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Date: Wed, 10 Apr 2024 08:02:25 -0700
From: Jakub Kicinski <kuba@kernel.org>
To: Julien Panis <jpanis@baylibre.com>
Cc: "David S. Miller" <davem@davemloft.net>, Eric Dumazet
 <edumazet@google.com>, Paolo Abeni <pabeni@redhat.com>, Russell King
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Subject: Re: [PATCH net-next v8 3/3] net: ethernet: ti: am65-cpsw: Add
 minimal XDP support
Message-ID: <20240410080225.2e024f7c@kernel.org>
In-Reply-To: <9cb903df-3e83-409a-aa4b-218742804cc6@baylibre.com>
References: <20240223-am65-cpsw-xdp-basic-v8-0-f3421b58da09@baylibre.com>
	<20240223-am65-cpsw-xdp-basic-v8-3-f3421b58da09@baylibre.com>
	<20240409174928.58a7c3f0@kernel.org>
	<9cb903df-3e83-409a-aa4b-218742804cc6@baylibre.com>
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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.