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Subject[PATCH 14/32] nohz/cpuset: Restart tick when nohz flag is cleared on cpuset
Date
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: Alessio Igor Bogani <abogani@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Avi Kivity <avi@redhat.com>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Max Krasnyansky <maxk@qualcomm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Zen Lin <zen@openhuawei.org>
---
include/linux/cpuset.h | 2 ++
kernel/cpuset.c | 23 +++++++++++++++++++++++
kernel/time/tick-sched.c | 8 ++++++++
3 files changed, 33 insertions(+), 0 deletions(-)
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 5510708..89ef5f3 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -263,6 +263,8 @@ static inline bool cpuset_adaptive_nohz(void)

return false;
}
+
+extern void cpuset_exit_nohz_interrupt(void *unused);
#else
static inline bool cpuset_cpu_adaptive_nohz(int cpu) { return false; }
static inline bool cpuset_adaptive_nohz(void) { return false; }
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 5a28cf8..00864a0 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1221,6 +1221,14 @@ 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;
@@ -1234,6 +1242,21 @@ 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.
+ * FIXME: We probably need more to ensure this value is really
+ * visible right away.
+ */
+ smp_mb();
+ cpu_exit_nohz(cpu);
+ }
}
}
#else
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index fc35d41..fe31add 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -875,6 +875,14 @@ void tick_nohz_check_adaptive(void)
}
}

+void cpuset_exit_nohz_interrupt(void *unused)
+{
+ struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
+
+ if (ts->tick_stopped && !is_idle_task(current))
+ tick_nohz_restart_adaptive();
+}
+
void tick_nohz_post_schedule(void)
{
struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);
--
1.7.5.4


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