netdev - Re: [PATCH v3 net-next 2/2] xdp: add multi-buff support for xdp running in generic mode

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Date: Wed, 6 Dec 2023 08:03:33 -0800
From: Jakub Kicinski <kuba@...nel.org>
To: Jesper Dangaard Brouer <hawk@...nel.org>
Cc: Lorenzo Bianconi <lorenzo@...nel.org>, aleksander.lobakin@...el.com,
 netdev@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
 pabeni@...hat.com, lorenzo.bianconi@...hat.com, bpf@...r.kernel.org,
 toke@...hat.com, willemdebruijn.kernel@...il.com, jasowang@...hat.com,
 sdf@...gle.com
Subject: Re: [PATCH v3 net-next 2/2] xdp: add multi-buff support for xdp
 running in generic mode

On Wed, 6 Dec 2023 13:41:49 +0100 Jesper Dangaard Brouer wrote:
> BUT then I realized that PP have a weakness, which is the return/free
> path that need to take a normal spin_lock, as that can be called from
> any CPU (unlike the RX/alloc case).  Thus, I fear that making multiple
> devices share a page_pool via softnet_data, increase the chance of lock
> contention when packets are "freed" returned/recycled.

I was thinking we can add a pcpu CPU ID to page pool so that
napi_pp_put_page() has a chance to realize that its on the "right CPU"
and feed the cache directly.