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clocksource: Cleanup clocksource selection 

If a non high-resolution clocksource is first set as override clock
and then registered it becomes active even if the system is in one-shot
mode. Move the override check from sysfs_override_clocksource to the
clocksource selection. That fixes the bug and simplifies the code. The
check in clocksource_register for double registration of the same
clocksource is removed without replacement.

To find the initial clocksource a new weak function in jiffies.c is
defined that returns the jiffies clocksource. The architecture code
can then override the weak function with a more suitable clocksource,
e.g. the TOD clock on s390.

[ tglx: Folded in a fix from John Stultz ]

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Acked-by: John Stultz <johnstul@us.ibm.com>
Cc: Daniel Walker <dwalker@fifo99.com>
LKML-Reference: <20090814134808.388024160@de.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Martin Schwidefsky 2009-08-14 15:47:21 +02:00 committed by Thomas Gleixner
parent 1be3967948
commit f1b82746c1
5 changed files with 66 additions and 88 deletions
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4
arch/s390/kernel/time.c
View File

@ -205,6 +205,10 @@ static struct clocksource clocksource_tod = {
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
struct clocksource * __init clocksource_default_clock(void)
{
return &clocksource_tod;
}
void update_vsyscall(struct timespec *wall_time, struct clocksource *clock)
{

2
include/linux/clocksource.h
View File

@ -14,6 +14,7 @@
#include <linux/list.h>
#include <linux/cache.h>
#include <linux/timer.h>
#include <linux/init.h>
#include <asm/div64.h>
#include <asm/io.h>
@ -322,6 +323,7 @@ extern void clocksource_touch_watchdog(void);
extern struct clocksource* clocksource_get_next(void);
extern void clocksource_change_rating(struct clocksource *cs, int rating);
extern void clocksource_resume(void);
extern struct clocksource * __init __weak clocksource_default_clock(void);
#ifdef CONFIG_GENERIC_TIME_VSYSCALL
extern void update_vsyscall(struct timespec *ts, struct clocksource *c);

