On Sun, Mar 3, 2019 at 9:55 PM Willem de Bruijn <willemdebruijn.ker...@gmail.com> wrote: > > On Fri, Mar 1, 2019 at 9:27 PM David Ahern <dsah...@gmail.com> wrote: > > > > On 2/28/19 10:57 AM, Peter Oskolkov wrote: > > > David: I'm not sure how to test GSO (I assume we are talking about GSO > > > here) in > > > the selftest: the encapping code sets SKB_GSO_DODGY flag, and veth does > > > not support > > > dodginess: "tx-gso-robust: off [fixed]". > > > > > > If the "dodgy" flag is not set, then gso validation in dev.c passes, and > > > large GSO packets > > > happily go through; if the "dodgy" flag is set, "dodgy" GSO packets are > > > rejected, TCP does > > > segmentation, and non-GSO packets happily go through (with an mtu tweak > > > to the LWT tunnel). > > Very few devices unconditionally accept dodgy packets (only veth?).
virtio-net, I meant. But there are a few other virtual devices, like macvlan and xen-netfront > A device that lacks the robust gso feature will cause a gso packet > with dodgy flag to enter software gso instead of passing to device > segmentation offload. > > That should be perfect for checking that the packets can be segmented > correctly with the new header. > > If the gso layer drops the packets, that is not due to dropping all > dodgy sources. It will be dropped somewhere else inside gso, > indication that something is not as expected with the packet. > > > > So I see three options: > > > - add a sysctl to _not_ set SKB_GSO_DODGY flag in lwt_bpf.c => > > > handle_gso_type(); > > > - change veth to accept "dodgy" GSO packets > > Neither, as these would bypass segmentation offload and pass the large > packet to the receive path. It is more interesting to validate the > packet in gso. That said, one solution would be to make veth gso_robust configurable through ethtool, by advertising it in hw_features. > > > - test the code "as is", meaning that GSO will be tried and disabled by > > > TCP stack > > > > > > Which approach would you prefer? > > > > > > > definitely not a sysctl. > > > > After that, I don't have a suggestion for GSO at the moment.
