[RFC][PATCH] trace: Add trace points for tasklet entry/exit

[John Stultz]

From: Lingutla Chandrasekhar <clingutla@xxxxxxxxxxxxxx>

Tasklets are supposed to finish their work quickly and
should not block the current running process, but it is not
guaranteed that. Currently softirq_entry/exit can be used to
know total tasklets execution time, but not helpful to track
individual tasklet's execution time. With that we can't find
any culprit tasklet function, which is taking more time.

Add tasklet_entry/exit trace point support to track
individual tasklet execution.

This patch has been carried in the Android tree for awhile
so I wanted to submit it for review upstream. Feedback would
be appreciated!

Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Cc: Connor O'Brien <connoro@xxxxxxxxxx>
Cc: kernel-team@xxxxxxxxxxx
Signed-off-by: Lingutla Chandrasekhar <clingutla@xxxxxxxxxxxxxx>
[elavila: Port to android-mainline]
Signed-off-by: J. Avila <elavila@xxxxxxxxxx>
[jstultz: Rebased to upstream, cut unused trace points, added
 comments for the tracepoints, reworded commit]
Signed-off-by: John Stultz <jstultz@xxxxxxxxxx>
---
 include/trace/events/irq.h | 43 ++++++++++++++++++++++++++++++++++++++
 kernel/softirq.c           |  9 ++++++--
 2 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/include/trace/events/irq.h b/include/trace/events/irq.h
index eeceafaaea4c..da85851d4ec1 100644
--- a/include/trace/events/irq.h
+++ b/include/trace/events/irq.h
@@ -160,6 +160,49 @@ DEFINE_EVENT(softirq, softirq_raise,
 	TP_ARGS(vec_nr)
 );
 
+DECLARE_EVENT_CLASS(tasklet,
+
+	TP_PROTO(void *func),
+
+	TP_ARGS(func),
+
+	TP_STRUCT__entry(
+		__field(	void *,	func)
+	),
+
+	TP_fast_assign(
+		__entry->func = func;
+	),
+
+	TP_printk("function=%ps", __entry->func)
+);
+
+/**
+ * tasklet_entry - called immediately before the tasklet is run
+ * @func:  tasklet callback or function being run
+ *
+ * Used to find individual tasklet execution time
+ */
+DEFINE_EVENT(tasklet, tasklet_entry,
+
+	TP_PROTO(void *func),
+
+	TP_ARGS(func)
+);
+
+/**
+ * tasklet_exit - called immediately after the tasklet is run
+ * @func:  tasklet callback or function being run
+ *
+ * Used to find individual tasklet execution time
+ */
+DEFINE_EVENT(tasklet, tasklet_exit,
+
+	TP_PROTO(void *func),
+
+	TP_ARGS(func)
+);
+
 #endif /*  _TRACE_IRQ_H */
 
 /* This part must be outside protection */
diff --git a/kernel/softirq.c b/kernel/softirq.c
index c8a6913c067d..dbd322524171 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -793,10 +793,15 @@ static void tasklet_action_common(struct softirq_action *a,
 		if (tasklet_trylock(t)) {
 			if (!atomic_read(&t->count)) {
 				if (tasklet_clear_sched(t)) {
-					if (t->use_callback)
+					if (t->use_callback) {
+						trace_tasklet_entry(t->callback);
 						t->callback(t);
-					else
+						trace_tasklet_exit(t->callback);
+					} else {
+						trace_tasklet_entry(t->func);
 						t->func(t->data);
+						trace_tasklet_exit(t->func);
+					}
 				}
 				tasklet_unlock(t);
 				continue;
-- 
2.39.0.rc1.256.g54fd8350bd-goog