src/oping.c: Add median and 'n'th percentile, remove average and stddev.

Average and standard deviation are not very useful for network latency.
Median and (95th) percentiles are routinely used to measure network
performance, so provide them instead.

diff --git a/src/oping.c b/src/oping.c
index ca92778..ff06670 100644 (file)
--- a/src/oping.c
+++ b/src/oping.c
@@ -163,7 +163,6 @@ typedef struct ping_context
        double latency_min;
        double latency_max;
        double latency_total;
-       double latency_total_square;
 
 /* 1000 + one "infinity" bucket. */
 #define OPING_HISTOGRAM_BUCKETS 1001
@@ -219,7 +218,6 @@ static ping_context_t *context_create (void) /* {{{ */
        ret->latency_min   = -1.0;
        ret->latency_max   = -1.0;
        ret->latency_total = 0.0;
-       ret->latency_total_square = 0.0;
 
        ret->latency_histogram_size = (size_t) OPING_HISTOGRAM_BUCKETS;
        ret->histogram_counters = calloc (ret->latency_histogram_size,
@@ -261,20 +259,6 @@ static void context_destroy (ping_context_t *context) /* {{{ */
        free (context);
 } /* }}} void context_destroy */
 
-static double context_get_average (ping_context_t *ctx) /* {{{ */
-{
-       double num_total;
-
-       if (ctx == NULL)
-               return (-1.0);
-
-       if (ctx->req_rcvd < 1)
-               return (-0.0);
-
-       num_total = (double) ctx->req_rcvd;
-       return (ctx->latency_total / num_total);
-} /* }}} double context_get_average */
-
 static double context_get_percentile (ping_context_t *ctx, /* {{{ */
                double percentile)
 {
@@ -308,24 +292,6 @@ static double context_get_percentile (ping_context_t *ctx, /* {{{ */
        return (ret);
 } /* }}} double context_get_percentile */
 
-static double context_get_stddev (ping_context_t *ctx) /* {{{ */
-{
-       double num_total;
-
-       if (ctx == NULL)
-               return (-1.0);
-
-       if (ctx->req_rcvd < 1)
-               return (-0.0);
-       else if (ctx->req_rcvd < 2)
-               return (0.0);
-
-       num_total = (double) ctx->req_rcvd;
-       return (sqrt (((num_total * ctx->latency_total_square)
-                                       - (ctx->latency_total * ctx->latency_total))
-                               / (num_total * (num_total - 1.0))));
-} /* }}} double context_get_stddev */
-
 static double context_get_packet_loss (const ping_context_t *ctx) /* {{{ */
 {
        if (ctx == NULL)
@@ -1095,23 +1061,17 @@ static int update_stats_from_context (ping_context_t *ctx, pingobj_iter_t *iter)
                        ctx->latency_total);
        if (ctx->req_rcvd != 0)
        {
-               double average;
-               double deviation;
+               double median;
                double percentile;
 
-               average = context_get_average (ctx);
-               deviation = context_get_stddev (ctx);
+               median = context_get_percentile (ctx, 50.0);
                percentile = context_get_percentile (ctx, opt_percentile);
 
                mvwprintw (ctx->window, /* y = */ 2, /* x = */ 2,
-                               "rtt min/avg/%.0f%%/max/sdev = "
-                               "%.3f/%.3f/%.0f/%.3f/%.3f ms\n",
-                               opt_percentile,
-                               ctx->latency_min,
-                               average,
-                               percentile,
-                               ctx->latency_max,
-                               deviation);
+                               "RTT[ms]: min = %.0f, median = %.0f, p(%.0f) = %.0f, max = %.0f",
+                               ctx->latency_min, median,
+                               opt_percentile, percentile,
+                               ctx->latency_max);
        }
 
        if (opt_show_graph == 1)
@@ -1334,7 +1294,6 @@ static void update_context (ping_context_t *context, double latency) /* {{{ */
 
        context->req_rcvd++;
        context->latency_total += latency;
-       context->latency_total_square += (latency * latency);
 
        if ((context->latency_max < 0.0) || (context->latency_max < latency))
                context->latency_max = latency;
@@ -1463,7 +1422,7 @@ static void update_host_hook (pingobj_iter_t *iter, /* {{{ */
                }
 #endif
        }
-       else
+       else /* if (!(latency > 0.0)) */
        {
 #if USE_NCURSES
                if (has_colors () == TRUE)
@@ -1528,22 +1487,16 @@ static int post_loop_hook (pingobj_t *ping) /* {{{ */
 
                if (context->req_rcvd != 0)
                {
-                       double average;
-                       double deviation;
+                       double median;
                        double percentile;
 
-                       average = context_get_average (context);
-                       deviation = context_get_stddev (context);
+                       median = context_get_percentile (context, 50.0);
                        percentile = context_get_percentile (context, opt_percentile);
 
-                       printf ("rtt min/avg/%.0f%%/max/sdev = "
-                                       "%.3f/%.3f/%.0f/%.3f/%.3f ms\n",
-                                       opt_percentile,
-                                       context->latency_min,
-                                       average,
-                                       percentile,
-                                       context->latency_max,
-                                       deviation);
+                       printf ("RTT[ms]: min = %.0f, median = %.0f, p(%.0f) = %.0f, max = %.0f\n",
+                                       context->latency_min, median,
+                                       opt_percentile, percentile,
+                                       context->latency_max);
                }
 
                ping_iterator_set_context (iter, NULL);