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SubjectRe: [PATCH 2/5] virtio_blk: implement REQ_FLUSH/FUA support

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 <>
>> 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.



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