1 files changed, 21 insertions, 3 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 2404b59b3097..3bcb340d6f02 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -264,6 +264,7 @@ struct ftrace_profile {
         unsigned long                   counter;
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
         unsigned long long              time;
+        unsigned long long              time_squared;
 #endif
 };
 
@@ -366,9 +367,9 @@ static int function_stat_headers(struct seq_file *m)
 {
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
         seq_printf(m, "  Function                               "
-                   "Hit    Time            Avg\n"
+                   "Hit    Time            Avg             s^2\n"
                       "  --------                               "
-                   "---    ----            ---\n");
+                   "---    ----            ---             ---\n");
 #else
         seq_printf(m, "  Function                               Hit\n"
                       "  --------                               ---\n");
@@ -384,6 +385,7 @@ static int function_stat_show(struct seq_file *m, void *v)
         static DEFINE_MUTEX(mutex);
         static struct trace_seq s;
         unsigned long long avg;
+        unsigned long long stddev;
 #endif
 
         kallsyms_lookup(rec->ip, NULL, NULL, NULL, str);
@@ -394,11 +396,25 @@ static int function_stat_show(struct seq_file *m, void *v)
         avg = rec->time;
         do_div(avg, rec->counter);
 
+        /* Sample standard deviation (s^2) */
+        if (rec->counter <= 1)
+                stddev = 0;
+        else {
+                stddev = rec->time_squared - rec->counter * avg * avg;
+                /*
+                 * Divide only 1000 for ns^2 -> us^2 conversion.
+                 * trace_print_graph_duration will divide 1000 again.
+                 */
+                do_div(stddev, (rec->counter - 1) * 1000);
+        }
+
         mutex_lock(&mutex);
         trace_seq_init(&s);
         trace_print_graph_duration(rec->time, &s);
         trace_seq_puts(&s, "    ");
         trace_print_graph_duration(avg, &s);
+        trace_seq_puts(&s, "    ");
+        trace_print_graph_duration(stddev, &s);
         trace_print_seq(m, &s);
         mutex_unlock(&mutex);
 #endif
@@ -668,8 +684,10 @@ static void profile_graph_return(struct ftrace_graph_ret *trace)
         }
 
         rec = ftrace_find_profiled_func(stat, trace->func);
-        if (rec)
+        if (rec) {
                 rec->time += calltime;
+                rec->time_squared += calltime * calltime;
+        }
 
  out:
         local_irq_restore(flags);