Thanks for all the input guys.
See some advice here: http://archives.seul.org/or/relays/Aug-2010/msg00034.html
Found that before and I have followed it to the letter when I set up the relay
Also are you running with a lot of iptables/ip6tables rules active (or any at all)? If you do, consider rewriting them so that at least 'conntrack' is not used (check that you can do "rmmod ipt_conntrack" cleanly, or it's not loaded in the first place).
No iptables rules active, and conntrack is not loaded.
Make sure you have the most recent OpenSSL library, with the ec_nistp_64_gcc_128 optimizations enabled. (Tor will print a big nasty warning on startup if the library is new enough but the optimizations aren't available.)
I have the latest OpenSSL library installed (version 1.0.1e-2) and no complaints from tor when it starts up.
You may get better utilization out of your CPU by running multiple tor daemons (try 4 to start) each with MaxCPUs=1 and bandwidth cap set to 1/N of the total available. They each have to be configured to use a distinct ORPort and state directory, and should all be tagged as the same family.
I have been thinking about this but I'm reluctant to "partition" my bandwidth. I'm afraid it will end up like harddrive partitions: lots of wasted space. i.e. one daemon hitting the bandwidth cap while the other is under utilized.
That CPU is powerful enough to handle 80 Mbps assuming there's no hardware performance problems; a similar Xeon handles around 140 Mbps per core.
Since the CPU is supposed to be able to handle 80mbit bandwidth I would much prefer to find out what the current problem is and continue to run with one daemon.
More info about the system: OS: debian 7.1. Only other thing running on the box is 2 GPU apps from Einstein@Home which use about 1/3 CPU core each. NIC: RTL-8169 on the motherboard.
The messages only appear about 1 to 5 times a day even though the bandwidth usage is mostly at the 80mbit cap. My guess is that some users create enormous amounts of circuits and my CPU fails to handle them. Any other tips for what I could look at?