statsd, utils_latency: allow to reduce bin width

diff --git a/src/utils_latency.c b/src/utils_latency.c
index bfb9292..c67752a 100644 (file)
--- a/src/utils_latency.c
+++ b/src/utils_latency.c
@@ -125,8 +125,8 @@ latency_counter_t *latency_counter_create (void) /* {{{ */
   if (lc == NULL)
     return (NULL);
 
-  latency_counter_reset (lc);
   lc->bin_width = HISTOGRAM_DEFAULT_BIN_WIDTH;
+  latency_counter_reset (lc);
   return (lc);
 } /* }}} latency_counter_t *latency_counter_create */
 
@@ -175,6 +175,28 @@ void latency_counter_reset (latency_counter_t *lc) /* {{{ */
     return;
 
   cdtime_t bin_width = lc->bin_width;
+  cdtime_t max_bin = (lc->max - 1) / lc->bin_width;
+
+/*
+  If max latency is REDUCE_THRESHOLD times less than histogram's range,
+  then cut it in half. REDUCE_THRESHOLD must be >= 2.
+  Value of 4 is selected to reduce frequent changes of bin width.
+*/
+#define REDUCE_THRESHOLD 4
+  if ((lc->num > 0) && (lc->bin_width >= HISTOGRAM_DEFAULT_BIN_WIDTH * 2)
+     && (max_bin < HISTOGRAM_NUM_BINS / REDUCE_THRESHOLD))
+  {
+    /* new bin width will be the previous power of 2 */
+    bin_width = bin_width / 2;
+
+    DEBUG("utils_latency: latency_counter_reset: max_latency = %.3f; "
+          "max_bin = %"PRIu64"; old_bin_width = %.3f; new_bin_width = %.3f;",
+        CDTIME_T_TO_DOUBLE (lc->max),
+        max_bin,
+        CDTIME_T_TO_DOUBLE (lc->bin_width),
+        CDTIME_T_TO_DOUBLE (bin_width));
+  }
+
   memset (lc, 0, sizeof (*lc));
 
   /* preserve bin width */