rcu: Event-trace markers for computing RCU CPU utilization

This commit adds the trace_rcu_utilization() marker that is to be
used to allow postprocessing scripts compute RCU's CPU utilization,
give or take event-trace overhead.  Note that we do not include RCU's
dyntick-idle interface because event tracing requires RCU protection,
which is not available in dyntick-idle mode.

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

1 files changed, 53 insertions, 20 deletions

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index db3f6e9..ab458eb 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -7,29 +7,58 @@
 #include <linux/tracepoint.h>
 
 /*
- * Tracepoint for calling rcu_do_batch, performed to start callback invocation:
+ * Tracepoint for start/end markers used for utilization calculations.
+ * By convention, the string is of the following forms:
+ *
+ * "Start <activity>" -- Mark the start of the specified activity,
+ *			 such as "context switch".  Nesting is permitted.
+ * "End <activity>" -- Mark the end of the specified activity.
+ */
+TRACE_EVENT(rcu_utilization,
+
+	TP_PROTO(char *s),
+
+	TP_ARGS(s),
+
+	TP_STRUCT__entry(
+		__field(char *,	s)
+	),
+
+	TP_fast_assign(
+		__entry->s = s;
+	),
+
+	TP_printk("%s", __entry->s)
+);
+
+/*
+ * Tracepoint for marking the beginning rcu_do_batch, performed to start
+ * RCU callback invocation.  The first argument is the total number of
+ * callbacks (including those that are not yet ready to be invoked),
+ * and the second argument is the current RCU-callback batch limit.
  */
 TRACE_EVENT(rcu_batch_start,
 
-	TP_PROTO(long callbacks_ready, int blimit),
+	TP_PROTO(long qlen, int blimit),
 
-	TP_ARGS(callbacks_ready, blimit),
+	TP_ARGS(qlen, blimit),
 
 	TP_STRUCT__entry(
-		__field(	long,	callbacks_ready		)
-		__field(	int,	blimit			)
+		__field(long, qlen)
+		__field(int, blimit)
 	),
 
 	TP_fast_assign(
-		__entry->callbacks_ready	= callbacks_ready;
-		__entry->blimit			= blimit;
+		__entry->qlen = qlen;
+		__entry->blimit = blimit;
 	),
 
-	TP_printk("CBs=%ld bl=%d", __entry->callbacks_ready, __entry->blimit)
+	TP_printk("CBs=%ld bl=%d", __entry->qlen, __entry->blimit)
 );
 
 /*
- * Tracepoint for the invocation of a single RCU callback
+ * Tracepoint for the invocation of a single RCU callback function.
+ * The argument is a pointer to the RCU callback itself.
  */
 TRACE_EVENT(rcu_invoke_callback,
 
@@ -38,20 +67,23 @@ TRACE_EVENT(rcu_invoke_callback,
 	TP_ARGS(rhp),
 
 	TP_STRUCT__entry(
-		__field(	void *,	rhp	)
-		__field(	void *,	func	)
+		__field(void *,	rhp)
+		__field(void *,	func)
 	),
 
 	TP_fast_assign(
-		__entry->rhp	= rhp;
-		__entry->func	= rhp->func;
+		__entry->rhp = rhp;
+		__entry->func = rhp->func;
 	),
 
 	TP_printk("rhp=%p func=%pf", __entry->rhp, __entry->func)
 );
 
 /*
- * Tracepoint for the invocation of a single RCU kfree callback
+ * Tracepoint for the invocation of a single RCU callback of the special
+ * kfree() form.  The first argument is a pointer to the RCU callback
+ * and the second argument is the offset of the callback within the
+ * enclosing RCU-protected data structure.
  */
 TRACE_EVENT(rcu_invoke_kfree_callback,
 
@@ -60,12 +92,12 @@ TRACE_EVENT(rcu_invoke_kfree_callback,
 	TP_ARGS(rhp, offset),
 
 	TP_STRUCT__entry(
-		__field(void *,	rhp	)
-		__field(unsigned long,	offset	)
+		__field(void *,	rhp)
+		__field(unsigned long, offset)
 	),
 
 	TP_fast_assign(
-		__entry->rhp	= rhp;
+		__entry->rhp = rhp;
 		__entry->offset	= offset;
 	),
 
@@ -73,7 +105,8 @@ TRACE_EVENT(rcu_invoke_kfree_callback,
 );
 
 /*
- * Tracepoint for leaving rcu_do_batch, performed after callback invocation:
+ * Tracepoint for exiting rcu_do_batch after RCU callbacks have been
+ * invoked.  The first argument is the number of callbacks actually invoked.
  */
 TRACE_EVENT(rcu_batch_end,
 
@@ -82,11 +115,11 @@ TRACE_EVENT(rcu_batch_end,
 	TP_ARGS(callbacks_invoked),
 
 	TP_STRUCT__entry(
-		__field(	int,	callbacks_invoked		)
+		__field(int, callbacks_invoked)
 	),
 
 	TP_fast_assign(
-		__entry->callbacks_invoked	= callbacks_invoked;
+		__entry->callbacks_invoked = callbacks_invoked;
 	),
 
 	TP_printk("CBs-invoked=%d", __entry->callbacks_invoked)