[tor-bugs] #12690 [Tor]: Raise the bandwidth threshold for being a guard

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#12690: Raise the bandwidth threshold for being a guard
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     Reporter:  asn     |      Owner:
         Type:  defect  |     Status:  needs_review
     Priority:  normal  |  Milestone:  Tor: 0.2.5.x-final
    Component:  Tor     |    Version:
   Resolution:          |   Keywords:  tor-guard tor-auth
Actual Points:          |  Parent ID:  #11480
       Points:          |
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Comment (by asn):

 Looks good to me.

 Also, see my branch `arma-ticket12690` for some unittests on the third
 quartile functionality.

 I think lowering the number to 1500 kilounits should be OK. I made a CDF
 graph for the 1500 kilounits threshold
 attachment:perf_cdf_guard_bw_desc_1500.png . You can compare it with the
 one I made for 2000:
 https://people.torproject.org/~asn/guards2/perf_cdf_guard_bw_desc.png

 As you can see, the one-guard curve of the 1500 graph is a bit slower than
 the 2000 graph, but the difference is not great and it's definitely better
 than one guard without any bw restrictions. The main difference is in the
 [0, 0.1] probability range, for the "unlucky" clients that pick the
 1500kb/s guards.

 If you need help on how to read those graphs, see the `Performance
 implications of switching to 1 guard` paragraph of:
 https://lists.torproject.org/pipermail/tor-dev/2014-March/006458.html

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Ticket URL: <https://trac.torproject.org/projects/tor/ticket/12690#comment:6>
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