linux/kernel/time/clocksource.c

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/*
* linux/kernel/time/clocksource.c
*
* This file contains the functions which manage clocksource drivers.
*
* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
* TODO WishList:
* o Allow clocksource drivers to be unregistered
*/
#include <linux/clocksource.h>
#include <linux/sysdev.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
#include <linux/tick.h>
#include <linux/kthread.h>
void timecounter_init(struct timecounter *tc,
const struct cyclecounter *cc,
u64 start_tstamp)
{
tc->cc = cc;
tc->cycle_last = cc->read(cc);
tc->nsec = start_tstamp;
}
EXPORT_SYMBOL(timecounter_init);
/**
* timecounter_read_delta - get nanoseconds since last call of this function
* @tc: Pointer to time counter
*
* When the underlying cycle counter runs over, this will be handled
* correctly as long as it does not run over more than once between
* calls.
*
* The first call to this function for a new time counter initializes
* the time tracking and returns an undefined result.
*/
static u64 timecounter_read_delta(struct timecounter *tc)
{
cycle_t cycle_now, cycle_delta;
u64 ns_offset;
/* read cycle counter: */
cycle_now = tc->cc->read(tc->cc);
/* calculate the delta since the last timecounter_read_delta(): */
cycle_delta = (cycle_now - tc->cycle_last) & tc->cc->mask;
/* convert to nanoseconds: */
ns_offset = cyclecounter_cyc2ns(tc->cc, cycle_delta);
/* update time stamp of timecounter_read_delta() call: */
tc->cycle_last = cycle_now;
return ns_offset;
}
u64 timecounter_read(struct timecounter *tc)
{
u64 nsec;
/* increment time by nanoseconds since last call */
nsec = timecounter_read_delta(tc);
nsec += tc->nsec;
tc->nsec = nsec;
return nsec;
}
EXPORT_SYMBOL(timecounter_read);
u64 timecounter_cyc2time(struct timecounter *tc,
cycle_t cycle_tstamp)
{
u64 cycle_delta = (cycle_tstamp - tc->cycle_last) & tc->cc->mask;
u64 nsec;
/*
* Instead of always treating cycle_tstamp as more recent
* than tc->cycle_last, detect when it is too far in the
* future and treat it as old time stamp instead.
*/
if (cycle_delta > tc->cc->mask / 2) {
cycle_delta = (tc->cycle_last - cycle_tstamp) & tc->cc->mask;
nsec = tc->nsec - cyclecounter_cyc2ns(tc->cc, cycle_delta);
} else {
nsec = cyclecounter_cyc2ns(tc->cc, cycle_delta) + tc->nsec;
}
return nsec;
}
EXPORT_SYMBOL(timecounter_cyc2time);
/*[Clocksource internal variables]---------
* curr_clocksource:
* currently selected clocksource.
* clocksource_list:
* linked list with the registered clocksources
* clocksource_mutex:
* protects manipulations to curr_clocksource and the clocksource_list
* override_name:
* Name of the user-specified clocksource.
*/
static struct clocksource *curr_clocksource;
static LIST_HEAD(clocksource_list);
static DEFINE_MUTEX(clocksource_mutex);
static char override_name[32];
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
static void clocksource_watchdog_work(struct work_struct *work);
static LIST_HEAD(watchdog_list);
static struct clocksource *watchdog;
static struct timer_list watchdog_timer;
static DECLARE_WORK(watchdog_work, clocksource_watchdog_work);
static DEFINE_SPINLOCK(watchdog_lock);
static cycle_t watchdog_last;
static int watchdog_running;
static int clocksource_watchdog_kthread(void *data);
static void __clocksource_change_rating(struct clocksource *cs, int rating);
/*
* Interval: 0.5sec Threshold: 0.0625s
*/
#define WATCHDOG_INTERVAL (HZ >> 1)
#define WATCHDOG_THRESHOLD (NSEC_PER_SEC >> 4)
static void clocksource_watchdog_work(struct work_struct *work)
{
/*
* If kthread_run fails the next watchdog scan over the
* watchdog_list will find the unstable clock again.
