I agree, been checking some of my more disk intensive VMs this morning, switching them to noop definitely improved responsiveness. All the virtio ones I’ve found were using deadline (with RHEL/Centos guests), but some of the virt-scsi were using deadline and some were noop, so I’m not sure of a definitive answer on that level yet. 

For the hosts, it depends on what your backend is running. With a separate storage server on my main cluster, it doesn’t matter what the hosts set for me. You mentioned you run hyper converged, so I’d say it depends on what your disks are. If you’re using SSDs, go none/noop as they don’t benefit from the queuing. If they are HDDs, I’d test cfq or deadline and see which gave better latency and throughput to your vms. I’d guess you’ll find deadline to offer better performance, but cfq to share better amongst multiple VMs. Unless you use ZFS underneath, then go noop and let ZFS take care of it.

On Mar 18, 2019, at 2:05 PM, Strahil <hunter86_bg@yahoo.com> wrote:

Hi Darrel,

Still, based on my experience we shouldn't queue our I/O in the VM, just to do the same in the Host.

I'm still considering if I should keep deadline  in my hosts or to switch to 'cfq'.
After all, I'm using Hyper-converged oVirt and this needs testing.
What I/O scheduler  are  you using on the  host?

Best Regards,
Strahil Nikolov

On Mar 18, 2019 19:15, Darrell Budic <budic@onholyground.com> wrote:

Checked this on mine, see the same thing. Switching the engine to noop definitely feels more responsive.

I checked on some VMs as well, it looks like virtio drives (vda, vdb….) get mq-deadline by default, but virtscsi gets noop. I used to think the tuned profile for virtual-guest would set noop, but apparently not…

  -Darrell

On Mar 18, 2019, at 1:58 AM, Strahil Nikolov <hunter86_bg@yahoo.com> wrote:

Hi All,

I have changed my I/O scheduler to none and here are the results so far:

Before (mq-deadline):

Adding a disk to VM (initial creation) START:     2019-03-17 16:34:46.709

Adding a disk to VM (initial creation) COMPLETED: 2019-03-17 16:45:17.996

After (none):

Adding a disk to VM (initial creation) START:     2019-03-18 08:52:02.xxx

Adding a disk to VM (initial creation) COMPLETED: 2019-03-18 08:52:20.xxx

Of course the results are inconclusive, as I have tested only once - but I feel the engine more responsive.

Best Regards,

Strahil Nikolov

В неделя, 17 март 2019 г., 18:30:23 ч. Гринуич+2, Strahil <hunter86_bg@yahoo.com> написа:

Dear All,

I have just noticed that my Hosted Engine has  a strange I/O scheduler:

Last login: Sun Mar 17 18:14:26 2019 from 192.168.1.43
[root@engine ~]# cat /sys/block/vda/queue/scheduler
[mq-deadline] kyber none
[root@engine ~]#

Based on my experience  anything than noop/none  is useless and performance degrading  for a VM.

Is there any reason that we have this scheduler ?
It is quite pointless  to process (and delay) the I/O in the VM and then process (and again delay)  on Host Level .

If there is no reason to keep the deadline, I will open a bug about it.

Best Regards,
Strahil Nikolov

Dear All,

I have just noticed that my Hosted Engine has  a strange I/O scheduler:

Last login: Sun Mar 17 18:14:26 2019 from 192.168.1.43
[root@engine ~]# cat /sys/block/vda/queue/scheduler
[mq-deadline] kyber none
[root@engine ~]#

Based on my experience  anything than noop/none  is useless and performance degrading  for a VM.

_______________________________________________
Users mailing list -- users@ovirt.org
To unsubscribe send an email to users-leave@ovirt.org
Privacy Statement: https://www.ovirt.org/site/privacy-policy/
oVirt Code of Conduct: https://www.ovirt.org/community/about/community-guidelines/
List Archives: https://lists.ovirt.org/archives/list/users@ovirt.org/message/MMTH6225GKYQEZ26BXDBTB52LNWMWVBH/