rcu: Add tracing for RCU_FAST_NO_HZ

This commit adds trace_rcu_prep_idle(), which is invoked from
rcu_prepare_for_idle() and rcu_wake_cpu() to trace attempts on
the part of RCU to force CPUs into 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, 37 insertions, 0 deletions

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
index 7f6877a35051..debe453c9623 100644
--- a/include/trace/events/rcu.h
+++ b/include/trace/events/rcu.h
@@ -275,6 +275,42 @@ TRACE_EVENT(rcu_dyntick,
 );
 
 /*
+ * Tracepoint for RCU preparation for idle, the goal being to get RCU
+ * processing done so that the current CPU can shut off its scheduling
+ * clock and enter dyntick-idle mode.  One way to accomplish this is
+ * to drain all RCU callbacks from this CPU, and the other is to have
+ * done everything RCU requires for the current grace period.  In this
+ * latter case, the CPU will be awakened at the end of the current grace
+ * period in order to process the remainder of its callbacks.
+ *
+ * These tracepoints take a string as argument:
+ *
+ *	"No callbacks": Nothing to do, no callbacks on this CPU.
+ *	"In holdoff": Nothing to do, holding off after unsuccessful attempt.
+ *	"Dyntick with callbacks": Callbacks remain, but RCU doesn't need CPU.
+ *	"Begin holdoff": Attempt failed, don't retry until next jiffy.
+ *	"More callbacks": Still more callbacks, try again to clear them out.
+ *	"Callbacks drained": All callbacks processed, off to dyntick idle!
+ *	"CPU awakened at GP end":
+ */
+TRACE_EVENT(rcu_prep_idle,
+
+	TP_PROTO(char *reason),
+
+	TP_ARGS(reason),
+
+	TP_STRUCT__entry(
+		__field(char *, reason)
+	),
+
+	TP_fast_assign(
+		__entry->reason = reason;
+	),
+
+	TP_printk("%s", __entry->reason)
+);
+
+/*
  * Tracepoint for the registration of a single RCU callback function.
  * The first argument is the type of RCU, the second argument is
  * a pointer to the RCU callback itself, and the third element is the
@@ -482,6 +518,7 @@ TRACE_EVENT(rcu_torture_read,
 #define trace_rcu_quiescent_state_report(rcuname, gpnum, mask, qsmask, level, grplo, grphi, gp_tasks) do { } while (0)
 #define trace_rcu_fqs(rcuname, gpnum, cpu, qsevent) do { } while (0)
 #define trace_rcu_dyntick(polarity, oldnesting, newnesting) do { } while (0)
+#define trace_rcu_prep_idle(reason) do { } while (0)
 #define trace_rcu_callback(rcuname, rhp, qlen) do { } while (0)
 #define trace_rcu_kfree_callback(rcuname, rhp, offset, qlen) do { } while (0)
 #define trace_rcu_batch_start(rcuname, qlen, blimit) do { } while (0)