The max bandwidth of of virtual ethernet over PCIe between two xaviers

I was using “virtual ethernet over PCIe” between two xaviers. One is root complex and another is end point. And I use iperf3 to test the bandwidth of it.
I run “iperf3 -s” on root complex and run “iperf3 -c 192.168.2.1” on end point.on end point,the result is showed below:
Connecting to host 192.168.2.1, port 5201
[ 4] local 192.168.2.2 port 60622 connected to 192.168.2.1 port 5201
[ ID] Interval Transfer Bandwidth Retr Cwnd
[ 4] 0.00-1.00 sec 334 MBytes 2.80 Gbits/sec 1 6.33 MBytes
[ 4] 1.00-2.00 sec 461 MBytes 3.87 Gbits/sec 0 6.33 MBytes
[ 4] 2.00-3.00 sec 495 MBytes 4.15 Gbits/sec 0 6.33 MBytes
[ 4] 3.00-4.00 sec 514 MBytes 4.31 Gbits/sec 0 6.33 MBytes
[ 4] 4.00-5.00 sec 506 MBytes 4.24 Gbits/sec 0 6.33 MBytes
[ 4] 5.00-6.00 sec 508 MBytes 4.27 Gbits/sec 0 6.33 MBytes
[ 4] 6.00-7.00 sec 514 MBytes 4.30 Gbits/sec 0 6.33 MBytes
[ 4] 7.00-8.00 sec 509 MBytes 4.27 Gbits/sec 0 6.33 MBytes
[ 4] 8.00-9.00 sec 508 MBytes 4.25 Gbits/sec 0 6.33 MBytes
[ 4] 9.00-10.00 sec 509 MBytes 4.27 Gbits/sec 0 6.33 MBytes


[ ID] Interval Transfer Bandwidth Retr
[ 4] 0.00-10.00 sec 4.74 GBytes 4.07 Gbits/sec 1 sender
[ 4] 0.00-10.00 sec 4.74 GBytes 4.07 Gbits/sec receiver

iperf Done.


The theoretical bandwidth of pcie 3.0 x 8 is 7.8Gb/s.
I test, the bandwidth is about 4Gbits/sec. Is this the max bandwidth of 8-lane PCIe?
What are the possible factors that affect pcie bandwidth?