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    Subject[PATCH V2 1/2] Tick: Introduce tick_nohz_check() to check nohz enable status
    Date
    In some cases, nohz enable status needs to be checked. E.G, in RCU and cpufreq
    ondemand governor. So add tick_nohz_check() to return tick_nohz_enabled value
    And use tick_nohz_check() instead of referencing tick_nohz_enabled in the rcutree_plugin.h.

    Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
    ---

    Change since V2:
    Add ACCESS_ONCE to tick_nohz_check().

    include/linux/tick.h | 2 ++
    kernel/rcutree_plugin.h | 4 +---
    kernel/time/tick-sched.c | 8 +++++++-
    3 files changed, 10 insertions(+), 4 deletions(-)

    diff --git a/include/linux/tick.h b/include/linux/tick.h
    index 5128d33..a9c5374 100644
    --- a/include/linux/tick.h
    +++ b/include/linux/tick.h
    @@ -136,6 +136,7 @@ static inline int tick_nohz_tick_stopped(void)
    extern void tick_nohz_idle_enter(void);
    extern void tick_nohz_idle_exit(void);
    extern void tick_nohz_irq_exit(void);
    +extern int tick_nohz_check(void);
    extern ktime_t tick_nohz_get_sleep_length(void);
    extern u64 get_cpu_idle_time_us(int cpu, u64 *last_update_time);
    extern u64 get_cpu_iowait_time_us(int cpu, u64 *last_update_time);
    @@ -155,6 +156,7 @@ static inline ktime_t tick_nohz_get_sleep_length(void)

    return len;
    }
    +static inline int tick_nohz_check(void) { return 0; }
    static inline u64 get_cpu_idle_time_us(int cpu, u64 *unused) { return -1; }
    static inline u64 get_cpu_iowait_time_us(int cpu, u64 *unused) { return -1; }
    # endif /* !CONFIG_NO_HZ_COMMON */
    diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
    index 130c97b..af167ec 100644
    --- a/kernel/rcutree_plugin.h
    +++ b/kernel/rcutree_plugin.h
    @@ -1627,8 +1627,6 @@ module_param(rcu_idle_gp_delay, int, 0644);
    static int rcu_idle_lazy_gp_delay = RCU_IDLE_LAZY_GP_DELAY;
    module_param(rcu_idle_lazy_gp_delay, int, 0644);

    -extern int tick_nohz_enabled;
    -
    /*
    * Try to advance callbacks for all flavors of RCU on the current CPU.
    * Afterwards, if there are any callbacks ready for immediate invocation,
    @@ -1718,7 +1716,7 @@ static void rcu_prepare_for_idle(int cpu)
    int tne;

    /* Handle nohz enablement switches conservatively. */
    - tne = ACCESS_ONCE(tick_nohz_enabled);
    + tne = tick_nohz_check();
    if (tne != rdtp->tick_nohz_enabled_snap) {
    if (rcu_cpu_has_callbacks(cpu, NULL))
    invoke_rcu_core(); /* force nohz to see update. */
    diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
    index 3612fc7..a568845 100644
    --- a/kernel/time/tick-sched.c
    +++ b/kernel/time/tick-sched.c
    @@ -361,7 +361,13 @@ void __init tick_nohz_init(void)
    /*
    * NO HZ enabled ?
    */
    -int tick_nohz_enabled __read_mostly = 1;
    +static int tick_nohz_enabled __read_mostly = 1;
    +
    +int tick_nohz_check(void)
    +{
    + return ACCESS_ONCE(tick_nohz_enabled);
    +}
    +EXPORT_SYMBOL_GPL(tick_nohz_check);

    /*
    * Enable / Disable tickless mode
    --
    1.8.4.rc0.1.g8f6a3e5.dirty


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