commit 9b088f490baa947fb76063a800fce43c1e1a1a45 Author: Mike Perry <mikeperry-git@fscked.org> Date: Thu Nov 17 15:15:18 2011 -0800 Update spec to include consensus params. These are still subject to change, especially in terms of defaults. --- NetworkScanners/BwAuthority/README.spec.txt | 54 ++++++++++++++++++++++++++- 1 files changed, 52 insertions(+), 2 deletions(-) diff --git a/NetworkScanners/BwAuthority/README.spec.txt b/NetworkScanners/BwAuthority/README.spec.txt index 96568c6..5ccf672 100644 --- a/NetworkScanners/BwAuthority/README.spec.txt +++ b/NetworkScanners/BwAuthority/README.spec.txt @@ -364,7 +364,7 @@ should cause convergence to this balanced ideal. See https://en.wikipedia.org/wiki/PID_controller for background, - especially: https://en.wikipedia.org/wiki/PID_controller#Pseudocode + especially https://en.wikipedia.org/wiki/PID_controller#Pseudocode 3.1. Modeling Measurement as PID Control @@ -463,7 +463,7 @@ pid_delta is purely informational, and is not used in feedback. -3.5. Tuning Parameters +3.5. Tuning PID Constants Internally, the source uses the Standard PID Form: https://en.wikipedia.org/wiki/PID_controller#Ideal_versus_standard_PID_form @@ -480,4 +480,54 @@ only gives us useful information for a fraction of a measurement interval, until clients begin to migrate to the new measurements. +3.6. Consensus Parameters + The bandwidth auths listen for several consensus parameters to tweak + behavior: + + "bwauthpid=1" + If present, enables the PID control features in Section 3. + + "bwauthcircs=1" + If present, F_node is multiplied by (1.0 - circ_fail_rate) + as described in Section 3.1. + + "bwauthkp=N" + Sets K_p to N/10000.0 + + "bwauthti=N" + Sets T_i to N/10000.0. For T_i=0, K_i is set to 0. + + "bwauthtd=N" + Sets T_d to N/10000.0. + + "bwauthtidecay=N" + Sets T_i_decay to N/10000.0. T_i_decay is an parameter + used to dampen the pid_error_sum accumulation. If non-zero, + the pid_error_sum integration becomes: + + K_i_decay = (1.0 - T_i_decay/T_i) + pid_control_sum = pid_control_sum*K_i_decay + pid_error + + Intuitively, this means that after T_i sample rounds, + the T_i'th round has experienced a reduction by T_i_decay + for the values of T_i that are relevant to us. + + If T_i is 0, K_i_decay is set to 0. + + "bwauthbestratio=1" + If present, the larger of stream bandwidth vs filtered bandwidth + is used to compute F_node. + + "bwauthdescbw=1" + If present, uses descriptor bandwidth instead of feeding back + PID control values. This may be functionally equivalent to NS + bandwidth so long as T_i is non-zero, because error will get + accumulated in pid_error_sum as opposed to the consensus value + itself. + + It also has the advantage of allowing the PID control code to be + exercised, yet produce identical results to Section 2 with + the following additional constants: + +