Den mån 21 jan. 2019 kl 17:42 skrev Paul Menzel <pmen...@molgen.mpg.de>: > > Dear Björn, > > > On 01/21/19 17:33, 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. > > Maybe mention the performance improvement already here. I’d also put it > into the commit message summary. Something like: > > > i40e: Speed up retpoline case by using if-clause >
Yes, this would, indeed, have been a better summary! > If that jump tables are a common problem, I wonder, why the compiler > cannot be adapted to generate better performing code or an option passed > to the compiler. > It might make sense to use -fno-jump-tables or a better value for the case-values-threshold param for the i40e code. However, doing that would require a much broader testing, since there are a number of different places where a switch-statement is used. And depending on the context, a jump table might still be a better option. Thank you for the comments! Björn > > 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% > > > > Signed-off-by: Björn Töpel <bjorn.to...@intel.com> > > --- > > drivers/net/ethernet/intel/i40e/i40e_txrx.c | 31 ++++--------------- > > .../ethernet/intel/i40e/i40e_txrx_common.h | 27 ++++++++++++++++ > > drivers/net/ethernet/intel/i40e/i40e_xsk.c | 24 ++------------ > > 3 files changed, 35 insertions(+), 47 deletions(-) > > […] > > > Kind regards, > > Paul > > _______________________________________________ > Intel-wired-lan mailing list > intel-wired-...@osuosl.org > https://lists.osuosl.org/mailman/listinfo/intel-wired-lan
