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Subject[tip:timers/core] clocksource: Cleanup clocksource selection
Commit-ID:  f1b82746c1e93daf24e1ab9bfbd39bcdb2e7018b
Gitweb: http://git.kernel.org/tip/f1b82746c1e93daf24e1ab9bfbd39bcdb2e7018b
Author: Martin Schwidefsky <schwidefsky@de.ibm.com>
AuthorDate: Fri, 14 Aug 2009 15:47:21 +0200
Committer: Thomas Gleixner <tglx@linutronix.de>
CommitDate: Sat, 15 Aug 2009 10:55:46 +0200

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>


---
arch/s390/kernel/time.c | 4 +
include/linux/clocksource.h | 2 +
kernel/time/clocksource.c | 134 ++++++++++++++++--------------------------
kernel/time/jiffies.c | 6 ++-
kernel/time/timekeeping.c | 4 +-
5 files changed, 64 insertions(+), 86 deletions(-)
diff --git a/arch/s390/kernel/time.c b/arch/s390/kernel/time.c
index d4c8e9c..afefe51 100644
--- a/arch/s390/kernel/time.c
+++ b/arch/s390/kernel/time.c
@@ -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)
{
diff --git a/include/linux/clocksource.h b/include/linux/clocksource.h
index a1ef46f..f263b3a 100644
--- a/include/linux/clocksource.h
+++ b/include/linux/clocksource.h
@@ -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);
diff --git a/kernel/time/clocksource.c b/kernel/time/clocksource.c
index 7466cb8..e91662e 100644
--- a/kernel/time/clocksource.c
+++ b/kernel/time/clocksource.c
@@ -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;
+ 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;
+}

- if (clocksource_override)
- next = clocksource_override;
- else
- next = list_entry(clocksource_list.next, struct clocksource,
- list);
+#else /* CONFIG_GENERIC_TIME */

- if (next == curr_clocksource)
- return NULL;
+static void clocksource_select(void) { }

- return next;
-}
+#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;
-
- list_for_each(tmp, &clocksource_list) {
- struct clocksource *cs;
+ struct list_head *entry = &clocksource_list;
+ struct clocksource *tmp;

- 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);

diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c
index c3f6c30..5404a84 100644
--- a/kernel/time/jiffies.c
+++ b/kernel/time/jiffies.c
@@ -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;
+}
diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c
index b567301..325a9b6 100644
--- a/kernel/time/timekeeping.c
+++ b/kernel/time/timekeeping.c
@@ -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 */

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