From: Steven Rostedt <rostedt@goodmis.org>
Date: Fri, 11 Jul 2008 00:58:09 +0000 (-0400)
Subject: ftrace: move sched_switch enable after markers
X-Git-Tag: v2.6.27-rc1~1102^2^2^2~8
X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=007c05d4d2ce42fabd58cb54ed98e0a1714d9d86;p=linux-2.6

ftrace: move sched_switch enable after markers

We have two markers now that are enabled on sched_switch. One that records
the context switching and the other that records task wake ups. Currently
we enable the tracing first and then set the markers. This causes some
confusing traces:

# tracer: sched_switch
#
#           TASK-PID   CPU#    TIMESTAMP  FUNCTION
#              | |      |          |         |
       trace-cmd-3973  [00]   115.834817:   3973:120:R   +     3:  0:S
       trace-cmd-3973  [01]   115.834910:   3973:120:R   +     6:  0:S
       trace-cmd-3973  [02]   115.834910:   3973:120:R   +     9:  0:S
       trace-cmd-3973  [03]   115.834910:   3973:120:R   +    12:  0:S
       trace-cmd-3973  [02]   115.834910:   3973:120:R   +     9:  0:S
          <idle>-0     [02]   115.834910:      0:140:R ==>  3973:120:R

Here we see that trace-cmd with PID 3973 wakes up task 9 but the next line
shows the idle task doing a context switch to task 3973.

Enabling the tracing to _after_ the markers are set creates a much saner
output:

# tracer: sched_switch
#
#           TASK-PID   CPU#    TIMESTAMP  FUNCTION
#              | |      |          |         |
          <idle>-0     [02]  7922.634225:      0:140:R ==>  4790:120:R
       trace-cmd-4789  [03]  7922.634225:      0:140:R   +  4790:120:R

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Cc: Steven Rostedt <srostedt@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---

diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
index 93a6620091..cb817a209a 100644
--- a/kernel/trace/trace_sched_switch.c
+++ b/kernel/trace/trace_sched_switch.c
@@ -227,14 +227,14 @@ void tracing_stop_cmdline_record(void)
 static void start_sched_trace(struct trace_array *tr)
 {
 	sched_switch_reset(tr);
-	tracer_enabled = 1;
 	tracing_start_cmdline_record();
+	tracer_enabled = 1;
 }
 
 static void stop_sched_trace(struct trace_array *tr)
 {
-	tracing_stop_cmdline_record();
 	tracer_enabled = 0;
+	tracing_stop_cmdline_record();
 }
 
 static void sched_switch_trace_init(struct trace_array *tr)