1 files changed, 8 insertions, 2 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 800a8a2fbddb..26e19105cdcc 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -641,12 +641,18 @@ static int function_stat_show(struct seq_file *m, void *v)
         if (rec->counter <= 1)
                 stddev = 0;
         else {
-                stddev = rec->time_squared - rec->counter * avg * avg;
+                /*
+                 * Apply Welford's method:
+                 * s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2)
+                 */
+                stddev = rec->counter * rec->time_squared -
+                         rec->time * rec->time;
+
                 /*
                  * Divide only 1000 for ns^2 -> us^2 conversion.
                  * trace_print_graph_duration will divide 1000 again.
                  */
-                do_div(stddev, (rec->counter - 1) * 1000);
+                do_div(stddev, rec->counter * (rec->counter - 1) * 1000);
         }
 
         trace_seq_init(&s);