From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [Qemu-devel] [PATCH 3/10] Add bdrv_flush_all() Date: Wed, 10 Sep 2008 18:39:47 +0300 Message-ID: <48C7EA43.5010102@qumranet.com> 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> <48C7E579.5040702@us.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Glauber Costa , Chris Wright , Uri Lublin , kvm@vger.kernel.org To: qemu-devel@nongnu.org Return-path: Received: from il.qumranet.com ([212.179.150.194]:19090 "EHLO il.qumranet.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752019AbYIJPjt (ORCPT ); Wed, 10 Sep 2008 11:39:49 -0400 In-Reply-To: <48C7E579.5040702@us.ibm.com> Sender: kvm-owner@vger.kernel.org List-ID: Anthony Liguori wrote: > > 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. I/O requests should complete in milliseconds; I don't see them as increasing migration latency. > That leads me to think that maybe we should be cancelling outstanding > requests, and somehow saving their state? Migration is enough of a special case that we should avoid special cases within it as much as possible. -- error compiling committee.c: too many arguments to function From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1KdRnK-00039J-80 for qemu-devel@nongnu.org; Wed, 10 Sep 2008 11:39:50 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1KdRnJ-00038t-9O for qemu-devel@nongnu.org; Wed, 10 Sep 2008 11:39:49 -0400 Received: from [199.232.76.173] (port=43171 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1KdRnJ-00038m-4D for qemu-devel@nongnu.org; Wed, 10 Sep 2008 11:39:49 -0400 Received: from il.qumranet.com ([212.179.150.194]:19091) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1KdRnI-00063u-MP for qemu-devel@nongnu.org; Wed, 10 Sep 2008 11:39:48 -0400 Message-ID: <48C7EA43.5010102@qumranet.com> Date: Wed, 10 Sep 2008 18:39:47 +0300 From: Avi Kivity 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> <48C7E579.5040702@us.ibm.com> In-Reply-To: <48C7E579.5040702@us.ibm.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: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Chris Wright , Glauber Costa , kvm@vger.kernel.org, Uri Lublin Anthony Liguori wrote: > > 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. I/O requests should complete in milliseconds; I don't see them as increasing migration latency. > That leads me to think that maybe we should be cancelling outstanding > requests, and somehow saving their state? Migration is enough of a special case that we should avoid special cases within it as much as possible. -- error compiling committee.c: too many arguments to function