netdev - Re: [RFC Optimizing veth xsk performance 09/10] veth: support zero copy for af xdp

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Date: Fri, 4 Aug 2023 23:05:02 +0200
From: Simon Horman <horms@...nel.org>
To: "huangjie.albert" <huangjie.albert@...edance.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	Björn Töpel <bjorn@...nel.org>,
	Magnus Karlsson <magnus.karlsson@...el.com>,
	Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
	Jonathan Lemon <jonathan.lemon@...il.com>,
	Pavel Begunkov <asml.silence@...il.com>,
	Yunsheng Lin <linyunsheng@...wei.com>,
	Kees Cook <keescook@...omium.org>,
	Richard Gobert <richardbgobert@...il.com>,
	"open list:NETWORKING DRIVERS" <netdev@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:XDP (eXpress Data Path)" <bpf@...r.kernel.org>
Subject: Re: [RFC Optimizing veth xsk performance 09/10] veth: support zero
 copy for af xdp

On Thu, Aug 03, 2023 at 10:04:35PM +0800, huangjie.albert wrote:

...

> +static struct sk_buff *veth_build_skb_zerocopy(struct net_device *dev, struct xsk_buff_pool *pool,
> +					      struct xdp_desc *desc)
> +{
> +	struct veth_seg_info *seg_info;
> +	struct sk_buff *skb;
> +	struct page *page;
> +	void *hard_start;
> +	u32 len, ts;
> +	void *buffer;
> +	int headroom;
> +	u64 addr;
> +	u32 index;
> +
> +	addr = desc->addr;
> +	len = desc->len;
> +	buffer = xsk_buff_raw_get_data(pool, addr);
> +	ts = pool->unaligned ? len : pool->chunk_size;
> +
> +	headroom = offset_in_page(buffer);
> +
> +	/* offset in umem pool buffer */
> +	addr = buffer - pool->addrs;
> +
> +	/* get the page of the desc */
> +	page = pool->umem->pgs[addr >> PAGE_SHIFT];
> +
> +	/* in order to avoid to get freed by kfree_skb */
> +	get_page(page);
> +
> +	hard_start = page_to_virt(page);
> +
> +	skb = veth_build_skb(hard_start, headroom, len, ts);
> +	seg_info = (struct veth_seg_info *)kmalloc(struct_size(seg_info, desc, MAX_SKB_FRAGS), GFP_KERNEL);

There is no need to explicitly case the return value of kmalloc,
as it returns void *.

	seg_info = kmalloc(struct_size(seg_info, desc, MAX_SKB_FRAGS),
			   GFP_KERNEL);

...