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clockevents: Make minimum delay adjustments configurable

The automatic increase of the min_delta_ns of a clockevents device
should be done in the clockevents code as the minimum delay is an
attribute of the clockevents device.

In addition not all architectures want the automatic adjustment, on a
massively virtualized system it can happen that the programming of a
clock event fails several times in a row because the virtual cpu has
been rescheduled quickly enough. In that case the minimum delay will
erroneously be increased with no way back. The new config symbol
GENERIC_CLOCKEVENTS_MIN_ADJUST is used to enable the automatic
adjustment. The config option is selected only for x86.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: john stultz <johnstul@us.ibm.com>
Link: http://lkml.kernel.org/r/20110823133142.494157493@de.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
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commit d1748302f70be7469809809283fe164156a34231 1 parent 29c158e
Martin Schwidefsky authored Thomas Gleixner committed
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1  arch/x86/Kconfig
@@ -68,6 +68,7 @@ config X86
select GENERIC_IRQ_PROBE
select GENERIC_PENDING_IRQ if SMP
select GENERIC_IRQ_SHOW
+ select GENERIC_CLOCKEVENTS_MIN_ADJUST
select IRQ_FORCED_THREADING
select USE_GENERIC_SMP_HELPERS if SMP
select HAVE_BPF_JIT if (X86_64 && NET)
View
2  include/linux/clockchips.h
@@ -140,7 +140,7 @@ extern void clockevents_set_mode(struct clock_event_device *dev,
enum clock_event_mode mode);
extern int clockevents_register_notifier(struct notifier_block *nb);
extern int clockevents_program_event(struct clock_event_device *dev,
- ktime_t expires, ktime_t now);
+ ktime_t expires, bool force);
extern void clockevents_handle_noop(struct clock_event_device *dev);
View
2  kernel/time/Kconfig
@@ -27,3 +27,5 @@ config GENERIC_CLOCKEVENTS_BUILD
default y
depends on GENERIC_CLOCKEVENTS || GENERIC_CLOCKEVENTS_MIGR
+config GENERIC_CLOCKEVENTS_MIN_ADJUST
+ bool
View
125 kernel/time/clockevents.c
@@ -94,42 +94,139 @@ void clockevents_shutdown(struct clock_event_device *dev)
dev->next_event.tv64 = KTIME_MAX;
}
+#ifdef CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST
+
+/* Limit min_delta to a jiffie */
+#define MIN_DELTA_LIMIT (NSEC_PER_SEC / HZ)
+
+/**
+ * clockevents_increase_min_delta - raise minimum delta of a clock event device
+ * @dev: device to increase the minimum delta
+ *
+ * Returns 0 on success, -ETIME when the minimum delta reached the limit.
+ */
+static int clockevents_increase_min_delta(struct clock_event_device *dev)
+{
+ /* Nothing to do if we already reached the limit */
+ if (dev->min_delta_ns >= MIN_DELTA_LIMIT) {
+ printk(KERN_WARNING "CE: Reprogramming failure. Giving up\n");
+ dev->next_event.tv64 = KTIME_MAX;
+ return -ETIME;
+ }
+
+ if (dev->min_delta_ns < 5000)
+ dev->min_delta_ns = 5000;
+ else
+ dev->min_delta_ns += dev->min_delta_ns >> 1;
+
+ if (dev->min_delta_ns > MIN_DELTA_LIMIT)
+ dev->min_delta_ns = MIN_DELTA_LIMIT;
+
+ printk(KERN_WARNING "CE: %s increased min_delta_ns to %llu nsec\n",
+ dev->name ? dev->name : "?",
+ (unsigned long long) dev->min_delta_ns);
+ return 0;
+}
+
+/**
+ * clockevents_program_min_delta - Set clock event device to the minimum delay.
+ * @dev: device to program
+ *
+ * Returns 0 on success, -ETIME when the retry loop failed.
+ */
+static int clockevents_program_min_delta(struct clock_event_device *dev)
+{
+ unsigned long long clc;
+ int64_t delta;
+ int i;
+
+ for (i = 0;;) {
+ delta = dev->min_delta_ns;
+ dev->next_event = ktime_add_ns(ktime_get(), delta);
+
+ if (dev->mode == CLOCK_EVT_MODE_SHUTDOWN)
+ return 0;
+
+ dev->retries++;
+ clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
+ if (dev->set_next_event((unsigned long) clc, dev) == 0)
+ return 0;
+
+ if (++i > 2) {
+ /*
+ * We tried 3 times to program the device with the
+ * given min_delta_ns. Try to increase the minimum
+ * delta, if that fails as well get out of here.
