From: Mel Gorman <mgorman@techsingularity.net>
To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
Li Aubrey <aubrey.li@linux.intel.com>,
Qais Yousef <qais.yousef@arm.com>,
LKML <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH 1/5] sched/fair: Remove SIS_AVG_CPU
Date: Fri, 15 Jan 2021 10:08:51 +0000 [thread overview]
Message-ID: <20210115100855.23679-2-mgorman@techsingularity.net> (raw)
In-Reply-To: <20210115100855.23679-1-mgorman@techsingularity.net>
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 4c77b18cf8b7 ("sched/fair: Make
select_idle_cpu() more aggressive") and later replaced with a proportional
search depth by commit 1ad3aaf3fcd2 ("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>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
---
kernel/sched/fair.c | 20 +++++++++-----------
kernel/sched/features.h | 1 -
2 files changed, 9 insertions(+), 12 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 04a3ce20da67..9f5682aeda2e 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6145,7 +6145,6 @@ 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;
@@ -6154,18 +6153,17 @@ 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_PROP)) {
+ u64 avg_cost, avg_idle, span_avg;
- if (sched_feat(SIS_AVG_CPU) && avg_idle < avg_cost)
- 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_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
diff --git a/kernel/sched/features.h b/kernel/sched/features.h
index 68d369cba9e4..e875eabb6600 100644
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -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)
/*
--
2.26.2
next prev parent reply other threads:[~2021-01-15 10:11 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-15 10:08 [PATCH v2 0/5] Scan for an idle sibling in a single pass Mel Gorman
2021-01-15 10:08 ` Mel Gorman [this message]
2021-01-15 10:08 ` [PATCH 2/5] sched/fair: Move avg_scan_cost calculations under SIS_PROP Mel Gorman
2021-01-15 10:08 ` [PATCH 3/5] sched/fair: Make select_idle_cpu() proportional to cores Mel Gorman
2021-01-18 8:14 ` Li, Aubrey
2021-01-18 9:27 ` Mel Gorman
2021-01-15 10:08 ` [PATCH 4/5] sched/fair: Remove select_idle_smt() Mel Gorman
2021-01-15 10:08 ` [PATCH 5/5] sched/fair: Merge select_idle_core/cpu() Mel Gorman
2021-01-18 12:55 ` Li, Aubrey
2021-01-18 14:41 ` Mel Gorman
-- strict thread matches above, loose matches on Subject: below --
2021-01-19 11:22 [PATCH v3 0/5] Scan for an idle sibling in a single pass Mel Gorman
2021-01-19 11:22 ` [PATCH 1/5] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2021-01-11 15:50 [PATCH 0/5] Scan for an idle sibling in a single pass Mel Gorman
2021-01-11 15:50 ` [PATCH 1/5] sched/fair: Remove SIS_AVG_CPU Mel Gorman
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