On Tue, Mar 25, 2014 at 3:41 PM, Mike Perry mikeperry@torproject.org 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....

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/

-- ------------------------------------------------------------------------ Nicholas Hopper Associate Professor, Computer Science & Engineering, University of Minnesota Visiting Research Director, The Tor Project ------------------------------------------------------------------------