linux-kernel - Re: [PATCH net-next v2] net: pppoe: implement GRO support

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Message-ID: <194828df-1e6e-762c-0887-5a68c914027e@gmail.com>
Date: Thu, 31 Jul 2025 16:08:30 +0200
From: Richard Gobert <richardbgobert@...il.com>
To: Felix Fietkau <nbd@....name>, netdev@...r.kernel.org,
 Michal Ostrowski <mostrows@...thlink.net>,
 Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v2] net: pppoe: implement GRO support

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@....name>
> ---
> v2: fix compile error
> 
>  drivers/net/ppp/pppoe.c | 104 +++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 103 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ppp/pppoe.c b/drivers/net/ppp/pppoe.c
> index 410effa42ade..5d35eafd06df 100644
> --- a/drivers/net/ppp/pppoe.c
> +++ b/drivers/net/ppp/pppoe.c
> @@ -77,6 +77,7 @@
>  #include <net/net_namespace.h>
>  #include <net/netns/generic.h>
>  #include <net/sock.h>
> +#include <net/gro.h>
>  
>  #include <linux/uaccess.h>
>  
> @@ -435,7 +436,7 @@ static int pppoe_rcv(struct sk_buff *skb, struct net_device *dev,
>  	if (skb->len < len)
>  		goto drop;
>  
> -	if (pskb_trim_rcsum(skb, len))
> +	if (!skb_is_gso(skb) && pskb_trim_rcsum(skb, len))
>  		goto drop;
>  
>  	ph = pppoe_hdr(skb);
> @@ -1173,6 +1174,105 @@ static struct pernet_operations pppoe_net_ops = {
>  	.size = sizeof(struct pppoe_net),
>  };
>  
> +static u16
> +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;
> +	__be16 type;
> +	int flush = 1;
> +
> +	off_pppoe = skb_gro_offset(skb);
> +	hlen = off_pppoe + sizeof(*phdr) + 2;
> +	phdr = skb_gro_header(skb, hlen, 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 - 2)
> +		goto out;
> +
> +	NAPI_GRO_CB(skb)->network_offsets[NAPI_GRO_CB(skb)->encap_mark] = hlen;
This is not required as {inet,ipv6}_gro_receive already set the network offset.

> +
> +	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 = ptype->callbacks.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 err = -ENOENT;
> +
> +	ptype = gro_find_complete_by_type(type);
> +	if (ptype)
> +		err = ptype->callbacks.gro_complete(skb, nhoff +
> +						    sizeof(*phdr) + 2);
> +
> +	return err;
> +}
Shouldn't pppoe_gro_complete fix the length field of the pppoe header?

> +
> +static struct packet_offload pppoe_packet_offload __read_mostly = {
> +	.type = cpu_to_be16(ETH_P_PPP_SES),
> +	.priority = 10,
> +	.callbacks = {
> +		.gro_receive = pppoe_gro_receive,
> +		.gro_complete = pppoe_gro_complete,
> +	},
> +};
> +
>  static int __init pppoe_init(void)
>  {
>  	int err;
> @@ -1189,6 +1289,7 @@ static int __init pppoe_init(void)
>  	if (err)
>  		goto out_unregister_pppoe_proto;
>  
> +	dev_add_offload(&pppoe_packet_offload);
>  	dev_add_pack(&pppoes_ptype);
>  	dev_add_pack(&pppoed_ptype);
>  	register_netdevice_notifier(&pppoe_notifier);
> @@ -1208,6 +1309,7 @@ static void __exit pppoe_exit(void)
>  	unregister_netdevice_notifier(&pppoe_notifier);
>  	dev_remove_pack(&pppoed_ptype);
>  	dev_remove_pack(&pppoes_ptype);
> +	dev_remove_offload(&pppoe_packet_offload);
>  	unregister_pppox_proto(PX_PROTO_OE);
>  	proto_unregister(&pppoe_sk_proto);
>  	unregister_pernet_device(&pppoe_net_ops);