On Fri, Jan 24, 2014 at 4:49 AM, Alexander Dietrich alexander@dietrich.cx wrote:
Hello,
a relay I'm running is currently at about 0.80 load average. It has a dual-core CPU and I have configured "NumCPUs 2". I'm still in the process of finding the bandwidth limit.
So, others have answered pretty well, but I'll add a little too.
Right now, Tor uses multiple cores to parallelize circuit extension handshakes, but not much else. I'm hoping that in future versions we can make serious progress on getting more of our crypto parallelized[*] to better take advantage of more cores, but for right now, NumCPUs is a good thing, but is not actually adequate for evenly dividing your Tor process's CPU load among a larger number of cores.
[*] See eg discussion at https://trac.torproject.org/projects/tor/wiki/org/projects/Tor/Multithreaded... . The design there is still sound, but it needs some C hackers with spare time.