From: Alexander Duyck <redacted>
Date: Tue, 24 Feb 2015 12:47:55 -0800

This patch series implements the second phase of the fib_trie changes.  I
presented on these and the previous changes at Netdev01 and netconf.  The
slides for the Netdev01 presentation can be found at
https://www.netdev01.org/docs/duyck-fib-trie.pdf.

I'm currently debating if I should just submit the entire patch-set as-is
or if I should hold off on submitting the last 10 patches as they currently
have a potential performance impact in the case of a large number of
entries placed in the local table.  Specifically I have seen that removing
an interface in the case of 8K local subnets being configured on it
resulted in the time for a dummy interface being removed increasing from
about .6 seconds to 2.4 seconds.  I am not sure how common of a use-case
something like this would be.  I have not seen the same issue if I assign
8K routes to the interface as I believe the fib_table_flush aggregates them
all in to one resize action.

The entire series reduces the total look-up time by another 20-35% versus
what is currently in the 4.0-rc1 kernel.  So for example a set of routing
look-ups which took 140ns in the 4.0-rc1 kernel will now only take about
105ns after these patches.

I did a quick once-over for these changes and conceptually they look
fine.

Why are sequences of removals so much more costly now?  Is it because
of the maintainence of the information in the parent when rebalancing?

In any event, I'll say two things:

1) You should submit these changes in smaller batches anyways.
   It's easier to review and get small sets of transformations
   tested as a unit.

2) For the device removal case, we can batch the inet addr removal
   based route delete operations, and thus mitigate the rebalancing
   costs.