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    Subject[patch 08/22] dynticks: extend next_timer_interrupt() to use a reference jiffie
    From: Thomas Gleixner <tglx@linutronix.de>

    For CONFIG_NO_HZ we need to calculate the next timer wheel event based to a
    given jiffie value. Extend the existing code to allow the extra now argument.
    Provide a compability function for the existing implementations to call the
    function with now = jiffies. This also solves the racyness of the original
    code vs. jiffies changing during the iteration.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>
    include/linux/timer.h | 10 +++++
    kernel/timer.c | 97 ++++++++++++++++++++++++++++++++++++--------------
    2 files changed, 81 insertions(+), 26 deletions(-)

    Index: linux-2.6.18-mm3/include/linux/timer.h
    ===================================================================
    --- linux-2.6.18-mm3.orig/include/linux/timer.h 2006-10-04 18:13:52.000000000 +0200
    +++ linux-2.6.18-mm3/include/linux/timer.h 2006-10-04 18:13:55.000000000 +0200
    @@ -61,7 +61,17 @@ extern int del_timer(struct timer_list *
    extern int __mod_timer(struct timer_list *timer, unsigned long expires);
    extern int mod_timer(struct timer_list *timer, unsigned long expires);

    +/*
    + * Return when the next timer-wheel timeout occurs (in absolute jiffies),
    + * locks the timer base:
    + */
    extern unsigned long next_timer_interrupt(void);
    +/*
    + * Return when the next timer-wheel timeout occurs (in absolute jiffies),
    + * locks the timer base and does the comparison against the given
    + * jiffie.
    + */
    +extern unsigned long get_next_timer_interrupt(unsigned long now);

    /***
    * add_timer - start a timer
    Index: linux-2.6.18-mm3/kernel/timer.c
    ===================================================================
    --- linux-2.6.18-mm3.orig/kernel/timer.c 2006-10-04 18:13:54.000000000 +0200
    +++ linux-2.6.18-mm3/kernel/timer.c 2006-10-04 18:13:55.000000000 +0200
    @@ -468,29 +468,14 @@ static inline void __run_timers(tvec_bas
    * is used on S/390 to stop all activity when a cpus is idle.
    * This functions needs to be called disabled.
    */
    -unsigned long next_timer_interrupt(void)
    +unsigned long __next_timer_interrupt(tvec_base_t *base, unsigned long now)
    {
    - tvec_base_t *base;
    struct list_head *list;
    - struct timer_list *nte;
    + struct timer_list *nte, *found = NULL;
    unsigned long expires;
    - unsigned long hr_expires = MAX_JIFFY_OFFSET;
    - ktime_t hr_delta;
    tvec_t *varray[4];
    int i, j;

    - hr_delta = hrtimer_get_next_event();
    - if (hr_delta.tv64 != KTIME_MAX) {
    - struct timespec tsdelta;
    - tsdelta = ktime_to_timespec(hr_delta);
    - hr_expires = timespec_to_jiffies(&tsdelta);
    - if (hr_expires < 3)
    - return hr_expires + jiffies;
    - }
    - hr_expires += jiffies;
    -
    - base = __get_cpu_var(tvec_bases);
    - spin_lock(&base->lock);
    expires = base->timer_jiffies + (LONG_MAX >> 1);
    list = NULL;

    @@ -499,6 +484,7 @@ unsigned long next_timer_interrupt(void)
    do {
    list_for_each_entry(nte, base->tv1.vec + j, entry) {
    expires = nte->expires;
    + found = nte;
    if (j < (base->timer_jiffies & TVR_MASK))
    list = base->tv2.vec + (INDEX(0));
    goto found;
    @@ -518,9 +504,12 @@ unsigned long next_timer_interrupt(void)
    j = (j + 1) & TVN_MASK;
    continue;
    }
    - list_for_each_entry(nte, varray[i]->vec + j, entry)
    - if (time_before(nte->expires, expires))
    + list_for_each_entry(nte, varray[i]->vec + j, entry) {
    + if (time_before(nte->expires, expires)) {
    expires = nte->expires;
    + found = nte;
    + }
    + }
    if (j < (INDEX(i)) && i < 3)
    list = varray[i + 1]->vec + (INDEX(i + 1));
    goto found;
    @@ -534,10 +523,59 @@ found:
    * where we found the timer element.
    */
    list_for_each_entry(nte, list, entry) {
    - if (time_before(nte->expires, expires))
    + if (time_before(nte->expires, expires)) {
    expires = nte->expires;
    + found = nte;
    + }
    }
    }
    + WARN_ON(!found);
    +
    + return expires;
    +}
    +
    +#ifdef CONFIG_NO_HZ
    +
    +unsigned long get_next_timer_interrupt(unsigned long now)
    +{
    + tvec_base_t *base = __get_cpu_var(tvec_bases);
    + unsigned long expires;
    +
    + spin_lock(&base->lock);
    + expires = __next_timer_interrupt(base, now);
    + spin_unlock(&base->lock);
    +
    + /*
    + * 'Timer wheel time' can lag behind 'jiffies time' due to
    + * delayed processing, so make sure we return a value that
    + * makes sense externally. base->timer_jiffies is unchanged,
    + * so it is safe to access it outside the lock.
    + */
    +
    + return expires - (now - base->timer_jiffies);
    +}
    +
    +#else
    +
    +unsigned long next_timer_interrupt(void)
    +{
    + tvec_base_t *base = __get_cpu_var(tvec_bases);
    + unsigned long expires;
    + unsigned long now = jiffies;
    + unsigned long hr_expires = MAX_JIFFY_OFFSET;
    + ktime_t hr_delta = hrtimer_get_next_event();
    +
    + if (hr_delta.tv64 != KTIME_MAX) {
    + struct timespec tsdelta;
    + tsdelta = ktime_to_timespec(hr_delta);
    + hr_expires = timespec_to_jiffies(&tsdelta);
    + if (hr_expires < 3)
    + return hr_expires + now;
    + }
    + hr_expires += now;
    +
    + spin_lock(&base->lock);
    + expires = __next_timer_interrupt(base, now);
    spin_unlock(&base->lock);

    /*
    @@ -553,16 +591,23 @@ found:
    * would falsely evaluate to true. If that is the case, just
    * return jiffies so that we can immediately fire the local timer
    */
    - if (time_before(expires, jiffies))
    - return jiffies;
    + if (time_before(expires, now))
    + expires = now;
    + else if (time_before(hr_expires, expires))
    + expires = hr_expires;

    - if (time_before(hr_expires, expires))
    - return hr_expires;
    -
    - return expires;
    + /*
    + * 'Timer wheel time' can lag behind 'jiffies time' due to
    + * delayed processing, so make sure we return a value that
    + * makes sense externally. base->timer_jiffies is unchanged,
    + * so it is safe to access it outside the lock.
    + */
    + return expires - (now - base->timer_jiffies);
    }
    #endif

    +#endif
    +
    /******************************************************************/

    /*
    --

    -
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