perf: Optimize perf_disable

Currently we always call hw_perf_disable(), even if its already disabled,
this seems superflous, esp. since it cannot be made NMI safe (see further
patches).

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: paulus@samba.org
Cc: eranian@google.com
Cc: robert.richter@amd.com
Cc: fweisbec@gmail.com
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/perf_event.c

@@ -93,25 +93,15 @@ void __weak perf_event_print_debug(void)	{ }
 
 static DEFINE_PER_CPU(int, perf_disable_count);
 
-void __perf_disable(void)
-{
-	__get_cpu_var(perf_disable_count)++;
-}
-
-bool __perf_enable(void)
-{
-	return !--__get_cpu_var(perf_disable_count);
-}
-
 void perf_disable(void)
 {
-	__perf_disable();
-	hw_perf_disable();
+	if (!__get_cpu_var(perf_disable_count)++)
+		hw_perf_disable();
 }
 
 void perf_enable(void)
 {
-	if (__perf_enable())
+	if (!--__get_cpu_var(perf_disable_count))
 		hw_perf_enable();
 }