Re: [Qemu-devel] IO performance test on the tcm-vhost scsi

[Stefan Hajnoczi]

On Wed, Jun 13, 2012 at 11:13 AM, mengcong <address@hidden> wrote:
>                    seq-read        seq-write       rand-read     rand-write
>                    8k     256k     8k     256k     8k   256k     8k   256k
> ----------------------------------------------------------------------------
> bare-metal          67951  69802    67064  67075    1758 29284    1969 26360
> tcm-vhost-iblock    61501  66575    51775  67872    1011 22533    1851 28216
> tcm-vhost-pscsi     66479  68191    50873  67547    1008 22523    1818 28304
> virtio-blk          26284  66737    23373  65735    1724 28962    1805 27774
> scsi-disk           36013  60289    46222  62527    1663 12992    1804 27670
>
> unit: KB/s
> seq-read/write = sequential read/write
> rand-read/write = random read/write
> 8k,256k are blocksize of the IO

What strikes me is how virtio-blk performs significantly worse than
bare metal and tcm_vhost for seq-read/seq-write 8k.  The good
tcm_vhost results suggest that the overhead is not the virtio
interface itself, since tcm_vhost implements virtio-scsi.

To drill down on the tcm_vhost vs userspace performance gap we need
virtio-scsi userspace results.  QEMU needs to use the same block
device as the tcm-vhost-iblock benchmark.

Cong: Is it possible to collect the virtio-scsi userspace results
using the same block device as tcm-vhost-iblock and -drive
format=raw,aio=native,cache=none?

Stefan