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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: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Vincent 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: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Dietmar Eggemann 2015-08-14 17:23:09 +01:00 committed by Ingo Molnar
parent 2a595721a1
commit e0f5f3afd2
2 changed files with 20 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/linux/sched.h
View File

@ -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

27
kernel/sched/fair.c
View File

@ -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;