[tor-relays] BWAUTH weightings too volatile. . ."twitchy"

[starlight.2015q2 at binnacle.cx]

At 02:43 6/6/2015 -0400, starlight.2015q2 at binnacle.cx wrote:
>I'm back to complain further about
>erratic bandwidth authority behavior,
>previously. . .

MYSTERY SOLVED!!!

Of course one should always RTFS (read
the fine specification) when trying to
understand all things Tor.

First, scratch my previous time-
averaging suggestion as the current
implementation incorporates a
sophisticated time averaging feedback
algorithm borrowed from industrial
control systems.

Turns out the problem of sudden, sharp,
"schizophrenic" consensus jumps is a
boundary artifact.

My relay is hovering right around the
12% threshold between the fastest and
second fastest groups of relays (out of
four groups).

These two groups operate as separate
statistical domains, and the algorithm
is complex enough that it would be
shocking if the measurement of any
one relay came out the same when moved
from one group to the other group.

Looks to me like the relay is bouncing
back-and-forth between the 0-12% band
and the 12-35% band.  This happens
independently for each of the four
BWauths.  The 0-12% band assigned
weight for the relay is anywhere 
from 130 to 200% of the weight
calculated in the 12-35% band.

Group-hopping explains why the individual
BWauth weights tend to jump dramatically
and suddenly.  The median-weight consensus
selection adds an additional element of
randomness.

Assigned-weight moves smoothly within
either group, but is discontinuous when
shifting from one group to the next.

Is interesting that 'moria1' consistently
reports much higher weights than the
three other BWauths.  Might be that
one of the algorithm parameters is
set to a different value for this
authority.