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    Subject[PATCH 11/32] nohz/cpuset: Don't turn off the tick if rcu needs it
    Date
    If RCU is waiting for the current CPU to complete a grace
    period, don't turn off the tick. Unlike dynctik-idle, we
    are not necessarily going to enter into rcu extended quiescent
    state, so we may need to keep the tick to note current CPU's
    quiescent states.

    [added build fix from Zen Lin]

    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/rcupdate.h | 1 +
    kernel/rcutree.c | 3 +--
    kernel/time/tick-sched.c | 22 ++++++++++++++++++----
    3 files changed, 20 insertions(+), 6 deletions(-)

    diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
    index 81c04f4..e06639e 100644
    --- a/include/linux/rcupdate.h
    +++ b/include/linux/rcupdate.h
    @@ -184,6 +184,7 @@ static inline int rcu_preempt_depth(void)
    extern void rcu_sched_qs(int cpu);
    extern void rcu_bh_qs(int cpu);
    extern void rcu_check_callbacks(int cpu, int user);
    +extern int rcu_pending(int cpu);
    struct notifier_block;
    extern void rcu_idle_enter(void);
    extern void rcu_idle_exit(void);
    diff --git a/kernel/rcutree.c b/kernel/rcutree.c
    index 6c4a672..e141c7e 100644
    --- a/kernel/rcutree.c
    +++ b/kernel/rcutree.c
    @@ -212,7 +212,6 @@ int rcu_cpu_stall_suppress __read_mostly;
    module_param(rcu_cpu_stall_suppress, int, 0644);

    static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
    -static int rcu_pending(int cpu);

    /*
    * Return the number of RCU-sched batches processed thus far for debug & stats.
    @@ -1915,7 +1914,7 @@ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
    * by the current CPU, returning 1 if so. This function is part of the
    * RCU implementation; it is -not- an exported member of the RCU API.
    */
    -static int rcu_pending(int cpu)
    +int rcu_pending(int cpu)
    {
    return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
    __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
    diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
    index 43fa7ac..4f99766 100644
    --- a/kernel/time/tick-sched.c
    +++ b/kernel/time/tick-sched.c
    @@ -506,9 +506,21 @@ void tick_nohz_idle_enter(void)
    local_irq_enable();
    }

    +#ifdef CONFIG_CPUSETS_NO_HZ
    +static bool can_stop_adaptive_tick(void)
    +{
    + if (!sched_can_stop_tick())
    + return false;
    +
    + /* Is there a grace period to complete ? */
    + if (rcu_pending(smp_processor_id()))
    + return false;
    +
    + return true;
    +}
    +
    static void tick_nohz_cpuset_stop_tick(struct tick_sched *ts)
    {
    -#ifdef CONFIG_CPUSETS_NO_HZ
    int cpu = smp_processor_id();

    if (!cpuset_adaptive_nohz() || is_idle_task(current))
    @@ -517,12 +529,14 @@ static void tick_nohz_cpuset_stop_tick(struct tick_sched *ts)
    if (!ts->tick_stopped && ts->nohz_mode == NOHZ_MODE_INACTIVE)
    return;

    - if (!sched_can_stop_tick())
    + if (!can_stop_adaptive_tick())
    return;

    tick_nohz_stop_sched_tick(ts, ktime_get(), cpu);
    -#endif
    }
    +#else
    +static void tick_nohz_cpuset_stop_tick(struct tick_sched *ts) { }
    +#endif

    /**
    * tick_nohz_irq_exit - update next tick event from interrupt exit
    @@ -852,7 +866,7 @@ void tick_nohz_check_adaptive(void)
    struct tick_sched *ts = &__get_cpu_var(tick_cpu_sched);

    if (ts->tick_stopped && !is_idle_task(current)) {
    - if (!sched_can_stop_tick())
    + if (!can_stop_adaptive_tick())
    tick_nohz_restart_sched_tick();
    }
    }
    --
    1.7.5.4


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