SK-AM64: AM64 OpenVPN performance issue

Part Number: SK-AM64

Hello,

I am currently testing OpenVPN on the SK-AM64, it's direct communication between my computer and AM64 via 1g Ethernet. The problem is throughput drops after some time (it can be seconds or minutes) you can see the iperf3 logs below. There are no dropped packets or any error, the only thing I observed is CPU usage increasing from around %20 to %25 when the throughput drop happens

~ # ./iperf3 -c 10.8.0.1  
Connecting to host 10.8.0.1, port 5201
[  5] local 10.8.0.2 port 34490 connected to 10.8.0.1 port 5201
[ ID] Interval           Transfer     Bitrate         Retr  Cwnd
[  5]   0.00-1.00   sec  14.5 MBytes   122 Mbits/sec    6    639 KBytes        
[  5]   1.00-2.00   sec  12.9 MBytes   108 Mbits/sec   21    541 KBytes        
[  5]   2.00-3.00   sec  13.6 MBytes   114 Mbits/sec    0    597 KBytes        
[  5]   3.00-4.00   sec  13.6 MBytes   114 Mbits/sec    0    635 KBytes        
[  5]   4.00-5.00   sec  11.7 MBytes  97.9 Mbits/sec    1    478 KBytes        
[  5]   5.00-6.00   sec  8.03 MBytes  67.3 Mbits/sec    0    511 KBytes        
[  5]   6.00-7.00   sec  8.03 MBytes  67.3 Mbits/sec    0    532 KBytes        
[  5]   7.00-8.00   sec  8.83 MBytes  74.1 Mbits/sec    0    543 KBytes        
[  5]   8.00-9.00   sec  8.03 MBytes  67.3 Mbits/sec    0    547 KBytes        
[  5]   9.00-10.00  sec  8.03 MBytes  67.3 Mbits/sec    0    547 KBytes      

Another iperf3 log

[  5]  19.00-20.00  sec  14.2 MBytes   120 Mbits/sec    0    229 KBytes        
[  5]  20.00-21.00  sec  14.4 MBytes   121 Mbits/sec    0    232 KBytes        
[  5]  21.00-22.00  sec  14.2 MBytes   120 Mbits/sec    0    232 KBytes        
[  5]  22.00-23.00  sec  14.4 MBytes   121 Mbits/sec    0    232 KBytes        
[  5]  23.00-24.00  sec  14.2 MBytes   120 Mbits/sec   24    188 KBytes        
[  5]  24.00-25.00  sec  14.4 MBytes   121 Mbits/sec    0    191 KBytes        
[  5]  25.00-26.00  sec  13.9 MBytes   116 Mbits/sec    0    206 KBytes        
[  5]  26.00-27.00  sec  9.00 MBytes  75.5 Mbits/sec    0    236 KBytes        
[  5]  27.00-28.00  sec  9.25 MBytes  77.6 Mbits/sec    0    262 KBytes        
[  5]  28.00-29.00  sec  8.88 MBytes  74.4 Mbits/sec    0    285 KBytes        
[  5]  29.00-30.00  sec  9.00 MBytes  75.5 Mbits/sec    0    308 KBytes        
[  5]  30.00-31.00  sec  9.25 MBytes  77.6 Mbits/sec    0    328 KBytes        

Another iperf3 log

[  5]  48.00-49.00  sec  15.5 MBytes   130 Mbits/sec    0    232 KBytes        
[  5]  49.00-50.00  sec  14.9 MBytes   125 Mbits/sec   35    203 KBytes        
[  5]  50.00-51.00  sec  15.1 MBytes   127 Mbits/sec    0    250 KBytes        
[  5]  51.00-52.00  sec  15.9 MBytes   133 Mbits/sec   55    206 KBytes        
[  5]  52.00-53.00  sec  16.2 MBytes   136 Mbits/sec   45    134 KBytes        
[  5]  53.00-54.00  sec  10.4 MBytes  87.0 Mbits/sec    0    184 KBytes        
[  5]  54.00-55.00  sec  8.50 MBytes  71.3 Mbits/sec    0    215 KBytes        
[  5]  55.00-56.00  sec  8.75 MBytes  73.4 Mbits/sec    0    242 KBytes        
[  5]  56.00-57.00  sec  8.75 MBytes  73.4 Mbits/sec    0    266 KBytes        
[  5]  57.00-58.00  sec  8.75 MBytes  73.4 Mbits/sec    0    289 KBytes        
[  5]  58.00-59.00  sec  8.38 MBytes  70.3 Mbits/sec    0    310 KBytes        

OpenVPN Version : OpenVPN 2.6.3 aarch64-none-linux-gnu [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [MH/PKTINFO] [AEAD]

Example client config: 

client
dev tun
proto udp
remote 192.168.1.42 1194
resolv-retry infinite
nobind
persist-key
persist-tun
remote-cert-tls server
auth SHA512
ignore-unknown-option block-outside-dns
verb 1
iproute /bin/ip

I also tested with tcp and no encryption options, the result was the same.