linux-kernel - [PATCH 05/32] nohz: Move rcu dynticks idle mode handling to idle enter/exit APIs

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Date:	Mon, 15 Aug 2011 17:52:02 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Anton Blanchard <anton@....ibm.com>,
	Avi Kivity <avi@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	Paul Menage <menage@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stephen Hemminger <shemminger@...tta.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Pepper <lnxninja@...ux.vnet.ibm.com>
Subject: [PATCH 05/32] nohz: Move rcu dynticks idle mode handling to idle enter/exit APIs

To prepare for nohz / idle logic split, pull out the rcu dynticks
idle mode switching to strict idle entry/exit areas.

So we make the dyntick mode possible without always involving rcu
extended quiescent state.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Anton Blanchard <anton@....ibm.com>
Cc: Avi Kivity <avi@...hat.com>
Cc: Ingo Molnar <mingo@...e.hu>
Cc: Lai Jiangshan <laijs@...fujitsu.com>
Cc: Paul E . McKenney <paulmck@...ux.vnet.ibm.com>
Cc: Paul Menage <menage@...gle.com>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Stephen Hemminger <shemminger@...tta.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Tim Pepper <lnxninja@...ux.vnet.ibm.com>
---
 kernel/time/tick-sched.c |   11 +++++++----
 1 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index df6bb4c..8937d4a 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -385,7 +385,6 @@ static void tick_nohz_stop_sched_tick(ktime_t now)
 			ts->idle_tick = hrtimer_get_expires(&ts->sched_timer);
 			ts->tick_stopped = 1;
 			ts->idle_jiffies = last_jiffies;
-			rcu_enter_nohz();
 		}
 
 		ts->idle_sleeps++;
@@ -429,9 +428,13 @@ out:
 static void __tick_nohz_enter_idle(struct tick_sched *ts, int cpu)
 {
 	ktime_t now;
+	int was_stopped = ts->tick_stopped;
 
 	now = tick_nohz_start_idle(cpu, ts);
 	tick_nohz_stop_sched_tick(now);
+
+	if (!was_stopped && ts->tick_stopped)
+		rcu_enter_nohz();
 }
 
 void tick_nohz_enter_idle(void)
@@ -499,8 +502,6 @@ static void tick_nohz_restart_sched_tick(ktime_t now, struct tick_sched *ts)
 	unsigned long ticks;
 #endif
 
-	rcu_exit_nohz();
-
 	/* Update jiffies first */
 	select_nohz_load_balancer(0);
 	tick_do_update_jiffies64(now);
@@ -547,8 +548,10 @@ void tick_nohz_exit_idle(void)
 	tick_nohz_stop_idle(smp_processor_id(), now);
 	ts->inidle = 0;
 
-	if (ts->tick_stopped)
+	if (ts->tick_stopped) {
+		rcu_exit_nohz();
 		tick_nohz_restart_sched_tick(now, ts);
+	}
 
 	local_irq_enable();
 }
-- 
1.7.5.4

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