[tor-relays] Network Performance Experiment - KISTSchedRunInterval - October 2020

[Roger Dingledine]

On Thu, Oct 15, 2020 at 11:40:34PM +0200, nusenu wrote:
> since it is in effect by now 
> https://consensus-health.torproject.org/#consensusparams
> could you publish the exact timestamp when it came into effect?

One can learn this from the recent consensus documents, e.g. at
https://collector.torproject.org/recent/relay-descriptors/consensuses/

And I agree that we should have a central experiment page (e.g. on gitlab)
that lists the experiments, when we ran them, when the network changes
occurred, what we expected to find, and what we *did* find.

David or Mike, can you make sure that page happens?

> I noticed some unusual things today (exits having a non-zero guard probability),
> did you change more parameters than this one or was this the only one?

No, that was the only change.

We had a good discussion with Florentin et al on #tor-dev just now,
where we concluded that yes, we're still in "case 3be (E scarce)", but
the math still allows a little bit of use of exits for other roles:
check out the networkstatus_compute_bw_weights_v10() function in
src/feature/dirauth/dirvote.c.

So as far as we can tell so far, we are still in the "exit scarce"
case of Mike's weight voodoo, but his math allows exits to be used
a little bit in non-exit roles even in this case.

Wed = (weight_scale*(D - 2*E + G + M))/(3*D);

Wgd = (weight_scale - Wed)/2;

And Wed in this case is 9849 rather than 10000.

So, to say it much more plainly, we are just barely on the other side
of the line from "exit capacity is so scarce that exits will only ever
be used for exiting."

Mike was expecting some rebalancing to be done by the bwauths, once
we shifted the Kist interval, but I don't know whether we're seeing
that rebalancing or if it this is a coincidence.

--Roger