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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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