From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:57953)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <namei.unix@gmail.com>) id 1Tst1Q-0001RV-6g
	for qemu-devel@nongnu.org; Wed, 09 Jan 2013 05:36:38 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <namei.unix@gmail.com>) id 1Tst1O-0006wf-Vn
	for qemu-devel@nongnu.org; Wed, 09 Jan 2013 05:36:36 -0500
Received: from mail-pb0-f49.google.com ([209.85.160.49]:40168)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <namei.unix@gmail.com>) id 1Tst1O-0006wR-Pm
	for qemu-devel@nongnu.org; Wed, 09 Jan 2013 05:36:34 -0500
Received: by mail-pb0-f49.google.com with SMTP id un15so867538pbc.36
	for <qemu-devel@nongnu.org>; Wed, 09 Jan 2013 02:36:33 -0800 (PST)
Message-ID: <50ED4829.1070302@gmail.com>
Date: Wed, 09 Jan 2013 18:36:25 +0800
From: Liu Yuan <namei.unix@gmail.com>
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>
In-Reply-To: <50ED45A8.5020706@redhat.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Subject: Re: [Qemu-devel] [PATCH] sheepdog: implement direct write semantics
List-Id: <qemu-devel.nongnu.org>
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>

On 01/09/2013 06:25 PM, Paolo Bonzini wrote:
> 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.

Thanks,
Yuan