Den ons 29 aug. 2018 kl 14:44 skrev Jesper Dangaard Brouer <bro...@redhat.com>: > > On Tue, 28 Aug 2018 14:44:35 +0200 > Björn Töpel <bjorn.to...@gmail.com> wrote: > > > From: Björn Töpel <bjorn.to...@intel.com> > > > > The -c/--copy -z/--zero-copy flags enforces either copy or zero-copy > > mode. > > Nice, thanks for adding this. It allows me to quickly test the > difference between normal-copy vs zero-copy modes. > (Kernel bpf-next without RETPOLINE). > > AF_XDP RX-drop: > Normal-copy mode: rx 13,070,318 pps - 76.5 ns > Zero-copy mode: rx 26,132,328 pps - 38.3 ns > > Compare to XDP_DROP: 34,251,464 pps - 29.2 ns > XDP_DROP + read : 30,756,664 pps - 32.5 ns > > The normal-copy mode is surprisingly fast (and it works for every > driver implemeting the regular XDP_REDIRECT action). It is still > faster to do in-kernel XDP_DROP than AF_XDP zero-copy mode dropping, > which was expected given frames travel to a remote CPU before returned > (don't think remote CPU reads payload?). The gap in nanosec is > actually quite small, thus I'm impressed by the SPSC-queue > implementation working across these CPUs. > > > AF_XDP layer2-fwd: > Normal-copy mode: rx 3,200,885 tx 3,200,892 > Zero-copy mode: rx 17,026,300 tx 17,026,269 > > Compare to XDP_TX: rx 14,529,079 tx 14,529,850 - 68.82 ns > XDP_REDIRECT: rx 13,235,785 tx 13,235,784 - 75.55 ns > > The copy-mode is slow because it allocates SKBs internally (I do > wonder if we could speed it up by using ndo_xdp_xmit + disable-BH). > More intersting is that the zero-copy is faster than XDP_TX and > XDP_REDIRECT. I think the speedup comes from avoiding some DMA mapping > calls with ZC. > > Side-note: XDP_TX vs. REDIRECT: 75.55 - 68.82 = 6.73 ns. The cost of > going through the xdp_do_redirect_map core is actually quite small :-) > (I have some micro optimizations that should help ~2ns). > > > AF_XDP TX-only: > Normal-copy mode: tx 2,853,461 pps > Zero-copy mode: tx 22,255,311 pps > > (There is not XDP mode that does TX to compare against) >
Kudos for doing the in-depth benchmarking! Thanks! Björn > -- > Best regards, > Jesper Dangaard Brouer > MSc.CS, Principal Kernel Engineer at Red Hat > LinkedIn: http://www.linkedin.com/in/brouer
