tracing: Show sample std dev in function profiling (e330b3bc) · Commits · 戴 / test

When combined with function graph tracing the ftrace function profiler also prints the average run time of functions. While this gives us some good information, it doesn't tell us anything about the variance of the run times of the function. This change prints out the s^2 sample standard deviation alongside the average. This change adds one entry to the profile record structure. This increases the memory footprint of the function profiler by 1/3 on a 32-bit system, and by 1/5 on a 64-bit system when function graphing is enabled, though the memory is only allocated when the profiler is turned on. During the profiling, one extra line of code adds the squared calltime to the new record entry, so this should not adversly affect performance. Note that the square of the sample standard deviation is printed because there is no sqrt implementation for unsigned long long in the kernel. Signed-off-by:

Chase Douglas <chase.douglas@canonical.com> LKML-Reference: <1272304925-2436-1-git-send-email-chase.douglas@canonical.com> [ fixed comment about ns^2 -> us^2 conversion ] Signed-off-by:

Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ftrace.c

+21 −3

Original line number	Diff line number	Diff line
		@@ -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);

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