From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1KdRUd-0006Up-GY
	for qemu-devel@nongnu.org; Wed, 10 Sep 2008 11:20:31 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1KdRUc-0006Tw-23
	for qemu-devel@nongnu.org; Wed, 10 Sep 2008 11:20:31 -0400
Received: from [199.232.76.173] (port=58316 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1KdRUb-0006Tr-N7
	for qemu-devel@nongnu.org; Wed, 10 Sep 2008 11:20:29 -0400
Received: from e31.co.us.ibm.com ([32.97.110.149]:40630)
	by monty-python.gnu.org with esmtps
	(TLS-1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.60)
	(envelope-from <aliguori@us.ibm.com>) id 1KdRUb-0002m2-7t
	for qemu-devel@nongnu.org; Wed, 10 Sep 2008 11:20:29 -0400
Received: from d03relay04.boulder.ibm.com (d03relay04.boulder.ibm.com
	[9.17.195.106])
	by e31.co.us.ibm.com (8.13.8/8.13.8) with ESMTP id m8AFKPPb017888
	for <qemu-devel@nongnu.org>; Wed, 10 Sep 2008 11:20:25 -0400
Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170])
	by d03relay04.boulder.ibm.com (8.13.8/8.13.8/NCO v9.1) with ESMTP id
	m8AFKBrq083278
	for <qemu-devel@nongnu.org>; Wed, 10 Sep 2008 09:20:11 -0600
Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1])
	by d03av04.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id
	m8AFKAvI017858
	for <qemu-devel@nongnu.org>; Wed, 10 Sep 2008 09:20:11 -0600
Message-ID: <48C7E579.5040702@us.ibm.com>
Date: Wed, 10 Sep 2008 10:19:21 -0500
From: Anthony Liguori <aliguori@us.ibm.com>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH 3/10] Add bdrv_flush_all()
References: <1220989802-13706-1-git-send-email-aliguori@us.ibm.com>
	<1220989802-13706-4-git-send-email-aliguori@us.ibm.com>
	<48C7CB05.8070107@redhat.com>
	<5d6222a80809100746kd4bcf21h5c3fd9afbec1067d@mail.gmail.com>
In-Reply-To: <5d6222a80809100746kd4bcf21h5c3fd9afbec1067d@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Glauber Costa <glommer@gmail.com>
Cc: Chris Wright <chrisw@redhat.com>, Uri Lublin <uri.lublin@qumranet.com>, qemu-devel@nongnu.org, kvm@vger.kernel.org

Glauber Costa wrote:
> On Wed, Sep 10, 2008 at 10:26 AM, Chris Lalancette <clalance@redhat.com> wrote:
>   
>> Anthony Liguori wrote:
>>     
>>> This patch adds a bdrv_flush_all() function.  It's necessary to ensure that all
>>> IO operations have been flushed to disk before completely a live migration.
>>>
>>> N.B. we don't actually use this now.  We really should flush the block drivers
>>> using an live savevm callback to avoid unnecessary guest down time.
>>>       
>> Simple enough, and follows the pattern in the KVM migration.
>>
>> Chris Lalancette
>>
>>     
> sounds ok.
>   

I'm actually liking bdrv_flush_all() less and less.  If there are any 
outstanding IO requests, it will increase the down time associated with 
live migration.  I think we definitely need to add a live save handler 
that waits until there are no outstanding IO requests to converge.  I'm 
concerned though that it's not totally unreasonable to expect a guest to 
always have an IO request in flight.  That leads me to think that maybe 
we should be cancelling outstanding requests, and somehow saving their 
state?

Regards,

Anthony Liguori