linux-kernel - [tip:sched/core] sched/cpufreq: Optimize cpufreq update kicker to avoid update multiple times

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Date:	Thu, 28 Apr 2016 03:26:42 -0700
From:	tip-bot for Wanpeng Li <tipbot@...or.com>
To:	linux-tip-commits@...r.kernel.org
Cc:	tglx@...utronix.de, peterz@...radead.org,
	linux-kernel@...r.kernel.org, hpa@...or.com,
	rafael.j.wysocki@...el.com, mingo@...nel.org,
	wanpeng.li@...mail.com
Subject: [tip:sched/core] sched/cpufreq: Optimize cpufreq update kicker to
 avoid update multiple times

Commit-ID:  594dd290cf5403a9a5818619dfff42d8e8e0518e
Gitweb:     http://git.kernel.org/tip/594dd290cf5403a9a5818619dfff42d8e8e0518e
Author:     Wanpeng Li <wanpeng.li@...mail.com>
AuthorDate: Fri, 22 Apr 2016 17:07:24 +0800
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Thu, 28 Apr 2016 10:39:54 +0200

sched/cpufreq: Optimize cpufreq update kicker to avoid update multiple times

Sometimes delta_exec is 0 due to update_curr() is called multiple times,
this is captured by:

	u64 delta_exec = rq_clock_task(rq) - curr->se.exec_start;

This patch optimizes the cpufreq update kicker by bailing out when nothing
changed, it will benefit the upcoming schedutil, since otherwise it will
(over)react to the special util/max combination.

Signed-off-by: Wanpeng Li <wanpeng.li@...mail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Link: http://lkml.kernel.org/r/1461316044-9520-1-git-send-email-wanpeng.li@hotmail.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 kernel/sched/deadline.c | 8 ++++----
 kernel/sched/rt.c       | 8 ++++----
 2 files changed, 8 insertions(+), 8 deletions(-)

diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index affd97e..8f9b5af 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -717,10 +717,6 @@ static void update_curr_dl(struct rq *rq)
 	if (!dl_task(curr) || !on_dl_rq(dl_se))
 		return;
 
-	/* Kick cpufreq (see the comment in linux/cpufreq.h). */
-	if (cpu_of(rq) == smp_processor_id())
-		cpufreq_trigger_update(rq_clock(rq));
-
 	/*
 	 * Consumed budget is computed considering the time as
 	 * observed by schedulable tasks (excluding time spent
@@ -736,6 +732,10 @@ static void update_curr_dl(struct rq *rq)
 		return;
 	}
 
+	/* kick cpufreq (see the comment in linux/cpufreq.h). */
+	if (cpu_of(rq) == smp_processor_id())
+		cpufreq_trigger_update(rq_clock(rq));
+
 	schedstat_set(curr->se.statistics.exec_max,
 		      max(curr->se.statistics.exec_max, delta_exec));
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index c41ea7a..19e1306 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -953,14 +953,14 @@ static void update_curr_rt(struct rq *rq)
 	if (curr->sched_class != &rt_sched_class)
 		return;
 
-	/* Kick cpufreq (see the comment in linux/cpufreq.h). */
-	if (cpu_of(rq) == smp_processor_id())
-		cpufreq_trigger_update(rq_clock(rq));
-
 	delta_exec = rq_clock_task(rq) - curr->se.exec_start;
 	if (unlikely((s64)delta_exec <= 0))
 		return;
 
+	/* Kick cpufreq (see the comment in linux/cpufreq.h). */
+	if (cpu_of(rq) == smp_processor_id())
+		cpufreq_trigger_update(rq_clock(rq));
+
 	schedstat_set(curr->se.statistics.exec_max,
 		      max(curr->se.statistics.exec_max, delta_exec));