I got similar iperf performance result as the following with LSDK 21.08 default software environment and two lx2160ardb boards connecting together. Is your user case termination traffic instead of forwarding?
root@localhost:/# iperf -c 100.1.1.64 -P 16 -t 30
------------------------------------------------------------
Client connecting to 100.1.1.64, TCP port 5001
TCP window size: 442 KByte (default)
------------------------------------------------------------
[ 4] local 100.1.1.65 port 44980 connected with 100.1.1.64 port 5001
[ 5] local 100.1.1.65 port 44982 connected with 100.1.1.64 port 5001
[ 3] local 100.1.1.65 port 44978 connected with 100.1.1.64 port 5001
[ 6] local 100.1.1.65 port 44984 connected with 100.1.1.64 port 5001
[ 7] local 100.1.1.65 port 44986 connected with 100.1.1.64 port 5001
[ 8] local 100.1.1.65 port 44988 connected with 100.1.1.64 port 5001
[ 12] local 100.1.1.65 port 44996 connected with 100.1.1.64 port 5001
[ 9] local 100.1.1.65 port 44990 connected with 100.1.1.64 port 5001
[ 10] local 100.1.1.65 port 44992 connected with 100.1.1.64 port 5001
[ 11] local 100.1.1.65 port 44994 connected with 100.1.1.64 port 5001
[ 13] local 100.1.1.65 port 44998 connected with 100.1.1.64 port 5001
[ 14] local 100.1.1.65 port 45000 connected with 100.1.1.64 port 5001
[ 15] local 100.1.1.65 port 45002 connected with 100.1.1.64 port 5001
[ 16] local 100.1.1.65 port 45004 connected with 100.1.1.64 port 5001
[ 17] local 100.1.1.65 port 45006 connected with 100.1.1.64 port 5001
[ 18] local 100.1.1.65 port 45008 connected with 100.1.1.64 port 5001
[ ID] Interval Transfer Bandwidth
[ 7] 0.0-30.0 sec 1.29 GBytes 369 Mbits/sec
[ 12] 0.0-30.0 sec 1.26 GBytes 362 Mbits/sec
[ 11] 0.0-30.0 sec 1.21 GBytes 346 Mbits/sec
[ 14] 0.0-30.0 sec 1.24 GBytes 355 Mbits/sec
[ 16] 0.0-30.0 sec 1.27 GBytes 364 Mbits/sec
[ 4] 0.0-30.0 sec 1.23 GBytes 352 Mbits/sec
[ 5] 0.0-30.0 sec 1.27 GBytes 362 Mbits/sec
[ 9] 0.0-30.0 sec 1.24 GBytes 356 Mbits/sec
[ 13] 0.0-30.0 sec 1.28 GBytes 365 Mbits/sec
[ 15] 0.0-30.0 sec 1.25 GBytes 357 Mbits/sec
[ 3] 0.0-30.1 sec 1.25 GBytes 356 Mbits/sec
[ 6] 0.0-30.0 sec 1.31 GBytes 376 Mbits/sec
[ 10] 0.0-30.1 sec 1.28 GBytes 365 Mbits/sec
[ 17] 0.0-30.0 sec 1.23 GBytes 353 Mbits/sec
[ 18] 0.0-30.0 sec 1.24 GBytes 354 Mbits/sec
[ 8] 0.0-30.1 sec 1.28 GBytes 366 Mbits/sec
[SUM] 0.0-30.1 sec 20.1 GBytes 5.75 Gbits/sec
root@localhost:/# iperf -c 100.1.1.64 -P 16 -t 30 -u -b 40G
------------------------------------------------------------
Client connecting to 100.1.1.64, UDP port 5001
Sending 1470 byte datagrams, IPG target: 0.27 us (kalman adjust)
UDP buffer size: 208 KByte (default)
------------------------------------------------------------
[ 3] local 100.1.1.65 port 47092 connected with 100.1.1.64 port 5001
[ 4] local 100.1.1.65 port 51398 connected with 100.1.1.64 port 5001
[ 5] local 100.1.1.65 port 51049 connected with 100.1.1.64 port 5001
[ 6] local 100.1.1.65 port 43814 connected with 100.1.1.64 port 5001
[ 7] local 100.1.1.65 port 45999 connected with 100.1.1.64 port 5001
[ 8] local 100.1.1.65 port 57700 connected with 100.1.1.64 port 5001
[ 9] local 100.1.1.65 port 60702 connected with 100.1.1.64 port 5001
