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    Subject[PATCH 19/32] 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: Andrew Morton <akpm@linux-foundation.org>
    Cc: Anton Blanchard <anton@au1.ibm.com>
    Cc: Avi Kivity <avi@redhat.com>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Lai Jiangshan <laijs@cn.fujitsu.com>
    Cc: Paul E . McKenney <paulmck@linux.vnet.ibm.com>
    Cc: Paul Menage <menage@google.com>
    Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
    Cc: Stephen Hemminger <shemminger@vyatta.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Tim Pepper <lnxninja@linux.vnet.ibm.com>
    ---
    include/linux/cpuset.h | 1 +
    kernel/cpuset.c | 21 +++++++++++++++++++++
    kernel/sched.c | 8 ++++++++
    3 files changed, 30 insertions(+), 0 deletions(-)

    diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
    index 799b9a4..7f9d78d 100644
    --- a/include/linux/cpuset.h
    +++ b/include/linux/cpuset.h
    @@ -265,6 +265,7 @@ static inline bool cpuset_adaptive_nohz(void)
    }

    extern void cpuset_update_nohz(void);
    +extern void cpuset_exit_nohz_interrupt(void *unused);
    #else
    static inline void cpuset_update_nohz(void) { }

    diff --git a/kernel/cpuset.c b/kernel/cpuset.c
    index 3135096..ee3b0d0 100644
    --- a/kernel/cpuset.c
    +++ b/kernel/cpuset.c
    @@ -1199,6 +1199,14 @@ 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;
    @@ -1212,6 +1220,19 @@ 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.
    + */
    + smp_mb();
    + cpu_exit_nohz(cpu);
    + }
    }
    }
    #else
    diff --git a/kernel/sched.c b/kernel/sched.c
    index 78ea0a5..75378be 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -2513,6 +2513,14 @@ void cpuset_update_nohz(void)
    cpuset_nohz_restart_tick();
    }

    +void cpuset_exit_nohz_interrupt(void *unused)
    +{
    + if (!tick_nohz_adaptive_mode())
    + return;
    +
    + cpuset_nohz_restart_tick();
    +}
    +
    static void cpuset_nohz_task_switch(struct task_struct *next)
    {
    int cpu = smp_processor_id();
    --
    1.7.5.4


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