In-Reply-To: <20140205090912.GA2398@work-vm> Content-Type: text/plain; charset=ISO-8859-1; 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: "Dr. David Alan Gilbert" Cc: Alexey Kardashevskiy , "qemu-devel@nongnu.org" , Alex Graf Il 05/02/2014 10:09, Dr. David Alan Gilbert ha scritto: > I think the case Alexey is hitting is: > 1 A few dirtied pages > 2 but because of the hpratio most of the data is actually zero > - indeed most of the target-page sized chunks are zero > 3 Thus the data compresses very heavily > 4 When the bandwidth/delay calculation happens it's spent a reasonable > amount of time transferring a reasonable amount of pages but not > actually many bytes on the wire, so the estimate of the available > bandwidth available is lower than reality. > 5 The max-downtime calculation is a comparison of pending-dirty uncompressed > bytes with compressed bandwidth > > (5) is bound to fail if the compression ratio is particularly high, which > because of the hpratio it is if we're just dirtying one word in an entire > host page. So far so good, but why isn't pending-dirty (aka migration_dirty_pages in the code) zero? Paolo