[tor-bugs] #4792 [Tor Relay]: Network throughput on tor relay stalls

Tor Bug Tracker & Wiki torproject-admin at torproject.org
Tue Dec 27 21:34:47 UTC 2011

#4792: Network throughput on tor relay stalls
 Reporter:  torland    |          Owner:                     
     Type:  defect     |         Status:  new                
 Priority:  normal     |      Milestone:                     
Component:  Tor Relay  |        Version:  Tor:
 Keywords:             |         Parent:                     
   Points:             |   Actualpoints:                     
 Im am running the torland relay family. On one of my servers I experience
 sudden network outages. The relays normally pump at a rate of 450-550
 MBit/s. When the outage happens, within minutes the rate goes down below
 about 5Mit/s. In this case it is difficult to connect to the server via
 ssh or to access the webserver with the traffic stats.
 I checked the logs but found nothing in there. During the outage the CPU
 runs at a pretty low level, so CPU is not the root cause of this issue.
 Doing a traceroute to the server showed that the server indeed was the
 point where packet loss happened. I also contacted the ISP and asked them
 to check their network but they found nothing.
 For me it looks as if the network stack on the machine runs at some point
 on some kind of lock which slows done throughout. Because the processes
 doing real work are tor processes (all are consuming nearly 100% CPU) I
 suppose tor is causing the outage. Are there any log options for tor I can
 use to investigate the cause of this issue?

 Fingerprints of the relays are:

 Just to visualize I attach a screen shot of network usage when the issue
 happens: http://goo.gl/vSe32

 Any hint is appreciated.

Ticket URL: <https://trac.torproject.org/projects/tor/ticket/4792>
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