[Tor-BSD] Tor BSD underperformance (was Recognizing Randomness Exhaustion)

[teor]

On 1 Jan 2015, at 07:39 , Greg Troxel <gdt at lexort.com> wrote:

> Libertas <libertas at mykolab.com> writes:
> 
>> Some of the people at tor-bsd at lists.nycbug.org and I are trying to
>> figure out why Tor relays under-perform when running on OpenBSD. Many
>> such relays aren't even close to being network-bound,
>> file-descriptor-bound, memory-bound, or CPU-bound, but relay at least
>> 33-50% less traffic than would be expected of a Linux machine in the
>> same situation.
> 
> I'm more familiar with NetBSD, but hopefully my comments are helpful.
> 
>> For those not familiar, a Tor relay will eventually have an open TCP
>> connection for each of the other >6,000 active relays, and (if it allows
>> exit traffic) must make outside TCP connections for the user's requests,
>> so it's pretty file-hungry and crypto-intensive.
> 
> It may also have something to do with TCP.  A few thoughts:
> 
> * run netstat -f inet and look and the send queues.  That's not really
>  cleanly diagnostic, but if they are all huge, it's a clue
> 
> * run netstat -m and vmstat -m (not sure those map from NetBSD).  Look
>  for runnig out of mbufs and mbuf clusters.   Perhaps bump up
>  NMBCLUSTERS in the kernel if it's not dynamic.

Tor 0.2.6.2-alpha (just in the process of being released) has some changes to queuing behaviour using the KIST algorithm. 

The KIST algorithm keeps the queues inside tor, and makes prioritisation decisions from there, rather than writing as much as possible to the OS TCP queues. I'm not sure how functional it is on *BSDs, but Nick Mathewson should be able to comment on that. (I've cc'd tor-dev and Nick.)


teor
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