*/
kthread_run(clocksource_watchdog_kthread, NULL, "kwatchdog");
}
static void __clocksource_unstable(struct clocksource *cs)
{
cs->flags &= ~(CLOCK_SOURCE_VALID_FOR_HRES | CLOCK_SOURCE_WATCHDOG);
cs->flags |= CLOCK_SOURCE_UNSTABLE;
schedule_work(&watchdog_work);
}
static void clocksource_unstable(struct clocksource *cs, int64_t delta)
{
printk(KERN_WARNING "Clocksource %s unstable (delta = %Ld ns)\n",
cs->name, delta);
__clocksource_unstable(cs);
}
/**
* clocksource_mark_unstable - mark clocksource unstable via watchdog
* @cs: clocksource to be marked unstable
*
* This function is called instead of clocksource_change_rating from
* cpu hotplug code to avoid a deadlock between the clocksource mutex
* and the cpu hotplug mutex. It defers the update of the clocksource
* to the watchdog thread.
*/
void clocksource_mark_unstable(struct clocksource *cs)
{
unsigned long flags;
spin_lock_irqsave(&watchdog_lock, flags);
if (!(cs->flags & CLOCK_SOURCE_UNSTABLE)) {
if (list_empty(&cs->wd_list))
list_add(&cs->wd_list, &watchdog_list);
__clocksource_unstable(cs);
}
spin_unlock_irqrestore(&watchdog_lock, flags);
}
static void clocksource_watchdog(unsigned long data)
{
struct clocksource *cs;
cycle_t csnow, wdnow;
int64_t wd_nsec, cs_nsec;
int next_cpu;
spin_lock(&watchdog_lock);
if (!watchdog_running)
goto out;
wdnow = watchdog->read(watchdog);
wd_nsec = clocksource_cyc2ns((wdnow - watchdog_last) & watchdog->mask,
watchdog->mult, watchdog->shift);
watchdog_last = wdnow;
list_for_each_entry(cs, &watchdog_list, wd_list) {
/* Clocksource already marked unstable? */
if (cs->flags & CLOCK_SOURCE_UNSTABLE) {
schedule_work(&watchdog_work);
continue;
}
csnow = cs->read(cs);
/* Clocksource initialized ? */
if (!(cs->flags & CLOCK_SOURCE_WATCHDOG)) {
cs->flags |= CLOCK_SOURCE_WATCHDOG;
cs->wd_last = csnow;
continue;
}
/* Check the deviation from the watchdog clocksource. */
cs_nsec = clocksource_cyc2ns((csnow - cs->wd_last) &
cs->mask, cs->mult, cs->shift);
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();
}
}
/*
* 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);
}
static inline void clocksource_start_watchdog(void)
{
if (watchdog_running || !watchdog || list_empty(&watchdog_list))
return;
init_timer(&watchdog_timer);
watchdog_timer.function = clocksource_watchdog;
watchdog_last = watchdog->read(watchdog);
watchdog_timer.expires = jiffies + WATCHDOG_INTERVAL;
add_timer_on(&watchdog_timer, cpumask_first(cpu_online_mask));
watchdog_running = 1;
}
static inline void clocksource_stop_watchdog(void)
{
if (!watchdog_running || (watchdog && !list_empty(&watchdog_list)))
return;
del_timer(&watchdog_timer);
watchdog_running = 0;
}
static inline void clocksource_reset_watchdog(void)
{
struct clocksource *cs;
list_for_each_entry(cs, &watchdog_list, wd_list)
cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
}
static void clocksource_resume_watchdog(void)
{
unsigned long flags;
spin_lock_irqsave(&watchdog_lock, flags);
clocksource_reset_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
}
static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
unsigned long flags;
spin_lock_irqsave(&watchdog_lock, flags);
