/* Copyright (c) 2001 Matej Pfajfar. * Copyright (c) 2001-2004, Roger Dingledine. * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson. * Copyright (c) 2007-2013, The Tor Project, Inc. */ /* See LICENSE for licensing information */ #define CIRCUITSTATS_PRIVATE #include "or.h" #include "circuitbuild.h" #include "circuitstats.h" #include "config.h" #include "confparse.h" #include "control.h" #include "networkstatus.h" #include "statefile.h" #undef log #include #define CBT_BIN_TO_MS(bin) ((bin)*CBT_BIN_WIDTH + (CBT_BIN_WIDTH/2)) /** Global list of circuit build times */ // XXXX: Add this as a member for entry_guard_t instead of global? // Then we could do per-guard statistics, as guards are likely to // vary in their own latency. The downside of this is that guards // can change frequently, so we'd be building a lot more circuits // most likely. /* XXXX024 Make this static; add accessor functions. */ circuit_build_times_t circ_times; /** If set, we're running the unit tests: we should avoid clobbering * our state file or accessing get_options() or get_or_state() */ static int unit_tests = 0; /** * This function decides if CBT learning should be disabled. It returns * true if one or more of the following four conditions are met: * * 1. If the cbtdisabled consensus parameter is set. * 2. If the torrc option LearnCircuitBuildTimeout is false. * 3. If we are a directory authority * 4. If we fail to write circuit build time history to our state file. */ int circuit_build_times_disabled(void) { if (unit_tests) { return 0; } else { int consensus_disabled = networkstatus_get_param(NULL, "cbtdisabled", 0, 0, 1); int config_disabled = !get_options()->LearnCircuitBuildTimeout; int dirauth_disabled = get_options()->AuthoritativeDir; int state_disabled = did_last_state_file_write_fail() ? 1 : 0; if (consensus_disabled || config_disabled || dirauth_disabled || state_disabled) { log_debug(LD_CIRC, "CircuitBuildTime learning is disabled. " "Consensus=%d, Config=%d, AuthDir=%d, StateFile=%d", consensus_disabled, config_disabled, dirauth_disabled, state_disabled); return 1; } else { log_debug(LD_CIRC, "CircuitBuildTime learning is not disabled. " "Consensus=%d, Config=%d, AuthDir=%d, StateFile=%d", consensus_disabled, config_disabled, dirauth_disabled, state_disabled); return 0; } } } /** * Retrieve and bounds-check the cbtmaxtimeouts consensus paramter. * * Effect: When this many timeouts happen in the last 'cbtrecentcount' * circuit attempts, the client should discard all of its history and * begin learning a fresh timeout value. */ static int32_t circuit_build_times_max_timeouts(void) { int32_t cbt_maxtimeouts; cbt_maxtimeouts = networkstatus_get_param(NULL, "cbtmaxtimeouts", CBT_DEFAULT_MAX_RECENT_TIMEOUT_COUNT, CBT_MIN_MAX_RECENT_TIMEOUT_COUNT, CBT_MAX_MAX_RECENT_TIMEOUT_COUNT); if (!(get_options()->LearnCircuitBuildTimeout)) { log_debug(LD_BUG, "circuit_build_times_max_timeouts() called, cbtmaxtimeouts is" " %d", cbt_maxtimeouts); } return cbt_maxtimeouts; } /** * Retrieve and bounds-check the cbtnummodes consensus paramter. * * 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. */ static int32_t circuit_build_times_default_num_xm_modes(void) { int32_t num = networkstatus_get_param(NULL, "cbtnummodes", CBT_DEFAULT_NUM_XM_MODES, CBT_MIN_NUM_XM_MODES, CBT_MAX_NUM_XM_MODES); if (!(get_options()->LearnCircuitBuildTimeout)) { log_debug(LD_BUG, "circuit_build_times_default_num_xm_modes() called, cbtnummodes" " is %d", num); } return num; } /** * Retrieve and bounds-check the cbtmincircs consensus paramter. * * Effect: This is the minimum number of circuits to build before * computing a timeout. */ static int32_t circuit_build_times_min_circs_to_observe(void) { int32_t num = networkstatus_get_param(NULL, "cbtmincircs", CBT_DEFAULT_MIN_CIRCUITS_TO_OBSERVE, CBT_MIN_MIN_CIRCUITS_TO_OBSERVE, CBT_MAX_MIN_CIRCUITS_TO_OBSERVE); if (!(get_options()->LearnCircuitBuildTimeout)) { log_debug(LD_BUG, "circuit_build_times_min_circs_to_observe() called, cbtmincircs" " is %d", num); } return num; } /** Return true iff cbt has recorded enough build times that we * want to start acting on the timeout it implies. */ int circuit_build_times_enough_to_compute(circuit_build_times_t *cbt) { return cbt->total_build_times >= circuit_build_times_min_circs_to_observe(); } /** * Retrieve and bounds-check the cbtquantile consensus paramter. * * Effect: This is the position on the quantile curve to use to set the * timeout value. It is a percent (10-99). */ double circuit_build_times_quantile_cutoff(void) { int32_t num = networkstatus_get_param(NULL, "cbtquantile", CBT_DEFAULT_QUANTILE_CUTOFF, CBT_MIN_QUANTILE_CUTOFF, CBT_MAX_QUANTILE_CUTOFF); if (!