On Thu, 2019-05-23 at 13:36 -0600, Sean Tranchetti wrote: > Currently, when resegmenting an unexpected UDP GRO packet, the full UDP > checksum will be calculated for every new SKB created by skb_segment() > because the netdev features passed in by udp_rcv_segment() lack any > information about checksum offload capabilities. > > We have no need to perform this calculation again, as > 1) The GRO implementation guarantees that any packets making it to the > udp_rcv_segment() function had correct checksums, and, more > importantly, > 2) Upon the successful return of udp_rcv_segment(), we immediately pull > the UDP header off and either queue the segment to the socket or > hand it off to a new protocol handler. In either case, the checksum > is not needed.
I *think* there is a possible, even if unlikely, exception to the above: if userspace has set the IP_CHECKSUM sockopt, recvmsg can later try to access skb csum. I think that setting NETIF_F_IP_CSUM | NETIF_F_IPV6_CSUM only if !inet_get_convert_csum() would address the above, Other than that LGTM, thanks for catching this! Paolo p.s. I suspect that with this patch GRO + resegmentation is notably faster than the plain unaggregated path, do you have by chance any related datapoint?
