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

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Message-ID: <20240409174928.58a7c3f0@kernel.org>
Date: Tue, 9 Apr 2024 17:49:28 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Julien Panis <jpanis@...libre.com>
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 Mon, 08 Apr 2024 11:38:04 +0200 Julien Panis wrote:
> +static struct sk_buff *am65_cpsw_alloc_skb(struct am65_cpsw_rx_chn *rx_chn,
> +					   struct net_device *ndev,
> +					   unsigned int len,
> +					   int desc_idx,
> +					   bool allow_direct)
> +{
> +	struct sk_buff *skb;
> +	struct page *page;
> +
> +	page = page_pool_dev_alloc_pages(rx_chn->page_pool);
> +	if (unlikely(!page))
> +		return NULL;
> +
> +	len += AM65_CPSW_HEADROOM;
> +
> +	skb = build_skb(page_address(page), len);

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.

> +	if (unlikely(!skb)) {
> +		page_pool_put_full_page(rx_chn->page_pool, page, allow_direct);
> +		rx_chn->pages[desc_idx] = NULL;
> +		return NULL;
> +	}