From mboxrd@z Thu Jan  1 00:00:00 1970
Received: from eggs.gnu.org ([208.118.235.92]:35525)
	by lists.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1TstYY-0004Zo-7L
	for qemu-devel@nongnu.org; Wed, 09 Jan 2013 06:10:54 -0500
Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1TstYW-0007P3-Cb
	for qemu-devel@nongnu.org; Wed, 09 Jan 2013 06:10:50 -0500
Received: from mx1.redhat.com ([209.132.183.28]:30662)
	by eggs.gnu.org with esmtp (Exim 4.71)
	(envelope-from <pbonzini@redhat.com>) id 1TstYW-0007Ow-0t
	for qemu-devel@nongnu.org; Wed, 09 Jan 2013 06:10:48 -0500
Message-ID: <50ED5027.8090008@redhat.com>
Date: Wed, 09 Jan 2013 12:10:31 +0100
From: Paolo Bonzini <pbonzini@redhat.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>
	<50ED4829.1070302@gmail.com> <50ED4933.3040001@redhat.com>
	<50ED4A90.2080808@gmail.com> <50ED4D39.9000900@gmail.com>
In-Reply-To: <50ED4D39.9000900@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: <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: Liu Yuan <namei.unix@gmail.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, qemu-devel@nongnu.org, MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>

Il 09/01/2013 11:58, Liu Yuan ha scritto:
> On 01/09/2013 06:46 PM, Liu Yuan wrote:
>> I'll collect some numbers on it.
> 
> Well, when I use hdparm -W 0 /dev/vdx to choose the writethrough cache
> in the Guest (virtio disk), it says:
> 
> test@vm1:~$ sudo hdparm -W 0 /dev/vdb
> 
> /dev/vdb:
>  setting drive write-caching to 0 (off)
>  HDIO_DRIVE_CMD(identify) failed: Inappropriate ioctl for device
>  HDIO_DRIVE_CMD(flushcache) failed: Inappropriate ioctl for device
>  HDIO_DRIVE_CMD(setcache) failed: Inappropriate ioctl for device
>  HDIO_DRIVE_CMD(identify) failed: Inappropriate ioctl for device
>  HDIO_DRIVE_CMD(flushcache) failed: Inappropriate ioctl for device
>  HDIO_DRIVE_CMD(identify) failed: Inappropriate ioctl for device
> 
> Do I need extra flags to enable WCE?

"hdparm" is specific for IDE devices.  sysfs is supported by SCSI
(including IDE with libata, and virtio-scsi) and virtio-blk.

You can use this for SCSI:

echo 'write back' > /sys/block/sda/device/scsi_disk/*/cache_type

and a similar command for virtio-blk.

Paolo

> Both Guest and Host kernel is 3.7 and I start QEMU by following command:
> 
> $ qemu-system-x86_64 --enable-kvm -drive
> file=~/images/test1,if=virtio,cache=writeback -smp 2 -cpu host -m 1024
> -drive file=sheepdog:test,if=virtio,cache=writeback
> 
> Thanks,
> Yuan
> 
>