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LPC2018 - TC SW Datapath: A Performance Analysis

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Published on Dec 3, 2018

url: https://linuxplumbersconf.org/event/2...
speaker: Paolo Abeni (Red Hat), Davide Caratti (Red Hat), Eelco Chaudron (Red Hat), Marcelo Ricardo Leitner (Red Hat)


Currently the Linux kernel implements two distinct datapaths for Open
vSwitch: the ovskdp and the TC DP. The latter has been added recently
mainly to allow HW offload, while the former is usually preferred for
SW based forwarding due to functional and performance reasons.

We evaluate both datapaths in a typical forwarding scenario - the PVP
test - using the perf tool to identify bottlenecks in the TC SW dp.
While similar steps usually incur in similar costs, the TC SW DP
requires an additional, per packet, skb_clone, due to a TC actions
constraint.

We propose to extend the existing act infrastructure, leveraging the
ACT_REDIRECT action and the bpf redirect code, to allow clone-free
forwarding from the mirred action and then re-evaluate the datapaths
performances: the gap is then almost already closed.

Nevertheless, TC SW performance can be further improved by completing
the RCU-ification of the TC actions and expanding the recent
listification infrastructure to the TC (ingress) hook. We plan also to
compare the TC/SW datapath with an custom eBPF program implementing the
equivalent flow set to tag a reference value for the target
performances.

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