[PATCH 18/32] nohz/cpuset: Don't stop the tick if posix cpu timers are running

From: Frederic Weisbecker
Date: Mon Aug 15 2011 - 11:56:53 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: 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>
include/linux/posix-timers.h | 1 +
kernel/posix-cpu-timers.c | 12 ++++++++++++
kernel/sched.c | 4 ++++
3 files changed, 17 insertions(+), 0 deletions(-)

diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h
index 959c141..5092cfd 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -116,6 +116,7 @@ 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 58f405b..f284fa4 100644
--- a/kernel/posix-cpu-timers.c
+++ b/kernel/posix-cpu-timers.c
@@ -6,6 +6,7 @@
#include <linux/posix-timers.h>
#include <linux/errno.h>
#include <linux/math64.h>
+#include <linux/cpuset.h>
#include <asm/uaccess.h>
#include <linux/kernel_stat.h>
#include <trace/events/timer.h>
@@ -1300,6 +1301,17 @@ 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/sched.c b/kernel/sched.c
index 8bf8280..78ea0a5 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -71,6 +71,7 @@
#include <linux/ctype.h>
#include <linux/ftrace.h>
#include <linux/slab.h>
+#include <linux/posix-timers.h>

#include <asm/tlb.h>
#include <asm/irq_regs.h>
@@ -2491,6 +2492,9 @@ bool cpuset_nohz_can_stop_tick(void)
if (rcu_pending(cpu))
return false;

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


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