Re: [PATCH 0/6] tcm_vhost/virtio-scsi WIP code for-3.6

On 07/05/12 17:53, Bart Van Assche wrote:

On 07/05/12 01:52, Nicholas A. Bellinger wrote:

quoted

fio randrw workload | virtio-scsi-raw | virtio-scsi+tcm_vhost | bare-metal raw block
------------------------------------------------------------------------------------
25 Write / 75 Read  |      ~15K       |         ~45K          |         ~70K
75 Write / 25 Read  |      ~20K       |         ~55K          |         ~60K

These numbers are interesting. To me these numbers mean that there is a
huge performance bottleneck in the virtio-scsi-raw storage path. Why is
the virtio-scsi-raw bandwidth only one third of the bare-metal raw block
bandwidth ?

(replying to my own e-mail)

Or maybe the above numbers mean that in the virtio-scsi-raw test I/O was
serialized (I/O depth 1) while the other two tests use a large I/O depth
(64) ? It can't be a coincidence that the virtio-scsi-raw results are
close to the bare-metal results for I/O depth 1.

Another question: which functionality does tcm_vhost provide that is not
yet provided by the SCSI emulation code in qemu + tcm_loop ?

Bart.