nohz: Assert existing housekeepers when nohz full enabled (7c8bb6cb) · Commits · 戴 / test

The code ensures that when nohz full is running, at least the boot CPU serves as a housekeeper and it can't be later offlined. Let's assert this assumption to make sure that we have CPUs to handle unbound jobs like workqueues and timers while nohz full CPUs run undisturbed. Also improve the comments on housekeeper offlining prevention. Signed-off-by:

Frederic Weisbecker <fweisbec@gmail.com> Acked-by:

Thomas Gleixner <tglx@linutronix.de> Cc: Chris Metcalf <cmetcalf@ezchip.com> Cc: Christoph Lameter <cl@linux.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com> Cc: Vatika Harlalka <vatikaharlalka@gmail.com> Link: http://lkml.kernel.org/r/1441119060-2230-3-git-send-email-fweisbec@gmail.com Signed-off-by:

Ingo Molnar <mingo@kernel.org>

kernel/time/tick-sched.c

+11 −4

Original line number	Original line	Diff line number	Diff line
	@@ -298,8 +298,9 @@ static int tick_nohz_cpu_down_callback(struct notifier_block *nfb,
	switch (action & ~CPU_TASKS_FROZEN) {		switch (action & ~CPU_TASKS_FROZEN) {
	case CPU_DOWN_PREPARE:		case CPU_DOWN_PREPARE:
	/*		/*
	* If we handle the timekeeping duty for full dynticks CPUs,		* The boot CPU handles housekeeping duty (unbound timers,
	* we can't safely shutdown that CPU.		* workqueues, timekeeping, ...) on behalf of full dynticks
			* CPUs. It must remain online when nohz full is enabled.
	*/		*/
	if (tick_nohz_full_running && tick_do_timer_cpu == cpu)		if (tick_nohz_full_running && tick_do_timer_cpu == cpu)
	return NOTIFY_BAD;		return NOTIFY_BAD;
	@@ -370,6 +371,12 @@ void __init tick_nohz_init(void)
	cpu_notifier(tick_nohz_cpu_down_callback, 0);		cpu_notifier(tick_nohz_cpu_down_callback, 0);
	pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",		pr_info("NO_HZ: Full dynticks CPUs: %*pbl.\n",
	cpumask_pr_args(tick_nohz_full_mask));		cpumask_pr_args(tick_nohz_full_mask));

			/*
			* We need at least one CPU to handle housekeeping work such
			* as timekeeping, unbound timers, workqueues, ...
			*/
			WARN_ON_ONCE(cpumask_empty(housekeeping_mask));
	}		}
	#endif		#endif

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