readtest: calculate running average and stddev

diff --git a/tools/readtest.c b/tools/readtest.c
index 00b761a65439c5ec1abf2978cb5e86aed273964d..0f2ae7ddd67c0559207fb390a9ba7808145bd99b 100644 (file)
--- a/tools/readtest.c
+++ b/tools/readtest.c
@@ -143,6 +143,9 @@ main (int argc, char* argv[])
        uint64_t _read = 0;
        double max_elapsed = 0;
        double total_time = 0;
+       double var_m = 0;
+       double var_s = 0;
+       uint64_t cnt = 0;
 
        while (1) {
                gint64 before;
@@ -165,6 +168,15 @@ main (int argc, char* argv[])
                
                total_time += elapsed;
 
+               ++cnt;
+               if (max_elapsed == 0) {
+                       var_m = elapsed;
+               } else {
+                       const double var_m1 = var_m;
+                       var_m = var_m + (elapsed - var_m) / (double)(cnt);
+                       var_s = var_s + (elapsed - var_m) * (elapsed - var_m1);
+               }
+
                if (elapsed > max_elapsed) {
                        max_elapsed = elapsed;
                }
@@ -173,12 +185,13 @@ main (int argc, char* argv[])
 
 out:
        if (max_elapsed > 0 && total_time > 0) {
+               double stddev = cnt > 1 ? sqrt(var_s / ((double)(cnt-1))) : 0;
                double bandwidth = ((nfiles * _read)/1048576.0) / (total_time/1000000.0);
                double min_throughput = ((nfiles * block_size)/1048576.0) / (max_elapsed/1000000.0);
                printf ("# Min: %.4f MB/sec Avg: %.4f MB/sec  || Max: %.3f sec \n", min_throughput, bandwidth, max_elapsed/1000000.0);
                printf ("# Max Track count: %d @ 48000SPS\n", (int) floor(1048576.0 * bandwidth / (4 * 48000.)));
                printf ("# Sus Track count: %d @ 48000SPS\n", (int) floor(1048576.0 * min_throughput / (4 * 48000.)));
-               printf ("%d %.4f %.4f %.4f\n", block_size, min_throughput, bandwidth, max_elapsed/1000000.0);
+               printf ("%d %.4f %.4f %.4f %.5f\n", block_size, min_throughput, bandwidth, max_elapsed/1000000.0, stddev/1000000.0);
        }
 
        return 0;