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author | Mike Perry <mikeperry-git@torproject.org> | 2021-02-18 18:17:18 +0000 |
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committer | Mike Perry <mikeperry-git@torproject.org> | 2021-02-18 18:17:18 +0000 |
commit | b2f025cb568673acd00b7158957d24193ed739d9 (patch) | |
tree | 575fed75c80142a7e570803987c96bf5db0da587 /src/core | |
parent | 2709828494b961c92b9389bb2fd934f932fe54bc (diff) | |
parent | 917f8beb54e6edaabe4d4426636043cad9f38450 (diff) | |
download | tor-b2f025cb568673acd00b7158957d24193ed739d9.tar.gz tor-b2f025cb568673acd00b7158957d24193ed739d9.zip |
Merge branch 'bug40168+34088-035-v3' into bug40168+34088-035-v3-master
Diffstat (limited to 'src/core')
-rw-r--r-- | src/core/or/circuitstats.c | 168 | ||||
-rw-r--r-- | src/core/or/circuitstats.h | 11 |
2 files changed, 59 insertions, 120 deletions
diff --git a/src/core/or/circuitstats.c b/src/core/or/circuitstats.c index 51bd9e1208..b7f5216d72 100644 --- a/src/core/or/circuitstats.c +++ b/src/core/or/circuitstats.c @@ -203,10 +203,10 @@ circuit_build_times_max_timeouts(void) * Retrieve and bounds-check the cbtnummodes consensus parameter. * * Effect: This value governs how many modes to use in the weighted - * average calculation of Pareto parameter Xm. A value of 3 introduces - * some bias (2-5% of CDF) under ideal conditions, but allows for better - * performance in the event that a client chooses guard nodes of radically - * different performance characteristics. + * average calculation of Pareto parameter Xm. Analysis of pairs of + * geographically near, far, and mixed guaeds has shown that a value of + * 10 introduces some allows for the actual timeout rate to be within + * 2-7% of the cutoff quantile, for quantiles between 60-80%. */ static int32_t circuit_build_times_default_num_xm_modes(void) @@ -851,58 +851,49 @@ circuit_build_times_create_histogram(const circuit_build_times_t *cbt, * Return the Pareto start-of-curve parameter Xm. * * Because we are not a true Pareto curve, we compute this as the - * weighted average of the N most frequent build time bins. N is either - * 1 if we don't have enough circuit build time data collected, or - * determined by the consensus parameter cbtnummodes (default 3). + * weighted average of the 10 most frequent build time bins. This + * heuristic allowed for the actual timeout rate to be closest + * to the chosen quantile cutoff, for quantiles 60-80%, out of + * many variant approaches (see #40157 for analysis). */ -static build_time_t +STATIC build_time_t circuit_build_times_get_xm(circuit_build_times_t *cbt) { - build_time_t i, nbins; + build_time_t nbins = 0; build_time_t *nth_max_bin; - int32_t bin_counts=0; - build_time_t ret = 0; - uint32_t *histogram = circuit_build_times_create_histogram(cbt, &nbins); - int n=0; + build_time_t xm_total = 0; + build_time_t Xm = 0; + int32_t xm_counts=0; int num_modes = circuit_build_times_default_num_xm_modes(); + uint32_t *histogram = circuit_build_times_create_histogram(cbt, &nbins); tor_assert(nbins > 0); tor_assert(num_modes > 0); - // Only use one mode if < 1000 buildtimes. Not enough data - // for multiple. - if (cbt->total_build_times < CBT_NCIRCUITS_TO_OBSERVE) - num_modes = 1; - nth_max_bin = tor_calloc(num_modes, sizeof(build_time_t)); - /* Determine