On Tue, Mar 25, 2014 at 3:41 PM, Mike Perry <mikeperry@xxxxxxxxxxxxxx> wrote:
> For control, it would be nice to know what we would be giving up if we
> used that same T=2000 cutoff with three guards and compare that to
> T=2000 with just one guard. Is it easy for you to rerun just that
> comparison (since you seem to be suggesting that T=2000 is a good cutoff
> anyway)?
Takes a few hours to run the scripts again, but the results look like this. For the "unluckiest 10%" with T=1000, having 3 guards is still better than having one, while with T=2000 the difference between 3 guards and 1 is less noticeable:
https://www-users.cs.umn.edu/~hopper/unlucky_threeguard_threshold_bandwidth.png
Interestingly, though, for the median user with the higher thresholds, having one guard results in a higher median circuit bandwidth (because a user with 3 guards is more likely to have selected one guard close to the cutoff, dragging the typical performance down):
https://www-users.cs.umn.edu/~hopper/threeguard_threshold_bandwidth.png
...but I don't think these results speak to this concern:
> ** The reason I ask is because I suspect there is actually an interplay
> between the current circuit build timeout code and the pool of 3 guards.
> The CBT cutoff will tend to cause you to avoid whichever of your guards
> may be temporarily overloaded at a given time.
because TorPS is a python reimplementation of the circuit selection algorithm only and doesn't have any way to simulate the CBT logic: http://torps.github.io/
--
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Nicholas Hopper
Associate Professor, Computer Science & Engineering, University of Minnesota
Visiting Research Director, The Tor Project
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