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Commit 9642d18e authored by Vatika Harlalka's avatar Vatika Harlalka Committed by Ingo Molnar
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nohz: Affine unpinned timers to housekeepers 



The problem addressed in this patch is about affining unpinned
timers. Adaptive or Full Dynticks CPUs are currently disturbed
by unnecessary jitter due to firing of such timers on them.

This patch will affine timers to online CPUs which are not full
dynticks in NOHZ_FULL configured systems. It should not
introduce overhead in nohz full off case due to static keys.

Signed-off-by: default avatarVatika Harlalka <vatikaharlalka@gmail.com>
Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: default avatarPreeti U Murthy <preeti@linux.vnet.ibm.com>
Acked-by: default avatarThomas 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>
Link: http://lkml.kernel.org/r/1441119060-2230-2-git-send-email-fweisbec@gmail.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent e713c80a

include/linux/tick.h

+9 −0
Original line number Diff line number Diff line
@@ -147,11 +147,20 @@ static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) 
		cpumask_or(mask, mask, tick_nohz_full_mask);

}



static inline int housekeeping_any_cpu(void)

{

	return cpumask_any_and(housekeeping_mask, cpu_online_mask);

}



extern void tick_nohz_full_kick(void);

extern void tick_nohz_full_kick_cpu(int cpu);

extern void tick_nohz_full_kick_all(void);

extern void __tick_nohz_task_switch(void);

#else

static inline int housekeeping_any_cpu(void)

{

	return smp_processor_id();

}

static inline bool tick_nohz_full_enabled(void) { return false; }

static inline bool tick_nohz_full_cpu(int cpu) { return false; }

static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }

kernel/sched/core.c

+5 −2
Original line number Diff line number Diff line
@@ -623,18 +623,21 @@ int get_nohz_timer_target(void) 
	int i, cpu = smp_processor_id();

	struct sched_domain *sd;



	if (!idle_cpu(cpu))

	if (!idle_cpu(cpu) && is_housekeeping_cpu(cpu))

		return cpu;



	rcu_read_lock();

	for_each_domain(cpu, sd) {

		for_each_cpu(i, sched_domain_span(sd)) {

			if (!idle_cpu(i)) {

			if (!idle_cpu(i) && is_housekeeping_cpu(cpu)) {

				cpu = i;

				goto unlock;

			}

		}

	}



	if (!is_housekeeping_cpu(cpu))

		cpu = housekeeping_any_cpu();

unlock:

	rcu_read_unlock();

	return cpu;