Congestion control param update and monitoring
I ran a handful of sims to lower queue usage a bit more. I think we should set these in two phases, since some will benefit from the increased metricsport data we put into 0.4.7.11, which we can monitor on d2d4 and potentially torservers.
The following params can be set right now: cc_vegas_alpha_exit=155 cc_vegas_delta_exit=310 cc_sscap_onion=425 cc_vegas_gamma_onion=248 cc_vegas_beta_onion=372 cc_vegas_delta_onion=434
This first set of params should reduce queue usage at guards, and may also boost exit performance a bit.
The following params should be set once 0.4.7.11 is deployed on our monitored relays: cc_vegas_alpha_exit=186 cc_sscap_exit=350 cc_cwnd_min=124 circ_max_cell_queue_size=1750 circ_max_cell_queue_size_out=1500 dos_num_circ_max_outq=5
The cc_sscap_exit param might degrade performance in Hong Kong (most likely affecting total 5MB download times; last 1MB throughput should remain the same). For monitoring that, #43 (closed) will be helpful. If this does happen, we can use cc_sscap_exit=375, which did not show any degraded first megabyte performance in Shadow.
If the exit dos or onion service rend flooding comes back, we can set circ_max_cell_queue_size_out=1250, but we should closely monitor guard relays to make sure this does not cause banning of normal clients/onions, via the DoS subsystem's usage of this value.
In 0.4.7.11, we also have onionskin processing params that may help if the ntor overload returns.