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Commit 4ec4412e authored by Vincent Guittot's avatar Vincent Guittot Committed by Ingo Molnar
Browse files

sched: Ensure cpu_power periodic update 



With a lot of small tasks, the softirq sched is nearly never called
when no_hz is enabled. In this case load_balance() is mainly called
with the newly_idle mode which doesn't update the cpu_power.

Add a next_update field which ensure a maximum update period when
there is short activity.

Having stale cpu_power information can skew the load-balancing
decisions, this is cured by the guaranteed update.

Signed-off-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1323717668-2143-1-git-send-email-vincent.guittot@linaro.org
parent 39be3501

include/linux/sched.h

+1 −0
Original line number Diff line number Diff line
@@ -905,6 +905,7 @@ struct sched_group_power { 
	 * single CPU.

	 */

	unsigned int power, power_orig;

	unsigned long next_update;

	/*

	 * Number of busy cpus in this group.

	 */

kernel/sched/fair.c

+16 −8
Original line number Diff line number Diff line
@@ -215,6 +215,8 @@ calc_delta_mine(unsigned long delta_exec, unsigned long weight, 


const struct sched_class fair_sched_class;



static unsigned long __read_mostly max_load_balance_interval = HZ/10;



/**************************************************************

 * CFS operations on generic schedulable entities:

 */
@@ -3776,6 +3778,11 @@ void update_group_power(struct sched_domain *sd, int cpu) 
	struct sched_domain *child = sd->child;

	struct sched_group *group, *sdg = sd->groups;

	unsigned long power;

	unsigned long interval;



	interval = msecs_to_jiffies(sd->balance_interval);

	interval = clamp(interval, 1UL, max_load_balance_interval);

	sdg->sgp->next_update = jiffies + interval;



	if (!child) {

		update_cpu_power(sd, cpu);
@@ -3883,12 +3890,15 @@ static inline void update_sg_lb_stats(struct sched_domain *sd, 
	 * domains. In the newly idle case, we will allow all the cpu's

	 * to do the newly idle load balance.

	 */

	if (idle != CPU_NEWLY_IDLE && local_group) {

	if (local_group) {

		if (idle != CPU_NEWLY_IDLE) {

			if (balance_cpu != this_cpu) {

				*balance = 0;

				return;

			}

			update_group_power(sd, this_cpu);

		} else if (time_after_eq(jiffies, group->sgp->next_update))

			update_group_power(sd, this_cpu);

	}



	/* Adjust by relative CPU power of the group */
@@ -4945,8 +4955,6 @@ static int __cpuinit sched_ilb_notifier(struct notifier_block *nfb, 


static DEFINE_SPINLOCK(balancing);



static unsigned long __read_mostly max_load_balance_interval = HZ/10;



/*

 * Scale the max load_balance interval with the number of CPUs in the system.

 * This trades load-balance latency on larger machines for less cross talk.