+ */
+ if (clockevents_increase_min_delta(dev))
+ return -ETIME;
+ i = 0;
+ }
+ }
+}
+
+#else /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */
+
+/**
+ * clockevents_program_min_delta - Set clock event device to the minimum delay.
+ * @dev: device to program
+ *
+ * Returns 0 on success, -ETIME when the retry loop failed.
+ */
+static int clockevents_program_min_delta(struct clock_event_device *dev)
+{
+ unsigned long long clc;
+ int64_t delta;
+
+ delta = dev->min_delta_ns;
+ dev->next_event = ktime_add_ns(ktime_get(), delta);
+
+ if (dev->mode == CLOCK_EVT_MODE_SHUTDOWN)
+ return 0;
+
+ dev->retries++;
+ clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
+ return dev->set_next_event((unsigned long) clc, dev);
+}
+
+#endif /* CONFIG_GENERIC_CLOCKEVENTS_MIN_ADJUST */
+
/**
* clockevents_program_event - Reprogram the clock event device.
+ * @dev: device to program
* @expires: absolute expiry time (monotonic clock)
+ * @force: program minimum delay if expires can not be set
*
* Returns 0 on success, -ETIME when the event is in the past.
*/
int clockevents_program_event(struct clock_event_device *dev, ktime_t expires,
- ktime_t now)
+ bool force)
{
unsigned long long clc;
int64_t delta;
+ int rc;
if (unlikely(expires.tv64 < 0)) {
WARN_ON_ONCE(1);
return -ETIME;
}
- delta = ktime_to_ns(ktime_sub(expires, now));
-
- if (delta <= 0)
- return -ETIME;
-
dev->next_event = expires;
if (dev->mode == CLOCK_EVT_MODE_SHUTDOWN)
return 0;
- if (delta > dev->max_delta_ns)
- delta = dev->max_delta_ns;
- if (delta < dev->min_delta_ns)
- delta = dev->min_delta_ns;
+ delta = ktime_to_ns(ktime_sub(expires, ktime_get()));
+ if (delta <= 0)
+ return force ? clockevents_program_min_delta(dev) : -ETIME;
- clc = delta * dev->mult;
- clc >>= dev->shift;
+ delta = min(delta, (int64_t) dev->max_delta_ns);
+ delta = max(delta, (int64_t) dev->min_delta_ns);
- return dev->set_next_event((unsigned long) clc, dev);
+ clc = ((unsigned long long) delta * dev->mult) >> dev->shift;
+ rc = dev->set_next_event((unsigned long) clc, dev);
+
+ return (rc && force) ? clockevents_program_min_delta(dev) : rc;
}
/**
@@ -258,7 +355,7 @@ int clockevents_update_freq(struct clock_event_device *dev, u32 freq)
if (dev->mode != CLOCK_EVT_MODE_ONESHOT)
return 0;
- return clockevents_program_event(dev, dev->next_event, ktime_get());
+ return clockevents_program_event(dev, dev->next_event, false);
}
/*
View
4 kernel/time/tick-broadcast.c
@@ -194,7 +194,7 @@ static void tick_handle_periodic_broadcast(struct clock_event_device *dev)
for (next = dev->next_event; ;) {
next = ktime_add(next, tick_period);
- if (!clockevents_program_event(dev, next, ktime_get()))
+ if (!clockevents_program_event(dev, next, false))
return;
tick_do_periodic_broadcast();
}
@@ -373,7 +373,7 @@ static int tick_broadcast_set_event(ktime_t expires, int force)
{
struct clock_event_device *bc = tick_broadcast_device.evtdev;
- return tick_dev_program_event(bc, expires, force);
+ return clockevents_program_event(bc, expires, force);
}
int tick_resume_broadcast_oneshot(struct clock_event_device *bc)
View
4 kernel/time/tick-common.c
@@ -94,7 +94,7 @@ void tick_handle_periodic(struct clock_event_device *dev)
*/
next = ktime_add(dev->next_event, tick_period);
for (;;) {
- if (!clockevents_program_event(dev, next, ktime_get()))
+ if (!clockevents_program_event(dev, next, false))
return;
/*
* Have to be careful here. If we're in oneshot mode,
@@ -137,7 +137,7 @@ void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
