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Subject[tip:timers/core] clocksource: Move watchdog downgrade to a work queue thread
Commit-ID:  c55c87c892c1875deace0c8fc28787335277fdf2
Gitweb: http://git.kernel.org/tip/c55c87c892c1875deace0c8fc28787335277fdf2
Author: Martin Schwidefsky <schwidefsky@de.ibm.com>
AuthorDate: Fri, 14 Aug 2009 15:47:25 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 15 Aug 2009 10:55:46 +0200

clocksource: Move watchdog downgrade to a work queue thread

Move the downgrade of an unstable clocksource from the timer interrupt
context into the process context of a work queue thread. This is
needed to be able to do the clocksource switch with stop_machine.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134809.354926067@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>


---
include/linux/clocksource.h | 1 +
kernel/time/clocksource.c | 56 ++++++++++++++++++++++++++++++-------------
2 files changed, 40 insertions(+), 17 deletions(-)

diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index f263b3a..19ad43a 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -213,6 +213,7 @@ extern struct clocksource *clock; /* current clocksource */

#define CLOCK_SOURCE_WATCHDOG 0x10
#define CLOCK_SOURCE_VALID_FOR_HRES 0x20
+#define CLOCK_SOURCE_UNSTABLE 0x40

/* simplify initialization of mask field */
#define CLOCKSOURCE_MASK(bits) (cycle_t)((bits) < 64 ? ((1ULL<<(bits))-1) : -1)
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 56aaa74..f150801 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -143,10 +143,13 @@ fs_initcall(clocksource_done_booting);
static LIST_HEAD(watchdog_list);
static struct clocksource *watchdog;
static struct timer_list watchdog_timer;
+static struct work_struct watchdog_work;
static DEFINE_SPINLOCK(watchdog_lock);
static cycle_t watchdog_last;
static int watchdog_running;

+static void clocksource_watchdog_work(struct work_struct *work);
+
/*
* Interval: 0.5sec Threshold: 0.0625s
*/
@@ -158,15 +161,16 @@ static void clocksource_unstable(struct clocksource *cs, int64_t delta)
printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
cs->name, delta);
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
- clocksource_change_rating(cs, 0);
- list_del(&cs->wd_list);
+ cs->flags |= CLOCK_SOURCE_UNSTABLE;
+ schedule_work(&watchdog_work);
}

static void clocksource_watchdog(unsigned long data)
{
- struct clocksource *cs, *tmp;
+ struct clocksource *cs;
cycle_t csnow, wdnow;
int64_t wd_nsec, cs_nsec;
+ int next_cpu;

spin_lock(&watchdog_lock);
if (!watchdog_running)
@@ -176,7 +180,12 @@ static void clocksource_watchdog(unsigned long data)
wd_nsec = cyc2ns(watchdog, (wdnow - watchdog_last) & watchdog->mask);
watchdog_last = wdnow;

- list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list) {
+ list_for_each_entry(cs, &watchdog_list, wd_list) {
+
+ /* Clocksource already marked unstable? */
+ if (cs->flags & CLOCK_SOURCE_UNSTABLE)
+ continue;
+
csnow = cs->read(cs);

/* Clocksource initialized ? */
@@ -207,19 +216,15 @@ static void clocksource_watchdog(unsigned long data)
}
}

- if (!list_empty(&watchdog_list)) {
- /*
- * Cycle through CPUs to check if the CPUs stay
- * synchronized to each other.
- */
- int next_cpu = cpumask_next(raw_smp_processor_id(),
- cpu_online_mask);
-
- if (next_cpu >= nr_cpu_ids)
- next_cpu = cpumask_first(cpu_online_mask);
- watchdog_timer.expires += WATCHDOG_INTERVAL;
- add_timer_on(&watchdog_timer, next_cpu);
- }
+ /*
+ * Cycle through CPUs to check if the CPUs stay synchronized
+ * to each other.
+ */
+ next_cpu = cpumask_next(raw_smp_processor_id(), cpu_online_mask);
+ if (next_cpu >= nr_cpu_ids)
+ next_cpu = cpumask_first(cpu_online_mask);
+ watchdog_timer.expires += WATCHDOG_INTERVAL;
+ add_timer_on(&watchdog_timer, next_cpu);
out:
spin_unlock(&watchdog_lock);
}
@@ -228,6 +233,7 @@ static inline void clocksource_start_watchdog(void)
{
if (watchdog_running || !watchdog || list_empty(&watchdog_list))
return;
+ INIT_WORK(&watchdog_work, clocksource_watchdog_work);
init_timer(&watchdog_timer);
watchdog_timer.function = clocksource_watchdog;
watchdog_last = watchdog->read(watchdog);
@@ -313,6 +319,22 @@ static void clocksource_dequeue_watchdog(struct clocksource *cs)
spin_unlock_irqrestore(&watchdog_lock, flags);
}

+static void clocksource_watchdog_work(struct work_struct *work)
+{
+ struct clocksource *cs, *tmp;
+ unsigned long flags;
+
+ spin_lock_irqsave(&watchdog_lock, flags);
+ list_for_each_entry_safe(cs, tmp, &watchdog_list, wd_list)
+ if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
+ list_del_init(&cs->wd_list);
+ clocksource_change_rating(cs, 0);
+ }
+ /* Check if the watchdog timer needs to be stopped. */
+ clocksource_stop_watchdog();
+ spin_unlock(&watchdog_lock);
+}
+
#else /* CONFIG_CLOCKSOURCE_WATCHDOG */

static void clocksource_enqueue_watchdog(struct clocksource *cs)

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