netdev - Re: [PATCH v10 12/12] bpf: add sample for xdp forwarding and rewrite

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Message-ID: <20160719220536.GH64618@ast-mbp.thefacebook.com>
Date:	Tue, 19 Jul 2016 15:05:37 -0700
From:	Alexei Starovoitov <alexei.starovoitov@...il.com>
To:	Brenden Blanco <bblanco@...mgrid.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	Jamal Hadi Salim <jhs@...atatu.com>,
	Saeed Mahameed <saeedm@....mellanox.co.il>,
	Martin KaFai Lau <kafai@...com>,
	Jesper Dangaard Brouer <brouer@...hat.com>,
	Ari Saha <as754m@....com>, Or Gerlitz <gerlitz.or@...il.com>,
	john.fastabend@...il.com, hannes@...essinduktion.org,
	Thomas Graf <tgraf@...g.ch>, Tom Herbert <tom@...bertland.com>,
	Daniel Borkmann <daniel@...earbox.net>,
	Tariq Toukan <ttoukan.linux@...il.com>
Subject: Re: [PATCH v10 12/12] bpf: add sample for xdp forwarding and rewrite

On Tue, Jul 19, 2016 at 12:16:57PM -0700, Brenden Blanco wrote:
> Add a sample that rewrites and forwards packets out on the same
> interface. Observed single core forwarding performance of ~10Mpps.
> 
> Since the mlx4 driver under test recycles every single packet page, the
> perf output shows almost exclusively just the ring management and bpf
> program work. Slowdowns are likely occurring due to cache misses.

long term we need to resurrect your prefetch patch. sux to leave
so much performance on the table.

> +static int parse_ipv4(void *data, u64 nh_off, void *data_end)
> +{
> +	struct iphdr *iph = data + nh_off;
> +
> +	if (iph + 1 > data_end)
> +		return 0;
> +	return iph->protocol;
> +}
> +
> +static int parse_ipv6(void *data, u64 nh_off, void *data_end)
> +{
> +	struct ipv6hdr *ip6h = data + nh_off;
> +
> +	if (ip6h + 1 > data_end)
> +		return 0;
> +	return ip6h->nexthdr;
> +}
...
> +	if (h_proto == htons(ETH_P_IP))
> +		index = parse_ipv4(data, nh_off, data_end);
> +	else if (h_proto == htons(ETH_P_IPV6))
> +		index = parse_ipv6(data, nh_off, data_end);
> +	else
> +		index = 0;
> +
> +	value = bpf_map_lookup_elem(&dropcnt, &index);
> +	if (value)
> +		*value += 1;
> +
> +	if (index == 17) {

not an obvious xdp example. if you'd have to respin for other
reasons please consider 'proto' name and IPPROTO_UDP here.

Acked-by: Alexei Starovoitov <ast@...nel.org>