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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>
This commit is contained in:
Martin Schwidefsky 2011-08-23 15:29:42 +02:00 committed by Thomas Gleixner
parent 29c158e81c
commit d1748302f7
8 changed files with 123 additions and 94 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/Kconfig
View File

@ -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)

2
include/linux/clockchips.h
View File

@ -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);

2
kernel/time/Kconfig
View File

@ -27,3 +27,5 @@ config GENERIC_CLOCKEVENTS_BUILD
default y
depends on GENERIC_CLOCKEVENTS || GENERIC_CLOCKEVENTS_MIGR
config GENERIC_CLOCKEVENTS_MIN_ADJUST
bool

125
kernel/time/clockevents.c
View File

@ -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);
}
/*

4
kernel/time/tick-broadcast.c
View File

@ -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)

4
kernel/time/tick-common.c
View File

@ -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);
}

2
kernel/time/tick-internal.h
View File

@ -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 *));

77
kernel/time/tick-oneshot.c
View File

@ -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);
}
/**