test-ratelim: calculate timers bias (for slow CPUs) to avoid false-positive

This can be/should be done for regression tests too.

Refs: https://ci.appveyor.com/project/libevent/libevent/builds/28916689/job/kg621aa194a0qbym
Refs: https://github.com/libevent/libevent/pull/917#issuecomment-553811834
v2: EVENT_BASE_FLAG_PRECISE_TIMER

diff --git a/test/test-ratelim.c b/test/test-ratelim.c
index 9ee989bd820e18716895c0bc8f15462810f37ce8..e47fd731a43f0232e4d936b705e761ee5ffaeee0 100644 (file)
--- a/test/test-ratelim.c
+++ b/test/test-ratelim.c
@@ -50,6 +50,10 @@
 #include "event2/listener.h"
 #include "event2/thread.h"
 
+#ifndef MIN
+#define MIN(a,b) (((a)<(b))?(a):(b))
+#endif
+
 static struct evutil_weakrand_state weakrand_state;
 
 static int cfg_verbose = 0;
@@ -85,6 +89,18 @@ struct client_state {
 };
 static const struct timeval *ms100_common=NULL;
 
+/* Timers bias for slow CPUs, affects:
+ * - cfg_connlimit_tolerance  (--check-connlimit)
+ * - cfg_grouplimit_tolerance (--check-grouplimit)
+ * - cfg_stddev_tolerance     (--check-stddev)
+ */
+static int timer_bias_events;
+static struct timeval timer_bias_start;
+double timer_bias_spend;
+/* Real cost is less (approximately ~5 usec),
+ * this macros adjusted to make the bias less */
+#define TIMER_MAX_COST_USEC 10
+
 /* info from check_bucket_levels_cb */
 static int total_n_bev_checks = 0;
 static ev_int64_t total_rbucket_level=0;
@@ -244,6 +260,62 @@ group_drain_cb(evutil_socket_t fd, short events, void *arg)
        bufferevent_rate_limit_group_decrement_write(ratelim_group, cfg_group_drain);
 }
 
+static void
+timer_bias_cb(evutil_socket_t fd, short events, void *arg)
+{
+       struct event *event = arg;
+       struct timeval end;
+       struct timeval diff;
+
+       /** XXX: use rdtsc? (portability issues?) */
+       evutil_gettimeofday(&end, NULL);
+       evutil_timersub(&end, &timer_bias_start, &diff);
+       timer_bias_spend += diff.tv_sec + diff.tv_usec * 1e6;
+       timer_bias_start = end;
+
+       if (++timer_bias_events == 100)
+               event_del(event);
+}
+static double
+timer_bias_calculate(void)
+{
+       struct event_config *cfg = NULL;
+       struct event_base *base = NULL;
+       struct event *timer = NULL;
+       struct timeval tv = { 0, 1 };
+
+       cfg = event_config_new();
+       if (!cfg)
+               goto err;
+       if (event_config_set_flag(cfg, EVENT_BASE_FLAG_PRECISE_TIMER))
+               goto err;
+       base = event_base_new_with_config(cfg);
+       if (!base)
+               goto err;
+
+       timer = event_new(base, -1, EV_PERSIST, timer_bias_cb, event_self_cbarg());
+       if (!timer || event_add(timer, &tv)) {
+               goto err;
+       }
+
+       evutil_gettimeofday(&timer_bias_start, NULL);
+       event_base_dispatch(base);
+       event_free(timer);
+
+       return MIN(timer_bias_spend / 1e6 / timer_bias_events / TIMER_MAX_COST_USEC, 5);
+
+err:
+       if (cfg)
+               event_config_free(cfg);
+       if (timer)
+               event_free(timer);
+       if (base)
+               event_base_free(base);
+
+       fprintf(stderr, "Couldn't create event for CPU cycle counter bias\n");
+       return -1;
+}
+
 static int
 test_ratelimiting(void)
 {
@@ -266,6 +338,7 @@ test_ratelimiting(void)
        struct event_config *base_cfg;
        struct event *periodic_level_check;
        struct event *group_drain_event=NULL;
+       double timer_bias;
 
        memset(&sin, 0, sizeof(sin));
        sin.sin_family = AF_INET;
@@ -275,6 +348,16 @@ test_ratelimiting(void)
        if (0)
                event_enable_debug_mode();
 
+       timer_bias = timer_bias_calculate();
+       if (timer_bias > 1) {
+               fprintf(stderr, "CPU is slow, timers bias is %f\n", timer_bias);
+               cfg_connlimit_tolerance  *= timer_bias;
+               cfg_grouplimit_tolerance *= timer_bias;
+               cfg_stddev_tolerance     *= timer_bias;
+       } else {
+               printf("CPU is fast enough, timers bias is %f\n", timer_bias);
+       }
+
        base_cfg = event_config_new();
 
 #ifdef _WIN32