[tor-dev] Bandwidth scanner: request for feedback

[Nick Mathewson]

On Mon, Nov 19, 2018 at 7:36 AM teor <teor at riseup.net> wrote:
>
> Hi,
>
> We have deployed sbws on one bandwidth authority (longclaw).
>
> Here's a request for additional feedback, and a progress update:
>
>
> Request for Feedback: Relay Bandwidth Self-Tests
>
> Torflow and sbws use relays' self-reported observed bandwidths for
> load balancing. But relays can have really low bandwidths because
> they're new, or due to random path selection.
>
> In torflow, relays can get stuck in a low-bandwidth partition. sbws
> doesn't have partitions. But in both systems, low bandwidths can
> cause inaccurate or unstable load balancing.
>
> Since torflow and sbws need accurate self-reported relay bandwidths,
> some component of the Tor network needs to send enough bandwidth
> through every relay.
>
> Here are our current choices:
>
> Tor relays can do a regular bandwidth self-test, so that their
> first descriptor has an accurate bandwidth (up to some minimum). But
> the current self-test is too small, and buggy.
>
> sbws already sends bandwidth to all relays to measure them. sbws gets
> accurate bandwidths for most relays within 2 weeks, but the fastest
> relays can take a month to ramp up. (sbws starts measuring at the
> median relay bandwidth, and can double every 5 days.)
>
> Should we improve relay bandwidth self-tests? (#22453)
> Or should we rely on sbws to create the bandwidths it needs?
> What about test networks?

Hi!  I don't think I have the answers here, but maybe I can think
aloud in a useful way.

>From my point of view, either of these is a fine idea, if it works.
We could decide based on a lot of factors, like:

* Which one is easier to do?
* Which creates the greater maintenance burden, moving forward?
* Which is more robust if something breaks in the future?
* Which consumes the most relay bandwidth?
* Which requires SBWS to use the most bandwidth?

Maybe if we had those figured out, we'd have a better time deciding.

> Should we make bandwidths grow faster in sbws?
> Or is a ramp-up period of 2-5 weeks fast enough?

I think that's fast enough, though I'm not sure.  How does it compare
with the current average torflow ramp-up time?

> (We won't modify and re-deploy torflow.)