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From: Peter Zijlstra <peterz@infradead.org>
To: mingo@kernel.org, linux-kernel@vger.kernel.org
Cc: subhra.mazumdar@oracle.com, steven.sistare@oracle.com,
	dhaval.giani@oracle.com, rohit.k.jain@oracle.com,
	umgwanakikbuti@gmail.com, matt@codeblueprint.co.uk,
	riel@surriel.com, peterz@infradead.org
Subject: [RFC 03/11] sched/fair: Only use time once
Date: Wed, 30 May 2018 16:22:39 +0200	[thread overview]
Message-ID: <20180530143106.029493355@infradead.org> (raw)
In-Reply-To: <20180530142236.667774973@infradead.org>

[-- Attachment #1: peterz-sis-again-3.patch --]
[-- Type: text/plain, Size: 2026 bytes --]

The goal is to not spend more time scanning for idle CPUs than we're
idle for. Otherwise we're inhibiting work.

This means that we need to consider the cost over all the wakeups
between consequtive idle periods.

Combined AGE+ONCE work better than the old code:

ORIG

1:        0.559639567 seconds time elapsed    ( +-  1.44% )
2:        0.630091207 seconds time elapsed    ( +-  2.93% )
5:        2.329768398 seconds time elapsed    ( +-  1.21% )
10:       3.920248646 seconds time elapsed    ( +-  2.39% )
20:       6.501776759 seconds time elapsed    ( +-  1.02% )
40:      10.482109619 seconds time elapsed    ( +-  2.16% )

AGE+ONCE

1:        0.546238431 seconds time elapsed    ( +-  0.84% )
2:        0.620581405 seconds time elapsed    ( +-  1.26% )
5:        2.161288964 seconds time elapsed    ( +-  1.90% )
10:       3.514636966 seconds time elapsed    ( +-  1.82% )
20:       6.228234657 seconds time elapsed    ( +-  0.67% )
40:       9.755615438 seconds time elapsed    ( +-  2.20% )

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/fair.c     |   15 +++++++++++++++
 kernel/sched/features.h |    1 +
 2 files changed, 16 insertions(+)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6429,6 +6429,21 @@ static int select_idle_cpu(struct task_s
 	}
 
 	time = local_clock() - time;
+
+	if (sched_feat(SIS_ONCE)) {
+		struct rq *this_rq = this_rq();
+
+		/*
+		 * We need to consider the cost of all wakeups between
+		 * consequtive idle periods. We can only use the predicted
+		 * idle time once.
+		 */
+		if (this_rq->wake_avg > time)
+			this_rq->wake_avg -= time;
+		else
+			this_rq->wake_avg = 0;
+	}
+
 	time = div_u64(time, loops);
 	cost = this_sd->avg_scan_cost;
 	delta = (s64)(time - cost) / 8;
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -59,6 +59,7 @@ SCHED_FEAT(SIS_AVG_CPU, false)
 SCHED_FEAT(SIS_PROP, true)
 
 SCHED_FEAT(SIS_AGE, true)
+SCHED_FEAT(SIS_ONCE, true)
 
 /*
  * Issue a WARN when we do multiple update_rq_clock() calls

  parent reply	other threads:[~2018-05-30 14:37 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-05-30 14:22 [RFC 00/11] select_idle_sibling rework Peter Zijlstra
2018-05-30 14:22 ` [RFC 01/11] sched/fair: Fix select_idle_cpu()s cost accounting Peter Zijlstra
2018-05-30 14:22 ` [RFC 02/11] sched/fair: Age the average idle time Peter Zijlstra
2018-05-30 14:22 ` Peter Zijlstra [this message]
2018-05-30 14:22 ` [RFC 04/11] sched/topology: Introduce sched_domain_cores() Peter Zijlstra
2018-05-30 14:22 ` [RFC 05/11] sched/fair: Re-arrange select_idle_cpu() Peter Zijlstra
2018-05-30 14:22 ` [RFC 06/11] sched/fair: Make select_idle_cpu() proportional to cores Peter Zijlstra
2018-05-30 14:22 ` [RFC 07/11] sched/fair: Fold the select_idle_sibling() scans Peter Zijlstra
2018-05-30 14:22 ` [RFC 08/11] sched/fair: Optimize SIS_FOLD Peter Zijlstra
2018-05-30 14:22 ` [RFC 09/11] sched/fair: Remove SIS_AVG_PROP Peter Zijlstra
2018-05-30 14:22 ` [RFC 10/11] sched/fair: Remove SIS_AGE/SIS_ONCE Peter Zijlstra
2018-05-30 14:22 ` [RFC 11/11] sched/fair: Remove SIS_FOLD Peter Zijlstra
2018-06-19 22:06 ` [RFC 00/11] select_idle_sibling rework Matt Fleming
2018-06-20 22:20   ` Steven Sistare

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