linux-kernel - [58/67] sched: Revert nohz

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Date:	Wed, 11 Aug 2010 17:06:13 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Ingo Molnar <mingo@...e.hu>
Subject: [58/67] sched: Revert nohz_ratelimit() for now

2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Peter Zijlstra <a.p.zijlstra@...llo.nl>

commit 396e894d289d69bacf5acd983c97cd6e21a14c08 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 include/linux/sched.h    |    6 ------
 kernel/sched.c           |   10 ----------
 kernel/time/tick-sched.c |    2 +-
 3 files changed, 1 insertion(+), 17 deletions(-)

--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -274,17 +274,11 @@ 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
 
 /*
--- 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)
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -325,7 +325,7 @@ void tick_nohz_stop_sched_tick(int inidl
 	} 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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