From: Martin Schwidefsky <[email protected]>
update_wall_time calls change_clocksource HZ times per second to check
if a new clock source is available. In close to 100% of all calls there
is no new clock. Replace the tick based check by an update done with
stop_machine.
Cc: Ingo Molnar <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: john stultz <[email protected]>
Signed-off-by: Martin Schwidefsky <[email protected]>
---
include/linux/clocksource.h | 2 -
kernel/time/clocksource.c | 82 ++++++++++++++++----------------------------
kernel/time/timekeeping.c | 2 -
3 files changed, 31 insertions(+), 55 deletions(-)
Index: linux-2.6/include/linux/clocksource.h
===================================================================
--- linux-2.6.orig/include/linux/clocksource.h
+++ linux-2.6/include/linux/clocksource.h
@@ -340,10 +340,8 @@ extern void clocksource_resume(void);
#ifdef CONFIG_GENERIC_TIME
extern void clocksource_forward_now(void);
-extern void change_clocksource(void);
#else
static inline void clocksource_forward_now(void) { }
-static inline void change_clocksource(void) { }
#endif
#ifdef CONFIG_GENERIC_TIME_VSYSCALL
Index: linux-2.6/kernel/time/clocksource.c
===================================================================
--- linux-2.6.orig/kernel/time/clocksource.c
+++ linux-2.6/kernel/time/clocksource.c
@@ -30,6 +30,7 @@
#include <linux/module.h>
#include <linux/sched.h> /* for spin_unlock_irq() using preempt_count() m68k */
#include <linux/tick.h>
+#include <linux/stop_machine.h>
void timecounter_init(struct timecounter *tc,
const struct cyclecounter *cc,
@@ -107,46 +108,26 @@ u64 timecounter_cyc2time(struct timecoun
}
EXPORT_SYMBOL(timecounter_cyc2time);
-/* XXX - Would like a better way for initializing curr_clocksource */
+/* XXX - Would like a better way for initializing clock */
extern struct clocksource clocksource_jiffies;
/* Currently selected clock source. */
struct clocksource *clock;
/*[Clocksource internal variables]---------
- * curr_clocksource:
- * currently selected clocksource. Initialized to clocksource_jiffies.
- * next_clocksource:
- * pending next selected clocksource.
* clocksource_list:
* linked list with the registered clocksources
* clocksource_lock:
- * protects manipulations to curr_clocksource and next_clocksource
- * and the clocksource_list
+ * protects manipulations to the clocksource_list
* override_name:
* Name of the user-specified clocksource.
*/
-static struct clocksource *curr_clocksource = &clocksource_jiffies;
-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];
static int finished_booting;
-/* 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;
- return 0;
-}
-fs_initcall(clocksource_done_booting);
-
#ifdef CONFIG_CLOCKSOURCE_WATCHDOG
static LIST_HEAD(watchdog_list);
static struct clocksource *watchdog;
@@ -323,24 +304,6 @@ void clocksource_touch_watchdog(void)
clocksource_resume_watchdog();
}
-/**
- * clocksource_get_next - Returns the selected clocksource
- *
- */
-struct clocksource *clocksource_get_next(void)
-{
- unsigned long flags;
-
- spin_lock_irqsave(&clocksource_lock, flags);
- if (next_clocksource && finished_booting) {
- curr_clocksource = next_clocksource;
- next_clocksource = NULL;
- }
- spin_unlock_irqrestore(&clocksource_lock, flags);
-
- return curr_clocksource;
-}
-
/*
* Enqueue the clocksource sorted by rating
*/
@@ -552,23 +515,22 @@ static struct clocksource *select_clocks
}
/**
- * change_clocksource - Swaps clocksources if a new one is available
+ * clocksource_swap - Swaps clocksources if a new one is available
*
* Accumulates current time interval and initializes new clocksource
*/
-void change_clocksource(void)
+static int clocksource_swap(void *dummy)
{
struct clocksource *new, *old;
- new = clocksource_get_next();
-
- if (clock == new)
- return;
+ new = select_clocksource();
+ if (!new || clock == new)
+ return 0;
clocksource_forward_now();
if (new->enable && !new->enable(new))
- return;
+ return 0;
/* save mult_orig after successful enable */
new->mult_orig = new->mult;
@@ -592,6 +554,7 @@ void change_clocksource(void)
printk(KERN_INFO "Time: %s clocksource has been installed.\n",
clock->name);
*/
+ return 0;
}
/**
@@ -602,11 +565,13 @@ static void clocksource_update(void)
struct clocksource *new;
unsigned long flags;
+ if (!finished_booting)
+ return;
spin_lock_irqsave(&clocksource_lock, flags);
new = select_clocksource();
- if (new)
- next_clocksource = new;
spin_unlock_irqrestore(&clocksource_lock, flags);
+ if (new && new != clock)
+ stop_machine(clocksource_swap, NULL, NULL);
}
#else /* CONFIG_GENERIC_TIME */
static inline void clocksource_update(void) { }
@@ -657,7 +622,7 @@ void clocksource_unregister(struct clock
*/
void __init clocksource_init(void)
{
- clock = clocksource_get_next();
+ clock = &clocksource_jiffies;
if (clock->enable)
clock->enable(clock);
/* save mult_orig on enable */
@@ -666,6 +631,21 @@ void __init clocksource_init(void)
clock->cycle_last = clock->read(clock);
}
+/**
+ * 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;
+ clocksource_update();
+ return 0;
+}
+fs_initcall(clocksource_done_booting);
+
#ifdef CONFIG_SYSFS
/**
* sysfs_show_current_clocksources - sysfs interface for current clocksource
@@ -681,7 +661,7 @@ sysfs_show_current_clocksources(struct s
ssize_t count = 0;
spin_lock_irq(&clocksource_lock);
- count = snprintf(buf, PAGE_SIZE, "%s\n", curr_clocksource->name);
+ count = snprintf(buf, PAGE_SIZE, "%s\n", clock->name);
spin_unlock_irq(&clocksource_lock);
return count;
Index: linux-2.6/kernel/time/timekeeping.c
===================================================================
--- linux-2.6.orig/kernel/time/timekeeping.c
+++ linux-2.6/kernel/time/timekeeping.c
@@ -491,8 +491,6 @@ void update_wall_time(void)
update_xtime_cache(cyc2ns(clock, offset));
- /* check to see if there is a new clocksource to use */
- change_clocksource();
update_vsyscall(&xtime, clock);
}
--
blue skies,
Martin.
"Reality continues to ruin my life." - Calvin.