src/oping.c: Add median and 'n'th percentile, remove average and stddev.
authorFlorian Forster <ff@octo.it>
Tue, 18 Nov 2014 17:23:56 +0000 (18:23 +0100)
committerFlorian Forster <ff@octo.it>
Tue, 18 Nov 2014 17:23:56 +0000 (18:23 +0100)
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.

src/oping.c

index ca92778..ff06670 100644 (file)
@@ -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);