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Re: [dm-devel] [PATCH 2/5] virtio_blk: implement REQ_FLUSH/FUA support



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


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