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

[Ilias Apalodimas]

On Tue, Dec 24, 2019 at 02:01:01AM +0100, Matteo Croce wrote:
> 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

This seems extremly high on the list. 

>    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.

Can you post the recycling perf for comparison?

> 
> Any idea on why I get such bad numbers?

Nop but it's indeed strange

> 
> 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.

I'll have a look right after holidays

> 
> 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.
> 

I am not sure i am following the hardware config here

> 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
> 
Cheers
/Ilias