[tor-commits] [tor/master] Rewrite time-handling in circuitmux_ewma to use monotime_coarse
nickm at torproject.org
nickm at torproject.org
Tue May 1 17:28:24 UTC 2018
commit 5e395ba2c2bf041cacf85e6ad38cb39ea8ae7419
Author: Nick Mathewson <nickm at torproject.org>
Date: Thu Apr 26 10:18:39 2018 -0400
Rewrite time-handling in circuitmux_ewma to use monotime_coarse
This part of the code was the only part that used "cached
getttimeofday" feature, which wasn't monotonic, which we updated at
slight expense, and which I'd rather not maintain.
---
changes/ticket25927.1 | 6 ++++
src/or/circuitmux_ewma.c | 79 ++++++++++++++++++++++++++++++++++------------
src/or/circuitmux_ewma.h | 7 ++++
src/or/main.c | 2 ++
src/test/test_channel.c | 2 ++
src/test/test_circuitmux.c | 40 +++++++++++++++++++++++
6 files changed, 115 insertions(+), 21 deletions(-)
diff --git a/changes/ticket25927.1 b/changes/ticket25927.1
new file mode 100644
index 000000000..84ac86e18
--- /dev/null
+++ b/changes/ticket25927.1
@@ -0,0 +1,6 @@
+ o Minor features (timekeeping, circuit scheduling):
+ - When keeping track of how busy each circuit have been recently on
+ a given connection, use coarse-grained monotonic timers rather than
+ gettimeofday(). This change should marginally increase accuracy
+ and performance. Implements part of ticket 25927.
+
diff --git a/src/or/circuitmux_ewma.c b/src/or/circuitmux_ewma.c
index 4b80124a7..a8a645ca5 100644
--- a/src/or/circuitmux_ewma.c
+++ b/src/or/circuitmux_ewma.c
@@ -28,7 +28,7 @@
*
**/
-#define TOR_CIRCUITMUX_EWMA_C_
+#define CIRCUITMUX_EWMA_PRIVATE
#include "orconfig.h"
@@ -169,8 +169,6 @@ TO_EWMA_POL_CIRC_DATA(circuitmux_policy_circ_data_t *pol)
static void add_cell_ewma(ewma_policy_data_t *pol, cell_ewma_t *ewma);
static int compare_cell_ewma_counts(const void *p1, const void *p2);
-static unsigned cell_ewma_tick_from_timeval(const struct timeval *now,
- double *remainder_out);
static circuit_t * cell_ewma_to_circuit(cell_ewma_t *ewma);
static inline double get_scale_factor(unsigned from_tick, unsigned to_tick);
static cell_ewma_t * pop_first_cell_ewma(ewma_policy_data_t *pol);
@@ -239,6 +237,13 @@ circuitmux_policy_t ewma_policy = {
/*.cmp_cmux =*/ ewma_cmp_cmux
};
+/** Have we initialized the ewma tick-counting logic? */
+static int ewma_ticks_initialized = 0;
+/** At what monotime_coarse_t did the current tick begin? */
+static monotime_coarse_t start_of_current_tick;
+/** What is the number of the current tick? */
+static unsigned current_tick_num;
+
/*** EWMA method implementations using the below EWMA helper functions ***/
/** Compute and return the current cell_ewma tick. */
@@ -421,8 +426,6 @@ ewma_notify_xmit_cells(circuitmux_t *cmux,
ewma_policy_circ_data_t *cdata = NULL;
unsigned int tick;
double fractional_tick, ewma_increment;
- /* The current (hi-res) time */
- struct timeval now_hires;
cell_ewma_t *cell_ewma, *tmp;
tor_assert(cmux);
@@ -435,8 +438,7 @@ ewma_notify_xmit_cells(circuitmux_t *cmux,
cdata = TO_EWMA_POL_CIRC_DATA(pol_circ_data);
/* Rescale the EWMAs if needed */
- tor_gettimeofday_cached(&now_hires);
- tick = cell_ewma_tick_from_timeval(&now_hires, &fractional_tick);
+ tick = cell_ewma_get_current_tick_and_fraction(&fractional_tick);
if (tick != pol->active_circuit_pqueue_last_recalibrated) {
scale_active_circuits(pol, tick);
@@ -597,24 +599,48 @@ cell_ewma_to_circuit(cell_ewma_t *ewma)
rescale.
