[tor-commits] [tor] 02/05: metrics: Use N_EWMA for moving avg, with N=100.
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Wed Nov 9 16:54:40 UTC 2022
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commit 09d32ac667b947da838c2645df1180d8b7ecc36e
Author: Mike Perry <mikeperry-git at torproject.org>
AuthorDate: Tue Nov 8 19:02:57 2022 +0000
metrics: Use N_EWMA for moving avg, with N=100.
Part of #40708.
---
src/core/or/circuitlist.c | 12 ++----------
src/core/or/congestion_control_flow.c | 10 ++--------
src/core/or/congestion_control_vegas.c | 25 +++++++------------------
src/lib/math/stats.h | 30 +++++++++++++++++++++++++-----
4 files changed, 36 insertions(+), 41 deletions(-)
diff --git a/src/core/or/circuitlist.c b/src/core/or/circuitlist.c
index d1c734bdd2..eb13e3bccd 100644
--- a/src/core/or/circuitlist.c
+++ b/src/core/or/circuitlist.c
@@ -154,10 +154,6 @@ double cc_stats_circ_close_cwnd_ma = 0;
/** Moving average of the cc->cwnd from each closed slow-start circuit. */
double cc_stats_circ_close_ss_cwnd_ma = 0;
-/* Running count of the above moving averages. Needed so we can update it. */
-static double stats_circ_close_cwnd_ma_count = 0;
-static double stats_circ_close_ss_cwnd_ma_count = 0;
-
/********* END VARIABLES ************/
/* Implement circuit handle helpers. */
@@ -2244,18 +2240,14 @@ circuit_mark_for_close_, (circuit_t *circ, int reason, int line,
* and a max RTT, and they are not the same. This prevents us from
* averaging and reporting unused and low-use circuits here */
if (circ->ccontrol->max_rtt_usec != circ->ccontrol->min_rtt_usec) {
- stats_circ_close_ss_cwnd_ma_count++;
cc_stats_circ_close_ss_cwnd_ma =
stats_update_running_avg(cc_stats_circ_close_ss_cwnd_ma,
- circ->ccontrol->cwnd,
- stats_circ_close_ss_cwnd_ma_count);
+ circ->ccontrol->cwnd);
}
} else {
- stats_circ_close_cwnd_ma_count++;
cc_stats_circ_close_cwnd_ma =
stats_update_running_avg(cc_stats_circ_close_cwnd_ma,
- circ->ccontrol->cwnd,
- stats_circ_close_cwnd_ma_count);
+ circ->ccontrol->cwnd);
}
}
diff --git a/src/core/or/congestion_control_flow.c b/src/core/or/congestion_control_flow.c
index 729e67b9a3..90b1927ef9 100644
--- a/src/core/or/congestion_control_flow.c
+++ b/src/core/or/congestion_control_flow.c
@@ -41,9 +41,7 @@ static uint32_t xon_rate_bytes;
uint64_t cc_stats_flow_num_xoff_sent;
uint64_t cc_stats_flow_num_xon_sent;
double cc_stats_flow_xoff_outbuf_ma = 0;
-static double cc_stats_flow_xoff_outbuf_ma_count = 0;
double cc_stats_flow_xon_outbuf_ma = 0;
-static double cc_stats_flow_xon_outbuf_ma_count = 0;
/* In normal operation, we can get a burst of up to 32 cells before returning
* to libevent to flush the outbuf. This is a heuristic from hardcoded values
@@ -485,11 +483,9 @@ flow_control_decide_xoff(edge_connection_t *stream)
total_buffered, buffer_limit_xoff);
tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xoff_sending), stream);
- cc_stats_flow_xoff_outbuf_ma_count++;
cc_stats_flow_xoff_outbuf_ma =
stats_update_running_avg(cc_stats_flow_xoff_outbuf_ma,
- total_buffered,
- cc_stats_flow_xoff_outbuf_ma_count);
+ total_buffered);
circuit_send_stream_xoff(stream);
@@ -646,11 +642,9 @@ flow_control_decide_xon(edge_connection_t *stream, size_t n_written)
total_buffered);
tor_trace(TR_SUBSYS(cc), TR_EV(flow_decide_xon_rate_change), stream);
- cc_stats_flow_xon_outbuf_ma_count++;
cc_stats_flow_xon_outbuf_ma =
stats_update_running_avg(cc_stats_flow_xon_outbuf_ma,
- total_buffered,
- cc_stats_flow_xon_outbuf_ma_count);
+ total_buffered);
circuit_send_stream_xon(stream);
}
diff --git a/src/core/or/congestion_control_vegas.c b/src/core/or/congestion_control_vegas.c
index ee1312699c..2b0ed3a507 100644
--- a/src/core/or/congestion_control_vegas.c
+++ b/src/core/or/congestion_control_vegas.c
@@ -56,12 +56,6 @@ double cc_stats_vegas_gamma_drop_ma = 0;
double cc_stats_vegas_delta_drop_ma = 0;
double cc_stats_vegas_ss_csig_blocked_ma = 0;
double cc_stats_vegas_csig_blocked_ma = 0;
-/* Running count of this moving average. Needed so we can update it. */
-static double stats_cwnd_exit_ss_ma_count = 0;
-static double stats_cwnd_gamma_drop_ma_count = 0;
