[RFC PATCH 1/6] sched: Let arch tell us if sched clock is NMI-safe

[Frederic Weisbecker <fweisbec@gmail.com>]

sched_clock() should be fast, scalable and not use any lock. As a
resuly it should be safely called from NMIs.

Now just in case there might be some implementation details proper
to some archs that make sched_clock() not reliable or not safe in NMIs,
lets provide a way through Kconfig for archs to testify about that
support.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Don Zickus <dzickus@redhat.com>
---
 arch/Kconfig |    5 +++++
 1 files changed, 5 insertions(+), 0 deletions(-)

diff --git a/arch/Kconfig b/arch/Kconfig
index 1feb169..52ad235 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -393,6 +393,11 @@ config HAVE_UNDERSCORE_SYMBOL_PREFIX
 	  Some architectures generate an _ in front of C symbols; things like
 	  module loading and assembly files need to know about this.
 
+config HAVE_SCHED_CLOCK_NMI
+	bool
+	help
+	  Architecture's sched_clock() implementation is safely callable from  NMIs.
+
 #
 # ABI hall of shame
 #
-- 
1.7.5.4