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