[PATCH 21/32] rcu: Restart the tick on non-responding adaptive nohz CPUs

[Frederic Weisbecker]

When a CPU in adaptive nohz mode doesn't respond to complete
a grace period, issue it a specific IPI so that it restarts
the tick and chases a quiescent state.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Anton Blanchard <anton@xxxxxxxxxxx>
Cc: Avi Kivity <avi@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Cc: Paul E . McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Paul Menage <menage@xxxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Cc: Stephen Hemminger <shemminger@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Tim Pepper <lnxninja@xxxxxxxxxxxxxxxxxx>
---
 kernel/rcutree.c |   17 +++++++++++++++++
 1 files changed, 17 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 0009bfc..d496c70 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -50,6 +50,7 @@
 #include <linux/wait.h>
 #include <linux/kthread.h>
 #include <linux/prefetch.h>
+#include <linux/cpuset.h>
 
 #include "rcutree.h"
 
@@ -295,6 +296,20 @@ static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
 
 #ifdef CONFIG_SMP
 
+static void cpuset_update_rcu_cpu(int cpu)
+{
+#ifdef CONFIG_CPUSETS_NO_HZ
+	unsigned long flags;
+
+	local_irq_save(flags);
+
+	if (cpuset_cpu_adaptive_nohz(cpu))
+		smp_cpuset_update_nohz(cpu);
+
+	local_irq_restore(flags);
+#endif
+}
+
 /*
  * If the specified CPU is offline, tell the caller that it is in
  * a quiescent state.  Otherwise, whack it with a reschedule IPI.
@@ -317,6 +332,8 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp)
 		return 1;
 	}
 
+	cpuset_update_rcu_cpu(rdp->cpu);
+
 	/* If preemptible RCU, no point in sending reschedule IPI. */
 	if (rdp->preemptible)
 		return 0;
-- 
1.7.5.4

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