if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
/* cs is a clocksource to be watched. */
list_add(&cs->wd_list, &watchdog_list);
cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
} else {
/* cs is a watchdog. */
if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
/* Pick the best watchdog. */
if (!watchdog || cs->rating > watchdog->rating) {
watchdog = cs;
/* Reset watchdog cycles */
clocksource_reset_watchdog();
}
}
/* Check if the watchdog timer needs to be started. */
clocksource_start_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
}
static void clocksource_dequeue_watchdog(struct clocksource *cs)
{
struct clocksource *tmp;
unsigned long flags;
spin_lock_irqsave(&watchdog_lock, flags);
if (cs->flags & CLOCK_SOURCE_MUST_VERIFY) {
/* cs is a watched clocksource. */
list_del_init(&cs->wd_list);
} else if (cs == watchdog) {
/* Reset watchdog cycles */
clocksource_reset_watchdog();
/* Current watchdog is removed. Find an alternative. */
watchdog = NULL;
list_for_each_entry(tmp, &clocksource_list, list) {
if (tmp == cs || tmp->flags & CLOCK_SOURCE_MUST_VERIFY)
continue;
if (!watchdog || tmp->rating > watchdog->rating)
watchdog = tmp;
}
}
cs->flags &= ~CLOCK_SOURCE_WATCHDOG;
/* Check if the watchdog timer needs to be stopped. */
clocksource_stop_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
}
static int clocksource_watchdog_kthread(void *data)
{
struct clocksource *cs, *tmp;
unsigned long flags;
LIST_HEAD(unstable);
mutex_lock(&clocksource_mutex);
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);
list_add(&cs->wd_list, &unstable);
}
/* Check if the watchdog timer needs to be stopped. */
clocksource_stop_watchdog();
spin_unlock_irqrestore(&watchdog_lock, flags);
/* Needs to be done outside of watchdog lock */
list_for_each_entry_safe(cs, tmp, &unstable, wd_list) {
list_del_init(&cs->wd_list);
__clocksource_change_rating(cs, 0);
}
mutex_unlock(&clocksource_mutex);
return 0;
}
#else /* CONFIG_CLOCKSOURCE_WATCHDOG */
static void clocksource_enqueue_watchdog(struct clocksource *cs)
{
if (cs->flags & CLOCK_SOURCE_IS_CONTINUOUS)
cs->flags |= CLOCK_SOURCE_VALID_FOR_HRES;
}
static inline void clocksource_dequeue_watchdog(struct clocksource *cs) { }
static inline void clocksource_resume_watchdog(void) { }
#endif /* CONFIG_CLOCKSOURCE_WATCHDOG */
/**
* clocksource_resume - resume the clocksource(s)
*/
void clocksource_resume(void)
{
struct clocksource *cs;
mutex_lock(&clocksource_mutex);
list_for_each_entry(cs, &clocksource_list, list)
if (cs->resume)
cs->resume();
clocksource_resume_watchdog();
mutex_unlock(&clocksource_mutex);
}
/**
* clocksource_touch_watchdog - Update watchdog
*
* Update the watchdog after exception contexts such as kgdb so as not
* to incorrectly trip the watchdog.
*
*/
void clocksource_touch_watchdog(void)
{
clocksource_resume_watchdog();
}
#ifdef CONFIG_GENERIC_TIME
static int finished_booting;
/**
* clocksource_select - Select the best clocksource available
*
* Private function. Must hold clocksource_mutex when called.
*
* Select the clocksource with the best rating, or the clocksource,
* which is selected by userspace override.
