originally used plist but removed it in this patch, and used a sorted list
which is just as fast with a lot less memory overhead.
Introduces some new API calls,
- clocksource_get_clock()
Allows a clock lookup by name.
- clocksource_rating_change()
Used by a clocksource to signal a rating change. Replaces
reselect_clocksource()
I also moved the the clock source list to a plist, which removes some lookup
overhead in the average case.
Signed-Off-By: Daniel Walker <[email protected]>
---
arch/i386/kernel/tsc.c | 2
include/linux/clocksource.h | 44 ++++++++-
kernel/time/clocksource.c | 213 ++++++++++++++++++++++++++++----------------
3 files changed, 179 insertions(+), 80 deletions(-)
Index: linux-2.6.18/arch/i386/kernel/tsc.c
===================================================================
--- linux-2.6.18.orig/arch/i386/kernel/tsc.c
+++ linux-2.6.18/arch/i386/kernel/tsc.c
@@ -351,7 +351,7 @@ static int tsc_update_callback(void)
/* check to see if we should switch to the safe clocksource: */
if (clocksource_tsc.rating != 50 && check_tsc_unstable()) {
clocksource_tsc.rating = 50;
- clocksource_reselect();
+ clocksource_rating_change(&clocksource_tsc);
change = 1;
}
Index: linux-2.6.18/include/linux/clocksource.h
===================================================================
--- linux-2.6.18.orig/include/linux/clocksource.h
+++ linux-2.6.18/include/linux/clocksource.h
@@ -12,12 +12,20 @@
#include <linux/timex.h>
#include <linux/time.h>
#include <linux/list.h>
+#include <linux/plist.h>
+#include <linux/sysdev.h>
#include <asm/div64.h>
#include <asm/io.h>
/* clocksource cycle base type */
typedef u64 cycle_t;
+/*
+ * This is the only generic clock, it should be used
+ * for early initialization.
+ */
+extern struct clocksource clocksource_jiffies;
+
/**
* struct clocksource - hardware abstraction for a free running counter
* Provides mostly state-free accessors to the underlying hardware.
@@ -148,6 +156,25 @@ static inline s64 cyc2ns(struct clocksou
}
/**
+ * ns2cyc - converts nanoseconds to clocksource cycles
+ * @cs: Pointer to clocksource
+ * @ns: Nanoseconds
+ *
+ * Uses the clocksource to convert nanoseconds back to cycles.
+ *
+ * XXX - This could use some mult_lxl_ll() asm optimization
+ */
+static inline cycle_t ns2cyc(struct clocksource *cs, s64 ns)
+{
+ u64 ret = ns;
+
+ ret <<= cs->shift;
+ do_div(ret, cs->mult);
+
+ return ret;
+}
+
+/**
* clocksource_calculate_interval - Calculates a clocksource interval struct
*
* @c: Pointer to clocksource.
@@ -178,8 +205,19 @@ static inline void clocksource_calculate
/* used to install a new clocksource */
-int clocksource_register(struct clocksource*);
-void clocksource_reselect(void);
-struct clocksource* clocksource_get_next(void);
+extern struct clocksource *clocksource_get_next(void);
+extern int clocksource_register(struct clocksource*);
+extern void clocksource_rating_change(struct clocksource*);
+extern struct clocksource * clocksource_get_clock(char*);
+/**
+ * clocksource_get_best_clock - Finds highest rated clocksource
+ *
+ * Returns the highest rated clocksource. If none are register the
+ * jiffies clock is returned.
+ */
+static inline struct clocksource * clocksource_get_best_clock(void)
+{
+ return clocksource_get_clock(NULL);
+}
#endif /* _LINUX_CLOCKSOURCE_H */
Index: linux-2.6.18/kernel/time/clocksource.c
===================================================================
--- linux-2.6.18.orig/kernel/time/clocksource.c
+++ linux-2.6.18/kernel/time/clocksource.c
@@ -31,8 +31,6 @@
/* XXX - Would like a better way for initializing curr_clocksource */
extern struct clocksource clocksource_jiffies;
-static int is_registered_source(struct clocksource *c);
-static struct clocksource *select_clocksource(void);
/*[Clocksource internal variables]---------
* curr_clocksource:
@@ -40,7 +38,7 @@ static struct clocksource *select_clocks
* next_clocksource:
* pending next selected clocksource.
