Paolo Abeni <pab...@redhat.com> writes: > On Fri, 2021-04-09 at 16:58 +0200, Toke Høiland-Jørgensen wrote: >> Paolo Abeni <pab...@redhat.com> writes: >> >> > Currently the veth device has the GRO feature bit set, even if >> > no GRO aggregation is possible with the default configuration, >> > as the veth device does not hook into the GRO engine. >> > >> > Flipping the GRO feature bit from user-space is a no-op, unless >> > XDP is enabled. In such scenario GRO could actually take place, but >> > TSO is forced to off on the peer device. >> > >> > This change allow user-space to really control the GRO feature, with >> > no need for an XDP program. >> > >> > The GRO feature bit is now cleared by default - so that there are no >> > user-visible behavior changes with the default configuration. >> > >> > When the GRO bit is set, the per-queue NAPI instances are initialized >> > and registered. On xmit, when napi instances are available, we try >> > to use them. >> >> Am I mistaken in thinking that this also makes XDP redirect into a veth >> work without having to load an XDP program on the peer device? That's >> been a long-outstanding thing we've been meaning to fix, so that would >> be awesome! :) > > I have not experimented that, and I admit gross ignorance WRT this > argument, but AFAICS the needed bits to get XDP redirect working on > veth are the ptr_ring initialization and the napi instance available. > > With this patch both are in place when GRO is enabled, so I guess XPD > redirect should work, too (modulo bugs for untested scenario).
OK, finally got around to testing this; it doesn't quite work with just your patch, because veth_xdp_xmit() still checks for rq->xdp_prog instead of rq->napi. Fixing this indeed enabled veth to be an XDP_REDIRECT target without an XDP program loaded on the peer. So yay! I'll send a followup fixing that check. So with this we seem to have some nice improvements in both functionality and performance when GRO is turned on; so any reason why we shouldn't just flip the default to on? -Toke