*/
static void clocksource_select(void)
{
struct clocksource *best, *cs;
if (!finished_booting || list_empty(&clocksource_list))
return;
/* First clocksource on the list has the best rating. */
best = list_first_entry(&clocksource_list, struct clocksource, list);
/* Check for the override clocksource. */
list_for_each_entry(cs, &clocksource_list, list) {
if (strcmp(cs->name, override_name) != 0)
continue;
/*
* Check to make sure we don't switch to a non-highres
* capable clocksource if the tick code is in oneshot
* mode (highres or nohz)
*/
if (!(cs->flags & CLOCK_SOURCE_VALID_FOR_HRES) &&
tick_oneshot_mode_active()) {
/* Override clocksource cannot be used. */
printk(KERN_WARNING "Override clocksource %s is not "
"HRT compatible. Cannot switch while in "
"HRT/NOHZ mode\n", cs->name);
override_name[0] = 0;
} else
/* Override clocksource can be used. */
best = cs;
break;
}
if (curr_clocksource != best) {
printk(KERN_INFO "Switching to clocksource %s\n", best->name);
curr_clocksource = best;
timekeeping_notify(curr_clocksource);
}
}
/*
* clocksource_done_booting - Called near the end of core bootup
*
* Hack to avoid lots of clocksource churn at boot time.
* We use fs_initcall because we want this to start before
* device_initcall but after subsys_initcall.
*/
static int __init clocksource_done_booting(void)
{
finished_booting = 1;
mutex_lock(&clocksource_mutex);
clocksource_select();
mutex_unlock(&clocksource_mutex);
return 0;
}
fs_initcall(clocksource_done_booting);
#else /* CONFIG_GENERIC_TIME */
static inline void clocksource_select(void) { }
#endif
/*
* Enqueue the clocksource sorted by rating
*/
static void clocksource_enqueue(struct clocksource *cs)
{
struct list_head *entry = &clocksource_list;
struct clocksource *tmp;
list_for_each_entry(tmp, &clocksource_list, list)
/* Keep track of the place, where to insert */
if (tmp->rating >= cs->rating)
entry = &tmp->list;
list_add(&cs->list, entry);
}
/**
* clocksource_register - Used to install new clocksources
* @t: clocksource to be registered
*
* Returns -EBUSY if registration fails, zero otherwise.
*/
int clocksource_register(struct clocksource *cs)
{
mutex_lock(&clocksource_mutex);
clocksource_enqueue(cs);
clocksource_select();
clocksource_enqueue_watchdog(cs);
mutex_unlock(&clocksource_mutex);
return 0;
}
EXPORT_SYMBOL(clocksource_register);
static void __clocksource_change_rating(struct clocksource *cs, int rating)
{
list_del(&cs->list);
cs->rating = rating;
clocksource_enqueue(cs);
clocksource_select();
}
/**
* clocksource_change_rating - Change the rating of a registered clocksource
*/
void clocksource_change_rating(struct clocksource *cs, int rating)
{
mutex_lock(&clocksource_mutex);
__clocksource_change_rating(cs, rating);
mutex_unlock(&clocksource_mutex);
}
EXPORT_SYMBOL(clocksource_change_rating);
/**
* clocksource_unregister - remove a registered clocksource
*/
void clocksource_unregister(struct clocksource *cs)
{
mutex_lock(&clocksource_mutex);
clocksource_dequeue_watchdog(cs);
list_del(&cs->list);
clocksource_select();
mutex_unlock(&clocksource_mutex);
}
EXPORT_SYMBOL(clocksource_unregister);
#ifdef CONFIG_SYSFS
/**
* sysfs_show_current_clocksources - sysfs interface for current clocksource
* @dev: unused
* @buf: char buffer to be filled with clocksource list
*
* Provides sysfs interface for listing current clocksource.
*/
static ssize_t
sysfs_show_current_clocksources(struct sys_device *dev,
struct sysdev_attribute *attr, char *buf)
{
ssize_t count = 0;
mutex_lock(&clocksource_mutex);
count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
mutex_unlock(&clocksource_mutex);
return count;
}
/**
* sysfs_override_clocksource - interface for manually overriding clocksource
* @dev: unused
* @buf: name of override clocksource
* @count: length of buffer
*
* Takes input from sysfs interface for manually overriding the default
* clocksource selction.
