Re: [PATCH net-next v3] net: pppoe: implement GRO/GSO support

[Felix Fietkau]

On 14.08.25 16:30, Richard Gobert wrote:
> Felix Fietkau wrote:
> > Only handles packets where the pppoe header length field matches the exact
> > packet length. Significantly improves rx throughput.
> >
> > When running NAT traffic through a MediaTek MT7621 devices from a host
> > behind PPPoE to a host directly connected via ethernet, the TCP throughput
> > that the device is able to handle improves from ~130 Mbit/s to ~630 Mbit/s,
> > using fraglist GRO.
> >
> > Signed-off-by: Felix Fietkau <nbd@xxxxxxxx>
> > ---
> > v2: fix compile error
> > v3:
> >   - increase priority value
> >   - implement GSO support
> >   - use INDIRECT_CALL_INET
> >   - update pppoe length field
> >   - remove unnecessary network_offsets update
> >
> >  drivers/net/ppp/pppoe.c | 160 +++++++++++++++++++++++++++++++++++++++-
> >  net/ipv4/af_inet.c      |   2 +
> >  net/ipv6/ip6_offload.c  |   2 +
> >  3 files changed, 163 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
> > index 410effa42ade..a8d8eb870bce 100644
> > --- a/drivers/net/ppp/pppoe.c
> > +++ b/drivers/net/ppp/pppoe.c
> > +compare_pppoe_header(struct pppoe_hdr *phdr, struct pppoe_hdr *phdr2)
> > +{
> > +	return (__force __u16)((phdr->sid ^ phdr2->sid) |
> > +			       (phdr->tag[0].tag_type ^ phdr2->tag[0].tag_type));
> > +}
> > +
> > +static __be16 pppoe_hdr_proto(struct pppoe_hdr *phdr)
> > +{
> > +	switch (phdr->tag[0].tag_type) {
> > +	case cpu_to_be16(PPP_IP):
> > +		return cpu_to_be16(ETH_P_IP);
> > +	case cpu_to_be16(PPP_IPV6):
> > +		return cpu_to_be16(ETH_P_IPV6);
> > +	default:
> > +		return 0;
> > +	}
> > +
> > +}
> > +
> > +static struct sk_buff *pppoe_gro_receive(struct list_head *head,
> > +					 struct sk_buff *skb)
> > +{
> > +	const struct packet_offload *ptype;
> > +	unsigned int hlen, off_pppoe;
> > +	struct sk_buff *pp = NULL;
> > +	struct pppoe_hdr *phdr;
> > +	struct sk_buff *p;
> > +	int flush = 1;
> > +	__be16 type;
> > +
> > +	off_pppoe = skb_gro_offset(skb);
> > +	hlen = off_pppoe + sizeof(*phdr);
> > +	phdr = skb_gro_header(skb, hlen + 2, off_pppoe);
> > +	if (unlikely(!phdr))
> > +		goto out;
> > +
> > +	/* ignore packets with padding or invalid length */
> > +	if (skb_gro_len(skb) != be16_to_cpu(phdr->length) + hlen)
> > +		goto out;
> > +
> > +	type = pppoe_hdr_proto(phdr);
> > +	if (!type)
> > +		goto out;
> > +
> > +	ptype = gro_find_receive_by_type(type);
> > +	if (!ptype)
> > +		goto out;
> > +
> > +	flush = 0;
> > +
> > +	list_for_each_entry(p, head, list) {
> > +		struct pppoe_hdr *phdr2;
> > +
> > +		if (!NAPI_GRO_CB(p)->same_flow)
> > +			continue;
> > +
> > +		phdr2 = (struct pppoe_hdr *)(p->data + off_pppoe);
> > +		if (compare_pppoe_header(phdr, phdr2))
> > +			NAPI_GRO_CB(p)->same_flow = 0;
> > +	}
> > +
> > +	skb_gro_pull(skb, sizeof(*phdr) + 2);
> > +	skb_gro_postpull_rcsum(skb, phdr, sizeof(*phdr) + 2);
> > +
> > +	pp = indirect_call_gro_receive_inet(ptype->callbacks.gro_receive,
> > +					    ipv6_gro_receive, inet_gro_receive,
> > +					    head, skb);
> > +
> > +out:
> > +	skb_gro_flush_final(skb, pp, flush);
> > +
> > +	return pp;
> > +}
> > +
> > +static int pppoe_gro_complete(struct sk_buff *skb, int nhoff)
> > +{
> > +	struct pppoe_hdr *phdr = (struct pppoe_hdr *)(skb->data + nhoff);
> > +	__be16 type = pppoe_hdr_proto(phdr);
> > +	struct packet_offload *ptype;
> > +	int len, err;
> > +
> > +	ptype = gro_find_complete_by_type(type);
> > +	if (!ptype)
> > +		return -ENOENT;
> > +
> > +	err = INDIRECT_CALL_INET(ptype->callbacks.gro_complete,
> > +				 ipv6_gro_complete, inet_gro_complete,
> > +				 skb, nhoff + sizeof(*phdr) + 2);
> > +	if (err)
> > +		return err;
> > +
> > +	len = skb->len - (nhoff + sizeof(*phdr));
> > +	phdr->length = cpu_to_be16(len);
> > +
> > +	return 0;
> > +}
> > +
> > +static struct sk_buff *pppoe_gso_segment(struct sk_buff *skb,
> > +					 netdev_features_t features)
> > +{
>
> I don't think this will be called for PPPoE over GRE packets,
> since gre_gso_segment skips everything up to the network header.

What's a good solution to this issue? Use the outer network header 
instead of the inner one when the protocol is PPPoE?

- Felix