[libvirt] [Qemu-devel] strange behavior when using iotune

[Andrey Korolyov]

On Mon, Nov 24, 2014 at 5:09 PM, Vasiliy Tolstov <v.tolstov at selfip.ru> wrote:
> 2014-11-24 16:57 GMT+03:00 Andrey Korolyov <andrey at xdel.ru>:
>> Hello Vasiliy,
>>
>> can you please check actual values via qemu-monitor-command domid '{
>> "execute": "query-block"}', just to be sure to pin the potential
>> problem to the emulator itself?
>
> virsh qemu-monitor-command 11151 '{ "execute": "query-block"}' | jq '.'
> {
>   "return": [
>     {
>       "io-status": "ok",
>       "device": "drive-scsi0-0-0-0",
>       "locked": false,
>       "removable": false,
>       "inserted": {
>         "iops_rd": 0,
>         "image": {
>           "virtual-size": 21474836480,
>           "filename": "/dev/vg3/11151",
>           "format": "raw",
>           "actual-size": 0,
>           "dirty-flag": false
>         },
>         "iops_wr": 0,
>         "ro": false,
>         "backing_file_depth": 0,
>         "drv": "raw",
>         "iops": 5000,
>         "bps_wr": 0,
>         "encrypted": false,
>         "bps": 0,
>         "bps_rd": 0,
>         "iops_max": 500,
>         "file": "/dev/vg3/11151",
>         "encryption_key_missing": false
>       },
>       "type": "unknown"
>     }
>   ],
>   "id": "libvirt-22"
> }
>
> i'm used this site
> http://www.ssdfreaks.com/content/599/how-to-convert-mbps-to-iops-or-calculate-iops-from-mbs
> root at 11151:~# dd if=/dev/sda bs=4K of=/dev/null
> 5242880+0 records in
> 5242880+0 records out
> 21474836480 bytes (21 GB) copied, 45.2557 s, 475 MB/s
>
> so in case of 5000 iops i need to get only 19-20 MB/s
>
>
> --
> Vasiliy Tolstov,
> e-mail: v.tolstov at selfip.ru
> jabber: vase at selfip.ru

I am not sure for friendliness of possible dd interpretations for new
leaky bucket mechanism, as its results can be a little confusing even
for fio (all operations which are above the limit for long-running
test will have 250ms latency, putting down score numbers in most
popular tests like UnixBench), also w/o sync options these results are
almost meaningless. May be fio with direct=1|fsync=1 (for fs) will
give a more appropriate numbers in your case.