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Commit e0f5f3af authored by Dietmar Eggemann's avatar Dietmar Eggemann Committed by Ingo Molnar
Browse files

sched/fair: Make load tracking frequency scale-invariant 



Apply frequency scaling correction factor to per-entity load tracking to
make it frequency invariant. Currently, load appears bigger when the CPU
is running slower which affects load-balancing decisions.

Each segment of the sched_avg.load_sum geometric series is now scaled by
the current frequency so that the sched_avg.load_avg of each sched entity
will be invariant from frequency scaling.

Moreover, cfs_rq.runnable_load_sum is scaled by the current frequency as
well.

Signed-off-by: default avatarDietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: default avatarMorten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: default avatarVincent Guittot <vincent.guittot@linaro.org>
Cc: Dietmar Eggemann <Dietmar.Eggemann@arm.com>
Cc: Juri Lelli <Juri.Lelli@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: daniel.lezcano@linaro.org
Cc: mturquette@baylibre.com
Cc: pang.xunlei@zte.com.cn
Cc: rjw@rjwysocki.net
Cc: sgurrappadi@nvidia.com
Cc: yuyang.du@intel.com
Link: http://lkml.kernel.org/r/1439569394-11974-2-git-send-email-morten.rasmussen@arm.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 2a595721

include/linux/sched.h

+3 −3
Original line number Diff line number Diff line
@@ -1177,9 +1177,9 @@ struct load_weight { 


/*

 * The load_avg/util_avg accumulates an infinite geometric series.

 * 1) load_avg factors the amount of time that a sched_entity is

 * runnable on a rq into its weight. For cfs_rq, it is the aggregated

 * such weights of all runnable and blocked sched_entities.

 * 1) load_avg factors frequency scaling into the amount of time that a

 * sched_entity is runnable on a rq into its weight. For cfs_rq, it is the

 * aggregated such weights of all runnable and blocked sched_entities.

 * 2) util_avg factors frequency scaling into the amount of time

 * that a sched_entity is running on a CPU, in the range [0..SCHED_LOAD_SCALE].

 * For cfs_rq, it is the aggregated such times of all runnable and

kernel/sched/fair.c

+17 −10
Original line number Diff line number Diff line
@@ -2515,6 +2515,8 @@ static u32 __compute_runnable_contrib(u64 n) 
	return contrib + runnable_avg_yN_sum[n];

}



#define scale(v, s) ((v)*(s) >> SCHED_CAPACITY_SHIFT)



/*

 * We can represent the historical contribution to runnable average as the

 * coefficients of a geometric series.  To do this we sub-divide our runnable
@@ -2547,9 +2549,9 @@ static __always_inline int 
__update_load_avg(u64 now, int cpu, struct sched_avg *sa,

		  unsigned long weight, int running, struct cfs_rq *cfs_rq)

{

	u64 delta, periods;

	u64 delta, scaled_delta, periods;

	u32 contrib;

	int delta_w, decayed = 0;

	int delta_w, scaled_delta_w, decayed = 0;

	unsigned long scale_freq = arch_scale_freq_capacity(NULL, cpu);



	delta = now - sa->last_update_time;
@@ -2585,13 +2587,16 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa, 
		 * period and accrue it.

		 */

		delta_w = 1024 - delta_w;

		scaled_delta_w = scale(delta_w, scale_freq);

		if (weight) {

			sa->load_sum += weight * delta_w;

			if (cfs_rq)

				cfs_rq->runnable_load_sum += weight * delta_w;

			sa->load_sum += weight * scaled_delta_w;

			if (cfs_rq) {

				cfs_rq->runnable_load_sum +=

						weight * scaled_delta_w;

			}

		}

		if (running)

			sa->util_sum += delta_w * scale_freq >> SCHED_CAPACITY_SHIFT;

			sa->util_sum += scaled_delta_w;



		delta -= delta_w;
@@ -2608,23 +2613,25 @@ __update_load_avg(u64 now, int cpu, struct sched_avg *sa, 


		/* Efficiently calculate \sum (1..n_period) 1024*y^i */

		contrib = __compute_runnable_contrib(periods);

		contrib = scale(contrib, scale_freq);

		if (weight) {

			sa->load_sum += weight * contrib;

			if (cfs_rq)

				cfs_rq->runnable_load_sum += weight * contrib;

		}

		if (running)

			sa->util_sum += contrib * scale_freq >> SCHED_CAPACITY_SHIFT;

			sa->util_sum += contrib;

	}



	/* Remainder of delta accrued against u_0` */

	scaled_delta = scale(delta, scale_freq);

	if (weight) {

		sa->load_sum += weight * delta;

		sa->load_sum += weight * scaled_delta;

		if (cfs_rq)

			cfs_rq->runnable_load_sum += weight * delta;

			cfs_rq->runnable_load_sum += weight * scaled_delta;

	}

	if (running)

		sa->util_sum += delta * scale_freq >> SCHED_CAPACITY_SHIFT;

		sa->util_sum += scaled_delta;



	sa->period_contrib += delta;