Re: [PATCH net] sctp: linearize early if it's not GSO

On 08/17/2016 12:35 AM, Marcelo Ricardo Leitner wrote:

Because otherwise when crc computation is still needed it's way more
expensive than on a linear buffer to the point that it affects
performance.

It's so expensive that netperf test gives a perf output as below:

Overhead  Shared Object        Symbol
   69,44%  [kernel]             [k] gf2_matrix_square
    2,84%  [kernel]             [k] crc32_generic_combine.part.0
    2,78%  [kernel]             [k] _raw_spin_lock_bh

What kernel is this, seems not net kernel?

$ git grep -n gf2_matrix_square
$ git grep -n crc32_generic_combine
$

Maybe RHEL? Did you consider backporting 6d514b4e7737 et al?

And performance goes from 2Gbit/s to 0.5Gbit/s on this test. Doing the
linearization before checksumming is enough to restore it.

Fixes: 3acb50c18d8d ("sctp: delay as much as possible skb_linearize")
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>