ftrace: trace preempt off critical timings

Add preempt off timings. A lot of kernel core code is taken from the RT patch
latency trace that was written by Ingo Molnar.

This adds "preemptoff" and "preemptirqsoff" to /debugfs/tracing/available_tracers

Now instead of just tracing irqs off, preemption off can be selected
to be recorded.

When this is selected, it shares the same files as irqs off timings.
One can either trace preemption off, irqs off, or one or the other off.

By echoing "preemptoff" into /debugfs/tracing/current_tracer, recording
of preempt off only is performed. "irqsoff" will only record the time
irqs are disabled, but "preemptirqsoff" will take the total time irqs
or preemption are disabled. Runtime switching of these options is now
supported by simpling echoing in the appropriate trace name into
/debugfs/tracing/current_tracer.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 0a20445dcbc..740c97dcf9c 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -58,4 +58,12 @@ extern void mcount(void);
 # define time_hardirqs_off(a0, a1)              do { } while (0)
 #endif
 
+#ifdef CONFIG_PREEMPT_TRACER
+  extern void notrace trace_preempt_on(unsigned long a0, unsigned long a1);
+  extern void notrace trace_preempt_off(unsigned long a0, unsigned long a1);
+#else
+# define trace_preempt_on(a0, a1)               do { } while (0)
+# define trace_preempt_off(a0, a1)              do { } while (0)
+#endif
+
 #endif /* _LINUX_FTRACE_H */