Commit 1c20091e authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

nohz: Wake up full dynticks CPUs when a timer gets enqueued 



Wake up a CPU when a timer list timer is enqueued there and
the target is part of the full dynticks range. Sending an IPI
to it makes it reconsidering the next timer to program on top
of recent updates.

This may later be improved by checking if the tick is really
stopped on the target. This would need some careful
synchronization though. So deal with such optimization later
and start simple.

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Namhyung Kim <namhyung.kim@lge.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
parent a382bf93

include/linux/sched.h

+2 −2
Original line number Diff line number Diff line
@@ -1851,9 +1851,9 @@ static inline void idle_task_exit(void) {} 
#endif



#if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)

extern void wake_up_idle_cpu(int cpu);

extern void wake_up_nohz_cpu(int cpu);

#else

static inline void wake_up_idle_cpu(int cpu) { }

static inline void wake_up_nohz_cpu(int cpu) { }

#endif



#ifdef CONFIG_SCHED_AUTOGROUP

kernel/sched/core.c

+19 −1
Original line number Diff line number Diff line
@@ -587,7 +587,7 @@ unlock: 
 * account when the CPU goes back to idle and evaluates the timer

 * wheel for the next timer event.

 */

void wake_up_idle_cpu(int cpu)

static void wake_up_idle_cpu(int cpu)

{

	struct rq *rq = cpu_rq(cpu);
@@ -617,6 +617,24 @@ void wake_up_idle_cpu(int cpu) 
		smp_send_reschedule(cpu);

}



static bool wake_up_extended_nohz_cpu(int cpu)

{

	if (tick_nohz_extended_cpu(cpu)) {

		if (cpu != smp_processor_id() ||

		    tick_nohz_tick_stopped())

			smp_send_reschedule(cpu);

		return true;

	}



	return false;

}



void wake_up_nohz_cpu(int cpu)

{

	if (!wake_up_extended_nohz_cpu(cpu))

		wake_up_idle_cpu(cpu);

}



static inline bool got_nohz_idle_kick(void)

{

	int cpu = smp_processor_id();

kernel/timer.c

+6 −6
Original line number Diff line number Diff line
@@ -930,14 +930,14 @@ void add_timer_on(struct timer_list *timer, int cpu) 
	debug_activate(timer, timer->expires);

	internal_add_timer(base, timer);

	/*

	 * Check whether the other CPU is idle and needs to be

	 * triggered to reevaluate the timer wheel when nohz is

	 * active. We are protected against the other CPU fiddling

	 * Check whether the other CPU is in dynticks mode and needs

	 * to be triggered to reevaluate the timer wheel.

	 * We are protected against the other CPU fiddling

	 * with the timer by holding the timer base lock. This also

	 * makes sure that a CPU on the way to idle can not evaluate

	 * the timer wheel.

	 * makes sure that a CPU on the way to stop its tick can not

	 * evaluate the timer wheel.

	 */

	wake_up_idle_cpu(cpu);

	wake_up_nohz_cpu(cpu);

	spin_unlock_irqrestore(&base->lock, flags);

}

EXPORT_SYMBOL_GPL(add_timer_on);

CRA Git | Maintained and supported by SUSTech CRA and CCSE