138
kernel/time/clocksource.c
View File

@ -21,7 +21,6 @@
*
* TODO WishList:
* o Allow clocksource drivers to be unregistered
* o get rid of clocksource_jiffies extern
*/
#include <linux/clocksource.h>
@ -107,12 +106,9 @@ u64 timecounter_cyc2time(struct timecounter *tc,
}
EXPORT_SYMBOL(timecounter_cyc2time);
/* XXX - Would like a better way for initializing curr_clocksource */
extern struct clocksource clocksource_jiffies;
/*[Clocksource internal variables]---------
* curr_clocksource:
* currently selected clocksource. Initialized to clocksource_jiffies.
* currently selected clocksource.
* next_clocksource:
* pending next selected clocksource.
* clocksource_list:
@ -123,9 +119,8 @@ extern struct clocksource clocksource_jiffies;
* override_name:
* Name of the user-specified clocksource.
*/
static struct clocksource *curr_clocksource = &clocksource_jiffies;
static struct clocksource *curr_clocksource;
static struct clocksource *next_clocksource;
static struct clocksource *clocksource_override;
static LIST_HEAD(clocksource_list);
static DEFINE_SPINLOCK(clocksource_lock);
static char override_name[32];
@ -320,6 +315,7 @@ void clocksource_touch_watchdog(void)
clocksource_resume_watchdog();
}
#ifdef CONFIG_GENERIC_TIME
/**
* clocksource_get_next - Returns the selected clocksource
*
@ -339,56 +335,65 @@ struct clocksource *clocksource_get_next(void)
}
/**
* select_clocksource - Selects the best registered clocksource.
* clocksource_select - Select the best clocksource available
*
* Private function. Must hold clocksource_lock when called.
*
* Select the clocksource with the best rating, or the clocksource,
* which is selected by userspace override.
*/
static struct clocksource *select_clocksource(void)
static void clocksource_select(void)
{
struct clocksource *next;
struct clocksource *best, *cs;
if (list_empty(&clocksource_list))
return NULL;
if (clocksource_override)
next = clocksource_override;
else
next = list_entry(clocksource_list.next, struct clocksource,
list);
if (next == curr_clocksource)
return NULL;
return next;
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)
next_clocksource = best;
}
#else /* CONFIG_GENERIC_TIME */
static void clocksource_select(void) { }
#endif
/*
* Enqueue the clocksource sorted by rating
*/
static int clocksource_enqueue(struct clocksource *c)
static void clocksource_enqueue(struct clocksource *cs)
{
struct list_head *tmp, *entry = &clocksource_list;
struct list_head *entry = &clocksource_list;
struct clocksource *tmp;
list_for_each(tmp, &clocksource_list) {
struct clocksource *cs;
cs = list_entry(tmp, struct clocksource, list);
if (cs == c)
return -EBUSY;
list_for_each_entry(tmp, &clocksource_list, list)
/* Keep track of the place, where to insert */
if (cs->rating >= c->rating)
entry = tmp;
}
list_add(&c->list, entry);
if (strlen(c->name) == strlen(override_name) &&
!strcmp(c->name, override_name))
clocksource_override = c;
return 0;
if (tmp->rating >= cs->rating)
entry = &tmp->list;
list_add(&cs->list, entry);
}
/**
@ -397,19 +402,16 @@ static int clocksource_enqueue(struct clocksource *c)
*
* Returns -EBUSY if registration fails, zero otherwise.
*/
int clocksource_register(struct clocksource *c)
int clocksource_register(struct clocksource *cs)
{
unsigned long flags;
int ret;
spin_lock_irqsave(&clocksource_lock, flags);
ret = clocksource_enqueue(c);
if (!ret)
next_clocksource = select_clocksource();
clocksource_enqueue(cs);
clocksource_select();
spin_unlock_irqrestore(&clocksource_lock, flags);
if (!ret)
clocksource_check_watchdog(c);
return ret;
clocksource_check_watchdog(cs);
return 0;
}
EXPORT_SYMBOL(clocksource_register);
@ -425,7 +427,7 @@ void clocksource_change_rating(struct clocksource *cs, int rating)
list_del(&cs->list);
cs->rating = rating;
clocksource_enqueue(cs);
next_clocksource = select_clocksource();
clocksource_select();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
@ -438,9 +440,7 @@ void clocksource_unregister(struct clocksource *cs)
spin_lock_irqsave(&clocksource_lock, flags);
list_del(&cs->list);
if (clocksource_override == cs)
clocksource_override = NULL;
next_clocksource = select_clocksource();
clocksource_select();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
@ -478,9 +478,7 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev,
struct sysdev_attribute *attr,
const char *buf, size_t count)
{
struct clocksource *ovr = NULL;
size_t ret = count;
int len;
/* strings from sysfs write are not 0 terminated! */
if (count >= sizeof(override_name))
@ -495,37 +493,7 @@ static ssize_t sysfs_override_clocksource(struct sys_device *dev,
if (count > 0)
memcpy(override_name, buf, count);
override_name[count] = 0;
len = strlen(override_name);
if (len) {
struct clocksource *cs;
ovr = clocksource_override;
/* try to select it: */
list_for_each_entry(cs, &clocksource_list, list) {
if (strlen(cs->name) == len &&
!strcmp(cs->name, override_name))
ovr = cs;
}
}
/*
* 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 (tick_oneshot_mode_active() && ovr &&
!(ovr->flags & CLOCK_SOURCE_VALID_FOR_HRES)) {
printk(KERN_WARNING "%s clocksource is not HRT compatible. "
"Cannot switch while in HRT/NOHZ mode\n", ovr->name);
ovr = NULL;
override_name[0] = 0;
}
/* Reselect, when the override name has changed */
if (ovr != clocksource_override) {
clocksource_override = ovr;
next_clocksource = select_clocksource();
}
clocksource_select();
spin_unlock_irq(&clocksource_lock);

6
kernel/time/jiffies.c
View File

@ -61,7 +61,6 @@ struct clocksource clocksource_jiffies = {
.read = jiffies_read,
.mask = 0xffffffff, /*32bits*/
.mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
.mult_orig = NSEC_PER_JIFFY << JIFFIES_SHIFT,
.shift = JIFFIES_SHIFT,
};
@ -71,3 +70,8 @@ static int __init init_jiffies_clocksource(void)
}
core_initcall(init_jiffies_clocksource);
struct clocksource * __init __weak clocksource_default_clock(void)
{
return &clocksource_jiffies;
}

4
kernel/time/timekeeping.c
View File

@ -269,7 +269,7 @@ static void change_clocksource(void)
new = clocksource_get_next();
if (clock == new)
if (!new || clock == new)
return;
clocksource_forward_now();
@ -446,7 +446,7 @@ void __init timekeeping_init(void)
ntp_init();
clock = clocksource_get_next();
clock = clocksource_default_clock();
if (clock->enable)
clock->enable(clock);
/* set mult_orig on enable */