[Bug 1281366] Re: ip command becomes slower with large number of network devices

[Rafael David Tinoco]

Bryan

Id like you to reconsider this test if possible. Better results have
also been confirmed by others (including customers).

Fake routers creation performance depends on other issues (not only
covered by this bug) like CPU scalability (since netlink generated work
is delayed by kernel and offloaded to RCU callbacks). There are some
other issues being investigated for fake router creation but for this
specific bug I can confirm results several times.

Keep in mind that results are sometimes less then 10% better because of
kernel RCU offload characteristics (like for example when using only 1
CPU for the test).

My testcase:

I'm using last good commit generated kernel for this case (34ed6246).
After this specific commit (upstream kernel) performance for fake router
creation brakes (I'll put other BUG information and # at the end of this
case, when appropriate).

By now, from kernel 3.2 to kernel 3.9 (up to this commit), general
behavior is to have RCU callbacks enabled (no configuration on what cpu
to offload up to this point) and this is what "NOCB" stands for on the
attached file.

Independently of the kernel (running on precise), iproute userland tool
+ this patch gives better results.

Please take a look at the attached file specifically on "average"
fields.

Thanks in advance.


** Attachment added: "1278534-iproute-kernel.png"
   https://bugs.launchpad.net/ubuntu/+source/iproute/+bug/1281366/+attachment/4121548/+files/1278534-iproute-kernel.png

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https://bugs.launchpad.net/bugs/1281366

Title:
  ip command becomes slower with large number of network devices

Status in “iproute” package in Ubuntu:
  Fix Released
Status in “iproute” source package in Precise:
  Fix Committed
Status in “iproute” source package in Quantal:
  Won't Fix

Bug description:
  [Impact]
  When using iproute commands with a large number of network devices (virtual ethernet adapters, etc) iproute performance becomes much slower.

  [Test Case]
  1) Download attached 'make_fake_routers.sh' and 'parse.py' scripts.
  2) ./make_fake_routers.sh 3000 ip > results
  3) ./parse.py results

  You should be able to graph and clearly see a performance improvement
  with the fix than without it.

  [Regression Potential]
  This patch fixes the issue:
  https://git.kernel.org/cgit/linux/kernel/git/shemminger/iproute2.git/commit/?id=f0124b0f0aa0e5b9288114eb8e6ff9b4f8c33ec8
  This patch is upstream and is currently in saucy and beyond.

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