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[tor-bugs] #28447 [Core Tor/sbws]: improve new SBWS rounding to exhibit uniform percent deltas
#28447: improve new SBWS rounding to exhibit uniform percent deltas
-------------------------------+-------------------------------
Reporter: starlight | Owner: (none)
Type: defect | Status: new
Priority: Medium | Component: Core Tor/sbws
Version: sbws: unspecified | Severity: Normal
Keywords: | Actual Points:
Parent ID: | Points:
Reviewer: | Sponsor:
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In ticket #27337 bandwidth vote rounding was changed from Torflow's three
significant decimal digits to two places in order to reduce
inconsequential consensus diff updates. The change is a good one except
that the resulting distribution of values exhibits large unevenness of
relative value changes, an effect which with was much smaller with three
digit rounding. To obtain the same benefit with an uniform change
distribution, rounding constructed on a natural log scale should be
applied. For example instead of
{{{
100000 -> 110000 +10.0%
40000 -> 41000 +2.5%
}}}
the proper way to accomplish this is to round by taking the natural log of
the value, round that to the nearest 1/20th for uniform 5% steps and then
raise `e` by the result:
{{{
100000 rounds to 98716
105000 rounds to 103777
98716 -> 103777 +5.1%
40000 rounds to 40135
42000 rounds to 42193
40135 -> 42193 +5.1%
1100 rounds to 1096
1050 rounds to 1043
1043 -> 1096 +5.1%
}}}
The overall goal of SBWS is improved consensus construction and while the
importance of this refinement can be debated, it is clearly beneficial, is
easy to implement and therefore a reasonable adjustment at this early
stage of testing deployment.
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/28447>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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