*/
-/** Given a timeval <b>now</b>, compute the cell_ewma tick in which it occurs
- * and the fraction of the tick that has elapsed between the start of the tick
- * and <b>now</b>. Return the former and store the latter in
- * *<b>remainder_out</b>.
+/**
+ * Initialize the system that tells which ewma tick we are in.
+ */
+STATIC void
+cell_ewma_initialize_ticks(void)
+{
+ if (ewma_ticks_initialized)
+ return;
+ monotime_coarse_get(&start_of_current_tick);
+ crypto_rand((char*)¤t_tick_num, sizeof(current_tick_num));
+ ewma_ticks_initialized = 1;
+}
+
+/** Compute the current cell_ewma tick and the fraction of the tick that has
+ * elapsed between the start of the tick and the current time. Return the
+ * former and store the latter in *<b>remainder_out</b>.
*
* These tick values are not meant to be shared between Tor instances, or used
* for other purposes. */
-
-static unsigned
-cell_ewma_tick_from_timeval(const struct timeval *now,
- double *remainder_out)
+STATIC unsigned
+cell_ewma_get_current_tick_and_fraction(double *remainder_out)
{
- unsigned res = (unsigned) (now->tv_sec / EWMA_TICK_LEN);
- /* rem */
- double rem = (now->tv_sec % EWMA_TICK_LEN) +
- ((double)(now->tv_usec)) / 1.0e6;
- *remainder_out = rem / EWMA_TICK_LEN;
- return res;
+ if (BUG(!ewma_ticks_initialized)) {
+ cell_ewma_initialize_ticks(); // LCOV_EXCL_LINE
+ }
+ monotime_coarse_t now;
+ monotime_coarse_get(&now);
+ // XXXX this does a division operation that can be slow on 32-bit
+ // XXXX systems.
+ int32_t msec_diff =
+ (int32_t)monotime_coarse_diff_msec(&start_of_current_tick,
+ &now);
+ if (msec_diff > (1000*EWMA_TICK_LEN)) {
+ unsigned ticks_difference = msec_diff / (1000*EWMA_TICK_LEN);
+ monotime_coarse_add_msec(&start_of_current_tick,
+ &start_of_current_tick,
+ ticks_difference * 1000 * EWMA_TICK_LEN);
+ current_tick_num += ticks_difference;
+ msec_diff %= 1000*EWMA_TICK_LEN;
+ }
+ *remainder_out = ((double)msec_diff) / (1.0e3 * EWMA_TICK_LEN);
+ return current_tick_num;
}
/* Default value for the CircuitPriorityHalflifeMsec consensus parameter in
@@ -678,6 +704,8 @@ cmux_ewma_set_options(const or_options_t *options,
double halflife;
const char *source;
+ cell_ewma_initialize_ticks();
+
/* Both options and consensus can be NULL. This assures us to either get a
* valid configured value or the default one. */
halflife = get_circuit_priority_halflife(options, consensus, &source);
@@ -788,3 +816,12 @@ pop_first_cell_ewma(ewma_policy_data_t *pol)
offsetof(cell_ewma_t, heap_index));
}
+/**
+ * Drop all resources held by circuitmux_ewma.c, and deinitialize the
+ * module. */
+void
+circuitmux_ewma_free_all(void)
+{
+ ewma_ticks_initialized = 0;
+}
+
diff --git a/src/or/circuitmux_ewma.h b/src/or/circuitmux_ewma.h
index 2ef8c2586..f0c4c3609 100644
--- a/src/or/circuitmux_ewma.h
+++ b/src/or/circuitmux_ewma.h
@@ -19,5 +19,12 @@ extern circuitmux_policy_t ewma_policy;
void cmux_ewma_set_options(const or_options_t *options,
const networkstatus_t *consensus);
