netdev - Re: [PATCH net-next 2/8] udp: skip fwd/list GRO for tunnel packets

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Date:   Mon, 22 Mar 2021 17:41:27 +0100
From:   Paolo Abeni <pabeni@...hat.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc:     Network Development <netdev@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Steffen Klassert <steffen.klassert@...unet.com>,
        Alexander Lobakin <alobakin@...me>
Subject: Re: [PATCH net-next 2/8] udp: skip fwd/list GRO for tunnel packets

On Mon, 2021-03-22 at 09:24 -0400, Willem de Bruijn wrote:
> On Sun, Mar 21, 2021 at 1:01 PM Paolo Abeni <pabeni@...hat.com> wrote:
> > If UDP GRO forwarding (or list) is enabled,
> 
> Please explicitly mention the gso type SKB_GSO_FRAGLIST. I, at least,
> didn't immediately grasp that gro forwarding is an alias for that.

I see the commit message was not clear at all, I'm sorry.

The above means:

gso_type & (NETIF_F_GSO_UDP_L4 | NETIF_F_GSO_FRAGLIST) 

:)

> > and there are
> > udp tunnel available in the system, we could end-up doing L4
> > aggregation for packets targeting the UDP tunnel.
> 
> Is this specific to UDP tunnels, or can this also occur with others,
> such as GRE? (not implying that this patchset needs to address those
> at the same time)

I did not look at that before your suggestion. Thanks for pointing out.

I think the problem is specific to UDP: when processing the outer UDP
header that is potentially eligible for both NETIF_F_GSO_UDP_L4 and
gro_receive aggregation and that is the root cause of the problem
addressed here.


> > Just skip the fwd GRO if this packet could land in an UDP
> > tunnel.
> 
> Could you make more clear that this does not skip UDP GRO, only
> switches from fraglist-based to pure SKB_GSO_UDP_L4.

Sure, I'll try to rewrite the commit message.

Thanks!

Paolo