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sched/fair: Remove SIS_AVG_CPU

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SIS_AVG_CPU was introduced as a means of avoiding a search when the
average search cost indicated that the search would likely fail. It was
a blunt instrument and disabled by commit 4c77b18cf8 ("sched/fair: Make
select_idle_cpu() more aggressive") and later replaced with a proportional
search depth by commit 1ad3aaf3fc ("sched/core: Implement new approach
to scale select_idle_cpu()").

While there are corner cases where SIS_AVG_CPU is better, it has now been
disabled for almost three years. As the intent of SIS_PROP is to reduce
the time complexity of select_idle_cpu(), lets drop SIS_AVG_CPU and focus
on SIS_PROP as a throttling mechanism.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Link: https://lkml.kernel.org/r/20210125085909.4600-2-mgorman@techsingularity.net
This commit is contained in:
Mel Gorman 2021-01-25 08:59:06 +00:00 committed by Peter Zijlstra
parent 1875dc5b8f
commit e6e0dc2d54
2 changed files with 10 additions and 13 deletions
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22
kernel/sched/fair.c
View file

@ -6158,7 +6158,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
{
struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
struct sched_domain *this_sd;
u64 avg_cost, avg_idle;
u64 time;
int this = smp_processor_id();
int cpu, nr = INT_MAX;
@ -6167,18 +6166,17 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
if (!this_sd)
return -1;
/*
* Due to large variance we need a large fuzz factor; hackbench in
* particularly is sensitive here.
*/
avg_idle = this_rq()->avg_idle / 512;
avg_cost = this_sd->avg_scan_cost + 1;
if (sched_feat(SIS_AVG_CPU) && avg_idle < avg_cost)
return -1;
if (sched_feat(SIS_PROP)) {
u64 span_avg = sd->span_weight * avg_idle;
u64 avg_cost, avg_idle, span_avg;
/*
* Due to large variance we need a large fuzz factor;
* hackbench in particularly is sensitive here.
*/
avg_idle = this_rq()->avg_idle / 512;
avg_cost = this_sd->avg_scan_cost + 1;
span_avg = sd->span_weight * avg_idle;
if (span_avg > 4*avg_cost)
nr = div_u64(span_avg, avg_cost);
else

1
kernel/sched/features.h
View file

@ -54,7 +54,6 @@ SCHED_FEAT(TTWU_QUEUE, true)
/*
* When doing wakeups, attempt to limit superfluous scans of the LLC domain.
*/
SCHED_FEAT(SIS_AVG_CPU, false)
SCHED_FEAT(SIS_PROP, true)
/*