From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kevin Wolf Subject: Re: [Qemu-devel] Re: KVM call minutes for Sept 14 Date: Wed, 15 Sep 2010 10:30:16 +0200 Message-ID: <4C908418.9070301@redhat.com> References: <20100914144758.GA19949@x200.localdomain> <4C8F90A9.8030407@codemonkey.ws> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Chris Wright , qemu-devel@nongnu.org, kvm@vger.kernel.org To: Anthony Liguori Return-path: Received: from mx1.redhat.com ([209.132.183.28]:10092 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752643Ab0IOIaA (ORCPT ); Wed, 15 Sep 2010 04:30:00 -0400 In-Reply-To: <4C8F90A9.8030407@codemonkey.ws> Sender: kvm-owner@vger.kernel.org List-ID: Am 14.09.2010 17:11, schrieb Anthony Liguori: > On 09/14/2010 09:47 AM, Chris Wright wrote: >> 0.13 >> - if all goes well...tomorrow >> > > To tag, it may be thursday for announcement. I need to run a regression > run tonight. > >> qed/qcow2 >> - increase concurrency, performance >> > > To achieve performance, a block driver must: 1) support concurrent > request handling 2) not hold the qemu_mutex for prolonged periods of time. > > QED never does (2) and supports (1) in all circumstances except cluster > allocation today. > > qcow2 can do (1) for the data read/write portions of an I/O request. > All metadata read/write is serialized. It also does (2) for all > metadata operations and for CoW operations. > > These are implementation details though. The real claim of QED is that > by having fewer IO ops required to satisfy a request, it achieves better > performance especially since it achieves zero syncs in the cluster > allocation path. qcow2 has two syncs in the cluster allocation path > today. One sync is due to the refcount table. Another sync is due to > the fact that it doesn't require fsck support. The refcount table sync is the sync that allows not doing an fsck. For a simple cluster allocation (no L2 allocation, no COW), we only have one sync (which is still one sync too much in this path, so we must move it). Kevin