MIPS: Trace: Don't trace irqsoff for the idle process

Like x86 did in arch/x86/kernel/{process_32.c,process_64.c}, also don't
trace irqsoff for idle.

If there's no useful work to be done, we don't care about the irqsoff
duration. If we trace the idle process, the max duration of irqsoff will
be the idle time and make the irqsoff tracer useless.
Signed-off-by: Wu Zhangjin <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@redhat.com>
Patchwork: http://patchwork.linux-mips.org/patch/1044/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/process.c

@@ -63,8 +63,13 @@ void __noreturn cpu_idle(void)
 
 			smtc_idle_loop_hook();
 #endif
-			if (cpu_wait)
+
+			if (cpu_wait) {
+				/* Don't trace irqs off for idle */
+				stop_critical_timings();
 				(*cpu_wait)();
+				start_critical_timings();
+			}
 		}
 #ifdef CONFIG_HOTPLUG_CPU
 		if (!cpu_online(cpu) && !cpu_isset(cpu, cpu_callin_map) &&