[PATCH 11/41] nohz/cpuset: Don't turn off the tick if rcu needs it

[Frederic Weisbecker]

If RCU is waiting for the current CPU to complete a grace
period, don't turn off the tick. Unlike dynctik-idle, we
are not necessarily going to enter into rcu extended quiescent
state, so we may need to keep the tick to note current CPU's
quiescent states.

[added build fix from Zen Lin]

Signed-off-by: Frederic Weisbecker <fweisbec at gmail.com>
Cc: Alessio Igor Bogani <abogani at kernel.org>
Cc: Andrew Morton <akpm at linux-foundation.org>
Cc: Avi Kivity <avi at redhat.com>
Cc: Chris Metcalf <cmetcalf at tilera.com>
Cc: Christoph Lameter <cl at linux.com>
Cc: Daniel Lezcano <daniel.lezcano at linaro.org>
Cc: Geoff Levand <geoff at infradead.org>
Cc: Gilad Ben Yossef <gilad at benyossef.com>
Cc: Hakan Akkan <hakanakkan at gmail.com>
Cc: Ingo Molnar <mingo at kernel.org>
Cc: Kevin Hilman <khilman at ti.com>
Cc: Max Krasnyansky <maxk at qualcomm.com>
Cc: Paul E. McKenney <paulmck at linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz at infradead.org>
Cc: Stephen Hemminger <shemminger at vyatta.com>
Cc: Steven Rostedt <rostedt at goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation at gmail.com>
Cc: Thomas Gleixner <tglx at linutronix.de>
---
 include/linux/rcupdate.h |    1 +
 kernel/rcutree.c         |    3 +--
 kernel/time/tick-sched.c |   22 ++++++++++++++++++----
 3 files changed, 20 insertions(+), 6 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 81c04f4..e06639e 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -184,6 +184,7 @@ static inline int rcu_preempt_depth(void)
 extern void rcu_sched_qs(int cpu);
 extern void rcu_bh_qs(int cpu);
 extern void rcu_check_callbacks(int cpu, int user);
+extern int rcu_pending(int cpu);
 struct notifier_block;
 extern void rcu_idle_enter(void);
 extern void rcu_idle_exit(void);
diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 6c4a672..e141c7e 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -212,7 +212,6 @@ int rcu_cpu_stall_suppress __read_mostly;
 module_param(rcu_cpu_stall_suppress, int, 0644);
 
 static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
-static int rcu_pending(int cpu);
 
 /*
  * Return the number of RCU-sched batches processed thus far for debug & stats.
@@ -1915,7 +1914,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
  * by the current CPU, returning 1 if so.  This function is part of the
  * RCU implementation; it is -not- an exported member of the RCU API.
  */
-static int rcu_pending(int cpu)
+int rcu_pending(int cpu)
 {
 	return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
 	       __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 43fa7ac..4f99766 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -506,9 +506,21 @@ void tick_nohz_idle_enter(void)
 	local_irq_enable();
 }
 
+#ifdef CONFIG_CPUSETS_NO_HZ
+static bool can_stop_adaptive_tick(void)
+{
+	if (!sched_can_stop_tick())
+		return false;
+
+	/* Is there a grace period to complete ? */
+	if (rcu_pending(smp_processor_id()))
+		return false;
+
+	return true;
+}
+
 static void tick_nohz_cpuset_stop_tick(struct tick_sched *ts)
 {
-#ifdef CONFIG_CPUSETS_NO_HZ
 	int cpu = smp_processor_id();
 
 	if (!cpuset_adaptive_nohz() || is_idle_task(current))
@@ -517,12 +529,14 @@ static void tick_nohz_cpuset_stop_tick(struct tick_sched *ts)
 	if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
 		return;
 
-	if (!sched_can_stop_tick())
+	if (!can_stop_adaptive_tick())
 		return;
 
 	tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
-#endif
 }
+#else
+static void tick_nohz_cpuset_stop_tick(struct tick_sched *ts) { }
+#endif
 
 /**
  * tick_nohz_irq_exit - update next tick event from interrupt exit
@@ -852,7 +866,7 @@ void tick_nohz_check_adaptive(void)
 	struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
 
 	if (ts->tick_stopped && !is_idle_task(current)) {
-		if (!sched_can_stop_tick())
+		if (!can_stop_adaptive_tick())
 			tick_nohz_restart_sched_tick();
 	}
 }
-- 
1.7.5.4