+void circuitmux_ewma_free_all(void);
+
+#ifdef CIRCUITMUX_EWMA_PRIVATE
+STATIC unsigned cell_ewma_get_current_tick_and_fraction(double *remainder_out);
+STATIC void cell_ewma_initialize_ticks(void);
+#endif
+
#endif /* !defined(TOR_CIRCUITMUX_EWMA_H) */
diff --git a/src/or/main.c b/src/or/main.c
index ffe407329..ee6a2459a 100644
--- a/src/or/main.c
+++ b/src/or/main.c
@@ -59,6 +59,7 @@
#include "circuitbuild.h"
#include "circuitlist.h"
#include "circuituse.h"
+#include "circuitmux_ewma.h"
#include "command.h"
#include "compress.h"
#include "config.h"
@@ -3488,6 +3489,7 @@ tor_free_all(int postfork)
consdiffmgr_free_all();
hs_free_all();
dos_free_all();
+ circuitmux_ewma_free_all();
if (!postfork) {
config_free_all();
or_state_free_all();
diff --git a/src/test/test_channel.c b/src/test/test_channel.c
index 812ec6c1a..7d5018ef5 100644
--- a/src/test/test_channel.c
+++ b/src/test/test_channel.c
@@ -544,6 +544,8 @@ test_channel_outbound_cell(void *arg)
(void) arg;
+ cmux_ewma_set_options(NULL,NULL);
+
/* The channel will be freed so we need to hijack this so the scheduler
* doesn't get confused. */
MOCK(scheduler_release_channel, scheduler_release_channel_mock);
diff --git a/src/test/test_circuitmux.c b/src/test/test_circuitmux.c
index 75b7a0ea4..14c759870 100644
--- a/src/test/test_circuitmux.c
+++ b/src/test/test_circuitmux.c
@@ -3,6 +3,7 @@
#define TOR_CHANNEL_INTERNAL_
#define CIRCUITMUX_PRIVATE
+#define CIRCUITMUX_EWMA_PRIVATE
#define RELAY_PRIVATE
#include "or.h"
#include "channel.h"
@@ -79,8 +80,47 @@ test_cmux_destroy_cell_queue(void *arg)
tor_free(dc);
}
+static void
+test_cmux_compute_ticks(void *arg)
+{
+ const int64_t NS_PER_S = 1000 * 1000 * 1000;
+ const int64_t START_NS = U64_LITERAL(1217709000)*NS_PER_S;
+ int64_t now;
+ double rem;
+ unsigned tick;
+ (void)arg;
+ circuitmux_ewma_free_all();
+ monotime_enable_test_mocking();
+
+ monotime_coarse_set_mock_time_nsec(START_NS);
+ cell_ewma_initialize_ticks();
+ const unsigned tick_zero = cell_ewma_get_current_tick_and_fraction(&rem);
+ tt_double_op(rem, OP_GT, -1e-9);
+ tt_double_op(rem, OP_LT, 1e-9);
+
+ /* 1.5 second later and we should still be in the same tick. */
+ now = START_NS + NS_PER_S + NS_PER_S/2;
+ monotime_coarse_set_mock_time_nsec(now);
+ tick = cell_ewma_get_current_tick_and_fraction(&rem);
+ tt_uint_op(tick, OP_EQ, tick_zero);
+ tt_double_op(rem, OP_GT, .149999999);
+ tt_double_op(rem, OP_LT, .150000001);
+
+ /* 25 second later and we should be in another tick. */
+ now = START_NS + NS_PER_S * 25;
+ monotime_coarse_set_mock_time_nsec(now);
+ tick = cell_ewma_get_current_tick_and_fraction(&rem);
+ tt_uint_op(tick, OP_EQ, tick_zero + 2);
+ tt_double_op(rem, OP_GT, .499999999);
+ tt_double_op(rem, OP_LT, .500000001);
+
+ done:
+ ;
+}
+
struct testcase_t circuitmux_tests[] = {
{ "destroy_cell_queue", test_cmux_destroy_cell_queue, TT_FORK, NULL, NULL },
+ { "compute_ticks", test_cmux_compute_ticks, TT_FORK, NULL, NULL },
END_OF_TESTCASES
};
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