[RFC net-next 0/2] mvpp2: page_pool support

[Matteo Croce <mcroce@redhat.com>]

This patches change the memory allocator of mvpp2 from the frag allocator to
the page_pool API. This change is needed to add later XDP support to mvpp2.

The reason I send it as RFC is that with this changeset, mvpp2 performs much
more slower. This is the tc drop rate measured with a single flow:

stock net-next with frag allocator:
rx: 900.7 Mbps 1877 Kpps

this patchset with page_pool:
rx: 423.5 Mbps 882.3 Kpps

This is the perf top when receiving traffic:

  27.68%  [kernel]            [k] __page_pool_clean_page
   9.79%  [kernel]            [k] get_page_from_freelist
   7.18%  [kernel]            [k] free_unref_page
   4.64%  [kernel]            [k] build_skb
   4.63%  [kernel]            [k] __netif_receive_skb_core
   3.83%  [mvpp2]             [k] mvpp2_poll
   3.64%  [kernel]            [k] eth_type_trans
   3.61%  [kernel]            [k] kmem_cache_free
   3.03%  [kernel]            [k] kmem_cache_alloc
   2.76%  [kernel]            [k] dev_gro_receive
   2.69%  [mvpp2]             [k] mvpp2_bm_pool_put
   2.68%  [kernel]            [k] page_frag_free
   1.83%  [kernel]            [k] inet_gro_receive
   1.74%  [kernel]            [k] page_pool_alloc_pages
   1.70%  [kernel]            [k] __build_skb
   1.47%  [kernel]            [k] __alloc_pages_nodemask
   1.36%  [mvpp2]             [k] mvpp2_buf_alloc.isra.0
   1.29%  [kernel]            [k] tcf_action_exec

I tried Ilias patches for page_pool recycling, I get an improvement
to ~1100, but I'm still far than the original allocator.

Any idea on why I get such bad numbers?

Another reason to send it as RFC is that I'm not fully convinced on how to
use the page_pool given the HW limitation of the BM.

The driver currently uses, for every CPU, a page_pool for short packets and
another for long ones. The driver also has 4 rx queue per port, so every
RXQ #1 will share the short and long page pools of CPU #1.

This means that for every RX queue I call xdp_rxq_info_reg_mem_model() twice,
on two different page_pool, can this be a problem?

As usual, ideas are welcome.

Matteo Croce (2):
  mvpp2: use page_pool allocator
  mvpp2: memory accounting

 drivers/net/ethernet/marvell/Kconfig          |   1 +
 drivers/net/ethernet/marvell/mvpp2/mvpp2.h    |   7 +
 .../net/ethernet/marvell/mvpp2/mvpp2_main.c   | 142 +++++++++++++++---
 3 files changed, 125 insertions(+), 25 deletions(-)

-- 
2.24.1