[Openstack-operators] UDP Buffer Filling

Saverio Proto zioproto at gmail.com
Fri Jul 28 07:59:00 UTC 2017

Hello John,

a common problem is packets being dropped when they pass from the
hypervisor to the instance. There is bottleneck there.

check the 'virsh dumpxml' of one of the instances that is dropping
packets. Check for the interface section, should look like:

    <interface type='bridge'>
      <mac address='xx:xx:xx:xx:xx:xx'/>
      <source bridge='qbr5b3fc033-e2'/>
      <target dev='tap5b3fc033-e2'/>
      <model type='virtio'/>
      <driver name='vhost' queues='4'/>
      <alias name='net0'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x03'

how many queues you have ??? Usually if you have only 1 or if the
parameter is missing completely is not good.

in Mitaka nova should use 1 queue for every instance CPU core you
have. It is worth to check if this is set correctly in your setup.



2017-07-27 17:49 GMT+02:00 John Petrini <jpetrini at coredial.com>:
> Hi List,
> We are running Mitaka with VLAN provider networking. We've recently
> encountered a problem where the UDP receive queue on instances is filling up
> and we begin dropping packets. Moving instances out of OpenStack onto bare
> metal resolves the issue completely.
> These instances are running asterisk which should be pulling these packets
> off the queue but it appears to be falling behind no matter the resources we
> give it.
> We can't seem to pin down a reason why we would see this behavior in KVM but
> not on metal. I'm hoping someone on the list might have some insight or
> ideas.
> Thank You,
> John
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> OpenStack-operators at lists.openstack.org
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