netdev - Re: [RFC net-next 1/2] udp: add NETIF_F_GSO_UDP_L4 to NETIF_F_SOFTWARE

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Date:   Wed, 8 Jul 2020 08:11:09 -0400
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     Huazhong Tan <tanhuazhong@...wei.com>
Cc:     David Miller <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        linuxarm@...wei.com, Jakub Kicinski <kuba@...nel.org>
Subject: Re: [RFC net-next 1/2] udp: add NETIF_F_GSO_UDP_L4 to NETIF_F_SOFTWARE_GSO

On Tue, Jul 7, 2020 at 11:50 PM Huazhong Tan <tanhuazhong@...wei.com> wrote:
>
> Add NETIF_F_SOFTWARE_GSO to the the list of GSO features with
> a software fallback.  This allows UDP GSO to be used even if
> the hardware does not support it,

That is already the case if just calling UDP_SEGMENT.

It seems the specific goal here is to postpone segmentation when
going through a vxlan device?

> and for virtual device such
> as VxLAN device, this UDP segmentation will be postponed to
> physical device.

See previous commits

commit 83aa025f535f76733e334e3d2a4d8577c8441a7e
Author: Willem de Bruijn <willemb@...gle.com>
Date:   Thu Apr 26 13:42:21 2018 -0400

    udp: add gso support to virtual devices

    Virtual devices such as tunnels and bonding can handle large packets.
    Only segment packets when reaching a physical or loopback device.

    Signed-off-by: Willem de Bruijn <willemb@...gle.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>

and

commit 8eea1ca82be90a7e7a4624ab9cb323574a5f71df
Author: Willem de Bruijn <willemb@...gle.com>
Date:   Tue May 22 11:34:40 2018 -0400

    gso: limit udp gso to egress-only virtual devices

    Until the udp receive stack supports large packets (UDP GRO), GSO
    packets must not loop from the egress to the ingress path.

    Revert the change that added NETIF_F_GSO_UDP_L4 to various virtual
    devices through NETIF_F_GSO_ENCAP_ALL as this included devices that
    may loop packets, such as veth and macvlan.

    Instead add it to specific devices that forward to another device's
    egress path, bonding and team.

    Fixes: 83aa025f535f ("udp: add gso support to virtual devices")
    CC: Alexander Duyck <alexander.duyck@...il.com>
    Signed-off-by: Willem de Bruijn <willemb@...gle.com>
    Signed-off-by: David S. Miller <davem@...emloft.net>

Though with UDP_GRO this specific loop concern is addressed.



> Signed-off-by: Huazhong Tan <tanhuazhong@...wei.com>
> ---
>  include/linux/netdev_features.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/netdev_features.h b/include/linux/netdev_features.h
> index 2cc3cf8..c7eef16 100644
> --- a/include/linux/netdev_features.h
> +++ b/include/linux/netdev_features.h
> @@ -207,7 +207,7 @@ static inline int find_next_netdev_feature(u64 feature, unsigned long start)
>                                  NETIF_F_FSO)
>
>  /* List of features with software fallbacks. */
> -#define NETIF_F_GSO_SOFTWARE   (NETIF_F_ALL_TSO | \
> +#define NETIF_F_GSO_SOFTWARE   (NETIF_F_ALL_TSO | NETIF_F_GSO_UDP_L4 | \
>                                  NETIF_F_GSO_SCTP)
>
>  /*
> --
> 2.7.4
>