From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Andrew Morton <akpm@linux-foundation.org>,
Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@gmail.com>
Subject: [for-next][PATCH 12/12] ftrace: Fix stddev calculation in function profiler
Date: Wed, 19 Jun 2013 23:35:28 -0400 [thread overview]
Message-ID: <20130620033640.383727161@goodmis.org> (raw)
In-Reply-To: 20130620033516.003166252@goodmis.org
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[-- Attachment #1: 0012-ftrace-Fix-stddev-calculation-in-function-profiler.patch --]
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From: Juri Lelli <juri.lelli@gmail.com>
When FUNCTION_GRAPH_TRACER is enabled, ftrace can profile kernel functions
and print basic statistics about them. Unfortunately, running stddev
calculation is wrong. This patch corrects it implementing Welford’s method:
s^2 = 1 / (n * (n-1)) * (n * \Sum (x_i)^2 - (\Sum x_i)^2) .
Link: http://lkml.kernel.org/r/1371031398-24048-1-git-send-email-juri.lelli@gmail.com
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Juri Lelli <juri.lelli@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/ftrace.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 800a8a2..26e1910 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);
--
1.7.10.4
prev parent reply other threads:[~2013-06-20 3:36 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-06-20 3:35 [for-next][PATCH 00/12] tracing: Updates and minor fixes for 3.11 Steven Rostedt
2013-06-20 3:35 ` [for-next][PATCH 01/12] tracing: Add function probe to trigger a ftrace dump to console Steven Rostedt
2013-06-20 3:35 ` [for-next][PATCH 02/12] tracing: Add function probe to trigger a ftrace dump of current CPU trace Steven Rostedt
2013-06-20 3:35 ` [for-next][PATCH 03/12] tracing/trivial: Consolidate error return condition Steven Rostedt
2013-06-20 3:35 ` [for-next][PATCH 04/12] tracing: Fix file mode of free_buffer Steven Rostedt
2013-06-20 3:35 ` [for-next][PATCH 05/12] ftrace: Use schedule_on_each_cpu() as a heavy synchronize_sched() Steven Rostedt
2013-06-20 3:35 ` [for-next][PATCH 06/12] ftrace: Remove ftrace_regex_lseek() Steven Rostedt
2013-06-20 3:35 ` [for-next][PATCH 07/12] tracing: Do not call kmem_cache_free() on allocation failure Steven Rostedt
2013-06-20 3:35 ` [for-next][PATCH 08/12] tracing: Add binary & filter for events Steven Rostedt
2013-06-20 8:09 ` Arend van Spriel
2013-06-20 12:14 ` Steven Rostedt
2013-06-20 18:28 ` Arend van Spriel
2013-06-20 18:34 ` Steven Rostedt
2013-06-20 18:38 ` Steven Rostedt
2013-06-20 19:15 ` Arend van Spriel
2013-06-20 3:35 ` [for-next][PATCH 09/12] tracing: Update documentation on tracepoint glob matching Steven Rostedt
2013-06-20 3:35 ` [for-next][PATCH 10/12] tracing: Disable tracing on warning Steven Rostedt
2013-06-20 3:35 ` [for-next][PATCH 11/12] tracing/kprobes: Remove unnecessary checking of trace_probe_is_enabled Steven Rostedt
2013-06-20 3:35 ` Steven Rostedt [this message]
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