brusts.diff

diff --git a/src/redis-cli.c b/src/redis-cli.c
index be37a91..82b8e04 100644
--- a/src/redis-cli.c
+++ b/src/redis-cli.c
@@ -1263,8 +1263,9 @@ static int evalMode(int argc, char **argv) {
  * Latency and latency history modes
  *--------------------------------------------------------------------------- */

-#define LATENCY_SAMPLE_RATE 10 /* milliseconds. */
+#define LATENCY_SAMPLE_RATE 1 /* milliseconds. */
 #define LATENCY_HISTORY_DEFAULT_INTERVAL 15000 /* milliseconds. */
+#define LATENCY_BRUST_SIZE 1000
 static void latencyMode(void) {
     redisReply *reply;
     long long start, latency, min = 0, max = 0, tot = 0, count = 0;
@@ -1273,6 +1274,7 @@ static void latencyMode(void) {
                           LATENCY_HISTORY_DEFAULT_INTERVAL;
     double avg;
     long long history_start = mstime();
+    int req = 0;

     if (!context) exit(1);
     while(1) {
@@ -1284,26 +1286,38 @@ static void latencyMode(void) {
         }
         latency = mstime()-start;
         freeReplyObject(reply);
-        count++;
-        if (count == 1) {
-            min = max = tot = latency;
-            avg = (double) latency;
-        } else {
-            if (latency < min) min = latency;
-            if (latency > max) max = latency;
-            tot += latency;
-            avg = (double) tot/count;
+
+        if (req > 10 && req < LATENCY_BRUST_SIZE-10) {
+            count++;
+            if (count == 1) {
+                min = max = tot = latency;
+                avg = (double) latency;
+            } else {
+                if (latency < min) min = latency;
+                if (latency > max) max = latency;
+                tot += latency;
+                avg = (double) tot/count;
+            }
+            printf("\x1b[0G\x1b[2Kmin: %lld, max: %lld, avg: %.2f (%lld samples)
+                min, max, avg, count);
+            fflush(stdout);
+            if (config.latency_history && mstime()-history_start > history_inter
+            {
+                printf(" -- %.2f seconds range\n", (float)(mstime()-history_star
+                history_start = mstime();
+                min = max = tot = count = 0;
+            }
         }
-        printf("\x1b[0G\x1b[2Kmin: %lld, max: %lld, avg: %.2f (%lld samples)",
-            min, max, avg, count);
-        fflush(stdout);
-        if (config.latency_history && mstime()-history_start > history_interval)
-        {
-            printf(" -- %.2f seconds range\n", (float)(mstime()-history_start)/1
-            history_start = mstime();
-            min = max = tot = count = 0;
+
+        /* Sleeping at every request creates scheduling artifacts that will
+         * report a latency higher than needed. So instead we do requests
+         * in brusts of 50, and wait a longer time later. We only sample the
+         * latency in the middle of brusts. */
+        req++;
+        if (req == LATENCY_BRUST_SIZE) {
+            req = 0;
+            usleep((LATENCY_SAMPLE_RATE * 1000)*LATENCY_BRUST_SIZE);
         }
-        usleep(LATENCY_SAMPLE_RATE * 1000);
     }
 }