[PATCH 1/8] ftrace: move sched_switch enable after markers

[Steven Rostedt]

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@xxxxxxxxxx>
---
 kernel/trace/trace_sched_switch.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Index: linux-tip.git/kernel/trace/trace_sched_switch.c
===================================================================
--- linux-tip.git.orig/kernel/trace/trace_sched_switch.c	2008-06-30 20:56:38.000000000 -0400
+++ linux-tip.git/kernel/trace/trace_sched_switch.c	2008-06-30 20:57:09.000000000 -0400
@@ -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)

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