[metrics-bugs] #34215 [Metrics/Onionperf]: Harmonize TTFB/TTLB definitions with Tor Metrics plots

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#34215: Harmonize TTFB/TTLB definitions with Tor Metrics plots
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 Reporter:  karsten            |          Owner:  karsten
     Type:  defect             |         Status:  needs_review
 Priority:  Medium             |      Milestone:
Component:  Metrics/Onionperf  |        Version:
 Severity:  Normal             |     Resolution:
 Keywords:                     |  Actual Points:
Parent ID:  #33327             |         Points:
 Reviewer:                     |        Sponsor:  Sponsor59
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Changes (by karsten):

 * status:  accepted => needs_review


Comment:

 The first question here is how we want to define TTFB/TTLB:
  - Right now, OnionPerf considers the time between the `tgen` client
 sending the HTTP request to the `tgen` server and receiving the first/last
 byte of the HTTP response back as TTFB/TTLB. This excludes all the magic
 happening inside the `tor` client to provide a circuit and attach a stream
 to it. In some cases this is pretty fast, for example, when it can reuse a
 pre-built circuit to connect via an exit to its own `tgen` server. In
 other cases this can take a while, for example, when it needs to do the
 entire ~~hidden~~onion service connection establishment dance.
  - The [https://metrics.torproject.org/torperf.html Time to download files
 over Tor graph] on the Tor Metrics website measures TTLB as the time
 between the `tgen` client starting a measurement and receiving the last
 byte of the HTTP response from the `tgen` server. This includes all the
 magic as written above.

 I'd argue that we do care about measuring what's going on in `tor`, so we
 should switch OnionPerf to the definitions used on the Tor Metrics website
 graph.
 [https://gitweb.torproject.org/user/karsten/onionperf.git/commit/?h=task-34215&id=a836f8747398d010646858743d62867ac1a35504
 Commit a836f87 in my task-34215 branch] contains the trivial patch.
 Comments welcome! I'll also bring this up for discussion at our next
 weekly meeting.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/34215#comment:3>
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