Commit 837c3c59 authored Jul 26, 2021 by Mel Gorman Committed by Zheng Zengkai Jul 26, 2021

sched/fair: Remove SIS_AVG_CPU

mainline inclusion
from mainline-5.12-rc1
commit e6e0dc2d
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I41A4K
CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=e6e0dc2d5497f7f3ed970052917e2923c6f453f4



---------------------------

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 4c77b18c ("sched/fair: Make
select_idle_cpu() more aggressive") and later replaced with a proportional
search depth by commit 1ad3aaf3 ("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


Signed-off-by: Zheng Zucheng <zhengzucheng@huawei.com>
Reviewed-by: Chen Hui <judy.chenhui@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>

parent 34df857d

kernel/sched/fair.c

+9 −11

Original line number	Diff line number	Diff line
		@@ -6170,7 +6170,6 @@ 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;
		@@ -6179,18 +6178,17 @@ static int select_idle_cpu(struct task_struct p, struct sched_domain sd, int t
		if (!this_sd)
		return -1;

		if (sched_feat(SIS_PROP)) {
		u64 avg_cost, avg_idle, span_avg;

		/*
		* Due to large variance we need a large fuzz factor; hackbench in
		* particularly is sensitive here.
		* 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;
		span_avg = sd->span_weight * avg_idle;
		if (span_avg > 4*avg_cost)
		nr = div_u64(span_avg, avg_cost);
		else

kernel/sched/features.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -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)

		/*