[tor-bugs] #13414 [Tor]: Increase Authorities' AuthDirMaxServersPerAddr to 4 or 8 to use more processors

[Tor Bug Tracker & Wiki]

#13414: Increase Authorities' AuthDirMaxServersPerAddr to 4 or 8 to use more
processors
----------------------------------------+---------------------
 Reporter:  teor                        |          Owner:
     Type:  defect                      |         Status:  new
 Priority:  normal                      |      Milestone:
Component:  Tor                         |        Version:
 Keywords:  tor-authorities tor-router  |  Actual Points:
Parent ID:                              |         Points:
----------------------------------------+---------------------
 Due to the increase in logical processors per machine, a recent
 conversation on the tor-dev mailing list suggested increasing the Tor
 Authorities' AuthDirMaxServersPerAddr,[0] (Mortiz Bartl) either to
 unlimited[1] (isis) or 4 or 8 [2][3] (mikeperry, teor).

 I suggest we initially increase the consensus parameter to 8, quadrupling
 CPU-bound throughput, and then, if successful, change the default in code
 in a major release.

 '''Details:'''

 The increase in logical and physical processors per machine has
 outstripped tor's ability to parallelise its workload, artificially
 limiting the network throughput.[4] (AFO-Admin)

 * Scarcity of IPv4 addresses, particularly in some regions
 * Multiple relays sharing IPv4 addresses due to VPSs and/or NAT - see
 #13234

 '''Long-term:'''

 Long-term work that will resolve this issue:
 * Parallelise more of tor's compute workload [5]
 * Optimise Cryptography, either through algorithm choice or code
 refactoring
 * Implement/Test/Deploy/Activate IPv6 ORPorts

 '''Potential Concerns:'''

 This could make Sybil attacks slightly easier, but we already mitigate
 against Syblils on the same IP using the /24 filter. isis wasn't concerned
 about extra Sybils from this change.[1]

 This change may slightly increase the size of the consensus. However,
 there are multiple upcoming plans to reduce consensus size, including:
 * Consensus Diffs
 * Reducing Consensus Size by Excluding the Slowest Relays

 [0]: https://lists.torproject.org/pipermail/tor-
 dev/2014-September/007570.html
 [1]: https://lists.torproject.org/pipermail/tor-
 dev/2014-September/007573.html
 [2]: https://lists.torproject.org/pipermail/tor-
 dev/2014-September/007574.html
 [3]: https://lists.torproject.org/pipermail/tor-
 dev/2014-October/007575.html
 [4]: https://lists.torproject.org/pipermail/tor-
 dev/2014-September/007565.html
 [5]: https://lists.torproject.org/pipermail/tor-
 dev/2014-September/007558.html

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/13414>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online