netdev - Re: [PATCH v2 2/2] net: ethernet: ti: am65-cpsw: Add minimal XDP support

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Date: Tue, 12 Mar 2024 11:28:59 +0100
From: Julien Panis <jpanis@...libre.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Russell King <linux@...linux.org.uk>,
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>,
 Jesper Dangaard Brouer <hawk@...nel.org>,
 John Fastabend <john.fastabend@...il.com>,
 Sumit Semwal <sumit.semwal@...aro.org>,
 Christian König <christian.koenig@....com>,
 Simon Horman <horms@...nel.org>, netdev@...r.kernel.org,
 linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
 linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
 linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v2 2/2] net: ethernet: ti: am65-cpsw: Add minimal XDP
 support

On 3/5/24 17:43, Andrew Lunn wrote:
>> 3) From 2), am65_cpsw_alloc_skb() function removed and replaced by
>> netdev_alloc_skb_ip_align(), as used by the driver before -> res = 506
>> Conclusion: Here is where the loss comes from.
>> IOW, My am65_cpsw_alloc_skb() function is not good.
>>
>> Initially, I mainly created this 'custom' am65_cpsw_alloc_skb() function
>> because I thought that none of XDP memory models could be used along
>> with netdev_alloc_skb_ip_align() function. Was I wrong ?
>> By creating this custom am65_cpsw_alloc_skb(), I also wanted to handle
>> the way headroom is reserved differently.
> What is special about your device? Why would
> netdev_alloc_skb_ip_align() not work?
>
> 	Andrew

Nothing special about my device, I just misunderstood.

Regarding page pool, I now have better performance.
Two things were missing:
- I did not call skb_mark_for_recycle(), so pages were freed instead of
being recycled !
- In page_pool_params, that's better when I specify the "napi" parameter.

Performance improvement is not that impressive, but it's better:
505 Mbits/sec (with page pool) instead of 495 Mbits/sec (without).
There is a ~ 5 Mbits/sec loss due to additional processing in the path, for XDP stuffs.
So, the difference in favor of page pool using is ~ 15 Mbits/sec.

I'll send a v4 soon.

Julien