Messages in this thread | | | Date | Thu, 02 Aug 2012 14:43:04 +0800 | From | Asias He <> | Subject | Re: [PATCH V5 4/4] virtio-blk: Add REQ_FLUSH and REQ_FUA support to bio path |
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On 08/02/2012 02:27 PM, Christoph Hellwig wrote: > On Thu, Aug 02, 2012 at 02:25:56PM +0800, Asias He wrote: >> We need to support both REQ_FLUSH and REQ_FUA for bio based path since >> it does not get the sequencing of REQ_FUA into REQ_FLUSH that request >> based drivers can request. >> >> REQ_FLUSH is emulated by: >> 1. Send VIRTIO_BLK_T_FLUSH to device >> 2. Wait until the flush is finished > > There is no need to wait for the flush to finish if the REQ_FLUSH > request has no data payload. > > Even if it has a payload waiting is highly suboptimal and it should > use a non-blocking sequencing like it is done in the request layer.
So, for REQ_FLUSH, what we need is that send out the VIRTIO_BLK_T_FLUSH and not to wait.
>> >> REQ_FUA is emulated by: >> 1. Send the actual write >> 2. Wait until the actual write is finished >> 3. Send VIRTIO_BLK_T_FLUSH to device >> 4. Wait until the flush is finished >> 5. Signal the end of the write to upper layer > > The same comment about not blocking applies here as well.
We still need to wait until the actual write is finished here? Like,
REQ_FUA is emulated by: 1. Send the actual write 2. Wait until the actual write is finished 3. Send VIRTIO_BLK_T_FLUSH to device 4. Signal the end of the write to upper layer -- Asias
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