[Qemu-devel] strange behavior when using iotune

[Qemu-devel] strange behavior when using iotune

[Vasiliy Tolstov]

Hi. I'm try to shape disk via total_iops_sec in libvirt
libvirt 1.2.10
qemu 2.0.0

Firstly when i'm run vm with predefined
<total_iops_sec>5000</total_iops_sec> i have around 11000 iops (dd
if=/dev/sda bs=512K of=/dev/null)
After that i'm try to set via virsh --total_iops_sec 10 to want to
minimize io, but nothing changed.
After that i'm reboot vm with <total_iops_sec>10</total_iops_sec> and
get very slow io, but this expected. But libvirt says that i have is
around 600 iops.

My questions is - why i can't change total_iops_sec in run-time, and
why entered values does not equal values getting from libvirt ?

Thanks for any suggestions and any help.

-- 
Vasiliy Tolstov,
e-mail: v.tolstov@selfip.ru
jabber: vase@selfip.ru

Re: [Qemu-devel] strange behavior when using iotune

[Andrey Korolyov]

On Mon, Nov 24, 2014 at 3:02 PM, Vasiliy Tolstov <v.tolstov@selfip.ru> wrote:
> Hi. I'm try to shape disk via total_iops_sec in libvirt
> libvirt 1.2.10
> qemu 2.0.0
>
> Firstly when i'm run vm with predefined
> <total_iops_sec>5000</total_iops_sec> i have around 11000 iops (dd
> if=/dev/sda bs=512K of=/dev/null)
> After that i'm try to set via virsh --total_iops_sec 10 to want to
> minimize io, but nothing changed.
> After that i'm reboot vm with <total_iops_sec>10</total_iops_sec> and
> get very slow io, but this expected. But libvirt says that i have is
> around 600 iops.
>
> My questions is - why i can't change total_iops_sec in run-time, and
> why entered values does not equal values getting from libvirt ?
>
> Thanks for any suggestions and any help.
>
> --
> Vasiliy Tolstov,
> e-mail: v.tolstov@selfip.ru
> jabber: vase@selfip.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?

Re: [Qemu-devel] strange behavior when using iotune

[Vasiliy Tolstov]

2014-11-24 16:57 GMT+03:00 Andrey Korolyov <andrey@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@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@selfip.ru
jabber: vase@selfip.ru

Re: [Qemu-devel] strange behavior when using iotune

[Andrey Korolyov]

On Mon, Nov 24, 2014 at 5:09 PM, Vasiliy Tolstov <v.tolstov@selfip.ru> wrote:
> 2014-11-24 16:57 GMT+03:00 Andrey Korolyov <andrey@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@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@selfip.ru
> jabber: vase@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.

Re: [Qemu-devel] strange behavior when using iotune

[Vasiliy Tolstov]

2014-11-24 17:18 GMT+03:00 Andrey Korolyov <andrey@xdel.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.


My fail. I'm forget to add iflag=direct to dd. Now all fine i get is
around 20 MB/s which compared to 5000 iops.
Thanks.

-- 
Vasiliy Tolstov,
e-mail: v.tolstov@selfip.ru
jabber: vase@selfip.ru