[metrics-team] Unusually slow OnionPerf measurements

[Karsten Loesing]

Hi Silvia, Rob, list,

I noticed today that OnionPerf "public server" measurements went up a
lot around May 22:

https://metrics.torproject.org/torperf.html?start=2017-05-06&end=2017-06-06&source=all&server=public&filesize=50kb

I quickly looked at the .tpf files available here:

https://collector.torproject.org/recent/torperf/

I found that the time between starting a request and writing the HTTP
request ("request" below) can be unusually high.  Likewise, the time
until receiving the first response ("response" below) has a quite large
maximum, too.

    request           response         first50          last50
 Min.   :   20.0   Min.   :  30.0   Min.   : 20.0   Min.   :  0.0
 1st Qu.:  150.0   1st Qu.: 140.0   1st Qu.: 80.0   1st Qu.: 80.0
 Median :  280.0   Median : 280.0   Median :150.0   Median :150.0
 Mean   :  597.7   Mean   : 387.3   Mean   :180.3   Mean   :183.3
 3rd Qu.:  430.0   3rd Qu.: 390.0   3rd Qu.:240.0   3rd Qu.:260.0
 Max.   :11610.0   Max.   :3100.0   Max.   :630.0   Max.   :890.0

(These numbers come from op-nl-51200-2017-06-04.tpf.)

What's going on there?  Is there anything unusual in the tor logs?  If
not, what could the reason?  What changed on May 22?

Thanks!

All the best,
Karsten

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