From: Mel Gorman <mgorman@techsingularity•net>
To: LKML <linux-kernel@vger•kernel.org>
Cc: Barry Song <song.bao.hua@hisilicon•com>,
Juri Lelli <juri.lelli@redhat•com>,
Vincent Guittot <vincent.guittot@linaro•org>,
Peter Ziljstra <peterz@infradead•org>,
Aubrey Li <aubrey.li@linux•intel.com>,
Ingo Molnar <mingo@redhat•com>,
Mel Gorman <mgorman@techsingularity•net>,
Valentin Schneider <valentin.schneider@arm•com>,
Linux-ARM <linux-arm-kernel@lists•infradead.org>
Subject: [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU
Date: Mon, 7 Dec 2020 09:15:13 +0000 [thread overview]
Message-ID: <20201207091516.24683-2-mgorman@techsingularity.net> (raw)
In-Reply-To: <20201207091516.24683-1-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 4c77b18cf8b7 ("sched/fair: Make
select_idle_cpu() more aggressive") and later replaced with a proportional
search depth by 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>
---
kernel/sched/fair.c | 3 ---
kernel/sched/features.h | 1 -
2 files changed, 4 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 98075f9ea9a8..23934dbac635 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6161,9 +6161,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
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;
if (span_avg > 4*avg_cost)
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
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next prev parent reply other threads:[~2020-12-07 9:17 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-07 9:15 [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling Mel Gorman
2020-12-07 9:15 ` Mel Gorman [this message]
2020-12-07 15:05 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Vincent Guittot
2020-12-08 10:07 ` Dietmar Eggemann
2020-12-08 10:59 ` Mel Gorman
2020-12-08 13:24 ` Vincent Guittot
2020-12-08 13:36 ` Mel Gorman
2020-12-08 13:43 ` Vincent Guittot
2020-12-08 13:53 ` Mel Gorman
2020-12-08 14:47 ` Vincent Guittot
2020-12-08 15:12 ` Mel Gorman
2020-12-08 15:19 ` Vincent Guittot
2020-12-07 9:15 ` [PATCH 2/4] sched/fair: Do not replace recent_used_cpu with the new target Mel Gorman
2020-12-08 9:57 ` Dietmar Eggemann
2020-12-08 11:02 ` Mel Gorman
2020-12-07 9:15 ` [PATCH 3/4] sched/fair: Return an idle cpu if one is found after a failed search for an idle core Mel Gorman
2020-12-07 15:06 ` Vincent Guittot
2020-12-07 9:15 ` [PATCH 4/4] sched/fair: Avoid revisiting CPUs multiple times during select_idle_sibling Mel Gorman
2020-12-07 15:04 ` [RFC PATCH 0/4] Reduce worst-case scanning of runqueues in select_idle_sibling Vincent Guittot
2020-12-07 15:42 ` Mel Gorman
2020-12-08 2:06 ` Li, Aubrey
-- strict thread matches above, loose matches on Subject: below --
2020-12-08 15:34 [PATCH 0/4] Reduce " Mel Gorman
2020-12-08 15:34 ` [PATCH 1/4] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2020-12-08 16:13 ` Vincent Guittot
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