From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43)
	id 1NwcFv-0005Ow-2i
	for qemu-devel@nongnu.org; Tue, 30 Mar 2010 10:17:23 -0400
Received: from [140.186.70.92] (port=40939 helo=eggs.gnu.org)
	by lists.gnu.org with esmtp (Exim 4.43) id 1NwcFt-0005O4-In
	for qemu-devel@nongnu.org; Tue, 30 Mar 2010 10:17:22 -0400
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.69)
	(envelope-from <anthony@codemonkey.ws>) id 1NwcFn-000860-I8
	for qemu-devel@nongnu.org; Tue, 30 Mar 2010 10:17:21 -0400
Received: from mail-pz0-f194.google.com ([209.85.222.194]:52320)
	by eggs.gnu.org with esmtp (Exim 4.69)
	(envelope-from <anthony@codemonkey.ws>) id 1NwcFn-00085g-CA
	for qemu-devel@nongnu.org; Tue, 30 Mar 2010 10:17:15 -0400
Received: by pzk32 with SMTP id 32so4551271pzk.4
	for <qemu-devel@nongnu.org>; Tue, 30 Mar 2010 07:17:13 -0700 (PDT)
Message-ID: <4BB2059C.8000209@codemonkey.ws>
Date: Tue, 30 Mar 2010 09:07:24 -0500
From: Anthony Liguori <anthony@codemonkey.ws>
MIME-Version: 1.0
Subject: Re: [Qemu-devel] [PATCH -V3 09/32] virtio-9p: Implement P9_TWRITE/
	Thread model in QEMU
References: <1269535420-31206-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com>	<1269535420-31206-10-git-send-email-aneesh.kumar@linux.vnet.ibm.com>	<4BB04A59.1040204@linux.vnet.ibm.com>	<4BB0C09D.7090204@linux.vnet.ibm.com>
	<4BB10E30.70908@redhat.com>	<4BB110B3.8040300@linux.vnet.ibm.com>
	<4BB1136B.6050506@redhat.com>	<4BB11A48.4060805@linux.vnet.ibm.com>
	<4BB1D143.5040308@redhat.com>	<4BB1F915.6020800@linux.vnet.ibm.com>
	<4BB1FC83.6000202@redhat.com>	<4BB202A5.8020105@linux.vnet.ibm.com>
	<4BB20496.3080102@redhat.com>
In-Reply-To: <4BB20496.3080102@redhat.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
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: ericvh@gmail.com, Kevin Wolf <kwolf@redhat.com>, jvrao <jvrao@linux.vnet.ibm.com>, "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>, qemu-devel@nongnu.org

On 03/30/2010 09:03 AM, Avi Kivity wrote:
>>
>> So it looks like we really only have one operation 
>> (qcow2_alloc_cluster_link_l2) that blocks.  Do we really think that 
>> it's sufficiently difficult to make this function asynchronous that 
>> it justifies threading the block layer?
>
> There are also tons of bdrv_pread()s and bdrv_pwrite()s.  Isn't 
> growing some of the tables synchronous? how about creating a snapshot?

Eh, that ruins my whole argument.

>
> If it were just one operation in qcow2, threading would be a big 
> overkill.  But threading also fixes all of the other format drivers, 
> and makes working on qcow2 easier.
>

Yeah, I think the only question is whether to stick threading in the 
generic block layer or within qcow2.

Regards,

Anthony Liguori