(get_options()->LearnCircuitBuildTimeout)) { log_debug(LD_BUG, "circuit_build_times_quantile_cutoff() called, cbtquantile" " is %d", num); } return num/100.0; } /** * Retrieve and bounds-check the cbtclosequantile consensus paramter. * * Effect: This is the position on the quantile curve to use to set the * timeout value to use to actually close circuits. It is a percent * (0-99). */ static double circuit_build_times_close_quantile(void) { int32_t param; /* Cast is safe - circuit_build_times_quantile_cutoff() is capped */ int32_t min = (int)tor_lround(100*circuit_build_times_quantile_cutoff()); param = networkstatus_get_param(NULL, "cbtclosequantile", CBT_DEFAULT_CLOSE_QUANTILE, CBT_MIN_CLOSE_QUANTILE, CBT_MAX_CLOSE_QUANTILE); if (!(get_options()->LearnCircuitBuildTimeout)) { log_debug(LD_BUG, "circuit_build_times_close_quantile() called, cbtclosequantile" " is %d", param); } if (param < min) { log_warn(LD_DIR, "Consensus parameter cbtclosequantile is " "too small, raising to %d", min); param = min; } return param / 100.0; } /** * Retrieve and bounds-check the cbttestfreq consensus paramter. * * Effect: Describes how often in seconds to build a test circuit to * gather timeout values. Only applies if less than 'cbtmincircs' * have been recorded. */ static int32_t circuit_build_times_test_frequency(void) { int32_t num = networkstatus_get_param(NULL, "cbttestfreq", CBT_DEFAULT_TEST_FREQUENCY, CBT_MIN_TEST_FREQUENCY, CBT_MAX_TEST_FREQUENCY); if (!(get_options()->LearnCircuitBuildTimeout)) { log_debug(LD_BUG, "circuit_build_times_test_frequency() called, cbttestfreq is %d", num); } return num; } /** * Retrieve and bounds-check the cbtmintimeout consensus parameter. * * Effect: This is the minimum allowed timeout value in milliseconds. * The minimum is to prevent rounding to 0 (we only check once * per second). */ static int32_t circuit_build_times_min_timeout(void) { int32_t num = networkstatus_get_param(NULL, "cbtmintimeout", CBT_DEFAULT_TIMEOUT_MIN_VALUE, CBT_MIN_TIMEOUT_MIN_VALUE, CBT_MAX_TIMEOUT_MIN_VALUE); if (!(get_options()->LearnCircuitBuildTimeout)) { log_debug(LD_BUG, "circuit_build_times_min_timeout() called, cbtmintimeout is %d", num); } return num; } /** * Retrieve and bounds-check the cbtinitialtimeout consensus paramter. * * Effect: This is the timeout value to use before computing a timeout, * in milliseconds. */ int32_t circuit_build_times_initial_timeout(void) { int32_t min = circuit_build_times_min_timeout(); int32_t param = networkstatus_get_param(NULL, "cbtinitialtimeout", CBT_DEFAULT_TIMEOUT_INITIAL_VALUE, CBT_MIN_TIMEOUT_INITIAL_VALUE, CBT_MAX_TIMEOUT_INITIAL_VALUE); if (!(get_options()->LearnCircuitBuildTimeout)) { log_debug(LD_BUG, "circuit_build_times_initial_timeout() called, " "cbtinitialtimeout is %d", param); } if (param < min) { log_warn(LD_DIR, "Consensus parameter cbtinitialtimeout is too small, " "raising to %d", min); param = min; } return param; } /** * Retrieve and bounds-check the cbtrecentcount consensus paramter. * * Effect: This is the number of circuit build times to keep track of * for deciding if we hit cbtmaxtimeouts and need to reset our state * and learn a new timeout. */ static int32_t circuit_build_times_recent_circuit_count(networkstatus_t *ns) { int32_t num; num = networkstatus_get_param(ns, "cbtrecentcount", CBT_DEFAULT_RECENT_CIRCUITS, CBT_MIN_RECENT_CIRCUITS, CBT_MAX_RECENT_CIRCUITS); if (!(get_options()->LearnCircuitBuildTimeout)) { log_debug(LD_BUG, "circuit_build_times_recent_circuit_count() called, " "cbtrecentcount is %d", num); } return num; } /** * This function is called when we get a consensus update. * * It checks to see if we have changed any consensus parameters * that require reallocation or discard of previous stats. */ void circuit_build_times_new_consensus_params(circuit_build_times_t *cbt, networkstatus_t *ns) { int32_t num; /* * First check if we're doing adaptive timeouts at all; nothing to * update if we aren't. */ if (!circuit_build_times_disabled()) { num = circuit_build_times_recent_circuit_count(ns); if (num > 0) { if (num != cbt->liveness.num_recent_circs) { int8_t *recent_circs; log_notice(LD_CIRC, "The Tor Directory Consensus has changed how many " "circuits we must track to detect network failures from %d " "to %d.", cbt->liveness.num_recent_circs, num); tor_assert(cbt->liveness.timeouts_after_firsthop || cbt->liveness.num_recent_circs == 0); /* * Technically this is a circular array that we are reallocating * and memcopying. However, since it only consists of either 1s * or 0s, and is only used in a statistical test to determine when * we should discard our history after a sufficient number of 1's * have been reached, it is fine if order is not preserved or * elements are lost. * * cbtrecentcount should only be changing in cases of severe network * distress anyway, so memory correctness here is paramount over * doing acrobatics to preserve the array. */ recent_circs = tor_malloc_zero(sizeof(int8_t)*num); if (cbt->liveness.timeouts_after_firsthop && cbt->liveness.num_recent_circs > 0) { memcpy(recent_circs, cbt->liveness.timeouts_after_firsthop, sizeof(int8_t)*MIN(num, cbt->liveness.num_recent_circs)); } // Adjust the index if it needs it. if (num < cbt->liveness.num_recent_circs) { cbt->liveness.after_firsthop_idx = MIN(num-1, cbt->liveness.after_firsthop_idx); } tor_free(cbt->liveness.timeouts_after_firsthop); cbt->liveness.timeouts_after_firsthop = recent_circs; cbt->liveness.num_recent_circs = num; } /* else no change, nothing to do */ } else { /* num == 0 */ /* * Weird. This probably shouldn't happen, so log a warning, but try * to do something sensible anyway. */ log_warn(LD_CIRC, "The cbtrecentcircs consensus parameter came back zero! " "This disables adaptive timeouts since we can't keep track of " "any recent circuits."); circuit_build_times_free_timeouts(cbt); } } else { /* * Adaptive timeouts are disabled; this might be because of the * LearnCircuitBuildTimes config parameter, and hence permanent, or * the cbtdisabled consensus parameter, so it may be a new condition. * Treat it like getting num == 0 above and free the circuit history * if we have any. */ circuit_build_times_free_timeouts(cbt); } } /** * Return the initial default or configured timeout in milliseconds */ static double circuit_build_times_get_initial_timeout(void) { double timeout; /* * Check if we have LearnCircuitBuildTimeout, and if we don't, * always use CircuitBuildTimeout, no questions asked. */ if (!unit_tests && get_options()->CircuitBuildTimeout) { timeout = get_options()->CircuitBuildTimeout*1000; if (get_options()->LearnCircuitBuildTimeout && timeout < circuit_build_times_min_timeout()) { log_warn(LD_CIRC, "Config CircuitBuildTimeout too low. Setting to %ds", circuit_build_times_min_timeout()/1000); timeout = circuit_build_times_min_timeout(); } } else { timeout = circuit_build_times_initial_timeout(); } return timeout; } /** * Reset the build time state. * * Leave estimated parameters, timeout and network liveness intact * for future use. */ void circuit_build_times_reset(circuit_build_times_t *cbt) { memset(cbt->circuit_build_times, 0, sizeof(cbt->circuit_build_times)); cbt->total_build_times = 0; cbt->build_times_idx = 0; cbt->have_computed_timeout = 0; } /** * Initialize the buildtimes structure for first use. * * Sets the initial timeout values based on either the config setting, * the consensus param, or the default (CBT_DEFAULT_TIMEOUT_INITIAL_VALUE). */ void circuit_build_times_init(circuit_build_times_t *cbt) { memset(cbt, 0, sizeof(*cbt)); /* * Check if we really are using adaptive timeouts, and don't keep * track of this stuff if not. */ if (!circuit_build_times_disabled()) { cbt->liveness.num_recent_circs = circuit_build_times_recent_circuit_count(NULL); cbt->liveness.timeouts_after_firsthop = tor_malloc_zero(sizeof(int8_t)*cbt->liveness.num_recent_circs); } else { cbt->liveness.num_recent_circs = 0; cbt->liveness.timeouts_after_firsthop = NULL; } cbt->close_ms = cbt->timeout_ms = circuit_build_times_get_initial_timeout(); control_event_buildtimeout_set(cbt, BUILDTIMEOUT_SET_EVENT_RESET); } /** * Free the saved timeouts, if the cbtdisabled consensus parameter got turned * on or something. */ void circuit_build_times_free_timeouts(circuit_build_times_t *cbt) { if (!cbt) return; if (cbt->liveness.timeouts_after_firsthop) { tor_free(cbt->liveness.timeouts_after_firsthop); } cbt->liveness.num_recent_circs = 0; } #if 0 /** * Rewind our build time history by n positions. */ static void circuit_build_times_rewind_history(circuit_build_times_t *cbt, int n) { int i = 0; cbt->build_times_idx -= n; cbt->build_times_idx %= CBT_NCIRCUITS_TO_OBSERVE; for (i = 0; i < n; i++) { cbt->circuit_build_times[(i+cbt->build_times_idx) %CBT_NCIRCUITS_TO_OBSERVE]=0; } if (cbt->total_build_times > n) { cbt->total_build_times -= n; } else { cbt->total_build_times = 0; } log_info(LD_CIRC, "Rewound history by %d places. Current index: %d. " "Total: %d", n, cbt->build_times_idx, cbt->total_build_times); } #endif /** * Add a new build time value time to the set of build times. Time * units are milliseconds. * * circuit_build_times cbt is a circular array, so loop around when * array is full. */ int circuit_build_times_add_time(circuit_build_times_t *cbt, build_time_t time) { if (time <= 0 || time > CBT_BUILD_TIME_MAX) { log_warn(LD_BUG, "Circuit build time is too large (%u)." "This is probably a bug.", time); tor_fragile_assert(); return -1; } log_debug(LD_CIRC, "Adding circuit build time %u", time); cbt->circuit_build_times[cbt->build_times_idx] = time; cbt->build_times_idx = (cbt->build_times_idx + 1) % CBT_NCIRCUITS_TO_OBSERVE; if (cbt->total_build_times < CBT_NCIRCUITS_TO_OBSERVE) cbt->total_build_times++; if ((cbt->total_build_times % CBT_SAVE_STATE_EVERY) == 0) { /* Save state every n circuit builds */ if (!unit_tests && !get_options()->AvoidDiskWrites) or_state_mark_dirty(get_or_state(), 0); } return 0; } /** * Return maximum circuit build time */ static build_time_t circuit_build_times_max(circuit_build_times_t *cbt) { int i = 0; build_time_t max_build_time = 0; for (i = 0; i < CBT_NCIRCUITS_TO_OBSERVE; i++) { if (cbt->circuit_build_times[i] > max_build_time && cbt->circuit_build_times[i] != CBT_BUILD_ABANDONED) max_build_time = cbt->circuit_build_times[i]; } return max_build_time; } #if 0 /** Return minimum circuit build time */ build_time_t circuit_build_times_min(circuit_build_times_t *cbt) { int i = 0; build_time_t min_build_time = CBT_BUILD_TIME_MAX; for (i = 0; i < CBT_NCIRCUITS_TO_OBSERVE; i++) { if (cbt->circuit_build_times[i] && /* 0 <-> uninitialized */ cbt->circuit_build_times[i] < min_build_time) min_build_time = cbt->circuit_build_times[i]; } if (min_build_time == CBT_BUILD_TIME_MAX) { log_warn(LD_CIRC, "No build times less than CBT_BUILD_TIME_MAX!"); } return min_build_time; } #endif /** * Calculate and return a histogram for the set of build times. * * Returns an allocated array of histrogram bins representing * the frequency of index*CBT_BIN_WIDTH millisecond * build times. Also outputs the number of bins in nbins. * * The return value must be freed by the caller. */ static uint32_t * circuit_build_times_create_histogram(circuit_build_times_t *cbt, build_time_t *nbins) { uint32_t *histogram; build_time_t max_build_time = circuit_build_times_max(cbt); int i, c; *nbins = 1 + (max_build_time / CBT_BIN_WIDTH); histogram = tor_malloc_zero(*nbins * sizeof(build_time_t)); // calculate histogram for (i = 0; i < CBT_NCIRCUITS_TO_OBSERVE; i++) { if (cbt->circuit_build_times[i] == 0 || cbt->circuit_build_times[i] == CBT_BUILD_ABANDONED) continue; /* 0 <-> uninitialized */ c = (cbt->circuit_build_times[i] / CBT_BIN_WIDTH); histogram[c]++; } return histogram; } /** * 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). */ static build_time_t circuit_build_times_get_xm(circuit_build_times_t *cbt) { build_time_t i, nbins; 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; int num_modes = circuit_build_times_default_num_xm_modes(); 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 = (build_time_t*)tor_malloc_zero(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]])) { 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]]); } /* The following assert is safe, because we don't get called when we * haven't observed at least CBT_MIN_MIN_CIRCUITS_TO_OBSERVE circuits. */ tor_assert(bin_counts > 0); ret /= bin_counts; tor_free(histogram); tor_free(nth_max_bin); return ret; } /** * Output a histogram of current circuit build times to * the or_state_t state structure. */ void circuit_build_times_update_state(circuit_build_times_t *cbt, or_state_t *state) { uint32_t *histogram; build_time_t i = 0; build_time_t nbins = 0; config_line_t **next, *line; histogram = circuit_build_times_create_histogram(cbt, &nbins); // write to state config_free_lines(state->BuildtimeHistogram); next = &state->BuildtimeHistogram; *next = NULL; state->TotalBuildTimes = cbt->total_build_times; state->CircuitBuildAbandonedCount = 0; for (i = 0; i < CBT_NCIRCUITS_TO_OBSERVE; i++) { if (cbt->circuit_build_times[i] == CBT_BUILD_ABANDONED) state->CircuitBuildAbandonedCount++; } for (i = 0; i < nbins; i++) { // compress the histogram by skipping the blanks if (histogram[i] == 0) continue; *next = line = tor_malloc_zero(sizeof(config_line_t)); line->key = tor_strdup("CircuitBuildTimeBin"); tor_asprintf(&line->value, "%d %d", CBT_BIN_TO_MS(i), histogram[i]); next = &(line->next); } if (!unit_tests) { if (!get_options()->AvoidDiskWrites) or_state_mark_dirty(get_or_state(), 0); } tor_free(histogram); } /** * Shuffle the build times array. * * Adapted from http://en.wikipedia.org/wiki/Fisher-Yates_shuffle */ static void circuit_build_times_shuffle_and_store_array(circuit_build_times_t *cbt, build_time_t *raw_times, uint32_t num_times) { uint32_t n = num_times; if (num_times > CBT_NCIRCUITS_TO_OBSERVE) { log_notice(LD_CIRC, "The number of circuit times that this Tor version " "uses to calculate build times is less than the number stored " "in your state file. Decreasing the circuit time history from " "%lu to %d.", (unsigned long)num_times, CBT_NCIRCUITS_TO_OBSERVE); } if (n > INT_MAX-1) { log_warn(LD_CIRC, "For some insane reasons, you had %lu circuit build " "observations in your state file. That's far too many; probably " "there's a bug here.", (unsigned long)n); n = INT_MAX-1; } /* This code can only be run on a compact array */ while (n-- > 1) { int k = crypto_rand_int(n + 1); /* 0 <= k <= n. */ build_time_t tmp = raw_times[k]; raw_times[k] = raw_times[n]; raw_times[n] = tmp; } /* Since the times are now shuffled, take a random CBT_NCIRCUITS_TO_OBSERVE * subset (ie the first CBT_NCIRCUITS_TO_OBSERVE