On 10/9/2019 6:06 PM, Alexei Starovoitov wrote:
Will update the patchset with the right performance data and address
feedback from Bjorn.
Hope you are not totally against direct XDP approach as it does provide
value when an AF_XDP socket is bound to a queue and a HW filter can
direct packets targeted for that queue.
I used to be in favor of providing "prog bypass" for af_xdp,
because of anecdotal evidence that it will make af_xdp faster.
Now seeing the numbers and the way they were collected
I'm against such bypass.
I want to see hard proof that trivial bpf prog is actually slowing things down
before reviewing any new patch sets.
Here is a more detailed performance report that compares the current AF_XDP rx_drop
with the patches that enable direct receive without any XDP program. I also collected
and included kernel rxdrop data too as Jakub requested and also perf reports.
Hope it addresses the concerns you raised with the earlier data I posted.
Test Setup
==========
2 Skylake servers with Intel 40Gbe NICs connected via 100Gb Switch
Server Configuration
====================
Intel(R) Xeon(R) Platinum 8180 CPU @ 2.50GHz (skylake)
CPU(s): 112
On-line CPU(s) list: 0-111
Thread(s) per core: 2
Core(s) per socket: 28
Socket(s): 2
NUMA node(s): 2
NUMA node0 CPU(s): 0-27,56-83
NUMA node1 CPU(s): 28-55,84-111
Memory: 96GB
NIC: Intel Corporation Ethernet Controller XL710 for 40GbE QSFP+ (rev 02)
Distro
======
Fedora 29 (Server Edition)
Kernel Configuration
====================
AF_XDP direct socket patches applied on top of
bpf-next git repo HEAD: 05949f63055fcf53947886ddb8e23c8a5d41bd80
# cat /proc/cmdline
BOOT_IMAGE=/vmlinuz-5.3.0-bpf-next-dxk+ root=/dev/mapper/fedora-root ro resume=/dev/mapper/fedora-swap rd.lvm.lv=fedora/root rd.lvm.lv=fedora/swap LANG=en_IN.UTF-8
For ‘mitigations OFF’ scenarios, the kernel command line parameter is changed to add ‘mitigations=off’
Packet Generator on the link partner
====================================
pktgen - sending 64 byte UDP packets at 43mpps
HW filter to redirect packet to a queue
=======================================
ethtool -N ens260f1 flow-type udp4 dst-ip 192.168.128.41 dst-port 9 action 28
Test Cases
==========
kernel rxdrop
taskset -c 28 samples/bpf/xdp_rxq_info -d ens260f1 -a XDP_DROP
AF_XDP default rxdrop
taskset -c 28 samples/bpf/xdpsock -i ens260f1 -r -q 28
AD_XDP direct rxdrop
taskset -c 28 samples/bpf/xdpsock -i ens260f1 -r -d -q 28
Performance Results
===================
Only 1 core is used in all these testcases as the app and the queue irq are pinned to the same core.
----------------------------------------------------------------------------------
mitigations ON mitigations OFF
Testcase ----------------------------------------------------------
no patches with patches no patches with patches
----------------------------------------------------------------------------------
AF_XDP default rxdrop X X Y Y
AF_XDP direct rxdrop N/A X+46% N/A Y+25%
Kernel rxdrop X+61% X+61% Y+53% Y+53%
----------------------------------------------------------------------------------
Here Y is pps with CPU security mitigations turned OFF and it is 26% better than X.
So there is 46% improvement in AF_XDP rxdrop performance with direct receive when
mitigations are ON (default configuration) and 25% improvement when mitigations are
turned OFF.
As expected, the in-kernel rxdrop performance is higher even with direct receive in
both scenarios.
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
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()
The above test results document performance of components on a particular test, in specific systems.
Differences in hardware, software, or configuration will affect actual performance.
Thanks
Sridhar