[ 10] local 100.1.1.65 port 43959 connected with 100.1.1.64 port 5001
[ 11] local 100.1.1.65 port 39367 connected with 100.1.1.64 port 5001
[ 12] local 100.1.1.65 port 52498 connected with 100.1.1.64 port 5001
[ 13] local 100.1.1.65 port 46112 connected with 100.1.1.64 port 5001
[ 14] local 100.1.1.65 port 48562 connected with 100.1.1.64 port 5001
[ 15] local 100.1.1.65 port 33950 connected with 100.1.1.64 port 5001
[ 16] local 100.1.1.65 port 37260 connected with 100.1.1.64 port 5001
[ 17] local 100.1.1.65 port 35469 connected with 100.1.1.64 port 5001
[ 18] local 100.1.1.65 port 32931 connected with 100.1.1.64 port 5001
[ ID] Interval Transfer Bandwidth
[ 5] 0.0-30.2 sec 275 MBytes 76.3 Mbits/sec
[ 5] Sent 196141 datagrams
[ 5] Server Report:
[ 5] 0.0-30.2 sec 192 KBytes 51.9 Kbits/sec 11.167 ms 3101/ 0 (inf%)
[ 10] 0.0-30.2 sec 277 MBytes 77.0 Mbits/sec
[ 10] Sent 197856 datagrams
[ 12] 0.0-30.2 sec 278 MBytes 77.1 Mbits/sec
[ 12] Sent 198121 datagrams
[ 14] 0.0-30.2 sec 276 MBytes 76.6 Mbits/sec
[ 14] Sent 196964 datagrams
[ 12] Server Report:
[ 12] 0.0-30.2 sec 193 KBytes 52.4 Kbits/sec 14.995 ms 3719/ 0 (inf%)
[ 10] Server Report:
[ 10] 0.0-30.2 sec 193 KBytes 52.4 Kbits/sec 20.850 ms 2843/ 0 (inf%)
[ 14] Server Report:
[ 14] 0.0-30.2 sec 192 KBytes 52.1 Kbits/sec 6.310 ms 7829/ 0 (inf%)
[ 6] 0.0-30.2 sec 279 MBytes 77.3 Mbits/sec
[ 6] Sent 198680 datagrams
[ 7] 0.0-30.2 sec 279 MBytes 77.3 Mbits/sec
[ 7] Sent 198676 datagrams
[ 8] 0.0-30.2 sec 275 MBytes 76.2 Mbits/sec
[ 8] Sent 195864 datagrams
[ 16] 0.0-30.2 sec 272 MBytes 75.5 Mbits/sec
[ 16] Sent 194226 datagrams
[ 7] Server Report:
[ 7] 0.0-30.2 sec 194 KBytes 52.6 Kbits/sec 14.559 ms 2173/ 0 (inf%)
[ 8] Server Report:
[ 8] 0.0-30.2 sec 191 KBytes 51.8 Kbits/sec 12.627 ms 831/ 0 (inf%)
[ 6] Server Report:
[ 6] 0.0-30.2 sec 194 KBytes 52.6 Kbits/sec 14.019 ms 8185/ 0 (inf%)
[ 16] Server Report:
[ 16] 0.0-30.2 sec 190 KBytes 51.4 Kbits/sec 0.001 ms 4134/ 0 (inf%)
[ 3] 0.0-30.2 sec 275 MBytes 76.4 Mbits/sec
[ 3] Sent 196386 datagrams
[ 13] 0.0-30.2 sec 273 MBytes 75.8 Mbits/sec
[ 13] Sent 194996 datagrams
[ 17] 0.0-30.2 sec 274 MBytes 75.9 Mbits/sec
[ 17] Sent 195257 datagrams
[ 13] Server Report:
[ 13] 0.0-30.2 sec 190 KBytes 51.6 Kbits/sec 9.668 ms 7045/ 0 (inf%)
[ 3] Server Report:
[ 3] 0.0-30.2 sec 192 KBytes 52.0 Kbits/sec 6.817 ms 2735/ 0 (inf%)
[ 17] Server Report:
[ 17] 0.0-30.2 sec 191 KBytes 51.7 Kbits/sec 0.446 ms 9778/ 0 (inf%)
[ 11] 0.0-30.2 sec 277 MBytes 76.7 Mbits/sec
[ 11] Sent 197250 datagrams
[ 15] 0.0-30.2 sec 275 MBytes 76.3 Mbits/sec
[ 15] Sent 196217 datagrams
[ 18] 0.0-30.2 sec 274 MBytes 76.0 Mbits/sec
[ 18] Sent 195509 datagrams
[ 18] Server Report:
[ 18] 0.0-30.2 sec 191 KBytes 51.7 Kbits/sec 3.367 ms 6324/ 0 (inf%)
[ 11] Server Report:
[ 11] 0.0-30.2 sec 193 KBytes 52.2 Kbits/sec 7.802 ms 4433/ 0 (inf%)
[ 15] Server Report:
[ 15] 0.0-30.2 sec 192 KBytes 51.9 Kbits/sec 3.930 ms 2006/ 0 (inf%)
[ 4] 0.0-30.2 sec 277 MBytes 76.8 Mbits/sec
[ 4] Sent 197401 datagrams
[ 9] 0.0-30.2 sec 279 MBytes 77.3 Mbits/sec
[ 9] Sent 198661 datagrams
[SUM] 0.0-30.2 sec 4.31 GBytes 1.22 Gbits/sec
[SUM] Sent 3148205 datagrams