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    Subject[PATCH 14/32] 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: 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: Ingo Molnar <mingo@kernel.org>
    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>
    Cc: Zen Lin <zen@openhuawei.org>
    ---
    include/linux/cpuset.h | 2 ++
    kernel/cpuset.c | 23 +++++++++++++++++++++++
    kernel/time/tick-sched.c | 8 ++++++++
    3 files changed, 33 insertions(+), 0 deletions(-)

    diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
    index 5510708..89ef5f3 100644
    --- a/include/linux/cpuset.h
    +++ b/include/linux/cpuset.h
    @@ -263,6 +263,8 @@ static inline bool cpuset_adaptive_nohz(void)

    return false;
    }
    +
    +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 5a28cf8..00864a0 100644
    --- a/kernel/cpuset.c
    +++ b/kernel/cpuset.c
    @@ -1221,6 +1221,14 @@ 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;
    @@ -1234,6 +1242,21 @@ 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.
    + * 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 fc35d41..fe31add 100644
    --- a/kernel/time/tick-sched.c
    +++ b/kernel/time/tick-sched.c
    @@ -875,6 +875,14 @@ 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);
    --
    1.7.5.4


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