linux-kernel - [PATCH 11/13] nohz: Wake up timekeeper on exit from sysidle state

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Date:	Tue, 17 Dec 2013 23:51:30 +0100
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	John Stultz <john.stultz@...aro.org>,
	Alex Shi <alex.shi@...aro.org>,
	Kevin Hilman <khilman@...aro.org>
Subject: [PATCH 11/13] nohz: Wake up timekeeper on exit from sysidle state

When a full dynticks CPU wakes up from sysidle state, which means that
all full dynticks CPUs were previously sleeping, it's possible that
all the potential timekeeping CPUs are sleeping as well and nobody
maintains the associated duty.

But full dynticks CPUs don't run the tick by definition so we need
to wake up a timekeeper such that it can handle the timekeeping
duty on behalf of the freshly awoken full dyntick CPU.

To achieve this and ensure that this CPU won't deal with stale
jiffies values, lets wake up the default timekeeper using the right
API.

Signed-off-by: Frederic Weisbecker <fweisbec@...il.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
Cc: John Stultz <john.stultz@...aro.org>
Cc: Alex Shi <alex.shi@...aro.org>
Cc: Kevin Hilman <khilman@...aro.org>
---
 kernel/rcu/tree_plugin.h | 2 +-
 kernel/time/tick-sched.c | 3 ++-
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 1795265..b43e32d 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2488,7 +2488,7 @@ void rcu_sysidle_force_exit(void)
 				      oldstate, RCU_SYSIDLE_NOT);
 		if (oldstate == newoldstate &&
 		    oldstate == RCU_SYSIDLE_FULL_NOTED) {
-			smp_send_reschedule(tick_timekeeping_default_cpu());
+			tick_nohz_full_kick_timekeeping();
 			return; /* We cleared it, done! */
 		}
 		oldstate = newoldstate;
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 94b6901..f5ae69f 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -302,7 +302,8 @@ void tick_nohz_full_kick_all(void)
 /**
  * tick_nohz_full_kick_timekeeping - kick the default timekeeper
  *
- * kick the default timekeeper when a secondary timekeeper goes offline.
+ * kick the default timekeeper when full dynticks CPUs exit full
+ * system idle state or when a secondary timekeeper goes offline.
  */
 void tick_nohz_full_kick_timekeeping(void)
 {
-- 
1.8.3.1

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