[tor-relays] big spike in cpu usage

[Andreas Krey]

On Sun, 07 Apr 2013 12:47:05 +0000, Mi??osz Gaczkowski wrote:
> On 07/04/2013 08:12, N Owen Gunden wrote:
> >Does tor traffic generally fluctuate a lot with time of day?
> 
> I'm pretty new to tor, but in my experience it does fluctuate quite a 
> lot. With my settings of:
> 
> RelayBandwidthRate 1536 KB
> RelayBandwidthBurst 2048 KB

I use 'RelayBandwidthBurst 1000 MB', as the point of my RelayBandwidthRate
is to keep below the traffic limit of my VPS. I have no problem of
accumulating lots of unused bandwith for later bursts (which then can
go over the BandwithRate for some time).

> it tends to switch between two "modes": hogging all of 1.5MiB/s of 
> bandwidth very consistently (and using a lot of CPU power), and dancing 
> somewhere between 0.5MiB/s-1MiB/s (and using hardly any CPU).

Hmm. The part that strikes me as strange is the 'a lot of CPU power'.
The CPU usage when in limit mode ('flatline') shouldn't be much higher
than when being shortly below the limit; there may be an actual problem
with the code there. (Otherwise, the pegging to the BandwithRate for
hours at a time is normal - don't know if it happens similarly for
nodes that have no explicit BandwithRate and are only limited by
their physical capability.)

> It seems 
> pretty regular to me, usually hogging between 14:00 and 24:00 UTC and 
> getting more relaxed outside of these times.

That is more or less a daily pattern, but the correlation between
the two relays (non-exit) I operate at least aren't very obvious;
see https://twitter.com/akrey/status/320943399752564736/photo/1
for a four-day period dump.

Also, on the 'he' relay I use a lower advertized bandwidth than
the actual RelayBandwidthRate so the node needs to be somewhat
overbooked before it actually 'flatlines'. Currently this seems
to be successful, but it isn't always. (When in 'flatline' a
relay IMHO imparts a substantially higher roundtrip time on
the circuits through it, so, for usability, I'd like to avoid
that.)

The 'hz' plot also shows the actual bursts that go over the
RelayBandwidthRate.

Andreas

-- 
"Totally trivial. Famous last words."
From: Linus Torvalds <torvalds@*.org>
Date: Fri, 22 Jan 2010 07:29:21 -0800