[PATCH] tracing, function graph: Remove the noisy output when use function graph filter

[Lai Jiangshan <laijs@cn.fujitsu.com>]

If we use function graph filter(echo some_functions >> set_graph_function)
we are only interested in the graph of some_functions.

But if a interrupt occurs when these functions are being traced(or preparing),
the graphs of the handlers of this interrupt are also recorded.
These events that we aren't interested in are totally noisy.

This patch remove them(very very seldom noise is still left,
It's OK for tracing, doesn't it?).

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
---
diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c
index 79f4bac..9c130b3 100644
--- a/kernel/trace/trace_functions_graph.c
+++ b/kernel/trace/trace_functions_graph.c
@@ -12,6 +12,8 @@
 #include <linux/slab.h>
 #include <linux/fs.h>
 
+#include <asm/irq_regs.h>
+
 #include "trace.h"
 #include "trace_output.h"
 
@@ -213,13 +215,19 @@ int trace_graph_entry(struct ftrace_graph_ent *trace)
 	int ret;
 	int cpu;
 	int pc;
+	int depth = trace->depth;
+	unsigned long long cntxt = (unsigned long)(void *)get_irq_regs();
 
 	if (!ftrace_trace_task(current))
 		return 0;
 
 	/* trace it when it is-nested-in or is a function enabled. */
-	if (!(trace->depth || ftrace_graph_addr(trace->func)))
-		return 0;
+	if (!ftrace_graph_addr(trace->func)) {
+		if (!depth || current->ret_stack[depth - 1].subtime != cntxt)
+			return 0;
+	}
+	/* We don't use subtime here, reuse it to save context. */
+	current->ret_stack[depth].subtime = cntxt;
 
 	local_irq_save(flags);
 	cpu = raw_smp_processor_id();