LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
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 02/11] sched/fair: Age the average idle time
Date: Wed, 30 May 2018 16:22:38 +0200	[thread overview]
Message-ID: <20180530143105.977759909@infradead.org> (raw)
In-Reply-To: <20180530142236.667774973@infradead.org>

[-- Attachment #1: peterz-sis-again-2.patch --]
[-- Type: text/plain, Size: 2908 bytes --]

Currently select_idle_cpu()'s proportional scheme uses the average
idle time *for when we are idle*, that is temporally challenged.

When we're not at all idle, we'll happily continue using whatever
value we did see when we did go idle. To fix this, introduce a seprate
average idle and age it (the existing value still makes sense for
things like new-idle balancing, which happens when we do go idle).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 kernel/sched/core.c     |    5 +++++
 kernel/sched/fair.c     |   29 ++++++++++++++++++++++++-----
 kernel/sched/features.h |    2 ++
 kernel/sched/sched.h    |    3 +++
 4 files changed, 34 insertions(+), 5 deletions(-)

--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1674,6 +1674,9 @@ static void ttwu_do_wakeup(struct rq *rq
 		if (rq->avg_idle > max)
 			rq->avg_idle = max;
 
+		rq->wake_stamp = jiffies;
+		rq->wake_avg = rq->avg_idle / 2;
+
 		rq->idle_stamp = 0;
 	}
 #endif
@@ -6051,6 +6054,8 @@ void __init sched_init(void)
 		rq->online = 0;
 		rq->idle_stamp = 0;
 		rq->avg_idle = 2*sysctl_sched_migration_cost;
+		rq->wake_stamp = jiffies;
+		rq->wake_avg = rq->avg_idle;
 		rq->max_idle_balance_cost = sysctl_sched_migration_cost;
 
 		INIT_LIST_HEAD(&rq->cfs_tasks);
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6378,11 +6378,30 @@ static int select_idle_cpu(struct task_s
 	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;
+	if (sched_feat(SIS_AGE)) {
+		unsigned long now = jiffies;
+		struct rq *this_rq = this_rq();
+
+		/*
+		 * If we're busy, the assumption that the last idle period
+		 * predicts the future is flawed; age away the remaining
+		 * predicted idle time.
+		 */
+		if (unlikely(this_rq->wake_stamp < now)) {
+			while (this_rq->wake_stamp < now && this_rq->wake_avg) {
+				this_rq->wake_stamp++;
+				this_rq->wake_avg >>= 1;
+			}
+		}
+
+		avg_idle = this_rq->wake_avg;
+	} else {
+		/*
+		 * 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)
--- a/kernel/sched/features.h
+++ b/kernel/sched/features.h
@@ -58,6 +58,8 @@ SCHED_FEAT(TTWU_QUEUE, true)
 SCHED_FEAT(SIS_AVG_CPU, false)
 SCHED_FEAT(SIS_PROP, true)
 
+SCHED_FEAT(SIS_AGE, true)
+
 /*
  * Issue a WARN when we do multiple update_rq_clock() calls
  * in a single rq->lock section. Default disabled because the
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -831,6 +831,9 @@ struct rq {
 	u64			idle_stamp;
 	u64			avg_idle;
 
+	unsigned long		wake_stamp;
+	u64			wake_avg;
+
 	/* This is used to determine avg_idle's max value */
 	u64			max_idle_balance_cost;
 #endif

  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 ` Peter Zijlstra [this message]
2018-05-30 14:22 ` [RFC 03/11] sched/fair: Only use time once Peter Zijlstra
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180530143105.977759909@infradead.org \
    --to=peterz@infradead.org \
    --cc=dhaval.giani@oracle.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=matt@codeblueprint.co.uk \
    --cc=mingo@kernel.org \
    --cc=riel@surriel.com \
    --cc=rohit.k.jain@oracle.com \
    --cc=steven.sistare@oracle.com \
    --cc=subhra.mazumdar@oracle.com \
    --cc=umgwanakikbuti@gmail.com \
    --subject='Re: [RFC 02/11] sched/fair: Age the average idle time' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).