[tor-bugs] #34171 [Core Tor/Tor]: possible single circuit maximum transfer rate regression in 0.3.4

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#34171: possible single circuit maximum transfer rate regression in 0.3.4
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 Reporter:  starlight     |          Owner:  (none)
     Type:  defect        |         Status:  needs_information
 Priority:  Medium        |      Milestone:
Component:  Core Tor/Tor  |        Version:  Tor: 0.3.4.10
 Severity:  Normal        |     Resolution:
 Keywords:                |  Actual Points:
Parent ID:                |         Points:
 Reviewer:                |        Sponsor:
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Comment (by starlight):

 Ran several experiments and found that I was wrong about possible
 performance regression.  Reproduced fast single-circuit transfer rates
 with 0.4.3 and that it may be a touch faster than older versions.  Will
 close this ticket after allowing  time for further comment.

 Earlier was running a client from a system lacking hardware acceleration
 for AES encryption, forgetting the change some time back in one of my
 typical setups.  What is interesting is cpu consumption was very low on
 the non-AES cpu during the flawed tests.  I suspect the problem in that
 case is an accumulation of store-de/encrypt-and-forward latencies
 interacting badly with various other path components, producing terrible
 throughput.

 This is notable if one examines a ranking of the fastest relays by SBWS
 absolute bandwidth, either mean or median, where fewer than five
 (literally five) relays at any time are rated faster than the 2Mbyte/sec
 maximum I observed in the problematic test.  Might indicate typical case
 degradation due to accumulation of end-to-end latencies deserves a close
 look with an eye toward discovering and correcting a performance cliff.
 Ticket #29427 could be the culprit--I haven't yet completely eliminated
 KIST in tests due to recent changes preventing one-hop circuits.  Seems to
 me reduction of default `KISTSchedRunInterval` to 2ms should be completed.

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/34171#comment:8>
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