* clocksource_list:
- * linked list with the registered clocksources
+ * priority list with the registered clocksources
* clocksource_lock:
* protects manipulations to curr_clocksource and next_clocksource
* and the clocksource_list
@@ -49,7 +47,7 @@ static struct clocksource *select_clocks
*/
static struct clocksource *curr_clocksource = &clocksource_jiffies;
static struct clocksource *next_clocksource;
-static LIST_HEAD(clocksource_list);
+static struct list_head clocksource_list = LIST_HEAD_INIT(clocksource_list);
static DEFINE_SPINLOCK(clocksource_lock);
static char override_name[32];
@@ -72,10 +70,122 @@ struct clocksource *clocksource_get_next
}
/**
+ * __is_registered - Returns a clocksource if it's registered
+ * @name: name of the clocksource to return
+ *
+ * Private function. Must hold clocksource_lock when called.
+ *
+ * Returns the clocksource if registered, zero otherwise.
+ * If no clocksources are registered the jiffies clock is
+ * returned.
+ */
+static struct clocksource * __is_registered(char * name)
+{
+ struct list_head *tmp;
+
+ list_for_each(tmp, &clocksource_list) {
+ struct clocksource *src;
+
+ src = list_entry(tmp, struct clocksource, list);
+ if (!strcmp(src->name, name))
+ return src;
+ }
+
+ return 0;
+}
+
+/**
+ * __get_clock - Finds a specific clocksource
+ * @name: name of the clocksource to return
+ *
+ * Private function. Must hold clocksource_lock when called.
+ *
+ * Returns the clocksource if registered, zero otherwise.
+ * If the @name is null the highest rated clock is returned.
+ */
+static inline struct clocksource * __get_clock(char * name)
+{
+
+ if (unlikely(list_empty(&clocksource_list)))
+ return &clocksource_jiffies;
+
+ if (!name)
+ return list_entry(clocksource_list.next,
+ struct clocksource, list);
+
+ return __is_registered(name);
+}
+
+/**
+ * clocksource_get_clock - Finds a specific clocksource
+ * @name: name of the clocksource to return
+ *
+ * Returns the clocksource if registered, zero otherwise.
+ */
+struct clocksource * clocksource_get_clock(char * name)
+{
+ struct clocksource * ret;
+ unsigned long flags;
+
+ spin_lock_irqsave(&clocksource_lock, flags);
+ ret = __get_clock(name);
+ spin_unlock_irqrestore(&clocksource_lock, flags);
+ return ret;
+}
+
+
+/**
+ * select_clocksource - Finds the best registered clocksource.
+ *
+ * Private function. Must hold clocksource_lock when called.
+ *
+ * Looks through the list of registered clocksources, returning
+ * the one with the highest rating value. If there is a clocksource
+ * name that matches the override string, it returns that clocksource.
+ */
+static struct clocksource *select_clocksource(void)
+{
+ if (!*override_name)
+ return list_entry(clocksource_list.next,
+ struct clocksource, list);
+
+ return __get_clock(override_name);
+}
+/*
+ * __sorted_list_add - Sorted clocksource add
+ * @c: clocksource to add
+ *
+ * Adds a clocksource to the clocksource_list in sorted order.
+ */
+static void __sorted_list_add(struct clocksource *c)
+{
+ struct list_head *tmp;
+
+ list_for_each(tmp, &clocksource_list) {
+ struct clocksource *src;
+
+ src = list_entry(tmp, struct clocksource, list);
+
+ if (c->rating > src->rating) {
+ list_add_tail(&c->list, &src->list);
+ return;
+ }
+ }
+
+ /*
+ * If it's bigger/smaller than all the other entries put it
+ * at the end.
+ */
+ list_add_tail(&c->list, &clocksource_list);
+}
+
+/**
* clocksource_register - Used to install new clocksources
* @t: clocksource to be registered
*
- * Returns -EBUSY if registration fails, zero otherwise.
+ * Returns -EBUSY clock is already registered,
+ * Returns -EINVAL if clocksource is invalid,
+ * Return zero otherwise.
