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    Subject[RFC][patch 04/12] clocksource watchdog highres enablement
    From: Martin Schwidefsky <schwidefsky@de.ibm.com>

    The clocksource watchdog marks a clock as highres capable before it
    checked the deviation from the watchdog clocksource even for a single
    time. Make sure that the deviation is at least checked once before
    doing the switch to highres mode.

    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: john stultz <johnstul@us.ibm.com>
    Cc: Daniel Walker <dwalker@fifo99.com>
    Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
    ---
    kernel/time/clocksource.c | 47 +++++++++++++++++++++-------------------------
    1 file changed, 22 insertions(+), 25 deletions(-)

    Index: linux-2.6/kernel/time/clocksource.c
    ===================================================================
    --- linux-2.6.orig/kernel/time/clocksource.c
    +++ linux-2.6/kernel/time/clocksource.c
    @@ -153,11 +153,8 @@ static unsigned long watchdog_resumed;
    #define WATCHDOG_INTERVAL (HZ >> 1)
    #define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)

    -static void clocksource_ratewd(struct clocksource *cs, int64_t delta)
    +static void clocksource_unstable(struct clocksource *cs, int64_t delta)
    {
    - if (delta > -WATCHDOG_THRESHOLD && delta < WATCHDOG_THRESHOLD)
    - return;
    -
    printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
    cs->name, delta);
    cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
    @@ -183,31 +180,31 @@ static void clocksource_watchdog(unsigne
    list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
    csnow = cs->read(cs);

    - if (unlikely(resumed)) {
    + /* Clocksource initialized ? */
    + if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
    + cs->flags |= CLOCK_SOURCE_WATCHDOG;
    cs->wd_last = csnow;
    continue;
    }

    - /* Initialized ? */
    - if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
    - if ((cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
    - (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
    - cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
    - /*
    - * We just marked the clocksource as
    - * highres-capable, notify the rest of the
    - * system as well so that we transition
    - * into high-res mode:
    - */
    - tick_clock_notify();
    - }
    - cs->flags |= CLOCK_SOURCE_WATCHDOG;
    - cs->wd_last = csnow;
    - } else {
    - cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
    - cs->wd_last = csnow;
    - /* Check the delta. Might remove from the list ! */
    - clocksource_ratewd(cs, cs_nsec - wd_nsec);
    + /* Check the deviation from the watchdog clocksource. */
    + cs_nsec = cyc2ns(cs, (csnow - cs->wd_last) & cs->mask);
    + cs->wd_last = csnow;
    + if (abs(cs_nsec - wd_nsec) > WATCHDOG_THRESHOLD) {
    + clocksource_unstable(cs, cs_nsec - wd_nsec);
    + continue;
    + }
    +
    + if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
    + (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS) &&
    + (watchdog->flags & CLOCK_SOURCE_IS_CONTINUOUS)) {
    + cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
    + /*
    + * We just marked the clocksource as highres-capable,
    + * notify the rest of the system as well so that we
    + * transition into high-res mode:
    + */
    + tick_clock_notify();
    }
    }

    --
    blue skies,
    Martin.

    "Reality continues to ruin my life." - Calvin.



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