nohz: Warn if the machine can not perform nohz_full
authorSteven Rostedt <rostedt@goodmis.org>
Fri, 10 May 2013 21:12:28 +0000 (17:12 -0400)
committerFrederic Weisbecker <fweisbec@gmail.com>
Wed, 19 Jun 2013 23:15:51 +0000 (01:15 +0200)
If the user configures NO_HZ_FULL and defines nohz_full=XXX on the
kernel command line, or enables NO_HZ_FULL_ALL, but nohz fails
due to the machine having a unstable clock, warn about it.

We do not want users thinking that they are getting the benefit
of nohz when their machine can not support it.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
kernel/time/tick-sched.c

index f4208138fbf4cd1a72791f99c31adcbea9180e3e..d87d22cb9bf2baeb31d854c3c731e70ee402f3da 100644 (file)
@@ -178,6 +178,11 @@ static bool can_stop_full_tick(void)
         */
        if (!sched_clock_stable) {
                trace_tick_stop(0, "unstable sched clock\n");
+               /*
+                * Don't allow the user to think they can get
+                * full NO_HZ with this machine.
+                */
+               WARN_ONCE(1, "NO_HZ FULL will not work with unstable sched clock");
                return false;
        }
 #endif