the N most common build times */ - for (i = 0; i < nbins; i++) { - if (histogram[i] >= histogram[nth_max_bin[0]]) { - nth_max_bin[0] = i; - } - - for (n = 1; n < num_modes; n++) { - if (histogram[i] >= histogram[nth_max_bin[n]] && - (!histogram[nth_max_bin[n-1]] - || histogram[i] < histogram[nth_max_bin[n-1]])) { + /* Determine the N most common build times, by selecting the + * nth largest mode, counting it, and removing it from the histogram. */ + for (int n = 0; n < num_modes; n++) { + /* Get nth mode */ + for (build_time_t i = 0; i < nbins; i++) { + if (histogram[i] > histogram[nth_max_bin[n]]) { nth_max_bin[n] = i; } } - } - for (n = 0; n < num_modes; n++) { - bin_counts += histogram[nth_max_bin[n]]; - ret += CBT_BIN_TO_MS(nth_max_bin[n])*histogram[nth_max_bin[n]]; - log_info(LD_CIRC, "Xm mode #%d: %u %u", n, CBT_BIN_TO_MS(nth_max_bin[n]), - histogram[nth_max_bin[n]]); + /* Update average */ + xm_counts += histogram[nth_max_bin[n]]; + xm_total += CBT_BIN_TO_MS(nth_max_bin[n])*histogram[nth_max_bin[n]]; + + /* Prevent from re-counting this value */ + histogram[nth_max_bin[n]] = 0; } - /* bin_counts can become zero if all of our last CBT_NCIRCUITS_TO_OBSERVE + /* xm_counts can become zero if all of our last CBT_NCIRCUITS_TO_OBSERVE * circuits were abandoned before they completed. This shouldn't happen, * though. We should have reset/re-learned a lower timeout first. */ - if (bin_counts == 0) { - ret = 0; + if (xm_counts == 0) { log_warn(LD_CIRC, "No valid circuit build time data out of %d times, %u modes, " "have_timeout=%d, %lfms", cbt->total_build_times, num_modes, @@ -910,15 +901,13 @@ circuit_build_times_get_xm(circuit_build_times_t *cbt) goto done; } - tor_assert(bin_counts > 0); - - ret /= bin_counts; + Xm = xm_total / xm_counts; done: tor_free(histogram); tor_free(nth_max_bin); - return ret; + return Xm; } /** @@ -1008,43 +997,6 @@ circuit_build_times_shuffle_and_store_array(circuit_build_times_t *cbt, } /** - * Filter old synthetic timeouts that were created before the - * new right-censored Pareto calculation was deployed. - * - * Once all clients before 0.2.1.13-alpha are gone, this code - * will be unused. - */ -static int -circuit_build_times_filter_timeouts(circuit_build_times_t *cbt) -{ - int num_filtered=0, i=0; - double timeout_rate = 0; - build_time_t max_timeout = 0; - - timeout_rate = circuit_build_times_timeout_rate(cbt); - max_timeout = (build_time_t)cbt->close_ms; - - for (i = 0; i < CBT_NCIRCUITS_TO_OBSERVE; i++) { - if (cbt->circuit_build_times[i] > max_timeout) { - build_time_t replaced = cbt->circuit_build_times[i]; - num_filtered++; - cbt->circuit_build_times[i] = CBT_BUILD_ABANDONED; - - log_debug(LD_CIRC, "Replaced timeout %d with %d", replaced, - cbt->circuit_build_times[i]); - } - } - - log_info(LD_CIRC, - "We had %d timeouts out of %d build times, " - "and filtered %d above the max of %u", - (int)(cbt->total_build_times*timeout_rate), - cbt->total_build_times, num_filtered, max_timeout); - - return num_filtered; -} - -/** * Load histogram from <b>state</b>, shuffling the resulting array * after we do so. Use this result to estimate parameters and * calculate the timeout. @@ -1169,10 +1121,6 @@ circuit_build_times_parse_state(circuit_build_times_t *cbt, circuit_build_times_set_timeout(cbt); - if (!state->CircuitBuildAbandonedCount && cbt->total_build_times) { - circuit_build_times_filter_timeouts(cbt); - } - done: tor_free(loaded_times); return err ? -1 : 0; @@ -1193,7 +1141,6 @@ circuit_build_times_update_alpha(circuit_build_times_t *cbt) build_time_t *x=cbt->circuit_build_times; double a = 0; int n=0,i=0,abandoned_count=0; - build_time_t max_time=0; /* https://en.wikipedia.org/wiki/Pareto_distribution#Parameter_estimation */ /* We sort of cheat here and make our samples slightly more pareto-like @@ -1213,14 +1160,13 @@ circuit_build_times_update_alpha(circuit_build_times_t *cbt) if (x[i] < cbt->Xm) { a += tor_mathlog(cbt->Xm); + n++; } else if (x[i] == CBT_BUILD_ABANDONED) { abandoned_count++; } else { a += tor_mathlog(x[i]); - if (x[i] > max_time) - max_time = x[i]; + n++; } - n++; } /* @@ -1229,30 +1175,23 @@ circuit_build_times_update_alpha(circuit_build_times_t *cbt) * performs this same check, and resets state if it hits it. If we * hit it at runtime, something serious has gone wrong. */ - if (n!=cbt->total_build_times) { + if (n!=cbt->total_build_times-abandoned_count) { log_err(LD_CIRC, "Discrepancy in build times count: %d vs %d", n, cbt->total_build_times); } - tor_assert(n==cbt->total_build_times); - - if (max_time <= 0) { - /* This can happen if Xm is actually the *maximum* value in the set. - * It can also happen if we've abandoned every single circuit somehow. - * In either case, tell the caller not to compute a new build timeout. */ - log_warn(LD_BUG, - "Could not determine largest build time (%d). " - "Xm is %dms and we've abandoned %d out of %d circuits.", max_time, - cbt->Xm, abandoned_count, n); - return 0; - } - - a += abandoned_count*tor_mathlog(max_time); + tor_assert_nonfatal(n==cbt->total_build_times-abandoned_count); + /* This is the "Maximum Likelihood Estimator" for parameter alpha of a Pareto + * Distribution. See: + * https://en.wikipedia.org/wiki/Pareto_distribution#Estimation_of_parameters + * + * The division in the estimator is done with subtraction outside the ln(), + * with the sum occurring in the for loop above. + * + * This done is to avoid the precision issues of logs of small values. + */ a -= n*tor_mathlog(cbt->Xm); - // Estimator comes from Eq #4 in: - // "Bayesian estimation based on trimmed samples from Pareto populations" - // by Arturo J. Fernández. We are right-censored only. - a = (n-abandoned_count)/a; + a = n/a; cbt->alpha = a; @@ -1661,9 +1600,8 @@ circuit_build_times_network_check_changed(circuit_build_times_t *cbt) log_notice(LD_CIRC, "Your network connection speed appears to have changed. Resetting " - "timeout to %lds after %d timeouts and %d buildtimes.", - tor_lround(cbt->timeout_ms/1000), timeout_count, - total_build_times); + "timeout to %ldms after %d timeouts and %d buildtimes.", + tor_lround(cbt->timeout_ms), timeout_count, total_build_times); return 1; } @@ -1829,7 +1767,7 @@ circuit_build_times_set_timeout(circuit_build_times_t *cbt) return; if (cbt->timeout_ms < circuit_build_times_min_timeout()) { - log_info(LD_CIRC, "Set buildtimeout to low value %fms. Setting to %dms", + log_notice(LD_CIRC, "Set buildtimeout to low value %fms. Setting to %dms", cbt->timeout_ms, circuit_build_times_min_timeout()); cbt->timeout_ms = circuit_build_times_min_timeout(); if (cbt->close_ms < cbt->timeout_ms) { @@ -1847,9 +1785,9 @@ circuit_build_times_set_timeout(circuit_build_times_t *cbt) log_info(LD_CIRC, "Based on %d circuit times, it looks like we don't need to " "wait so long for circuits to finish. We will now assume a " - "circuit is too slow to use after waiting %ld seconds.", + "circuit is too slow to use after waiting %ld milliseconds.", cbt->total_build_times, - tor_lround(cbt->timeout_ms/1000)); + tor_lround(cbt->timeout_ms)); log_info(LD_CIRC, "Circuit timeout data: %fms, %fms, Xm: %d, a: %f, r: %f", cbt->timeout_ms, cbt->close_ms, cbt->Xm, cbt->alpha, @@ -1858,18 +1796,18 @@ circuit_build_times_set_timeout(circuit_build_times_t *cbt) log_info(LD_CIRC, "Based on %d circuit times, it looks like we need to wait " "longer for circuits to finish. We will now assume a " - "circuit is too slow to use after waiting %ld seconds.", + "circuit is too slow to use after waiting %ld milliseconds.", cbt->total_build_times, - tor_lround(cbt->timeout_ms/1000)); + tor_lround(cbt->timeout_ms)); log_info(LD_CIRC, "Circuit timeout data: %fms, %fms, Xm: %d, a: %f, r: %f", cbt->timeout_ms, cbt->close_ms, cbt->Xm, cbt->alpha, timeout_rate); } else { log_info(LD_CIRC, - "Set circuit build timeout to %lds (%fms, %fms, Xm: %d, a: %f," + "Set circuit build timeout to %ldms (%fms, %fms, Xm: %d, a: %f," " r: %f) based on %d circuit times", - tor_lround(cbt->timeout_ms/1000), + tor_lround(cbt->timeout_ms), cbt->timeout_ms, cbt->close_ms, cbt->Xm, cbt->alpha, timeout_rate, cbt->total_build_times); } diff --git a/src/core/or/circuitstats.h b/src/core/or/circuitstats.h index 930e0a9ba3..f9efa2df6c 100644 --- a/src/core/or/circuitstats.h +++ b/src/core/or/circuitstats.h @@ -56,10 +56,10 @@ void circuit_build_times_reset(circuit_build_times_t *cbt); #define CBT_NCIRCUITS_TO_OBSERVE 1000 /** Width of the histogram bins in milliseconds */ -#define CBT_BIN_WIDTH ((build_time_t)50) +#define CBT_BIN_WIDTH ((build_time_t)10) /** Number of modes to use in the weighted-avg computation of Xm */ -#define CBT_DEFAULT_NUM_XM_MODES 3 +#define CBT_DEFAULT_NUM_XM_MODES 10 #define CBT_MIN_NUM_XM_MODES 1 #define CBT_MAX_NUM_XM_MODES 20 @@ -79,7 +79,7 @@ void circuit_build_times_reset(circuit_build_times_t *cbt); * How long to wait before actually closing circuits that take too long to * build in terms of CDF quantile. */ -#define CBT_DEFAULT_CLOSE_QUANTILE 95 +#define CBT_DEFAULT_CLOSE_QUANTILE 99 #define CBT_MIN_CLOSE_QUANTILE CBT_MIN_QUANTILE_CUTOFF #define CBT_MAX_CLOSE_QUANTILE CBT_MAX_QUANTILE_CUTOFF @@ -120,8 +120,8 @@ double circuit_build_times_quantile_cutoff(void); #define CBT_MAX_TEST_FREQUENCY INT32_MAX /** Lowest allowable value for CircuitBuildTimeout in milliseconds */ -#define CBT_DEFAULT_TIMEOUT_MIN_VALUE (1500) -#define CBT_MIN_TIMEOUT_MIN_VALUE 500 +#define CBT_DEFAULT_TIMEOUT_MIN_VALUE (CBT_BIN_WIDTH) +#define CBT_MIN_TIMEOUT_MIN_VALUE CBT_BIN_WIDTH #define CBT_MAX_TIMEOUT_MIN_VALUE INT32_MAX /** Initial circuit build timeout in milliseconds */ @@ -142,6 +142,7 @@ STATIC int circuit_build_times_update_alpha(circuit_build_times_t *cbt); /* Network liveness functions */ STATIC int circuit_build_times_network_check_changed( circuit_build_times_t *cbt); +STATIC build_time_t circuit_build_times_get_xm(circuit_build_times_t *cbt); #endif /* defined(CIRCUITSTATS_PRIVATE) */ #ifdef TOR_UNIT_TESTS |