Created benchmarks modules for page_pool

[Jesper Dangaard Brouer <brouer@redhat.com>]

Hi Ilias and Lorenzo, (Cc others + netdev)

I've created two benchmarks modules for page_pool.

[1] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_simple.c
[2] https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/lib/bench_page_pool_cross_cpu.c

I think we/you could actually use this as part of your presentation[3]?

The first benchmark[1] illustrate/measure what happen when page_pool
alloc and free/return happens on the same CPU.  Here there are 3 modes
of operations with different performance characteristic.

Fast_path NAPI recycle (XDP_DROP use-case)
 - cost per elem: 15 cycles(tsc) 4.437 ns

Recycle via ptr_ring
 - cost per elem: 48 cycles(tsc) 13.439 ns

Failed recycle, return to page-allocator
 - cost per elem: 256 cycles(tsc) 71.169 ns


The second benchmark[2] measures what happens cross-CPU.  It is
primarily the concurrent return-path that I want to capture. As this
is page_pool's weak spot, that we/I need to improve performance of.
Hint when SKBs use page_pool return this will happen more often.
It is a little more tricky to get proper measurement as we want to
observe the case, where return-path isn't stalling/waiting on pages to
return.

- 1 CPU returning  , cost per elem: 110 cycles(tsc)   30.709 ns
- 2 concurrent CPUs, cost per elem: 989 cycles(tsc)  274.861 ns
- 3 concurrent CPUs, cost per elem: 2089 cycles(tsc) 580.530 ns
- 4 concurrent CPUs, cost per elem: 2339 cycles(tsc) 649.984 ns

[3] https://netdevconf.info/0x14/session.html?tutorial-add-XDP-support-to-a-NIC-driver
-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer