---

yaml
---
r: 191447
b: refs/heads/master
c: e330b3b
h: refs/heads/master
i:
  191445: 66ddcae
  191443: 84fc9ae
  191439: 286ecc0
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 07271aa42d13378e67ebd79ea9ca1c4a5e2ad46f
+refs/heads/master: e330b3bcd83199dd63a819d8d12e40f9edae6c77

trunk/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);