commit bb7253403f7a4670a128e4c080fd8ea1bd4d5029
author Steven Rostedt <srostedt@redhat.com> Wed Feb 11 12:45:49 2009 -0800
committer Benjamin Herrenschmidt <benh@kernel.crashing.org> Mon Feb 23 10:48:54 2009 +1100
tree f2ee8c966035a67be77fad922ada4c4d52a53be9
parent 465428884765b43d642a967915e16c6c7cacbe8e

powerpc64, ftrace: save toc only on modules for function graph

The TOCS used by modules are different than the one used by
the core kernel code. The function graph tracer must save and
restore the TOC whenever it traces a module call. But this
is an added overhead to burden the majority of core kernel
code being traced.

Benjamin Herrenschmidt suggested in testing the entry of
the call to tell if it is a core kernel function or a module.
He recommended using the REGION_ID() macro to perform this test.

This patch implements Benjamin's idea, and uses a different
return_to_handler routine dependent on if the entry is a core
kernel function or not. The module version saves the TOC, where as
the core kernel version does not.

Geoff Lavand tested on PS3.

Tested-by: Geoff Levand <geoffrey.levand@am.sony.com>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/ftrace.c

diff --git a/arch/powerpc/kernel/ftrace.c b/arch/powerpc/kernel/ftrace.c
index 7538b94..5c6dfa9 100644
--- a/arch/powerpc/kernel/ftrace.c
+++ b/arch/powerpc/kernel/ftrace.c
@@ -567,6 +567,10 @@
 }
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
+#ifdef CONFIG_PPC64
+extern void mod_return_to_handler(void);
+#endif
+
 /*
  * Hook the return address and push it in the stack of return addrs
  * in current thread info.
@@ -577,12 +581,17 @@
 	unsigned long long calltime;
 	int faulted;
 	struct ftrace_graph_ent trace;
-	unsigned long return_hooker = (unsigned long)
-				&return_to_handler;
+	unsigned long return_hooker = (unsigned long)&return_to_handler;
 
 	if (unlikely(atomic_read(&current->tracing_graph_pause)))
 		return;
 
+#if CONFIG_PPC64
+	/* non core kernel code needs to save and restore the TOC */
+	if (REGION_ID(self_addr) != KERNEL_REGION_ID)
+		return_hooker = (unsigned long)&mod_return_to_handler;
+#endif
+
 	return_hooker = GET_ADDR(return_hooker);
 
 	/*