[tor-dev] Scaling tor for a global population

[teor]

[thread reconstructed]
>> On 09/30/2014 06:28 AM, AFO-Admin wrote:
>>> if we would get multithread support, this would boost the bandwith
>>> that is avaible, there i'm sure.
>>> All my relays run in CPU limit because i don't think wasting even more
>>> ipv4 addresses is great, today you get more and more cpu cores that is
>>> not linier with the IPC increase.
>>> 
>>> E.g. you have a Server with 2x E5-2683 v3  v3 and a 10 Gbit/s pipe you
>>> would need atleast 14 IP's to use most of the CPU. And every IP's gets
>>> blacklistet, with that much Tor nodes in the same /24 maybe the entire
>>> /24. So most ISP's wouldn't be happy with that and with the IPv4
>>> shortage this days im also not very happy with that.
>>> We really shouldn't waste more IPv4 IP's then needed and the only
>>> solution is to change the max amount of Tor Processes from 2 to a
>>> higher number or move to IPv6 or get multithreading working.

[Moritz quoted]
>>> E.g. you have a Server with 2x E5-2683 v3  v3 and a 10 Gbit/s pipe you
>>> would need atleast 14 IP's to use most of the CPU.
> 
> Moritz Bartl transcribed 0.5K bytes:
>> Raising the limit from 2 relays per IP to x per IP has been discussed in the
>> past and would be an easy change.
> 
Date: Tue, 30 Sep 2014 20:35:21 +0000

From: isis <isis at torproject.org>
> We *still* have that limit? I thought we killed it a long time ago.
> 
> Can we kill it now? It's not going to do anything to prevent Sybils, it'll
> only prevent good relay operators on larger machines from giving more
> bandwidth.

Allowing multiple (>2) tor instances would alleviate AFO's issue in the short term, although in this particular case, they might need 14(!) instances (or AES-NI).

Given the shortage of IPv4s, and the availability of multi-processor, high-bandwidth servers, we could trial raising the Tor instance limit per IP. (As this is an authority parameter, the change could happen much sooner than predominantly-IPv6 tor or multithreaded tor.)

4 would allow 1 tor process per logical processor in many server machines (e.g. 4x1 and 2x2). At ~320Mbps per tor process (the maximum bandwidth in the current network), this could saturate a 1 Gbps link with 1 IP.

8 would allow 1 tor process per logical processor in almost all servers (e.g. 4x2 and 8x1), and could saturate a 2.5 Gbps link with 1 IP. In AFO's 10 Gbps case, they'd need 32 processes, or 4 IPs. (Which doesn't seem as unreasonable as 14 IPs.)

The only drawback I can see is that IPs with slow connections/few CPUs could then launch 4 or 8 instances, and slow down the network. This could exacerbate the "wasted consensus entry" issue, where the consensus bytes used for a router outweigh its contribution. (But this seems unlikely.)

In the short term, can we trial raising the Tor instance limit per IP to 4 or 8?

(In the longer term, I'm happy to help with (network) performance, multithreading, or IPv6 - probably in that order.)

T

teor
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