for (;;) {
- if (!clockevents_program_event(dev, next, ktime_get()))
+ if (!clockevents_program_event(dev, next, false))
return;
next = ktime_add(next, tick_period);
}
View
2  kernel/time/tick-internal.h
@@ -26,8 +26,6 @@ extern void clockevents_shutdown(struct clock_event_device *dev);
extern void tick_setup_oneshot(struct clock_event_device *newdev,
void (*handler)(struct clock_event_device *),
ktime_t nextevt);
-extern int tick_dev_program_event(struct clock_event_device *dev,
- ktime_t expires, int force);
extern int tick_program_event(ktime_t expires, int force);
extern void tick_oneshot_notify(void);
extern int tick_switch_to_oneshot(void (*handler)(struct clock_event_device *));
View
77 kernel/time/tick-oneshot.c
@@ -21,74 +21,6 @@
#include "tick-internal.h"
-/* Limit min_delta to a jiffie */
-#define MIN_DELTA_LIMIT (NSEC_PER_SEC / HZ)
-
-static int tick_increase_min_delta(struct clock_event_device *dev)
-{
- /* Nothing to do if we already reached the limit */
- if (dev->min_delta_ns >= MIN_DELTA_LIMIT)
- return -ETIME;
-
- if (dev->min_delta_ns < 5000)
- dev->min_delta_ns = 5000;
- else
- dev->min_delta_ns += dev->min_delta_ns >> 1;
-
- if (dev->min_delta_ns > MIN_DELTA_LIMIT)
- dev->min_delta_ns = MIN_DELTA_LIMIT;
-
- printk(KERN_WARNING "CE: %s increased min_delta_ns to %llu nsec\n",
- dev->name ? dev->name : "?",
- (unsigned long long) dev->min_delta_ns);
- return 0;
-}
-
-/**
- * tick_program_event internal worker function
- */
-int tick_dev_program_event(struct clock_event_device *dev, ktime_t expires,
- int force)
-{
- ktime_t now = ktime_get();
- int i;
-
- for (i = 0;;) {
- int ret = clockevents_program_event(dev, expires, now);
-
- if (!ret || !force)
- return ret;
-
- dev->retries++;
- /*
- * We tried 3 times to program the device with the given
- * min_delta_ns. If that's not working then we increase it
- * and emit a warning.
- */
- if (++i > 2) {
- /* Increase the min. delta and try again */
- if (tick_increase_min_delta(dev)) {
- /*
- * Get out of the loop if min_delta_ns
- * hit the limit already. That's
- * better than staying here forever.
- *
- * We clear next_event so we have a
- * chance that the box survives.
- */
- printk(KERN_WARNING
- "CE: Reprogramming failure. Giving up\n");
- dev->next_event.tv64 = KTIME_MAX;
- return -ETIME;
- }
- i = 0;
- }
-
- now = ktime_get();
- expires = ktime_add_ns(now, dev->min_delta_ns);
- }
-}
-
/**
* tick_program_event
*/
@@ -96,7 +28,7 @@ int tick_program_event(ktime_t expires, int force)
{
struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
- return tick_dev_program_event(dev, expires, force);
+ return clockevents_program_event(dev, expires, force);
}
/**
@@ -104,11 +36,10 @@ int tick_program_event(ktime_t expires, int force)
*/
void tick_resume_oneshot(void)
{
- struct tick_device *td = &__get_cpu_var(tick_cpu_device);
- struct clock_event_device *dev = td->evtdev;
+ struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
clockevents_set_mode(dev, CLOCK_EVT_MODE_ONESHOT);
- tick_program_event(ktime_get(), 1);
+ clockevents_program_event(dev, ktime_get(), true);
}
/**
@@ -120,7 +51,7 @@ void tick_setup_oneshot(struct clock_event_device *newdev,
{
newdev->event_handler = handler;
clockevents_set_mode(newdev, CLOCK_EVT_MODE_ONESHOT);
- tick_dev_program_event(newdev, next_event, 1);
+ clockevents_program_event(newdev, next_event, true);
}
/**
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