Xenial, ethtool hangs while enabling MQ and consumes 100% if executed after OVS+DPDK startup

Christian Ehrhardt christian.ehrhardt at canonical.com
Wed Apr 13 20:01:39 UTC 2016

On Wed, Apr 13, 2016 at 9:28 PM, Martinx - ジェームズ <thiagocmartinsc at gmail.com>
I couldn't exactly follow all of your setup, but since it is working lets
assume that was fine.

>  1- Reboot the VM and try to run ethtool again:

To confirm after the reboot the device should have 1 of X queues enabled as
it is not persistent across reboots.
But OVS-DPDK is starting, likely trying to create X queues as you
configured but can't get them.

>  ethtool -L ens6 combined 4
 # FAIL! It hangs, consuming 100% of guest's CPU...

Hmm, I'll need to reproduce that tomorrow.
I mean you switch queues underneath OVS-DPDK using one of them, which isn't
nice - but it shouldn't totally block.

>  So, is this the right procedure? I mean, I believe that ethtool settings
> doesn't survive across reboots, but, OVS settings are on its DB... Question
> is, do we need to run ethtool on each reboot before starting OVS+DPDK with
> VirtIO again?
I agree your issue is that ethtool combined queues is not persistent while
starting OVS and its config are.
You will have to get the queues persistent before OVS-DPDK gets to start.
It is not really a task for DPDK, nor OVS - more like sysctl but for
network config.
I haven't looked into that yet - let me know if you found a nice way -
otherwise I'll start on it tomorrow together with analyzing what/why hangs
on changing #queues.
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