Tunneled LSO/CSO Support #614
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Accidentally over-counted by the ETH header, and illumos is sending down chunks of size n×MSS. This would split one TSO packet into three (versus baseline two).
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This PR makes use of in-progress illumos bits to detect common offloads between underlay devices, and readvertises LSO/CSO capabilities on
opteports if both underlay devices advertise Geneve-aware offloads.Ultimately, we have control over the MSS we advertise to the NIC for LSO. The useful part of this is that when we know we are using a purely rack-internal path, we can elevate the MSS up to
MTU - overheads. Given that the use of a larger MTU vastly reduces inbound packet rate on the receive half (the main bottleneck today), this gets us to around 8Gbps iPerf for rack-local traffic (and 17Gbps for two or more parallel streams).