R35.1 PCIe i210 throughput slow

On Xavier NX, R32.6.1, custom carrier board: everything works well.

On Xavier NX, R35.1, same hardware: PCIe performance to i210 GigE Ethernet ICs seems to be very poor in the Tx (Xavier NX egress) path. Rx (Xavier NX ingress) path does not seem to be affected.

Benchmarks:

R35.1:

# iperf3 -c 192.168.1.157 -u -b 950M

Connecting to host 192.168.1.157, port 5201

[  5] local 192.168.1.225 port 44297 connected to 192.168.1.157 port 5201

[ ID] Interval           Transfer     Bitrate         Total Datagrams

[  5]   0.00-1.00   sec  7.33 MBytes  61.4 Mbits/sec  5305

R32.6:

# iperf3 -c 192.168.1.157 -u -b 950M

Connecting to host 192.168.1.157, port 5201

[  4] local 192.168.1.226 port 56975 connected to 192.168.1.157 port 5201

[ ID] Interval           Transfer     Bandwidth       Total Datagrams

[  4]   0.00-1.00   sec   112 MBytes   943 Mbits/sec  14388

Any ideas? Only thing that might be ‘special’ about the configuration is that the i210 is behind a PCIe switch. Running nvpmodel doesn’t seem to make any difference to the throughput.