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    Subject[PATCH 2/4] timer: Provide mod_timer_on()
    In order to convert queue_work_on() to mod_timer (so that we can avoid
    calling cancel_delayed_work() every time we want to modify a delayed
    work) we need to have a mod_timer_on().

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    LKML-Reference: <new-submission>
    ---
    include/linux/timer.h | 1
    kernel/timer.c | 75 ++++++++++++++++++++++++++++++++------------------
    2 files changed, 50 insertions(+), 26 deletions(-)

    Index: linux-2.6/include/linux/timer.h
    ===================================================================
    --- linux-2.6.orig/include/linux/timer.h
    +++ linux-2.6/include/linux/timer.h
    @@ -209,6 +209,7 @@ static inline int timer_pending(const st
    extern void add_timer_on(struct timer_list *timer, int cpu);
    extern int del_timer(struct timer_list * timer);
    extern int mod_timer(struct timer_list *timer, unsigned long expires);
    +extern int mod_timer_on(struct timer_list *timer, unsigned long expires, int cpu);
    extern int mod_timer_pending(struct timer_list *timer, unsigned long expires);
    extern int mod_timer_pinned(struct timer_list *timer, unsigned long expires);

    Index: linux-2.6/kernel/timer.c
    ===================================================================
    --- linux-2.6.orig/kernel/timer.c
    +++ linux-2.6/kernel/timer.c
    @@ -648,8 +648,8 @@ static struct tvec_base *lock_timer_base
    }

    static inline int
    -__mod_timer(struct timer_list *timer, unsigned long expires,
    - bool pending_only, int pinned)
    +__mod_timer_on(struct timer_list *timer, unsigned long expires,
    + bool pending_only, int pinned, int cpu)
    {
    struct tvec_base *base, *new_base;
    unsigned long flags;
    @@ -673,12 +673,14 @@ __mod_timer(struct timer_list *timer, un

    debug_activate(timer, expires);

    - cpu = smp_processor_id();
    + if (cpu == -1) {
    + cpu = smp_processor_id();

    #if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
    - if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
    - cpu = get_nohz_timer_target();
    + if (!pinned && get_sysctl_timer_migration() && idle_cpu(cpu))
    + cpu = get_nohz_timer_target();
    #endif
    + }
    new_base = per_cpu(tvec_bases, cpu);

    if (base != new_base) {
    @@ -705,12 +707,30 @@ __mod_timer(struct timer_list *timer, un
    base->next_timer = timer->expires;
    internal_add_timer(base, timer);

    + if (cpu != smp_processor_id()) {
    + /*
    + * Check whether the other CPU is idle and needs to be
    + * triggered to reevaluate the timer wheel when nohz is
    + * active. We are protected against the other CPU fiddling
    + * with the timer by holding the timer base lock. This also
    + * makes sure that a CPU on the way to idle can not evaluate
    + * the timer wheel.
    + */
    + wake_up_idle_cpu(cpu);
    + }
    out_unlock:
    spin_unlock_irqrestore(&base->lock, flags);

    return ret;
    }

    +static inline int
    +__mod_timer(struct timer_list *timer, unsigned long expires,
    + bool pending_only, int pinned)
    +{
    + return __mod_timer_on(timer, expires, pending_only, pinned, -1);
    +}
    +
    /**
    * mod_timer_pending - modify a pending timer's timeout
    * @timer: the pending timer to be modified
    @@ -826,6 +846,29 @@ int mod_timer_pinned(struct timer_list *
    EXPORT_SYMBOL(mod_timer_pinned);

    /**
    + * mod_timer_on - modify a timer's timeout and move it to a specific cpu
    + * @timer: the timer to be modified
    + * @expires: new timeout in jiffies
    + * @cpu: cpu to migrate the timer to
    + *
    + * See mod_timer(), equivalent to:
    + *
    + * del_timer(timer); timer->expires = expires; add_timer_on(timer, cpu);
    + *
    + * The function returns whether it has modified a pending timer or not.
    + */
    +int mod_timer_on(struct timer_list *timer, unsigned long expires, int cpu)
    +{
    + if (timer_pending(timer) && timer->expires == expires)
    + return 1;
    +
    + expires = apply_slack(timer, expires);
    +
    + return __mod_timer_on(timer, expires, false, TIMER_NOT_PINNED, cpu);
    +}
    +EXPORT_SYMBOL(mod_timer_on);
    +
    +/**
    * add_timer - start a timer
    * @timer: the timer to be added
    *
    @@ -855,28 +898,8 @@ EXPORT_SYMBOL(add_timer);
    */
    void add_timer_on(struct timer_list *timer, int cpu)
    {
    - struct tvec_base *base = per_cpu(tvec_bases, cpu);
    - unsigned long flags;
    -
    - timer_stats_timer_set_start_info(timer);
    BUG_ON(timer_pending(timer) || !timer->function);
    - spin_lock_irqsave(&base->lock, flags);
    - timer_set_base(timer, base);
    - debug_activate(timer, timer->expires);
    - if (time_before(timer->expires, base->next_timer) &&
    - !tbase_get_deferrable(timer->base))
    - base->next_timer = timer->expires;
    - internal_add_timer(base, timer);
    - /*
    - * Check whether the other CPU is idle and needs to be
    - * triggered to reevaluate the timer wheel when nohz is
    - * active. We are protected against the other CPU fiddling
    - * with the timer by holding the timer base lock. This also
    - * makes sure that a CPU on the way to idle can not evaluate
    - * the timer wheel.
    - */
    - wake_up_idle_cpu(cpu);
    - spin_unlock_irqrestore(&base->lock, flags);
    + mod_timer_on(timer, timer->expires, cpu);
    }
    EXPORT_SYMBOL_GPL(add_timer_on);




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