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    Subject[PATCH 13/41] nohz/cpuset: Don't stop the tick if posix cpu timers are running
    Date
    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@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: Hakan Akkan <hakanakkan@gmail.com>
    Cc: Ingo Molnar <mingo@kernel.org>
    Cc: Kevin Hilman <khilman@ti.com>
    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>
    ---
    include/linux/posix-timers.h | 1 +
    kernel/posix-cpu-timers.c | 12 ++++++++++++
    kernel/time/tick-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 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 125cb67..79d4c24 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>
    @@ -1274,6 +1275,17 @@ 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 4f99766..fc35d41 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/cpuset.h>
    +#include <linux/posix-timers.h>

    #include <asm/irq_regs.h>

    @@ -512,6 +513,9 @@ static bool can_stop_adaptive_tick(void)
    if (!sched_can_stop_tick())
    return false;

    + if (posix_cpu_timers_running(current))
    + return false;
    +
    /* Is there a grace period to complete ? */
    if (rcu_pending(smp_processor_id()))
    return false;
    --
    1.7.5.4


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