[PATCH 19/32] nohz/cpuset: Restart tick when nohz flag is cleared on cpuset

Frederic Weisbecker
2011-08-15T15:53:48Z

Issue an IPI to restart the tick on a CPU that belongs
to a cpuset when its nohz flag gets cleared.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Anton Blanchard <anton@au1.ibm.com>
Cc: Avi Kivity <avi@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Menage <menage@google.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Pepper <lnxninja@linux.vnet.ibm.com>
---
include/linux/cpuset.h | 1 +
kernel/cpuset.c | 21 +++++++++++++++++++++
kernel/sched.c | 8 ++++++++
3 files changed, 30 insertions(+), 0 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 799b9a4..7f9d78d 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -265,6 +265,7 @@ static inline bool cpuset_adaptive_nohz(void)
}

extern void cpuset_update_nohz(void);
+extern void cpuset_exit_nohz_interrupt(void *unused);
#else
static inline void cpuset_update_nohz(void) { }

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 3135096..ee3b0d0 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1199,6 +1199,14 @@ static void cpuset_change_flag(struct task_struct *tsk,

DEFINE_PER_CPU(int, cpu_adaptive_nohz_ref);

+static void cpu_exit_nohz(int cpu)
+{
+ preempt_disable();
+ smp_call_function_single(cpu, cpuset_exit_nohz_interrupt,
+ NULL, true);
+ preempt_enable();
+}
+
static void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs)
{
int cpu;
@@ -1212,6 +1220,19 @@ static void update_nohz_cpus(struct cpuset *old_cs, struct cpuset *cs)
per_cpu(cpu_adaptive_nohz_ref, cpu) += 1;
else
per_cpu(cpu_adaptive_nohz_ref, cpu) -= 1;
+
+ val = per_cpu(cpu_adaptive_nohz_ref, cpu);
+
+ if (!val) {
+ /*
+ * The update to cpu_adaptive_nohz_ref must be
+ * visible right away. So that once we restart the tick
+ * from the IPI, it won't be stopped again due to cache
+ * update lag.
+ */
+ smp_mb();
+ cpu_exit_nohz(cpu);
+ }
}
}
#else
diff --git a/kernel/sched.c b/kernel/sched.c
index 78ea0a5..75378be 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2513,6 +2513,14 @@ void cpuset_update_nohz(void)
cpuset_nohz_restart_tick();
}

+void cpuset_exit_nohz_interrupt(void *unused)
+{
+ if (!tick_nohz_adaptive_mode())
+ return;
+
+ cpuset_nohz_restart_tick();
+}
+
static void cpuset_nohz_task_switch(struct task_struct *next)
{
int cpu = smp_processor_id();
--
1.7.5.4