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Hi all,

I've recently done some disk benchmarks (dd and bonnie++) between instances
with virtio-blk and with virtio-scsi and found that on my test bed
virtio-scsi performed 11.68% slower for writes and 4.83% slower for reads.
I wasn't expecting a performance loss with virtio-scsi. Has anyone else
experienced this? I was looking at using virtio-scsi to gain discard/trim
support but not if it results in a net loss in disk performance.

Test bed details:
Ubuntu 14.04 LTS
Kernel: 3.13.0-111-generic
Libvirt:1.3.1-1ubuntu10.6~cloud0
qemu:2.5+dfsg-5ubuntu10.5~cloud0

Attached are the detailed results of the benchmarking. I am going to pursue
some tests with Ubuntu 16.04 as the host.

Thanks,

Jared
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virtio

Bonnie 1
Version  1.97       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
virtio           4G   917  99 227598  24 189488  22  4102  99 1429562  84 13324 149
Latency             10703us     383ms     467ms    2259us    5672us    2646us
Version  1.97       ------Sequential Create------ --------Random Create--------
virtio              -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
Latency               339us     329us    1271us     120us      28us     125us

Bonnie 2
Version  1.97       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
virtio           4G   917  99 231821  22 194734  20  4114 100 1756669  80 12997 147
Latency              9306us     536ms     372ms    2249us    7030us   10802us
Version  1.97       ------Sequential Create------ --------Random Create--------
virtio              -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
Latency               862us     332us     447us     120us      18us     129us

Bonnie 3
Version  1.97       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
virtio           4G   915  99 228310  22 199567  19  4063  99 2017469  77 14048 159
Latency             13840us     440ms     458ms    3346us     790us    2483us
Version  1.97       ------Sequential Create------ --------Random Create--------
virtio              -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
Latency               328us     332us     354us     514us      50us     171us
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virtio-scsi

Bonnie 1
Version  1.97       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
virtio-scsi      4G   923  99 200432  27 184818  24  4011  99 1308526  81 +++++ +++
Latency              9052us     269ms     713ms    3391us    6405us    5934us
Version  1.97       ------Sequential Create------ --------Random Create--------
virtio-scsi         -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
Latency               110us     340us     345us     124us      15us     161us

Bonnie 2
Version  1.97       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
virtio-scsi      4G   918  99 196409  28 196646  26  4061  99 1261905  81 +++++ +++
Latency             10665us     698ms     681ms    3910us    8179us    2331us
Version  1.97       ------Sequential Create------ --------Random Create--------
virtio-scsi         -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
Latency               809us     336us    3278us     488us      20us     926us

Bonnie 3
Version  1.97       ------Sequential Output------ --Sequential Input- --Random-
Concurrency   1     -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine        Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP  /sec %CP
virtio-scsi      4G   920  99 203097  28 205820  27  3981  99 1289584  82 10212 123
Latency             10882us     694ms     760ms    2337us    7544us    4411us
Version  1.97       ------Sequential Create------ --------Random Create--------
virtio-scsi         -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
              files  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP  /sec %CP
                 16 +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++ +++++ +++
Latency               603us     329us     349us     114us      20us     174us