values) */ for (n = 0; n < MIN(num_times, CBT_NCIRCUITS_TO_OBSERVE); n++) { circuit_build_times_add_time(cbt, raw_times[n]); } } /** * 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 state, shuffling the resulting array * after we do so. Use this result to estimate parameters and * calculate the timeout. * * Return -1 on error. */ int circuit_build_times_parse_state(circuit_build_times_t *cbt, or_state_t *state) { int tot_values = 0; uint32_t loaded_cnt = 0, N = 0; config_line_t *line; unsigned int i; build_time_t *loaded_times; int err = 0; circuit_build_times_init(cbt); if (circuit_build_times_disabled()) { return 0; } /* build_time_t 0 means uninitialized */ loaded_times = tor_malloc_zero(sizeof(build_time_t)*state->TotalBuildTimes); for (line = state->BuildtimeHistogram; line; line = line->next) { smartlist_t *args = smartlist_new(); smartlist_split_string(args, line->value, " ", SPLIT_SKIP_SPACE|SPLIT_IGNORE_BLANK, 0); if (smartlist_len(args) < 2) { log_warn(LD_GENERAL, "Unable to parse circuit build times: " "Too few arguments to CircuitBuildTime"); err = 1; SMARTLIST_FOREACH(args, char*, cp, tor_free(cp)); smartlist_free(args); break; } else { const char *ms_str = smartlist_get(args,0); const char *count_str = smartlist_get(args,1); uint32_t count, k; build_time_t ms; int ok; ms = (build_time_t)tor_parse_ulong(ms_str, 0, 0, CBT_BUILD_TIME_MAX, &ok, NULL); if (!ok) { log_warn(LD_GENERAL, "Unable to parse circuit build times: " "Unparsable bin number"); err = 1; SMARTLIST_FOREACH(args, char*, cp, tor_free(cp)); smartlist_free(args); break; } count = (uint32_t)tor_parse_ulong(count_str, 0, 0, UINT32_MAX, &ok, NULL); if (!ok) { log_warn(LD_GENERAL, "Unable to parse circuit build times: " "Unparsable bin count"); err = 1; SMARTLIST_FOREACH(args, char*, cp, tor_free(cp)); smartlist_free(args); break; } if (loaded_cnt+count+state->CircuitBuildAbandonedCount > state->TotalBuildTimes) { log_warn(LD_CIRC, "Too many build times in state file. " "Stopping short before %d", loaded_cnt+count); SMARTLIST_FOREACH(args, char*, cp, tor_free(cp)); smartlist_free(args); break; } for (k = 0; k < count; k++) { loaded_times[loaded_cnt++] = ms; } N++; SMARTLIST_FOREACH(args, char*, cp, tor_free(cp)); smartlist_free(args); } } log_info(LD_CIRC, "Adding %d timeouts.", state->CircuitBuildAbandonedCount); for (i=0; i < state->CircuitBuildAbandonedCount; i++) { loaded_times[loaded_cnt++] = CBT_BUILD_ABANDONED; } if (loaded_cnt != state->TotalBuildTimes) { log_warn(LD_CIRC, "Corrupt state file? Build times count mismatch. " "Read %d times, but file says %d", loaded_cnt, state->TotalBuildTimes); err = 1; circuit_build_times_reset(cbt); goto done; } circuit_build_times_shuffle_and_store_array(cbt, loaded_times, loaded_cnt); /* Verify that we didn't overwrite any indexes */ for (i=0; i < CBT_NCIRCUITS_TO_OBSERVE; i++) { if (!cbt->circuit_build_times[i]) break; tot_values++; } log_info(LD_CIRC, "Loaded %d/%d values from %d lines in circuit time histogram", tot_values, cbt->total_build_times, N); if (cbt->total_build_times != tot_values || cbt->total_build_times > CBT_NCIRCUITS_TO_OBSERVE) { log_warn(LD_CIRC, "Corrupt state file? Shuffled build times mismatch. " "Read %d times, but file says %d", tot_values, state->TotalBuildTimes); err = 1; circuit_build_times_reset(cbt); goto done; } 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; } /** * Estimates the Xm and Alpha parameters using * http://en.wikipedia.org/wiki/Pareto_distribution#Parameter_estimation * * The notable difference is that we use mode instead of min to estimate Xm. * This is because our distribution is frechet-like. We claim this is * an acceptable approximation because we are only concerned with the * accuracy of the CDF of the tail. */ int 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; /* http://en.wikipedia.org/wiki/Pareto_distribution#Parameter_estimation */ /* We sort of cheat here and make our samples slightly more pareto-like * and less frechet-like. */ cbt->Xm = circuit_build_times_get_xm(cbt); tor_assert(cbt->Xm > 0); for (i=0; i< CBT_NCIRCUITS_TO_OBSERVE; i++) { if (!x[i]) { continue; } if (x[i] < cbt->Xm) { a += tor_mathlog(cbt->Xm); } 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++; } /* * We are erring and asserting here because this can only happen * in codepaths other than startup. The startup state parsing code * 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) { 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); 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; cbt->alpha = a; return 1; } /** * This is the Pareto Quantile Function. It calculates the point x * in the distribution such that F(x) = quantile (ie quantile*100% * of the mass of the density function is below x on the curve). * * We use it to calculate the timeout and also to generate synthetic * values of time for circuits that timeout before completion. * * See http://en.wikipedia.org/wiki/Quantile_function, * http://en.wikipedia.org/wiki/Inverse_transform_sampling and * http://en.wikipedia.org/wiki/Pareto_distribution#Generating_a_ * random_sample_from_Pareto_distribution * That's right. I'll cite wikipedia all day long. * * Return value is in milliseconds. */ double circuit_build_times_calculate_timeout(circuit_build_times_t *cbt, double quantile) { double ret; tor_assert(quantile >= 0); tor_assert(1.0-quantile > 0); tor_assert(cbt->Xm > 0); ret = cbt->Xm/pow(1.0-quantile,1.0/cbt->alpha); if (ret > INT32_MAX) { ret = INT32_MAX; } tor_assert(ret > 0); return ret; } /** Pareto CDF */ double circuit_build_times_cdf(circuit_build_times_t *cbt, double x) { double ret; tor_assert(cbt->Xm > 0); ret = 1.0-pow(cbt->Xm/x,cbt->alpha); tor_assert(0 <= ret && ret <= 1.0); return ret; } /** * Generate a synthetic time using our distribution parameters. * * The return value will be within the [q_lo, q_hi) quantile points * on the CDF. */ build_time_t circuit_build_times_generate_sample(circuit_build_times_t *cbt, double q_lo, double q_hi) { double randval = crypto_rand_double(); build_time_t ret; double u; /* Generate between [q_lo, q_hi) */ /*XXXX This is what nextafter is supposed to be for; we should use it on the * platforms that support it. */ q_hi -= 1.0/(INT32_MAX); tor_assert(q_lo >= 0); tor_assert(q_hi < 1); tor_assert(q_lo < q_hi); u = q_lo + (q_hi-q_lo)*randval; tor_assert(0 <= u && u < 1.0); /* circuit_build_times_calculate_timeout returns <= INT32_MAX */ ret = (build_time_t) tor_lround(circuit_build_times_calculate_timeout(cbt, u)); tor_assert(ret > 0); return ret; } /** * Estimate an initial alpha parameter by solving the quantile * function with a quantile point and a specific timeout value. */ void circuit_build_times_initial_alpha(circuit_build_times_t *cbt, double quantile, double timeout_ms) { // Q(u) = Xm/((1-u)^(1/a)) // Q(0.8) = Xm/((1-0.8))^(1/a)) = CircBuildTimeout // CircBuildTimeout = Xm/((1-0.8))^(1/a)) // CircBuildTimeout = Xm*((1-0.8))^(-1/a)) // ln(CircBuildTimeout) = ln(Xm)+ln(((1-0.8)))*(-1/a) // -ln(1-0.8)/(ln(CircBuildTimeout)-ln(Xm))=a tor_assert(quantile >= 0); tor_assert(cbt->Xm > 0); cbt->alpha = tor_mathlog(1.0-quantile)/ (tor_mathlog(cbt->Xm)-tor_mathlog(timeout_ms)); tor_assert(cbt->alpha > 0); } /** * Returns true if we need circuits to be built */ int circuit_build_times_needs_circuits(circuit_build_times_t *cbt) { /* Return true if < MIN_CIRCUITS_TO_OBSERVE */ return !circuit_build_times_enough_to_compute(cbt); } /** * Returns true if we should build a timeout test circuit * right now. */ int circuit_build_times_needs_circuits_now(circuit_build_times_t *cbt) { return circuit_build_times_needs_circuits(cbt) && approx_time()-cbt->last_circ_at > circuit_build_times_test_frequency(); } /** * Called to indicate that the network showed some signs of liveness, * i.e. we received a cell. * * This is used by circuit_build_times_network_check_live() to decide * if we should record the circuit build timeout or not. * * This function is called every time we receive a cell. Avoid * syscalls, events, and other high-intensity work. */ void circuit_build_times_network_is_live(circuit_build_times_t *cbt) { time_t now = approx_time(); if (cbt->liveness.nonlive_timeouts > 0) { log_notice(LD_CIRC, "Tor now sees network activity. Restoring circuit build " "timeout recording. Network was down for %d seconds " "during %d circuit attempts.", (int)(now - cbt->liveness.network_last_live), cbt->liveness.nonlive_timeouts); } cbt->liveness.network_last_live = now; cbt->liveness.nonlive_timeouts = 0; } /** * Called to indicate that we completed a circuit. Because this circuit * succeeded, it doesn't count as a timeout-after-the-first-hop. * * This is used by circuit_build_times_network_check_changed() to determine * if we had too many recent timeouts and need to reset our learned timeout * to something higher. */ void circuit_build_times_network_circ_success(circuit_build_times_t *cbt) { /* Check for NULLness because we might not be using adaptive timeouts */ if (cbt->liveness.timeouts_after_firsthop && cbt->liveness.num_recent_circs > 0) { cbt->liveness.timeouts_after_firsthop[cbt->liveness.after_firsthop_idx] = 0; cbt->liveness.after_firsthop_idx++; cbt->liveness.after_firsthop_idx %= cbt->liveness.num_recent_circs; } } /** * A circuit just timed out. If it failed after the first hop, record it * in our history for later deciding if the network speed has changed. * * This is used by circuit_build_times_network_check_changed() to determine * if we had too many recent timeouts and need to reset our learned timeout * to something higher. */ static void circuit_build_times_network_timeout(circuit_build_times_t *cbt, int did_onehop) { /* Check for