On Mon, Mar 29, 2021 at 12:24 PM Paolo Abeni <pab...@redhat.com> wrote: > > 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?
Definitely. Thanks! > > > 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? Yep :) > Thanks! > > Paolo > >
