linux-kernel - [RFA][PATCH] ftrace/x86: Have function graph tracer use its own trampoline

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Date:	Wed, 16 Jul 2014 11:06:15 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: [RFA][PATCH] ftrace/x86: Have function graph tracer use its own
 trampoline

Peter,

Here's a really trivial patch that touches arch/x86/include/asm/ftrace.h

Can you ack it. Thanks.

This is based on the patches here:

  http://marc.info/?l=linux-kernel&m=140513619913439&w=2

Thanks,

-- Steve

>From 32443f104c172cc368882101cd65604dc046f099 Mon Sep 17 00:00:00 2001
From: "Steven Rostedt (Red Hat)" <rostedt@...dmis.org>
Date: Fri, 11 Jul 2014 23:23:53 -0400
Subject: [PATCH] ftrace/x86: Have function graph tracer use its own trampoline

The function graph trampoline is called from the function trampoline
and both do a save and restore of registers. The save of registers
done by the function trampoline when only the function graph tracer
is running is a waste of CPU cycles.

As the function graph tracer trampoline in x86 is dependent from
the function trampoline, we can call it directly when a function
is only being traced by the function graph trampoline.

Cc: "H. Peter Anvin" <hpa@...or.com>
Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
---
 arch/x86/include/asm/ftrace.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/x86/include/asm/ftrace.h b/arch/x86/include/asm/ftrace.h
index 0525a8b..e1f7fec 100644
--- a/arch/x86/include/asm/ftrace.h
+++ b/arch/x86/include/asm/ftrace.h
@@ -68,6 +68,8 @@ struct dyn_arch_ftrace {

 int ftrace_int3_handler(struct pt_regs *regs);

+#define FTRACE_GRAPH_TRAMP_ADDR FTRACE_GRAPH_ADDR
+
 #endif /*  CONFIG_DYNAMIC_FTRACE */
 #endif /* __ASSEMBLY__ */
 #endif /* CONFIG_FUNCTION_TRACER */
-- 
1.8.1.4

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