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nohz: Warn if the machine can not perform nohz_full

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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>
This commit is contained in:
Steven Rostedt 2013-05-10 17:12:28 -04:00 committed by Frederic Weisbecker
parent 7d13205581
commit e12d027177
1 changed files with 5 additions and 0 deletions
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5
kernel/time/tick-sched.c
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@ -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