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

From: Brenden Blanco <[email-masked]>
Date: Wed, 20 Jul 2016 10:38:28 -0700

On Tue, Jul 19, 2016 at 03:05:37PM -0700, Alexei Starovoitov wrote:
> 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.

I know :( Let's keep working at it, in a way that's good for both
xdp/non-xdp.
> 
> > +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.
Will collect this into a followup.
> 
> Acked-by: Alexei Starovoitov <[email-masked]>
>