rcu: Add event-tracing for RCU callback invocation

There was recently some controversy about the overhead of invoking RCU
callbacks.  Add TRACE_EVENT()s to obtain fine-grained timings for the
start and stop of a batch of callbacks and also for each callback invoked.

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

1 files changed, 98 insertions, 0 deletions

diff --git a/include/trace/events/rcu.h b/include/trace/events/rcu.h
new file mode 100644
index 000000000000..db3f6e9e63e6
--- /dev/null
+++ b/include/trace/events/rcu.h
@@ -0,0 +1,98 @@
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM rcu
+
+#if !defined(_TRACE_RCU_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_RCU_H
+
+#include <linux/tracepoint.h>
+
+/*
+ * Tracepoint for calling rcu_do_batch, performed to start callback invocation:
+ */
+TRACE_EVENT(rcu_batch_start,
+
+        TP_PROTO(long callbacks_ready, int blimit),
+
+        TP_ARGS(callbacks_ready, blimit),
+
+        TP_STRUCT__entry(
+                __field(        long,   callbacks_ready         )
+                __field(        int,    blimit                  )
+        ),
+
+        TP_fast_assign(
+                __entry->callbacks_ready        = callbacks_ready;
+                __entry->blimit                 = blimit;
+        ),
+
+        TP_printk("CBs=%ld bl=%d", __entry->callbacks_ready, __entry->blimit)
+);
+
+/*
+ * Tracepoint for the invocation of a single RCU callback
+ */
+TRACE_EVENT(rcu_invoke_callback,
+
+        TP_PROTO(struct rcu_head *rhp),
+
+        TP_ARGS(rhp),
+
+        TP_STRUCT__entry(
+                __field(        void *, rhp     )
+                __field(        void *, func    )
+        ),
+
+        TP_fast_assign(
+                __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
+ */
+TRACE_EVENT(rcu_invoke_kfree_callback,
+
+        TP_PROTO(struct rcu_head *rhp, unsigned long offset),
+
+        TP_ARGS(rhp, offset),
+
+        TP_STRUCT__entry(
+                __field(void *, rhp     )
+                __field(unsigned long,  offset  )
+        ),
+
+        TP_fast_assign(
+                __entry->rhp    = rhp;
+                __entry->offset = offset;
+        ),
+
+        TP_printk("rhp=%p func=%ld", __entry->rhp, __entry->offset)
+);
+
+/*
+ * Tracepoint for leaving rcu_do_batch, performed after callback invocation:
+ */
+TRACE_EVENT(rcu_batch_end,
+
+        TP_PROTO(int callbacks_invoked),
+
+        TP_ARGS(callbacks_invoked),
+
+        TP_STRUCT__entry(
+                __field(        int,    callbacks_invoked               )
+        ),
+
+        TP_fast_assign(
+                __entry->callbacks_invoked      = callbacks_invoked;
+        ),
+
+        TP_printk("CBs-invoked=%d", __entry->callbacks_invoked)
+);
+
+#endif /* _TRACE_RCU_H */
+
+/* This part must be outside protection */
+#include <trace/define_trace.h>