automatic sampling interval calibration

src/stats.c

@@ -25,6 +25,11 @@ void stats_reset(stats *stats) {
     stats->max   = 0;
 }
 
+void stats_rewind(stats *stats) {
+    stats->limit = 0;
+    stats->index = 0;
+}
+
 void stats_record(stats *stats, uint64_t x) {
     stats->data[stats->index++] = x;
     if (x < stats->min) stats->min = x;

src/stats.h

@@ -19,6 +19,7 @@ typedef struct {
 stats *stats_alloc(uint64_t);
 void stats_free(stats *);
 void stats_reset(stats *);
+void stats_rewind(stats *);
 
 void stats_record(stats *, uint64_t);
 

src/wrk.c

@@ -288,17 +288,20 @@ static int reconnect_socket(thread *thread, connection *c) {
 static int calibrate(aeEventLoop *loop, long long id, void *data) {
     thread *thread = data;
 
-    uint64_t elapsed_ms = (time_us() - thread->start) / 1000;
+    (void) stats_summarize(thread->latency);
-    uint64_t req_per_ms = ceil(thread->requests / (double) elapsed_ms);
+    long double latency = stats_percentile(thread->latency, 90.0) / 1000.0L;
+    long double interval = MAX(latency * 2, 10);
+    long double rate = (interval / latency) * thread->connections;
 
-    if (!req_per_ms) return CALIBRATE_DELAY_MS / 2;
+    if (latency == 0) return CALIBRATE_DELAY_MS;
 
-    thread->rate  = (req_per_ms * SAMPLE_INTERVAL_MS) / 10;
+    thread->interval = interval;
-    thread->start = time_us();
+    thread->rate     = ceil(rate / 10);
+    thread->start    = time_us();
     thread->requests = 0;
     stats_reset(thread->latency);
 
-    aeCreateTimeEvent(loop, SAMPLE_INTERVAL_MS, sample_rate, thread, NULL);
+    aeCreateTimeEvent(loop, thread->interval, sample_rate, thread, NULL);
 
     return AE_NOMORE;
 }
@@ -316,14 +319,12 @@ static int sample_rate(aeEventLoop *loop, long long id, void *data) {
     stats_record(statistics.requests, requests);
     pthread_mutex_unlock(&statistics.mutex);
 
-    uint64_t max = thread->latency->max;
     thread->missed  += missed;
     thread->requests = 0;
     thread->start    = time_us();
-    stats_reset(thread->latency);
+    stats_rewind(thread->latency);
-    thread->latency->max = max;
 
-    return SAMPLE_INTERVAL_MS;
+    return thread->interval;
 }
 
 static int request_complete(http_parser *parser) {

src/wrk.h

@@ -13,12 +13,11 @@
 #include "ae.h"
 #include "http_parser.h"
 
-#define VERSION  "2.2.1"
+#define VERSION  "2.2.2"
 #define RECVBUF  8192
 #define SAMPLES  100000000
 
 #define SOCKET_TIMEOUT_MS   2000
-#define SAMPLE_INTERVAL_MS  10
 #define CALIBRATE_DELAY_MS  500
 #define TIMEOUT_INTERVAL_MS 2000
 
@@ -34,6 +33,7 @@ typedef struct {
     pthread_t thread;
     aeEventLoop *loop;
     uint64_t connections;
+    int interval;
     uint64_t stop_at;
     uint64_t complete;
     uint64_t requests;