From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1Kplt5-0001vD-Oz
	for qemu-devel@nongnu.org; Tue, 14 Oct 2008 11:32:43 -0400
Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43)
	id 1Kplt3-0001v1-5N
	for qemu-devel@nongnu.org; Tue, 14 Oct 2008 11:32:42 -0400
Received: from [199.232.76.173] (port=33940 helo=monty-python.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1Kplt2-0001uy-Sd
	for qemu-devel@nongnu.org; Tue, 14 Oct 2008 11:32:40 -0400
Received: from qw-out-1920.google.com ([74.125.92.146]:33372)
	by monty-python.gnu.org with esmtp (Exim 4.60)
	(envelope-from <anthony@codemonkey.ws>) id 1Kplt2-0001br-Ls
	for qemu-devel@nongnu.org; Tue, 14 Oct 2008 11:32:40 -0400
Received: by qw-out-1920.google.com with SMTP id 5so583445qwc.4
	for <qemu-devel@nongnu.org>; Tue, 14 Oct 2008 08:32:38 -0700 (PDT)
Message-ID: <48F4BB93.5030709@codemonkey.ws>
Date: Tue, 14 Oct 2008 10:32:35 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [RFC] Disk integrity in QEMU
References: <48EE38B9.2050106@codemonkey.ws>
	<48EF1D55.7060307@redhat.com>	<48F0E83E.2000907@redhat.com>
	<48F10DFD.40505@codemonkey.ws>
	<20081012004401.GA9763@acer.localdomain>
	<48F1CF9E.9030500@redhat.com> <48F23AF1.2000104@codemonkey.ws>
	<48F24320.9010201@redhat.com> <48F25720.9010306@codemonkey.ws>
	<48F26171.70109@redhat.com> <48F2681A.1030401@codemonkey.ws>
	<48F4B904.6000608@redhat.com>
In-Reply-To: <48F4B904.6000608@redhat.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Reply-To: qemu-devel@nongnu.org
List-Id: qemu-devel.nongnu.org
List-Unsubscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.gnu.org/pipermail/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <http://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
To: Avi Kivity <avi@redhat.com>
Cc: Chris Wright <chrisw@redhat.com>, Mark McLoughlin <markmc@redhat.com>, kvm-devel <kvm-devel@lists.sourceforge.net>, Laurent Vivier <Laurent.Vivier@bull.net>, qemu-devel@nongnu.org, Ryan Harper <ryanh@us.ibm.com>

Avi Kivity wrote:
> I don't think O_DIRECT should be qemu's default, since anyone using qemu
> directly is likely a "causal virtualization" user.  Management systems
> like ovirt should definitely default to O_DIRECT (really, they shouldn't
> even offer caching).
>   

ovirt isn't a good example because the default storage model is iSCSI.  
Since you aren't preserving zero-copy, I doubt that you'll see any 
advantage to using O_DIRECT (I suspect the code paths aren't even 
different).

Regards,

Anthony Liguori