X-Git-Url: https://git.kernel.dk/?a=blobdiff_plain;ds=sidebyside;f=stat.c;h=8be4be5761cbfda454da47f541965a67115c6b26;hb=b6cf38f0aed8b12db1c8fd520c09e5a74066ebc9;hp=d95be758334329b0e681347d419522e82ee1cd45;hpb=2b13e716c0921356c0930522718e00b8df34293a;p=fio.git

diff --git a/stat.c b/stat.c
index d95be758..8be4be57 100644
--- a/stat.c
+++ b/stat.c
@@ -169,7 +169,7 @@ static void show_ddir_status(struct group_run_stats *rs, struct thread_stat *ts,
 	io_p = num2str(ts->io_bytes[ddir], 6, 1, i2p);
 	bw_p = num2str(bw, 6, 1, i2p);
 
-	iops = (1000 * ts->total_io_u[ddir]) / runt;
+	iops = (1000 * (uint64_t)ts->total_io_u[ddir]) / runt;
 	iops_p = num2str(iops, 6, 1, 0);
 
 	log_info("  %s: io=%sB, bw=%sB/s, iops=%s, runt=%6llumsec\n",
@@ -474,21 +474,28 @@ static void sum_stat(struct io_stat *dst, struct io_stat *src, int nr)
 
 	dst->min_val = min(dst->min_val, src->min_val);
 	dst->max_val = max(dst->max_val, src->max_val);
-	dst->samples += src->samples;
 
 	/*
-	 * Needs a new method for calculating stddev, we cannot just
-	 * average them we do below for nr > 1
+	 * Compute new mean and S after the merge
+	 * <http://en.wikipedia.org/wiki/Algorithms_for_calculating_variance
+	 *  #Parallel_algorithm>
 	 */
 	if (nr == 1) {
 		mean = src->mean;
 		S = src->S;
 	} else {
-		mean = ((src->mean * (double) (nr - 1))
-				+ dst->mean) / ((double) nr);
-		S = ((src->S * (double) (nr - 1)) + dst->S) / ((double) nr);
+		double delta = src->mean - dst->mean;
+
+		mean = ((src->mean * src->samples) +
+			(dst->mean * dst->samples)) /
+			(dst->samples + src->samples);
+
+		S =  src->S + dst->S + pow(delta, 2.0) *
+			(dst->samples * src->samples) /
+			(dst->samples + src->samples);
 	}
 
+	dst->samples += src->samples;
 	dst->mean = mean;
 	dst->S = S;
 }