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    Subject[patch 3/4] timers: Add accounting of non deferrable timers
    The code in get_next_timer_interrupt() is suboptimal as it has to run
    through the cascade to find the next expiring timer. On a completely
    idle core we should only do that when there is an active timer
    enqueued and base->next_timer does not give us an fast answer.

    Add accounting of the active timers to the now consolidated
    attach/detach code. I deliberately avoided sanity checks because the
    code is fully symetric and any fiddling with timers w/o using the API
    functions will lead to cute explosions anyway. ulong is big enough
    even on 32bit and if we really run into the situation to have more
    than 1<<32 timers enqueued there, then we are definitely not in a
    state to go idle and run through that code.

    This allows us to fix another shortcoming of get_next_timer_interrupt().

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    ---
    kernel/timer.c | 31 +++++++++++++++++++++++--------
    1 file changed, 23 insertions(+), 8 deletions(-)

    Index: tip/kernel/timer.c
    ===================================================================
    --- tip.orig/kernel/timer.c
    +++ tip/kernel/timer.c
    @@ -77,6 +77,7 @@ struct tvec_base {
    struct timer_list *running_timer;
    unsigned long timer_jiffies;
    unsigned long next_timer;
    + unsigned long active_timers;
    struct tvec_root tv1;
    struct tvec tv2;
    struct tvec tv3;
    @@ -377,11 +378,13 @@ static void internal_add_timer(struct tv
    {
    __internal_add_timer(base, timer);
    /*
    - * Update base->next_timer if this is the earliest one.
    + * Update base->active_timers and base->next_timer
    */
    - if (time_before(timer->expires, base->next_timer) &&
    - !tbase_get_deferrable(timer->base))
    - base->next_timer = timer->expires;
    + if (!tbase_get_deferrable(timer->base)) {
    + if (time_before(timer->expires, base->next_timer))
    + base->next_timer = timer->expires;
    + base->active_timers++;
    + }
    }

    #ifdef CONFIG_TIMER_STATS
    @@ -678,6 +681,14 @@ static inline void detach_timer(struct t
    entry->prev = LIST_POISON2;
    }

    +static inline void
    +detach_expired_timer(struct timer_list *timer, struct tvec_base *base)
    +{
    + detach_timer(timer, true);
    + if (!tbase_get_deferrable(timer->base))
    + timer->base->active_timers--;
    +}
    +
    static int detach_if_pending(struct timer_list *timer, struct tvec_base *base,
    bool clear_pending)
    {
    @@ -685,9 +696,11 @@ static int detach_if_pending(struct time
    return 0;

    detach_timer(timer, clear_pending);
    - if (timer->expires == base->next_timer &&
    - !tbase_get_deferrable(timer->base))
    - base->next_timer = base->timer_jiffies;
    + if (!tbase_get_deferrable(timer->base)) {
    + timer->base->active_timers--;
    + if (timer->expires == base->next_timer)
    + base->next_timer = base->timer_jiffies;
    + }
    return 1;
    }

    @@ -1175,7 +1188,7 @@ static inline void __run_timers(struct t
    timer_stats_account_timer(timer);

    base->running_timer = timer;
    - detach_timer(timer, true);
    + detach_expired_timer(timer, base);

    spin_unlock_irq(&base->lock);
    call_timer_fn(timer, fn, data);
    @@ -1701,6 +1714,7 @@ static int __cpuinit init_timers_cpu(int

    base->timer_jiffies = jiffies;
    base->next_timer = base->timer_jiffies;
    + base->active_timers = 0;
    return 0;
    }

    @@ -1711,6 +1725,7 @@ static void migrate_timer_list(struct tv

    while (!list_empty(head)) {
    timer = list_first_entry(head, struct timer_list, entry);
    + /* We ignore the accounting on the dying cpu */
    detach_timer(timer, false);
    timer_set_base(timer, new_base);
    internal_add_timer(new_base, timer);



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