tracing: Add "last_func_repeats" to struct trace_array

The field is used to keep track of the consecutive (on the same CPU) calls
of a single function. This information is needed in order to consolidate
the function tracing record in the cases when a single function is called
number of times.

Link: https://lkml.kernel.org/r/20210415181854.147448-4-y.karadz@gmail.com

Signed-off-by: Yordan Karadzhov (VMware) <y.karadz@gmail.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -9104,6 +9104,7 @@ static int __remove_instance(struct trace_array *tr)
 	ftrace_clear_pids(tr);
 	ftrace_destroy_function_files(tr);
 	tracefs_remove(tr->dir);
+	free_percpu(tr->last_func_repeats);
 	free_trace_buffers(tr);
 
 	for (i = 0; i < tr->nr_topts; i++) {

kernel/trace/trace.h

@@ -262,6 +262,17 @@ struct cond_snapshot {
 	cond_update_fn_t		update;
 };
 
+/*
+ * struct trace_func_repeats - used to keep track of the consecutive
+ * (on the same CPU) calls of a single function.
+ */
+struct trace_func_repeats {
+	unsigned long	ip;
+	unsigned long	parent_ip;
+	unsigned long	count;
+	u64		ts_last_call;
+};
+
 /*
  * The trace array - an array of per-CPU trace arrays. This is the
  * highest level data structure that individual tracers deal with.
@@ -358,6 +369,7 @@ struct trace_array {
 #ifdef CONFIG_TRACER_SNAPSHOT
 	struct cond_snapshot	*cond_snapshot;
 #endif
+	struct trace_func_repeats	__percpu *last_func_repeats;
 };
 
 enum {