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There is a cost associated with reading the packet data payload
that this test ignored. Add option --read to allow enabling
reading part of the payload.
This sample/tool helps us analyse an issue observed with a NIC
mlx5 (ConnectX-5 Ex) and an Intel(R) Xeon(R) CPU E5-1650 v4.
With no_touch of data:
Running XDP on dev:mlx5p1 (ifindex:8) action:XDP_DROP options:no_touch
XDP stats CPU pps issue-pps
XDP-RX CPU 0 14,465,157 0
XDP-RX CPU 1 14,464,728 0
XDP-RX CPU 2 14,465,283 0
XDP-RX CPU 3 14,465,282 0
XDP-RX CPU 4 14,464,159 0
XDP-RX CPU 5 14,465,379 0
XDP-RX CPU total 86,789,992
When not touching data, we observe that the CPUs have idle cycles.
When reading data the CPUs are 100% busy in softirq.
With reading data:
Running XDP on dev:mlx5p1 (ifindex:8) action:XDP_DROP options:read
XDP stats CPU pps issue-pps
XDP-RX CPU 0 9,620,639 0
XDP-RX CPU 1 9,489,843 0
XDP-RX CPU 2 9,407,854 0
XDP-RX CPU 3 9,422,289 0
XDP-RX CPU 4 9,321,959 0
XDP-RX CPU 5 9,395,242 0
XDP-RX CPU total 56,657,828
The effect seen above is a result of cache-misses occuring when
more RXQs are being used. Based on perf-event observations, our
conclusion is that the CPUs DDIO (Direct Data I/O) choose to
deliver packet into main memory, instead of L3-cache. We also
found, that this can be mitigated by either using less RXQs or by
reducing NICs the RX-ring size.
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Toke Høiland-Jørgensen <toke@toke.dk>
Acked-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
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This sample program can be used for monitoring and reporting how many
packets per sec (pps) are received per NIC RX queue index and which
CPU processed the packet. In itself it is a useful tool for quickly
identifying RSS imbalance issues, see below.
The default XDP action is XDP_PASS in-order to provide a monitor
mode. For benchmarking purposes it is possible to specify other XDP
actions on the cmdline --action.
Output below shows an imbalance RSS case where most RXQ's deliver to
CPU-0 while CPU-2 only get packets from a single RXQ. Looking at
things from a CPU level the two CPUs are processing approx the same
amount, BUT looking at the rx_queue_index levels it is clear that
RXQ-2 receive much better service, than other RXQs which all share CPU-0.
Running XDP on dev:i40e1 (ifindex:3) action:XDP_PASS
XDP stats CPU pps issue-pps
XDP-RX CPU 0 900,473 0
XDP-RX CPU 2 906,921 0
XDP-RX CPU total 1,807,395
RXQ stats RXQ:CPU pps issue-pps
rx_queue_index 0:0 180,098 0
rx_queue_index 0:sum 180,098
rx_queue_index 1:0 180,098 0
rx_queue_index 1:sum 180,098
rx_queue_index 2:2 906,921 0
rx_queue_index 2:sum 906,921
rx_queue_index 3:0 180,098 0
rx_queue_index 3:sum 180,098
rx_queue_index 4:0 180,082 0
rx_queue_index 4:sum 180,082
rx_queue_index 5:0 180,093 0
rx_queue_index 5:sum 180,093
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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