[PATCH 24/33] nohz: Don't stop the tick if posix cpu timers are running

From: Frederic Weisbecker
Date: Mon Jan 07 2013 - 21:09:28 EST

If either a per thread or a per process posix cpu timer is running,
don't stop the tick.

TODO: restart the tick if it is stopped and a posix cpu timer is
enqueued. Check we probably need a memory barrier for the per
process posix timer that can be enqueued from another task
of the group.

Signed-off-by: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Alessio Igor Bogani <abogani@xxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
Cc: Christoph Lameter <cl@xxxxxxxxx>
Cc: Geoff Levand <geoff@xxxxxxxxxxxxx>
Cc: Gilad Ben Yossef <gilad@xxxxxxxxxxxxx>
Cc: Hakan Akkan <hakanakkan@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx>
Cc: Namhyung Kim <namhyung.kim@xxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Cc: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
include/linux/posix-timers.h | 1 +
kernel/posix-cpu-timers.c | 11 +++++++++++
kernel/time/tick-sched.c | 4 ++++
3 files changed, 16 insertions(+), 0 deletions(-)

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 042058f..97480c2 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -119,6 +119,7 @@ int posix_timer_event(struct k_itimer *timr, int si_private);
void posix_cpu_timer_schedule(struct k_itimer *timer);

void run_posix_cpu_timers(struct task_struct *task);
+bool posix_cpu_timers_running(struct task_struct *tsk);
void posix_cpu_timers_exit(struct task_struct *task);
void posix_cpu_timers_exit_group(struct task_struct *task);

diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
index 165d476..15f8f4f 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -1269,6 +1269,17 @@ static inline int fastpath_timer_check(struct task_struct *tsk)
return 0;

+bool posix_cpu_timers_running(struct task_struct *tsk)
+ if (!task_cputime_zero(&tsk->cputime_expires))
+ return true;
+ if (tsk->signal->cputimer.running)
+ return true;
+ return false;
* This is called from the timer interrupt handler. The irq handler has
* already updated our counts. We need to check if any timers fire now.
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 743b021..5543a4d 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -21,6 +21,7 @@
#include <linux/sched.h>
#include <linux/module.h>
#include <linux/irq_work.h>
+#include <linux/posix-timers.h>

#include <asm/irq_regs.h>

@@ -599,6 +600,9 @@ static bool can_stop_full_tick(int cpu)
if (rcu_pending(cpu))
return false;

+ if (posix_cpu_timers_running(current))
+ return false;
return true;

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