tinc performance relatively slow

[Pallinger Péter]

------- TL;DR -------

Performance seems slow (around 300-400Mbit peak).
How to improve?

------- The Long Version -------

I tried to test tinc performance for an upcoming project that may need
to use NFS over a VPN. Our current tinc network seems to be able to
transmit at around 30-40 MB/s. (I used an 1GB random testfile to copy
to/from /dev/shm/; using netcat and http.) In comparison, HTTP and scp
are 300MB/s and 200MB/s respectively (over 10Gb link; over 1Gb link,
both are around 112MB/s).

By observing _top_ output, it seems that the CPU usage is around 90% for
the tinc process on at least one of the transmitting machines.

I tried to change the cipher to aes-128-cbc, but it did not have any
significant effect on transmit speed.

How can I know tinc operation eats up my CPU? Are there any simple best
practices to achieve better performance?

Thanks in advance:
	PP

P.s.: With regards to my memory problems last month: since then, I have
no problems with memory usage at all: usage remains constantly under
10MB per daemon. CNR. :(