NULLness because we might not be using adaptive timeouts */ if (cbt->liveness.timeouts_after_firsthop && cbt->liveness.num_recent_circs > 0) { if (did_onehop) { cbt->liveness.timeouts_after_firsthop[cbt->liveness.after_firsthop_idx] = 1; cbt->liveness.after_firsthop_idx++; cbt->liveness.after_firsthop_idx %= cbt->liveness.num_recent_circs; } } } /** * A circuit was just forcibly closed. If there has been no recent network * activity at all, but this circuit was launched back when we thought the * network was live, increment the number of "nonlive" circuit timeouts. * * This is used by circuit_build_times_network_check_live() to decide * if we should record the circuit build timeout or not. */ static void circuit_build_times_network_close(circuit_build_times_t *cbt, int did_onehop, time_t start_time) { time_t now = time(NULL); /* * Check if this is a timeout that was for a circuit that spent its * entire existence during a time where we have had no network activity. */ if (cbt->liveness.network_last_live < start_time) { if (did_onehop) { char last_live_buf[ISO_TIME_LEN+1]; char start_time_buf[ISO_TIME_LEN+1]; char now_buf[ISO_TIME_LEN+1]; format_local_iso_time(last_live_buf, cbt->liveness.network_last_live); format_local_iso_time(start_time_buf, start_time); format_local_iso_time(now_buf, now); log_notice(LD_CIRC, "A circuit somehow completed a hop while the network was " "not live. The network was last live at %s, but the circuit " "launched at %s. It's now %s. This could mean your clock " "changed.", last_live_buf, start_time_buf, now_buf); } cbt->liveness.nonlive_timeouts++; if (cbt->liveness.nonlive_timeouts == 1) { log_notice(LD_CIRC, "Tor has not observed any network activity for the past %d " "seconds. Disabling circuit build timeout recording.", (int)(now - cbt->liveness.network_last_live)); } else { log_info(LD_CIRC, "Got non-live timeout. Current count is: %d", cbt->liveness.nonlive_timeouts); } } } /** * When the network is not live, we do not record circuit build times. * * The network is considered not live if there has been at least one * circuit build that began and ended (had its close_ms measurement * period expire) since we last received a cell. * * Also has the side effect of rewinding the circuit time history * in the case of recent liveness changes. */ int circuit_build_times_network_check_live(circuit_build_times_t *cbt) { if (cbt->liveness.nonlive_timeouts > 0) { return 0; } return 1; } /** * Returns true if we have seen more than MAX_RECENT_TIMEOUT_COUNT of * the past RECENT_CIRCUITS time out after the first hop. Used to detect * if the network connection has changed significantly, and if so, * resets our circuit build timeout to the default. * * Also resets the entire timeout history in this case and causes us * to restart the process of building test circuits and estimating a * new timeout. */ int circuit_build_times_network_check_changed(circuit_build_times_t *cbt) { int total_build_times = cbt->total_build_times; int timeout_count=0; int i; if (cbt->liveness.timeouts_after_firsthop && cbt->liveness.num_recent_circs > 0) { /* how many of our recent circuits made it to the first hop but then * timed out? */ for (i = 0; i < cbt->liveness.num_recent_circs; i++) { timeout_count += cbt->liveness.timeouts_after_firsthop[i]; } } /* If 80% of our recent circuits are timing out after the first hop, * we need to re-estimate a new initial alpha and timeout. */ if (timeout_count < circuit_build_times_max_timeouts()) { return 0; } circuit_build_times_reset(cbt); if (cbt->liveness.timeouts_after_firsthop && cbt->liveness.num_recent_circs > 0) { memset(cbt->liveness.timeouts_after_firsthop, 0, sizeof(*cbt->liveness.timeouts_after_firsthop)* cbt->liveness.num_recent_circs); } cbt->liveness.after_firsthop_idx = 0; /* Check to see if this has happened before. If so, double the timeout * to give people on abysmally bad network connections a shot at access */ if (cbt->timeout_ms >= circuit_build_times_get_initial_timeout()) { if (cbt->timeout_ms > INT32_MAX/2 || cbt->close_ms > INT32_MAX/2) { log_warn(LD_CIRC, "Insanely large circuit build timeout value. " "(timeout = %fmsec, close = %fmsec)", cbt->timeout_ms, cbt->close_ms); } else { cbt->timeout_ms *= 2; cbt->close_ms *= 2; } } else { cbt->close_ms = cbt->timeout_ms = circuit_build_times_get_initial_timeout(); } control_event_buildtimeout_set(cbt, BUILDTIMEOUT_SET_EVENT_RESET); 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); return 1; } /** * Count the number of timeouts in a set of cbt data. */ double circuit_build_times_timeout_rate(const circuit_build_times_t *cbt) { int i=0,timeouts=0; for (i = 0; i < CBT_NCIRCUITS_TO_OBSERVE; i++) { if (cbt->circuit_build_times[i] >= cbt->timeout_ms) { timeouts++; } } if (!cbt->total_build_times) return 0; return ((double)timeouts)/cbt->total_build_times; } /** * Count