netdev - Re: [PATCH net-next v8 3/3] net: ethernet: ti: am65-cpsw: Add minimal XDP support

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Message-ID: <16790d82-e134-4a3b-b67e-d56c041362c0@baylibre.com>
Date: Fri, 12 Apr 2024 15:56:39 +0200
From: Julien Panis <jpanis@...libre.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, 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>, Andrew Lunn <andrew@...n.ch>,
 Ratheesh Kannoth <rkannoth@...vell.com>,
 Naveen Mamindlapalli <naveenm@...vell.com>, danishanwar@...com,
 yuehaibing@...wei.com, rogerq@...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 net-next v8 3/3] net: ethernet: ti: am65-cpsw: Add minimal
 XDP support

On 4/10/24 17:02, Jakub Kicinski wrote:
> On Wed, 10 Apr 2024 16:02:00 +0200 Julien Panis wrote:
>>> You shouldn't build the skb upfront any more. Give the page to the HW,
>>> once HW sends you a completion - build the skbs. If build fails
>>> (allocation failure) just give the page back to HW. If it succeeds,
>>> however, you'll get a skb which is far more likely to be cache hot.
>> Not sure I get this point.
>>
>> "Give the page to the HW" = Do you mean that I should dma_map_single()
>> a full page (|PAGE_SIZE|) in am65_cpsw_nuss_rx_push() ?
> Yes, I think so. I think that's what you effectively do now anyway,
> you just limit the len and wrap it in an skb. But
> am65_cpsw_nuss_rx_push() will effectively get that page back from
> skb->data and map it.

That's much better indeed, with the implementation you suggest: 600 Mbits/sec
instead of 500. I did not expect such improvement.
I'll send a new version when I finish retesting.