From: Frederic Weisbecker <fweis...@gmail.com>
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 <fweis...@gmail.com>
Cc: Alessio Igor Bogani <abog...@kernel.org>
Cc: Andrew Morton <a...@linux-foundation.org>
Cc: Avi Kivity <a...@redhat.com>
Cc: Chris Metcalf <cmetc...@tilera.com>
Cc: Christoph Lameter <c...@linux.com>
Cc: Daniel Lezcano <daniel.lezc...@linaro.org>
Cc: Geoff Levand <ge...@infradead.org>
Cc: Gilad Ben Yossef <gi...@benyossef.com>
Cc: Hakan Akkan <hakanak...@gmail.com>
Cc: Ingo Molnar <mi...@kernel.org>
Cc: Kevin Hilman <khil...@ti.com>
Cc: Max Krasnyansky <m...@qualcomm.com>
Cc: Paul E. McKenney <paul...@linux.vnet.ibm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Stephen Hemminger <shemmin...@vyatta.com>
Cc: Steven Rostedt <rost...@goodmis.org>
Cc: Sven-Thorsten Dietrich <thebigcorporat...@gmail.com>
Cc: Thomas Gleixner <t...@linutronix.de>
---
include/linux/cpuset.h | 2 ++
kernel/cpuset.c | 25 +++++++++++++++++++++++--
kernel/time/tick-sched.c | 8 ++++++++
3 files changed, 33 insertions(+), 2 deletions(-)
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index 7e7eb41..631968b 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -260,6 +260,8 @@ static inline bool cpuset_adaptive_nohz(void)
*/
return cpuset_cpu_adaptive_nohz(smp_processor_id());
}
+
+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 6319d8e..1b67e5b 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1200,6 +1200,14 @@ static void cpuset_change_flag(struct task_struct *tsk,
DEFINE_PER_CPU(atomic_t, 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;
@@ -1211,9 +1219,22 @@ static void update_nohz_cpus(struct cpuset *old_cs,
struct cpuset *cs)
for_each_cpu(cpu, cs->cpus_allowed) {
atomic_t *ref = &per_cpu(cpu_adaptive_nohz_ref, cpu);
if (is_adaptive_nohz(cs))
- atomic_inc(ref);
+ val = atomic_inc_return(ref);
else
- atomic_dec(ref);
+ val = atomic_dec_return(ref);
+
+ 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 0a5e650..de7de68 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -884,6 +884,14 @@ 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);
--
1.7.10.4
--
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