*/
static ssize_t sysfs_override_clocksource(struct sys_device *dev,
struct sysdev_attribute *attr,
const char *buf, size_t count)
{
size_t ret = count;
/* strings from sysfs write are not 0 terminated! */
if (count >= sizeof(override_name))
return -EINVAL;
/* strip of \n: */
if (buf[count-1] == '\n')
count--;
mutex_lock(&clocksource_mutex);
if (count > 0)
memcpy(override_name, buf, count);
override_name[count] = 0;
clocksource_select();
mutex_unlock(&clocksource_mutex);
return ret;
}
/**
* sysfs_show_available_clocksources - sysfs interface for listing clocksource
* @dev: unused
* @buf: char buffer to be filled with clocksource list
*
* Provides sysfs interface for listing registered clocksources
*/
static ssize_t
sysfs_show_available_clocksources(struct sys_device *dev,
struct sysdev_attribute *attr,
char *buf)
{
struct clocksource *src;
ssize_t count = 0;
mutex_lock(&clocksource_mutex);
list_for_each_entry(src, &clocksource_list, list) {
/*
* Don't show non-HRES clocksource if the tick code is
* in one shot mode (highres=on or nohz=on)
*/
if (!tick_oneshot_mode_active() ||
(src->flags & CLOCK_SOURCE_VALID_FOR_HRES))
count += snprintf(buf + count,
max((ssize_t)PAGE_SIZE - count, (ssize_t)0),
"%s ", src->name);
}
mutex_unlock(&clocksource_mutex);
count += snprintf(buf + count,
max((ssize_t)PAGE_SIZE - count, (ssize_t)0), "\n");
return count;
}
/*
* Sysfs setup bits:
*/
static SYSDEV_ATTR(current_clocksource, 0644, sysfs_show_current_clocksources,
sysfs_override_clocksource);
static SYSDEV_ATTR(available_clocksource, 0444,
sysfs_show_available_clocksources, NULL);
static struct sysdev_class clocksource_sysclass = {
.name = "clocksource",
};
static struct sys_device device_clocksource = {
.id = 0,
.cls = &clocksource_sysclass,
};
static int __init init_clocksource_sysfs(void)
{
int error = sysdev_class_register(&clocksource_sysclass);
if (!error)
error = sysdev_register(&device_clocksource);
if (!error)
error = sysdev_create_file(
&device_clocksource,
&attr_current_clocksource);
if (!error)
error = sysdev_create_file(
&device_clocksource,
&attr_available_clocksource);
return error;
}
device_initcall(init_clocksource_sysfs);
#endif /* CONFIG_SYSFS */
/**
* boot_override_clocksource - boot clock override
* @str: override name
*
* Takes a clocksource= boot argument and uses it
* as the clocksource override name.
*/
static int __init boot_override_clocksource(char* str)
{
mutex_lock(&clocksource_mutex);
if (str)
strlcpy(override_name, str, sizeof(override_name));
mutex_unlock(&clocksource_mutex);
return 1;
}
__setup("clocksource=", boot_override_clocksource);
/**
* boot_override_clock - Compatibility layer for deprecated boot option
* @str: override name
*
* DEPRECATED! Takes a clock= boot argument and uses it
* as the clocksource override name
*/
static int __init boot_override_clock(char* str)
{
if (!strcmp(str, "pmtmr")) {
printk("Warning: clock=pmtmr is deprecated. "
"Use clocksource=acpi_pm.\n");
return boot_override_clocksource("acpi_pm");
}
printk("Warning! clock= boot option is deprecated. "
"Use clocksource=xyz\n");
return boot_override_clocksource(str);
}
__setup("clock=", boot_override_clock);