sched: x86: allow single-depth wchan output

sched.o gets smaller and faster if we compile it with -fomit-frame-pointers,
so make this a config option. The cost is the loss of multi-depth wchan
lookups - but SysRq-T is a sufficient replacement for them anyway, so their
utility is much lower these days.

the size difference is significant:

   text    data     bss     dec     hex filename
  34005    3462      24   37491    9273 sched.o.before
  33470    3462      24   36956    905c sched.o.after
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>

arch/i386/Kconfig

@@ -214,6 +214,17 @@ config X86_ES7000
 
 endchoice
 
+config SCHED_NO_NO_OMIT_FRAME_POINTER
+	bool "Single-depth WCHAN output"
+	default y
+	help
+	  Calculate simpler /proc/<PID>/wchan values. If this option
+	  is disabled then wchan values will recurse back to the
+	  caller function. This provides more accurate wchan values,
+	  at the expense of slightly more scheduling overhead.
+
+	  If in doubt, say "Y".
+
 config PARAVIRT
 	bool "Paravirtualization support (EXPERIMENTAL)"
 	depends on EXPERIMENTAL