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Reviewed:  https://review.openstack.org/416400
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=9a022e7d7b85b7c21cf26698fe59c818c4577194
Submitter: Jenkins
Branch:    master

commit 9a022e7d7b85b7c21cf26698fe59c818c4577194
Author: Kevin Benton <kevin@xxxxxxxxxx>
Date:   Tue Jan 3 18:10:36 2017 -0800

    Reduce IP link show calls for SR-IOV scan loop
    
    The device scanning logic was calling 'ip link show' for every
    vf_index on the system, which was taking an excessive amount of
    time an CPU cycles on very dense SR-IOV servers (>64 interfaces).
    This was being executed every 2 seconds so it would cause the
    agent to take a large percentage of the CPU time.
    
    This patch adjusts the logic to use two 'ip link show' commands for
    checking all of the operations in a single get_assigned_devices_info
    call.
    
    Closes-Bug: #1653880
    Change-Id: I361caaf7f70580ee8c7b48a4a9c9477bdefd8b4b


** Changed in: neutron
       Status: In Progress => Fix Released

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

Title:
  sr-iov device scanning takes significant time

Status in neutron:
  Fix Released

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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