netdev - Re: [PATCH net-next 0/2] net: two updates related to UDP GSO

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Date:   Mon, 7 Sep 2020 17:35:48 +0200
From:   Willem de Bruijn <willemdebruijn.kernel@...il.com>
To:     tanhuazhong <tanhuazhong@...wei.com>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        David Miller <davem@...emloft.net>,
        Network Development <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        salil.mehta@...wei.com, yisen.zhuang@...wei.com,
        linuxarm@...wei.com
Subject: Re: [PATCH net-next 0/2] net: two updates related to UDP GSO

On Mon, Sep 7, 2020 at 3:38 PM tanhuazhong <tanhuazhong@...wei.com> wrote:
>
>
>
> On 2020/9/7 17:22, Willem de Bruijn wrote:
> > On Sun, Sep 6, 2020 at 8:42 PM Jakub Kicinski <kuba@...nel.org> wrote:
> >>
> >> On Sat, 5 Sep 2020 14:11:11 +0800 Huazhong Tan wrote:
> >>> There are two updates relates to UDP GSO.
> >>> #1 adds a new GSO type for UDPv6
> >>> #2 adds check for UDP GSO when csum is disable in netdev_fix_features().
> >>>
> >>> Changes since RFC V2:
> >>> - modifies the timing of setting UDP GSO type when doing UDP GRO in #1.
> >>>
> >>> Changes since RFC V1:
> >>> - updates NETIF_F_GSO_LAST suggested by Willem de Bruijn.
> >>>    and add NETIF_F_GSO_UDPV6_L4 feature for each driver who support UDP GSO in #1.
> >>>    - add #2 who needs #1.
> >>
> >> Please CC people who gave you feedback (Willem).
> >>
> >> I don't feel good about this series. IPv6 is not optional any more.
> >> AFAIU you have some issues with csum support in your device? Can you
> >> use .ndo_features_check() to handle this?
> >>
> >> The change in semantics of NETIF_F_GSO_UDP_L4 from "v4 and v6" to
> >> "just v4" can trip people over; this is not a new feature people
> >> may be depending on the current semantics.
> >>
> >> Willem, what are your thoughts on this?
> >
> > If that is the only reason, +1 on fixing it up in the driver's
> > ndo_features_check.
> >
>
> Hi, Willem & Jakub.
>
> This series mainly fixes the feature dependency between hardware
> checksum and UDP GSO.
> When turn off hardware checksum offload, run 'ethtool -k [devname]'
> we can see TSO is off as well, but udp gso still is on.

I see. That does not entirely require separate IPv4 and IPv6 flags. It
can be disabled if either checksum offload is disabled. I'm not aware
of any hardware that only supports checksum offload for one of the two
network protocols.

Alternatively, the real value of splitting the type is in advertising
the features separately through ethtool. That requires additional
changes.