From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:58820) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tst5o-00034Y-Dv for qemu-devel@nongnu.org; Wed, 09 Jan 2013 05:41:09 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Tst5n-0008Gp-8c for qemu-devel@nongnu.org; Wed, 09 Jan 2013 05:41:08 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50427) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Tst5m-0008Gd-VS for qemu-devel@nongnu.org; Wed, 09 Jan 2013 05:41:07 -0500 Message-ID: <50ED4933.3040001@redhat.com> Date: Wed, 09 Jan 2013 11:40:51 +0100 From: Paolo Bonzini MIME-Version: 1.0 References: <1355941771-3418-1-git-send-email-namei.unix@gmail.com> <87k3s6shdv.wl%morita.kazutaka@lab.ntt.co.jp> <50D967C3.7020109@gmail.com> <50E58B19.2050701@gmail.com> <20130104163830.GF6310@stefanha-thinkpad.hitronhub.home> <50E7AEC4.5080309@gmail.com> <50E7BA41.3020307@gmail.com> <50E7DC9B.4080309@gmail.com> <50EACC61.2020603@redhat.com> <50EBB1CB.9030608@gmail.com> <20130108094025.GE2557@stefanha-thinkpad.redhat.com> <50EBEAD2.6070608@gmail.com> <50EBEE42.7010407@redhat.com> <50EBF755.3050607@gmail.com> <50EBFA3F.8030808@redhat.com> <50EBFE20.9010100@gmail.com> <50EC00CE.80205@redhat.com> <50EC0493.8030701@gmail.com> <50EC0D41.4070200@redhat.com> <50EC1C9A.5040006@gmail.com> <50ED45A8.5020706@redhat.com> <50ED4829.1070302@gmail.com> In-Reply-To: <50ED4829.1070302@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Liu Yuan Cc: Kevin Wolf , Stefan Hajnoczi , qemu-devel@nongnu.org, MORITA Kazutaka Il 09/01/2013 11:36, Liu Yuan ha scritto: >> But why is it useful to force-disable writeback caching? Do you have >> > any performance numbers? > This is not related to performance. What I want is to allow users to > choose Sheepdog cache mode (writethrough/writeback/directio) from cache=xxx. > > Obviously writeback mode show much better write performance over > writethrough cache in Sheepdog. NOTE: writethrough cache in Sheepdog is > a readonly cache which is always consistent with cluster data thus need > no flush at all. This is to boost read performance for read intensive > Guest over Sheepdog iamges. Ok, so the questions are (compared to older QEMU's writethrough mode): 1) how slower is QEMU's emulated-writethrough mode for writes, due to the extra requests? 2) how slower is QEMU's writeback mode for reads, due to the different structure of the cache? Paolo