[tor-relays] CPU usage

Julien ROBIN julien.robin28 at free.fr
Tue Jul 8 00:02:52 UTC 2014


In effect this CPU usage is quite normal : a Tor Relay use a lot of CPU, proportionally with amount of data passing trough the relay.
With an Intel Atom D510 I was above 40 Mbps, while CPU was giving everything.

The problem with Tor is the "single-thread working" for encryption/relaying, so if you have a second CPU core available, may be you can open a second Tor instance in order to use the second core capacity.

In fact, when your Tor daemon reaches 100% of 1 core usage, you can see what is the current bandwith and set it into your torrc file as maximum. When a Tor instance exceeds 100% it's a little bit like a "congestion" into your Tor process, so it's better for 100% value to be a limit per Tor process. 
Your relay may average a little bit under the limit bandwidth of your torrc file, but this give better performance for Tor circuits established through your relay so it's not a bad ;)

An interesting webpage here, full of usefull informations that doesn't appear on the official tutorial :

Even if what you've done is more simple, or a little bit different, this tutorial will make you aware of a lot of interesting details and possibilities.

Good luck !
Julien ROBIN

----- Mail original -----
De: "kingqueen" <kingqueen at btnf.tw>
À: tor-relays at lists.torproject.org
Envoyé: Lundi 7 Juillet 2014 22:31:02
Objet: [tor-relays] CPU usage

Hi, I'm running a Tor relay on a low cost dedicated server.

The tor relay is named kingqueen and it's running on an Intel Atom N2700 dual core hyperthreaded CPU with 2gb of memory, in a data centre with a symmetric 100mbps connection.

I have found as time goes on and usage of my relay increases (about 3 weeks now) that the Tor process is increasingly using more of the CPU. TOP shows Tor using over 100% of CPU and the load average is 2 or more.

I use the dedi for other, less intensive things (OpenVPN, seedbox, also Owncloud though this falls over). I know that this is sub-optimal and ideally the dedi should be for the relay alone.

I was wondering if the CPU usage is standard. I guess it could be, given it has decryption work to be done? Is it high? Is there anything I can do to lower it, other than rate limiting, which I don't want to do?

Thank you
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