On Mon, 2021-03-29 at 11:24 -0400, Willem de Bruijn wrote:
> On Mon, Mar 29, 2021 at 11:01 AM Paolo Abeni <pab...@redhat.com> wrote:
> > On Mon, 2021-03-29 at 09:52 -0400, Willem de Bruijn wrote:
> > > > + if (skb->ip_summed == CHECKSUM_NONE && !skb->csum_valid)
> > > > + skb->csum_valid = 1;
> > >
> > > Not entirely obvious is that UDP packets arriving on a device with rx
> > > checksum offload off, i.e., with CHECKSUM_NONE, are not matched by
> > > this test.
> > >
> > > I assume that such packets are not coalesced by the GRO layer in the
> > > first place. But I can't immediately spot the reason for it..
>
> As you point out, such packets will already have had their checksum
> verified at this point, so this branch only matches tunneled packets.
> That point is just not immediately obvious from the code.
I understand is a matter of comment clarity ?!?
I'll rewrite the related code comment - in udp_post_segment_fix_csum()
- as:
/* UDP packets generated with UDP_SEGMENT and traversing:
*
* UDP tunnel(xmit) -> veth (segmentation) -> veth (gro) -> UDP tunnel
(rx)
*
* land here with CHECKSUM_NONE, because __iptunnel_pull_header()
converts
* CHECKSUM_PARTIAL into NONE.
* SKB_GSO_UDP_L4 or SKB_GSO_FRAGLIST packets with no UDP tunnel will
land
* here with valid checksum, as the GRO engine validates the UDP csum
* before the aggregation and nobody strips such info in between.
* Instead of adding another check in the tunnel fastpath, we can force
* a valid csum here.
* Additionally fixup the UDP CB.
*/
Would that be clear enough?
> > I do see checksum validation in the GRO engine for CHECKSUM_NONE UDP
> > packet prior to this series.
> >
> > I *think* the checksum-and-copy optimization is lost
> > since 573e8fca255a27e3573b51f9b183d62641c47a3d.
>
> Wouldn't this have been introduced with UDP_GRO?
Uhmm.... looks like the checksum-and-copy optimization has been lost
and recovered a few times. I think the last one
with 9fd1ff5d2ac7181844735806b0a703c942365291, which move the csum
validation before the static branch on udp_encap_needed_key.
Can we agree re-introducing the optimization is independent from this
series?
Thanks!
Paolo
