linux-kernel - [tip:sched/urgent] sched: Revert nohz

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Date:	Sat, 17 Jul 2010 11:12:38 GMT
From:	tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	a.p.zijlstra@...llo.nl, efault@....de, preining@...ic.at,
	arjan@...radead.org, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/urgent] sched: Revert nohz_ratelimit() for now

Commit-ID:  396e894d289d69bacf5acd983c97cd6e21a14c08
Gitweb:     http://git.kernel.org/tip/396e894d289d69bacf5acd983c97cd6e21a14c08
Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Fri, 9 Jul 2010 15:12:27 +0200
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Sat, 17 Jul 2010 12:05:44 +0200

sched: Revert nohz_ratelimit() for now

Norbert reported that nohz_ratelimit() causes his laptop to burn about
4W (40%) extra. For now back out the change and see if we can adjust
the power management code to make better decisions.

Reported-by: Norbert Preining <preining@...ic.at>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Acked-by: Mike Galbraith <efault@....de>
Cc: Arjan van de Ven <arjan@...radead.org>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 include/linux/sched.h    |    6 ------
 kernel/sched.c           |   10 ----------
 kernel/time/tick-sched.c |    2 +-
 3 files changed, 1 insertions(+), 17 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 747fcae..6e0bb86 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -273,17 +273,11 @@ extern cpumask_var_t nohz_cpu_mask;
 #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ)
 extern int select_nohz_load_balancer(int cpu);
 extern int get_nohz_load_balancer(void);
-extern int nohz_ratelimit(int cpu);
 #else
 static inline int select_nohz_load_balancer(int cpu)
 {
 	return 0;
 }
-
-static inline int nohz_ratelimit(int cpu)
-{
-	return 0;
-}
 #endif
 
 /*
diff --git a/kernel/sched.c b/kernel/sched.c
index f52a880..63b4a14 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1232,16 +1232,6 @@ void wake_up_idle_cpu(int cpu)
 		smp_send_reschedule(cpu);
 }
 
-int nohz_ratelimit(int cpu)
-{
-	struct rq *rq = cpu_rq(cpu);
-	u64 diff = rq->clock - rq->nohz_stamp;
-
-	rq->nohz_stamp = rq->clock;
-
-	return diff < (NSEC_PER_SEC / HZ) >> 1;
-}
-
 #endif /* CONFIG_NO_HZ */
 
 static u64 sched_avg_period(void)
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 813993b..f898af6 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -325,7 +325,7 @@ void tick_nohz_stop_sched_tick(int inidle)
 	} while (read_seqretry(&xtime_lock, seq));
 
 	if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
-	    arch_needs_cpu(cpu) || nohz_ratelimit(cpu)) {
+	    arch_needs_cpu(cpu)) {
 		next_jiffies = last_jiffies + 1;
 		delta_jiffies = 1;
 	} else {
--
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