*/
int clocksource_register(struct clocksource *c)
{
@@ -83,14 +193,13 @@ int clocksource_register(struct clocksou
unsigned long flags;
spin_lock_irqsave(&clocksource_lock, flags);
- /* check if clocksource is already registered */
- if (is_registered_source(c)) {
- printk("register_clocksource: Cannot register %s. "
+ if (unlikely(!list_empty(&c->list) && __is_registered(c->name))) {
+ printk("register_clocksource: Cannot register %s clocksource. "
"Already registered!", c->name);
ret = -EBUSY;
} else {
- /* register it */
- list_add(&c->list, &clocksource_list);
+ INIT_LIST_HEAD(&c->list);
+ __sorted_list_add(c);
/* scan the registered clocksources, and pick the best one */
next_clocksource = select_clocksource();
}
@@ -100,21 +209,31 @@ int clocksource_register(struct clocksou
EXPORT_SYMBOL(clocksource_register);
/**
- * clocksource_reselect - Rescan list for next clocksource
+ * clocksource_rating_change - Allows dynamic rating changes for register
+ * clocksources.
*
- * A quick helper function to be used if a clocksource changes its
- * rating. Forces the clocksource list to be re-scanned for the best
- * clocksource.
+ * Signals that a clocksource is dynamically changing it's rating.
+ * This could happen if a clocksource becomes more/less stable.
*/
-void clocksource_reselect(void)
+void clocksource_rating_change(struct clocksource *c)
{
unsigned long flags;
+ if (unlikely(list_empty(&c->list)))
+ return;
+
spin_lock_irqsave(&clocksource_lock, flags);
+
+ /*
+ * Re-register the clocksource with it's new rating.
+ */
+ list_del_init(&c->list);
+ __sorted_list_add(c);
+
next_clocksource = select_clocksource();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
-EXPORT_SYMBOL(clocksource_reselect);
+EXPORT_SYMBOL(clocksource_rating_change);
/**
* sysfs_show_current_clocksources - sysfs interface for current clocksource
@@ -179,7 +298,8 @@ static ssize_t sysfs_override_clocksourc
* @dev: unused
* @buf: char buffer to be filled with clocksource list
*
- * Provides sysfs interface for listing registered clocksources
+ * Provides sysfs interface for listing registered clocksources.
+ * Output in priority sorted order.
*/
static ssize_t
sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
@@ -277,62 +397,3 @@ static int __init boot_override_clock(ch
}
__setup("clock=", boot_override_clock);
-
-/**
- * select_clocksource - Finds the best registered clocksource.
- *
- * Private function. Must hold clocksource_lock when called.
- *
- * Looks through the list of registered clocksources, returning
- * the one with the highest rating value. If there is a clocksource
- * name that matches the override string, it returns that clocksource.
- */
-static struct clocksource *select_clocksource(void)
-{
- struct clocksource *best = NULL;
- struct list_head *tmp;
-
- list_for_each(tmp, &clocksource_list) {
- struct clocksource *src;
-
- src = list_entry(tmp, struct clocksource, list);
- if (!best)
- best = src;
-
- /* check for override: */
- if (strlen(src->name) == strlen(override_name) &&
- !strcmp(src->name, override_name)) {
- best = src;
- break;
- }
- /* pick the highest rating: */
- if (src->rating > best->rating)
- best = src;
- }
-
- return best;
-}
-
-/**
- * is_registered_source - Checks if clocksource is registered
- * @c: pointer to a clocksource
- *
- * Private helper function. Must hold clocksource_lock when called.
- *
- * Returns one if the clocksource is already registered, zero otherwise.
- */
-static int is_registered_source(struct clocksource *c)
-{
- int len = strlen(c->name);
- struct list_head *tmp;
-
- list_for_each(tmp, &clocksource_list) {
- struct clocksource *src;
-
- src = list_entry(tmp, struct clocksource, list);
- if (strlen(src->name) == len && !strcmp(src->name, c->name))
- return 1;
- }
-
- return 0;
-}
--
On Fri, 2006-10-06 at 11:54 -0700, Daniel Walker wrote:
> plain text document attachment (clocksource_user_api.patch)
> originally used plist but removed it in this patch, and used a sorted list
> which is just as fast with a lot less memory overhead.
>
> Introduces some new API calls,
>
> - clocksource_get_clock()
> Allows a clock lookup by name.
> - clocksource_rating_change()
> Used by a clocksource to signal a rating change. Replaces
> reselect_clocksource()
Adds ns2cyc interface. Just to keep things in logical chunks, maybe
would that chunk be better added with the patch that uses it?
> I also moved the the clock source list to a plist, which removes some lookup
> overhead in the average case.
Probably need to update the header, as you don't use a plist now. :)
> Signed-Off-By: Daniel Walker <[email protected]>
Otherwise this patch looks like a good cleanup to me.
Acked-by: John Stultz <[email protected]>
thanks
-john