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

[Cong Meng <mc@linux.vnet.ibm.com>]

On Thu, 2012-06-14 at 09:30 +0100, Stefan Hajnoczi wrote:
> On Wed, Jun 13, 2012 at 11:13 AM, mengcong <mc@linux.vnet.ibm.com> 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?
> 

virtio-scsi-raw     43065  69729    52052  67378    1757 29419    2024 28135

qemu ....\
-drive file=/dev/sdb,format=raw,if=none,id=sdb,cache=none,aio=native \
-device virtio-scsi-pci,id=mcbus \
-device scsi-disk,drive=sdb

there is only one scsi HBA. 
/dev/sdb is the disk on which all tests have been done. 

Is this what you want?

Cong Meng


> Stefan
>