ftrace: Access ret_stack->subtime only in the function profiler

The subtime is used only for function profiler with function graph
tracer enabled.  Move the definition of subtime under
CONFIG_FUNCTION_PROFILER to reduce the memory usage.  Also move the
initialization of subtime into the graph entry callback.

Link: http://lkml.kernel.org/r/20160831025529.24018-1-namhyung@kernel.org

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Documentation/trace/ftrace.txt

@@ -858,11 +858,11 @@ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
 	       When enabled, it will account time the task has been
 	       scheduled out as part of the function call.
 
-  graph-time - When running function graph tracer, to include the
-  	       time to call nested functions. When this is not set,
-	       the time reported for the function will only include
-	       the time the function itself executed for, not the time
-	       for functions that it called.
+  graph-time - When running function profiler with function graph tracer,
+	       to include the time to call nested functions. When this is
+	       not set, the time reported for the function will only
+	       include the time the function itself executed for, not the
+	       time for functions that it called.
 
   record-cmd - When any event or tracer is enabled, a hook is enabled
   	       in the sched_switch trace point to fill comm cache

include/linux/ftrace.h

@@ -794,7 +794,9 @@ struct ftrace_ret_stack {
 	unsigned long ret;
 	unsigned long func;
 	unsigned long long calltime;
+#ifdef CONFIG_FUNCTION_PROFILER
 	unsigned long long subtime;
+#endif
 	unsigned long fp;
 };
 

kernel/trace/ftrace.c

@@ -872,7 +872,13 @@ function_profile_call(unsigned long ip, unsigned long parent_ip,
 #ifdef CONFIG_FUNCTION_GRAPH_TRACER
 static int profile_graph_entry(struct ftrace_graph_ent *trace)
 {
+	int index = trace->depth;
+
 	function_profile_call(trace->func, 0, NULL, NULL);
+
+	if (index >= 0 && index < FTRACE_RETFUNC_DEPTH)
+		current->ret_stack[index].subtime = 0;
+
 	return 1;
 }
 

kernel/trace/trace_functions_graph.c

@@ -170,7 +170,6 @@ ftrace_push_return_trace(unsigned long ret, unsigned long func, int *depth,
 	current->ret_stack[index].ret = ret;
 	current->ret_stack[index].func = func;
 	current->ret_stack[index].calltime = calltime;
-	current->ret_stack[index].subtime = 0;
 	current->ret_stack[index].fp = frame_pointer;
 	*depth = current->curr_ret_stack;