diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/or/circuitmux_ewma.c | 27 |
1 files changed, 25 insertions, 2 deletions
diff --git a/src/or/circuitmux_ewma.c b/src/or/circuitmux_ewma.c index 13836cdcfa..5c2ebde73b 100644 --- a/src/or/circuitmux_ewma.c +++ b/src/or/circuitmux_ewma.c @@ -4,6 +4,28 @@ /** * \file circuitmux_ewma.c * \brief EWMA circuit selection as a circuitmux_t policy + * + * The "EWMA" in this module stands for the "exponentially weighted moving + * average" of the number of cells sent on each circuit. The goal is to + * prioritize cells on circuits that have been quiet recently, by looking at + * those that have sent few cells over time, prioritizing recent times + * more than older ones. + * + * Specifically, a cell sent at time "now" has weight 1, but a time X ticks + * before now has weight ewma_scale_factor ^ X , where ewma_scale_factor is + * between 0.0 and 1.0. + * + * For efficiency, we do not re-scale these averages every time we send a + * cell: that would be horribly inefficient. Instead, we we keep the cell + * count on all circuits on the same circuitmux scaled relative to a single + * tick. When we add a new cell, we scale its weight depending on the time + * that has elapsed since the tick. We do re-scale the circuits on the + * circuitmux periodically, so that we don't overflow double. + * + * + * This module should be used through the interfaces in circuitmux.c, which it + * implements. + * **/ #define TOR_CIRCUITMUX_EWMA_C_ @@ -28,9 +50,10 @@ /*** Some useful constant #defines ***/ -/*DOCDOC*/ +/** Any halflife smaller than this number of seconds is considered to be + * "disabled". */ #define EPSILON 0.00001 -/*DOCDOC*/ +/** The natural logarithm of 0.5. */ #define LOG_ONEHALF -0.69314718055994529 /*** EWMA structures ***/ |