From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([2001:4830:134:3::10]:60607)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <Chris.Friesen@windriver.com>) id 1aOAH0-0000nL-0T
	for qemu-devel@nongnu.org; Tue, 26 Jan 2016 15:31:34 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <Chris.Friesen@windriver.com>) id 1aOAGw-0007cO-Qs
	for qemu-devel@nongnu.org; Tue, 26 Jan 2016 15:31:33 -0500
Received: from mail1.windriver.com ([147.11.146.13]:50017)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <Chris.Friesen@windriver.com>) id 1aOAGw-0007bm-Jv
	for qemu-devel@nongnu.org; Tue, 26 Jan 2016 15:31:30 -0500
Message-ID: <56A7D79D.1020307@windriver.com>
Date: Tue, 26 Jan 2016 14:31:25 -0600
From: Chris Friesen <chris.friesen@windriver.com>
MIME-Version: 1.0
References: <56A7A1A8.4060704@windriver.com>
	<20160126164521.GK15172@redhat.com>
In-Reply-To: <20160126164521.GK15172@redhat.com>
Content-Type: text/plain; charset="utf-8"; format=flowed
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] high outage times for qemu virtio network links
 during live migration, trying to debug
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: "Daniel P. Berrange" <berrange@redhat.com>
Cc: libvir-list@redhat.com, qemu-devel@nongnu.org

On 01/26/2016 10:45 AM, Daniel P. Berrange wrote:
> On Tue, Jan 26, 2016 at 10:41:12AM -0600, Chris Friesen wrote:

>> My question is, why doesn't qemu continue processing virtio packets while
>> the dirty page scanning and memory transfer over the network is proceeding?
>
> The qemuDomainMigratePrepareTunnel3Params() method is responsible for
> starting the QEMU process on the target host. This should not normally
> have any impact on host networking connectivity, since the CPUs on that
> target QEMU wouldn't be running at that point. Perhaps the mere act of
> starting QEMU and plugging the TAP dev into the network on the target
> host causes some issue though ? eg are you using a bridge that is doing
> STP or something like that.

Well, looks like your suspicions were correct.  Our fast-path backend was 
mistakenly sending out a GARP when the backend was initialized as part of 
creating the qemu process on the target host.  Oops.

Thanks for your help.

Chris