-static double stats_cwnd_delta_drop_ma_count = 0;
-static double stats_ss_csig_blocked_ma_count = 0;
-static double stats_csig_blocked_ma_count = 0;
/** Stats on how many times we reached "delta" param. */
uint64_t cc_stats_vegas_above_delta = 0;
@@ -263,10 +257,9 @@ congestion_control_vegas_exit_slow_start(const circuit_t *circ,
congestion_control_vegas_log(circ, cc);
/* Update running cc->cwnd average for metrics. */
- stats_cwnd_exit_ss_ma_count++;
cc_stats_vegas_exit_ss_cwnd_ma =
stats_update_running_avg(cc_stats_vegas_exit_ss_cwnd_ma,
- cc->cwnd, stats_cwnd_exit_ss_ma_count);
+ cc->cwnd);
/* We need to report that slow start has exited ASAP,
* for sbws bandwidth measurement. */
@@ -347,21 +340,19 @@ congestion_control_vegas_process_sendme(congestion_control_t *cc,
/* Account the amount we reduced the cwnd by for the gamma cutoff */
cwnd_diff = (old_cwnd > cc->cwnd ? old_cwnd - cc->cwnd : 0);
- stats_cwnd_gamma_drop_ma_count++;
cc_stats_vegas_gamma_drop_ma =
stats_update_running_avg(cc_stats_vegas_gamma_drop_ma,
- cwnd_diff, stats_cwnd_gamma_drop_ma_count);
+ cwnd_diff);
- stats_ss_csig_blocked_ma_count++;
/* Compute the percentage we experience a blocked csig vs RTT sig */
if (cc->blocked_chan) {
cc_stats_vegas_ss_csig_blocked_ma =
stats_update_running_avg(cc_stats_vegas_ss_csig_blocked_ma,
- 100, stats_ss_csig_blocked_ma_count);
+ 100);
} else {
cc_stats_vegas_ss_csig_blocked_ma =
stats_update_running_avg(cc_stats_vegas_ss_csig_blocked_ma,
- 0, stats_ss_csig_blocked_ma_count);
+ 0);
}
congestion_control_vegas_exit_slow_start(circ, cc);
@@ -384,23 +375,21 @@ congestion_control_vegas_process_sendme(congestion_control_t *cc,
/* Account the amount we reduced the cwnd by for the gamma cutoff */
cwnd_diff = (old_cwnd > cc->cwnd ? old_cwnd - cc->cwnd : 0);
- stats_cwnd_delta_drop_ma_count++;
cc_stats_vegas_delta_drop_ma =
stats_update_running_avg(cc_stats_vegas_delta_drop_ma,
- cwnd_diff, stats_cwnd_delta_drop_ma_count);
+ cwnd_diff);
cc_stats_vegas_above_delta++;
} else if (queue_use > cc->vegas_params.beta || cc->blocked_chan) {
- stats_csig_blocked_ma_count++;
/* Compute the percentage we experience a blocked csig vs RTT sig */
if (cc->blocked_chan) {
cc_stats_vegas_csig_blocked_ma =
stats_update_running_avg(cc_stats_vegas_csig_blocked_ma,
- 100, stats_csig_blocked_ma_count);
+ 100);
} else {
cc_stats_vegas_csig_blocked_ma =
stats_update_running_avg(cc_stats_vegas_csig_blocked_ma,
- 0, stats_csig_blocked_ma_count);
+ 0);
}
cc->cwnd -= CWND_INC(cc);
diff --git a/src/lib/math/stats.h b/src/lib/math/stats.h
index 328d61a9d6..14315a2506 100644
--- a/src/lib/math/stats.h
+++ b/src/lib/math/stats.h
@@ -10,13 +10,33 @@
#ifndef TOR_STATS_H
#define TOR_STATS_H
-/** Update an average making it a "running average". The "avg" is the current
- * value that will be updated to the new one. The "value" is the new value to
- * add to the average and "n" is the new count as in including the "value". */
+/**
+ * Compute an N-count EWMA, aka N-EWMA. N-EWMA is defined as:
+ * EWMA = alpha*value + (1-alpha)*EWMA_prev
+ * with alpha = 2/(N+1).
+ *
+ * This works out to:
+ * EWMA = value*2/(N+1) + EMA_prev*(N-1)/(N+1)
+ * = (value*2 + EWMA_prev*(N-1))/(N+1)
+ */
static inline double
-stats_update_running_avg(double avg, double value, double n)
+n_count_ewma_double(double avg, double value, uint64_t N)
{
- return ((avg * (n - 1)) + value) / n;
+ /* If the average was not previously computed, return value.
+ * The less than is because we have stupid C warning flags that
+ * prevent exact comparison to 0.0, so we can't do an exact
+ * check for unitialized double values. Yay pedantry!
+ * Love it when it introduces surprising edge case bugs like
+ * this will. */
+ if (avg < 0.0000002)
+ return value;
+ else
+ return (2*value + (N-1)*avg)/(N+1);
}
+/* For most stats, an N_EWMA of 100 is sufficient */
+#define DEFAULT_STATS_N_EWMA_COUNT 100
+#define stats_update_running_avg(avg, value) \
+ n_count_ewma_double(avg, value, DEFAULT_STATS_N_EWMA_COUNT)
+
#endif /* !defined(TOR_STATS_H) */
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