From mboxrd@z Thu Jan  1 00:00:00 1970
From: Tejun Heo <tj@kernel.org>
Subject: Re: [PATCH 2/5] virtio_blk: implement REQ_FLUSH/FUA support
Date: Tue, 17 Aug 2010 10:17:15 +0200
Message-ID: <4C6A458B.5040407@kernel.org>
References: <1281977523-19335-1-git-send-email-tj@kernel.org> <1281977523-19335-3-git-send-email-tj@kernel.org> <20100816183317.GA28171@lst.de>
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Cc: jaxboe@fusionio.com, linux-fsdevel@vger.kernel.org,
	linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org,
	linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org,
	James.Bottomley@suse.de, tytso@mit.edu, chris.mason@oracle.com,
	swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp,
	dm-devel@redhat.com, vst@vlnb.net, jack@suse.cz,
	rwheeler@redhat.com, hare@suse.de, neilb@suse.de,
	rusty@rustcorp.com.au, mst@redhat.com
To: Christoph Hellwig <hch@lst.de>
Return-path: <linux-scsi-owner@vger.kernel.org>
In-Reply-To: <20100816183317.GA28171@lst.de>
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List-Id: linux-fsdevel.vger.kernel.org

Hello,

On 08/16/2010 08:33 PM, Christoph Hellwig wrote:
> On Mon, Aug 16, 2010 at 06:52:00PM +0200, Tejun Heo wrote:
>> From: Tejun Heo <tj@kernle.org>
>>
>> Remove now unused REQ_HARDBARRIER support and implement REQ_FLUSH/FUA
>> support instead.  A new feature flag VIRTIO_BLK_F_FUA is added to
>> indicate the support for FUA.
> 
> I'm not sure it's worth it.  The pure REQ_FLUSH path works not and is
> well tested with kvm/qemu.   We can still easily add a FUA bit, and
> even a pre-flush bit if the protocol roundtrips matter in real life
> benchmarking.

Hmmm... the underlying storage could be md/dm RAIDs in which case FUA
should be cheaper than FLUSH.

Thanks.

-- 
tejun