[tor-bugs] #25687 [Core Tor/Tor]: extreme over-report of observed / self-measure bandwidth on fast hardware -- critical to torflow / peerflow

[Tor Bug Tracker & Wiki]

#25687: extreme over-report of observed / self-measure bandwidth  on fast hardware
-- critical to torflow / peerflow
--------------------------+------------------------------------
 Reporter:  starlight     |          Owner:  (none)
     Type:  defect        |         Status:  new
 Priority:  Medium        |      Milestone:  Tor: unspecified
Component:  Core Tor/Tor  |        Version:  Tor: 0.3.3.3-alpha
 Severity:  Normal        |     Resolution:
 Keywords:                |  Actual Points:
Parent ID:                |         Points:
 Reviewer:                |        Sponsor:
--------------------------+------------------------------------
Changes (by starlight):

 * version:   => Tor: 0.3.3.3-alpha


Comment:

 In my view the problem constitutes a critical measurement error.  The most
 important consumer of this value is `torflow` and overstating true
 available bandwidth distorts consensus allocations.  No chance
 overstatements are correct, especially in the traffic-control scenario
 where Linux caps bandwidth with fine-grained, reliable precision.  Some
 ISPs permit traffic to burst briefly before enforcing bandwidth
 restrictions, but in the cases I've seen bandwidth self-measure is well in
 excess of the the line burst rate and anyway reporting burst-rate maximum
 capacity to torflow is counterproductive.  The impact of the issue may be
 acute due to torflow's control-signal reliance on measurements of marginal
 unused bandwidth rather than actual capacity.

 To venture a guess, any of queuing (as suggested), chunky event-loop
 processing delays, course time precision, misalignment of time
 determination vs. data accounting are likely culprits.

 Setting milestone was unintended, was thinking of the latest reproducing
 version.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/25687#comment:3>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online