On Mon, 21 Jan 2019 17:33:56 +0100 bjorn.to...@gmail.com wrote: > From: Björn Töpel <bjorn.to...@intel.com> > > GCC will generate jump tables for switch-statements with more than 5 > case statements. An entry into the jump table is an indirect call, > which means that for CONFIG_RETPOLINE builds, this is rather > expensive. > > This commit replaces the switch-statement that acts on the XDP program > result with an if-clause. > > The if-clause was also refactored into a common function that can be > used by AF_XDP zero-copy and non-zero-copy code. > > Performance prior this patch: > $ sudo ./xdp_rxq_info --dev enp134s0f0 --action XDP_DROP > Running XDP on dev:enp134s0f0 (ifindex:7) action:XDP_DROP options:no_touch > XDP stats CPU pps issue-pps > XDP-RX CPU 20 18983018 0 > XDP-RX CPU total 18983018 > > RXQ stats RXQ:CPU pps issue-pps > rx_queue_index 20:20 18983012 0 > rx_queue_index 20:sum 18983012 > > $ sudo ./xdpsock -i enp134s0f0 -q 20 -n 2 -z -r > sock0@enp134s0f0:20 rxdrop > pps pkts 2.00 > rx 14,641,496 144,751,092 > tx 0 0 > > And after: > $ sudo ./xdp_rxq_info --dev enp134s0f0 --action XDP_DROP > Running XDP on dev:enp134s0f0 (ifindex:7) action:XDP_DROP options:no_touch > XDP stats CPU pps issue-pps > XDP-RX CPU 20 24000986 0 > XDP-RX CPU total 24000986 > > RXQ stats RXQ:CPU pps issue-pps > rx_queue_index 20:20 24000985 0 > rx_queue_index 20:sum 24000985 > > +26% > > $ sudo ./xdpsock -i enp134s0f0 -q 20 -n 2 -z -r > sock0@enp134s0f0:20 rxdrop > pps pkts 2.00 > rx 17,623,578 163,503,263 > tx 0 0 > > +20%
The saving/cost of the retpoline is around 11 nanosec, which corresponds well with my previous experience and microbenchmarking around 12 ns. ((1/18983012)-(1/24000986))*10^9 11.01372430029000000000 nanosec ((1/14641496)-(1/17623578))*10^9 11.55686507951000000000 nanosec -- Best regards, Jesper Dangaard Brouer MSc.CS, Principal Kernel Engineer at Red Hat LinkedIn: http://www.linkedin.com/in/brouer
