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[Kevin Benton <1653880@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

The excessive calls to 'ip link show' can consume significant amounts of
CPU cycles on every scan_devices iteration on densely packed SR-IOV
systems.

Snip from https://bugs.launchpad.net/mos/+bug/1653131 :

On a node with SR-IOV interfaces neutron-sriov-agent seems to call 'ip
link show' every 2 second for each interface. This leads to CPU
utilization up to 60+% (I've seen 32% for neutron-rootwrap and 32% for
neutron-sriov-nic-agent)

Since output of `ip link show' is the same for all interfaces, it is
enough to call it only once per 2 sec interval

root@node-7:~# grep '15:10:' /var/log/neutron/neutron-sriov-agent.log | grep "'ip', 'link', 'show'" | wc -l
5783

** Affects: neutron
     Importance: High
     Assignee: Kevin Benton (kevinbenton)
         Status: In Progress

** Changed in: neutron
     Assignee: (unassigned) => Kevin Benton (kevinbenton)

** Changed in: neutron
   Importance: Undecided => High

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https://bugs.launchpad.net/bugs/1653880

Title:
  sr-iov device scanning takes significant time

Status in neutron:
  In Progress

Bug description:
  The excessive calls to 'ip link show' can consume significant amounts
  of CPU cycles on every scan_devices iteration on densely packed SR-IOV
  systems.

  Snip from https://bugs.launchpad.net/mos/+bug/1653131 :

  On a node with SR-IOV interfaces neutron-sriov-agent seems to call 'ip
  link show' every 2 second for each interface. This leads to CPU
  utilization up to 60+% (I've seen 32% for neutron-rootwrap and 32% for
  neutron-sriov-nic-agent)

  Since output of `ip link show' is the same for all interfaces, it is
  enough to call it only once per 2 sec interval

  root@node-7:~# grep '15:10:' /var/log/neutron/neutron-sriov-agent.log | grep "'ip', 'link', 'show'" | wc -l
  5783

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