the number of closed circuits in a set of cbt data. */ double circuit_build_times_close_rate(const circuit_build_times_t *cbt) { int i=0,closed=0; for (i = 0; i < CBT_NCIRCUITS_TO_OBSERVE; i++) { if (cbt->circuit_build_times[i] == CBT_BUILD_ABANDONED) { closed++; } } if (!cbt->total_build_times) return 0; return ((double)closed)/cbt->total_build_times; } /** * Store a timeout as a synthetic value. * * Returns true if the store was successful and we should possibly * update our timeout estimate. */ int circuit_build_times_count_close(circuit_build_times_t *cbt, int did_onehop, time_t start_time) { if (circuit_build_times_disabled()) { cbt->close_ms = cbt->timeout_ms = circuit_build_times_get_initial_timeout(); return 0; } /* Record this force-close to help determine if the network is dead */ circuit_build_times_network_close(cbt, did_onehop, start_time); /* Only count timeouts if network is live.. */ if (!circuit_build_times_network_check_live(cbt)) { return 0; } circuit_build_times_add_time(cbt, CBT_BUILD_ABANDONED); return 1; } /** * Update timeout counts to determine if we need to expire * our build time history due to excessive timeouts. * * We do not record any actual time values at this stage; * we are only interested in recording the fact that a timeout * happened. We record the time values via * circuit_build_times_count_close() and circuit_build_times_add_time(). */ void circuit_build_times_count_timeout(circuit_build_times_t *cbt, int did_onehop) { if (circuit_build_times_disabled()) { cbt->close_ms = cbt->timeout_ms = circuit_build_times_get_initial_timeout(); return; } /* Register the fact that a timeout just occurred. */ circuit_build_times_network_timeout(cbt, did_onehop); /* If there are a ton of timeouts, we should reset * the circuit build timeout. */ circuit_build_times_network_check_changed(cbt); } /** * Estimate a new timeout based on history and set our timeout * variable accordingly. */ static int circuit_build_times_set_timeout_worker(circuit_build_times_t *cbt) { build_time_t max_time; if (!circuit_build_times_enough_to_compute(cbt)) return 0; if (!circuit_build_times_update_alpha(cbt)) return 0; cbt->timeout_ms = circuit_build_times_calculate_timeout(cbt, circuit_build_times_quantile_cutoff()); cbt->close_ms = circuit_build_times_calculate_timeout(cbt, circuit_build_times_close_quantile()); max_time = circuit_build_times_max(cbt); if (cbt->timeout_ms > max_time) { log_info(LD_CIRC, "Circuit build timeout of %dms is beyond the maximum build " "time we have ever observed. Capping it to %dms.", (int)cbt->timeout_ms, max_time); cbt->timeout_ms = max_time; } if (max_time < INT32_MAX/2 && cbt->close_ms > 2*max_time) { log_info(LD_CIRC, "Circuit build measurement period of %dms is more than twice " "the maximum build time we have ever observed. Capping it to " "%dms.", (int)cbt->close_ms, 2*max_time); cbt->close_ms = 2*max_time; } /* Sometimes really fast guard nodes give us such a steep curve * that this ends up being not that much greater than timeout_ms. * Make it be at least 1 min to handle this case. */ cbt->close_ms = MAX(cbt->close_ms, circuit_build_times_initial_timeout()); cbt->have_computed_timeout = 1; return 1; } /** * Exposed function to compute a new timeout. Dispatches events and * also filters out extremely high timeout values. */ void circuit_build_times_set_timeout(circuit_build_times_t *cbt) { long prev_timeout = tor_lround(cbt->timeout_ms/1000); double timeout_rate; /* * Just return if we aren't using adaptive timeouts */ if (circuit_build_times_disabled()) return; if (!circuit_build_times_set_timeout_worker(cbt)) return; if (cbt->timeout_ms < circuit_build_times_min_timeout()) { log_info(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) { /* This shouldn't happen because of MAX() in timeout_worker above, * but doing it just in case */ cbt->close_ms = circuit_build_times_initial_timeout(); } } control_event_buildtimeout_set(cbt, BUILDTIMEOUT_SET_EVENT_COMPUTED); timeout_rate = circuit_build_times_timeout_rate(cbt); if (prev_timeout > tor_lround(cbt->timeout_ms/1000)) { 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.", cbt->total_build_times, tor_lround(cbt->timeout_ms/1000)); 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 if (prev_timeout < tor_lround(cbt->timeout_ms/1000)) { 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.", cbt->total_build_times, tor_lround(cbt->timeout_ms/1000)); 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," " r: %f) based on %d circuit times", tor_lround(cbt->timeout_ms/1000), cbt->timeout_ms, cbt->close_ms, cbt->Xm, cbt->alpha, timeout_rate, cbt->total_build_times); } } /** Make a note that we're running unit tests (rather than running Tor * itself), so we avoid clobbering our state file. */ void circuitbuild_running_unit_tests(void) { unit_tests = 1; }