On Fri, Oct 18, 2019 at 05:45:26PM -0700, Samudrala, Sridhar wrote: > On 10/18/2019 5:14 PM, Alexei Starovoitov wrote: > > On Fri, Oct 18, 2019 at 11:40:07AM -0700, Samudrala, Sridhar wrote: > > > > > > Perf report for "AF_XDP default rxdrop" with patched kernel - mitigations ON > > > ========================================================================== > > > Samples: 44K of event 'cycles', Event count (approx.): 38532389541 > > > Overhead Command Shared Object Symbol > > > 15.31% ksoftirqd/28 [i40e] [k] i40e_clean_rx_irq_zc > > > 10.50% ksoftirqd/28 bpf_prog_80b55d8a76303785 [k] bpf_prog_80b55d8a76303785 > > > 9.48% xdpsock [i40e] [k] i40e_clean_rx_irq_zc > > > 8.62% xdpsock xdpsock [.] main > > > 7.11% ksoftirqd/28 [kernel.vmlinux] [k] xsk_rcv > > > 5.81% ksoftirqd/28 [kernel.vmlinux] [k] xdp_do_redirect > > > 4.46% xdpsock bpf_prog_80b55d8a76303785 [k] bpf_prog_80b55d8a76303785 > > > 3.83% xdpsock [kernel.vmlinux] [k] xsk_rcv > > > > why everything is duplicated? > > Same code runs in different tasks ? > > Yes. looks like these functions run from both the app(xdpsock) context and ksoftirqd context. > > > > > > 2.81% ksoftirqd/28 [kernel.vmlinux] [k] bpf_xdp_redirect_map > > > 2.78% ksoftirqd/28 [kernel.vmlinux] [k] xsk_map_lookup_elem > > > 2.44% xdpsock [kernel.vmlinux] [k] xdp_do_redirect > > > 2.19% ksoftirqd/28 [kernel.vmlinux] [k] __xsk_map_redirect > > > 1.62% ksoftirqd/28 [kernel.vmlinux] [k] xsk_umem_peek_addr > > > 1.57% xdpsock [kernel.vmlinux] [k] xsk_umem_peek_addr > > > 1.32% ksoftirqd/28 [kernel.vmlinux] [k] dma_direct_sync_single_for_cpu > > > 1.28% xdpsock [kernel.vmlinux] [k] bpf_xdp_redirect_map > > > 1.15% xdpsock [kernel.vmlinux] [k] dma_direct_sync_single_for_device > > > 1.12% xdpsock [kernel.vmlinux] [k] xsk_map_lookup_elem > > > 1.06% xdpsock [kernel.vmlinux] [k] __xsk_map_redirect > > > 0.94% ksoftirqd/28 [kernel.vmlinux] [k] dma_direct_sync_single_for_device > > > 0.75% ksoftirqd/28 [kernel.vmlinux] [k] __x86_indirect_thunk_rax > > > 0.66% ksoftirqd/28 [i40e] [k] i40e_clean_programming_status > > > 0.64% ksoftirqd/28 [kernel.vmlinux] [k] net_rx_action > > > 0.64% swapper [kernel.vmlinux] [k] intel_idle > > > 0.62% ksoftirqd/28 [i40e] [k] i40e_napi_poll > > > 0.57% xdpsock [kernel.vmlinux] [k] dma_direct_sync_single_for_cpu > > > > > > Perf report for "AF_XDP direct rxdrop" with patched kernel - mitigations ON > > > ========================================================================== > > > Samples: 46K of event 'cycles', Event count (approx.): 38387018585 > > > Overhead Command Shared Object Symbol > > > 21.94% ksoftirqd/28 [i40e] [k] i40e_clean_rx_irq_zc > > > 14.36% xdpsock xdpsock [.] main > > > 11.53% ksoftirqd/28 [kernel.vmlinux] [k] xsk_rcv > > > 11.32% xdpsock [i40e] [k] i40e_clean_rx_irq_zc > > > 4.02% xdpsock [kernel.vmlinux] [k] xsk_rcv > > > 2.91% ksoftirqd/28 [kernel.vmlinux] [k] xdp_do_redirect > > > 2.45% ksoftirqd/28 [kernel.vmlinux] [k] xsk_umem_peek_addr > > > 2.19% xdpsock [kernel.vmlinux] [k] xsk_umem_peek_addr > > > 2.08% ksoftirqd/28 [kernel.vmlinux] [k] bpf_direct_xsk > > > 2.07% ksoftirqd/28 [kernel.vmlinux] [k] dma_direct_sync_single_for_cpu > > > 1.53% ksoftirqd/28 [kernel.vmlinux] [k] dma_direct_sync_single_for_device > > > 1.39% xdpsock [kernel.vmlinux] [k] dma_direct_sync_single_for_device > > > 1.22% ksoftirqd/28 [kernel.vmlinux] [k] xdp_get_xsk_from_qid > > > 1.12% ksoftirqd/28 [i40e] [k] i40e_clean_programming_status > > > 0.96% ksoftirqd/28 [i40e] [k] i40e_napi_poll > > > 0.95% ksoftirqd/28 [kernel.vmlinux] [k] net_rx_action > > > 0.89% xdpsock [kernel.vmlinux] [k] xdp_do_redirect > > > 0.83% swapper [i40e] [k] i40e_clean_rx_irq_zc > > > 0.70% swapper [kernel.vmlinux] [k] intel_idle > > > 0.66% xdpsock [kernel.vmlinux] [k] dma_direct_sync_single_for_cpu > > > 0.60% xdpsock [kernel.vmlinux] [k] bpf_direct_xsk > > > 0.50% ksoftirqd/28 [kernel.vmlinux] [k] xsk_umem_discard_addr > > > > > > Based on the perf reports comparing AF_XDP default and direct rxdrop, we can say that > > > AF_XDP direct rxdrop codepath is avoiding the overhead of going through these functions > > > bpf_prog_xxx > > > bpf_xdp_redirect_map > > > xsk_map_lookup_elem > > > __xsk_map_redirect > > > With AF_XDP direct, xsk_rcv() is directly called via bpf_direct_xsk() in xdp_do_redirect() > > > > I don't think you're identifying the overhead correctly. > > xsk_map_lookup_elem is 1% > > but bpf_xdp_redirect_map() suppose to call __xsk_map_lookup_elem() > > which is a different function: > > ffffffff81493fe0 T __xsk_map_lookup_elem > > ffffffff81492e80 t xsk_map_lookup_elem > > > > 10% for bpf_prog_80b55d8a76303785 is huge. > > It's the actual code of the program _without_ any helpers. > > How does the program actually look? > > It is the xdp program that is loaded via xsk_load_xdp_prog() in tools/lib/bpf/xsk.c > https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/lib/bpf/xsk.c#n268 I see. Looks like map_gen_lookup was never implemented for xskmap. How about adding it first the way array_map_gen_lookup() is implemented? This will easily give 2x perf gain.
