From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: Live migration broken when under heavy IO Date: Tue, 16 Jun 2009 07:50:12 -0500 Message-ID: <4A379504.4080100@us.ibm.com> References: <4A36B025.2080602@us.ibm.com> <4A37618E.6040606@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: "qemu-devel@nongnu.org" , kvm-devel To: Avi Kivity Return-path: Received: from e9.ny.us.ibm.com ([32.97.182.139]:33638 "EHLO e9.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752042AbZFPMuN (ORCPT ); Tue, 16 Jun 2009 08:50:13 -0400 Received: from d01relay02.pok.ibm.com (d01relay02.pok.ibm.com [9.56.227.234]) by e9.ny.us.ibm.com (8.13.1/8.13.1) with ESMTP id n5GCbicA020280 for ; Tue, 16 Jun 2009 08:37:44 -0400 Received: from d01av02.pok.ibm.com (d01av02.pok.ibm.com [9.56.224.216]) by d01relay02.pok.ibm.com (8.13.8/8.13.8/NCO v9.2) with ESMTP id n5GCoFuI253472 for ; Tue, 16 Jun 2009 08:50:15 -0400 Received: from d01av02.pok.ibm.com (loopback [127.0.0.1]) by d01av02.pok.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id n5GClvwZ015634 for ; Tue, 16 Jun 2009 08:47:58 -0400 In-Reply-To: <4A37618E.6040606@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: >> Does anyone have a clever idea how to fix this without just waiting >> for all IO requests to complete? > > What's wrong with waiting for requests to complete? It should take a > few tens of milliseconds. An alternative would be to attempt to cancel the requests. This incurs no non-deterministic latency. The tricky bit is that this has to happen at the device layer because the opaques cannot be saved in a meaningful way. > We could start throttling requests late in the live stage, but I don't > really see the point. > > Isn't virtio migration currently broken due to the qdev changes? > -- Regards, Anthony Liguori