[PATCH] Fix deviation overflow

[fio.git] / stat.c

diff --git a/stat.c b/stat.c
index 6e55925b1cf288ebadc565a4d4c506248ed22b9e..068aa923e7203e2996ade5a5d857d6189339d3a7 100644 (file)
--- a/stat.c
+++ b/stat.c
@@ -271,7 +271,7 @@ void update_rusage_stat(struct thread_data *td)
 static int calc_lat(struct io_stat *is, unsigned long *min, unsigned long *max,
                    double *mean, double *dev)
 {
-       double n;
+       double n, o;
 
        if (is->samples == 0)
                return 0;
@@ -281,12 +281,17 @@ static int calc_lat(struct io_stat *is, unsigned long *min, unsigned long *max,
 
        n = (double) is->samples;
        *mean = (double) is->val / n;
-       *dev = 0;
+       *dev = 0.01;
 
-       if (n <= 1)
+       if (n <= 1.0)
                return 1;
 
-       *dev = sqrt(((double) is->val_sq - (*mean * *mean) / n) / (n - 1));
+       o = (double) is->val_sq - ((*mean * *mean) / n);
+       if (o < 0.0)
+               *dev = -1.0;
+       else
+               *dev = sqrt(o / (n - 1.0));
+
        return 1;
 }