Re: [PATCH net-next] bareudp: Enable BIG TCP packets

["Alice Mikityanska" <alice.kernel@fastmail.im>]

On Thu, Oct 1, 2026, at 07:23, Haishuang Yan wrote:
> Commit f3d0f753f066 ("vxlan: Enable BIG TCP packets") and commit
> 03ebe91b0f61 ("geneve: Enable BIG TCP packets") allowed BIG TCP on vxlan
> and geneve, after the preceding patches of that series made the common
> UDP tunnel transmit path handle GSO packets larger than 64KB.
>
> bareudp transmits through the same helpers, udp_tunnel_handle_offloads()
> followed by udp_tunnel_xmit_skb() or udp_tunnel6_xmit_skb(), and does
> not fill in any length field itself. Bump tso_max_size up to
> GSO_MAX_SIZE so that the admin can use BIG TCP with bareudp too.
>
> The default gso_max_size and gso_ipv4_max_size stay at 64KB, so nothing
> changes unless they are raised explicitly.
>
> iperf3 TCP over bareudp (ethertype ipv4, IPv4 outer) between two netns
> connected by veth, MTU 1600 on veth, 3 runs of 20 seconds each. This
> was measured in a QEMU TCG guest, so only the relative numbers are
> meaningful:
>
>   gso_max_size/gso_ipv4_max_size 65536:
>     4380.6, 4404.2, 4354.5 Mbit/s, average 4379.8 Mbit/s
>
>   gso_max_size/gso_ipv4_max_size 196608:
>     5509.4, 5454.7, 5497.4 Mbit/s, average 5487.2 Mbit/s (+25%)
>
> With 196608, about 90k to 100k packets larger than 64KB were
> transmitted on the bareudp device per run, none with 65536. Without
> this patch, setting gso_max_size to 196608 is rejected.
>
> Assisted-by: LLM
> Signed-off-by: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>
> ---
>  drivers/net/bareudp.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/net/bareudp.c b/drivers/net/bareudp.c
> index c3b5ed52d877..fcc33e302b9c 100644
> --- a/drivers/net/bareudp.c
> +++ b/drivers/net/bareudp.c
> @@ -589,6 +589,7 @@ static void bareudp_setup(struct net_device *dev)
>  	dev->max_mtu = IP_MAX_MTU - BAREUDP_BASE_HLEN;
>  	dev->type = ARPHRD_NONE;
>  	netif_keep_dst(dev);
> +	netif_set_tso_max_size(dev, GSO_MAX_SIZE);

Acked-by: Alice Mikityanska <alice.kernel@fastmail.im>

Do you mind extending the big_tcp_tunnels.sh selftest to cover bareudp?

Besides, enabling BIG TCP with fou would also be a one-liner, the
basement was added in "udp: Support BIG TCP GSO packets where they
can occur":

https://lore.kernel.org/netdev/20260710134242.216538-4-alice.kernel@fastmail.im

>  	dev->priv_flags |= IFF_NO_QUEUE;
>  	dev->lltx = true;
>  	dev->flags = IFF_POINTOPOINT | IFF_NOARP | IFF_MULTICAST;
> -- 
> 2.43.0