[PATCH 05/10] -mm: clocksource: convert generic timeofday

From: Daniel Walker
Date: Fri Oct 06 2006 - 15:02:52 EST

Delete alot of remaining code in kernel/time/clocksource.c that
is replaced with this patch. Removed the deprecated "clock" kernel
parameter.

Shifts some of the code around so that the time of day override
happens inside kernel/timer.c.

The biggest timeofday changes are in update_wall_time() and
change_clocksource(). I removed the unconditional call to
change_clocksource(), and replaced it with a single atomic
check. The atomic is asserted only when a clock change is
needed. update_callback is no longer driven from
update_wall_time().

The fast path is now a single atomic check.

Signed-Off-By: Daniel Walker <dwalker@xxxxxxxxxx>

---
include/linux/clocksource.h | 3
kernel/time/clocksource.c | 216 ++++++--------------------------------------
kernel/timer.c | 167 +++++++++++++++++++++++++++++-----
3 files changed, 178 insertions(+), 208 deletions(-)

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
@@ -205,7 +205,8 @@ static inline void clocksource_calculate


/* used to install a new clocksource */
-extern struct clocksource *clocksource_get_next(void);
+extern int clocksource_sysfs_register(struct sysdev_attribute*);
+extern void clocksource_sysfs_unregister(struct sysdev_attribute*);
extern int clocksource_register(struct clocksource*);
extern void clocksource_rating_change(struct clocksource*);
extern struct clocksource * clocksource_get_clock(char*);
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
@@ -5,6 +5,8 @@
*
* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@xxxxxxxxxx)
*
+ * Copyright (C) 2006 MontaVista Daniel Walker (dwalker@xxxxxxxxxx)
+ *
* 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
@@ -21,7 +23,6 @@
*
* TODO WishList:
* o Allow clocksource drivers to be unregistered
- * o get rid of clocksource_jiffies extern
*/

#include <linux/clocksource.h>
@@ -29,45 +30,15 @@
#include <linux/init.h>
#include <linux/module.h>

-/* 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.
- * next_clocksource:
- * pending next selected clocksource.
* clocksource_list:
* priority list with the registered clocksources
* clocksource_lock:
- * protects manipulations to curr_clocksource and next_clocksource
- * and the clocksource_list
- * override_name:
- * Name of the user-specified clocksource.
+ * protects manipulations to the clocksource_list
*/
-static struct clocksource *curr_clocksource = &clocksource_jiffies;
-static struct clocksource *next_clocksource;
-static struct list_head clocksource_list = LIST_HEAD_INIT(clocksource_list);
+static __read_mostly
+struct list_head clocksource_list = LIST_HEAD_INIT(clocksource_list);
static DEFINE_SPINLOCK(clocksource_lock);
-static char override_name[32];
-
-/**
- * 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) {
- curr_clocksource = next_clocksource;
- next_clocksource = NULL;
- }
- spin_unlock_irqrestore(&clocksource_lock, flags);
-
- return curr_clocksource;
-}

/**
* __is_registered - Returns a clocksource if it's registered
@@ -95,28 +66,6 @@ static struct clocksource * __is_registe
}

/**
- * __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
*
@@ -128,29 +77,17 @@ struct clocksource * clocksource_get_clo
unsigned long flags;

spin_lock_irqsave(&clocksource_lock, flags);
- ret = __get_clock(name);
+ if (unlikely(list_empty(&clocksource_list)))
+ ret = &clocksource_jiffies;
+ else if (!name)
+ ret = list_entry(clocksource_list.next,
+ struct clocksource, list);
+ else
+ ret = __is_registered(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
@@ -200,8 +137,6 @@ int clocksource_register(struct clocksou
} else {
INIT_LIST_HEAD(&c->list);
__sorted_list_add(c);
- /* scan the registered clocksources, and pick the best one */
- next_clocksource = select_clocksource();
}
spin_unlock_irqrestore(&clocksource_lock, flags);
return ret;
@@ -230,70 +165,12 @@ void clocksource_rating_change(struct cl
list_del_init(&c->list);
__sorted_list_add(c);

- next_clocksource = select_clocksource();
+ /* XXX: Add block notifier to signal new rating */
spin_unlock_irqrestore(&clocksource_lock, flags);
}
EXPORT_SYMBOL(clocksource_rating_change);

/**
- * 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, char *buf)
-{
- char *curr = buf;
-
- spin_lock_irq(&clocksource_lock);
- curr += sprintf(curr, "%s ", curr_clocksource->name);
- spin_unlock_irq(&clocksource_lock);
-
- curr += sprintf(curr, "\n");
-
- return curr - buf;
-}
-
-/**
- * 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,
- 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--;
- if (count < 1)
- return -EINVAL;
-
- spin_lock_irq(&clocksource_lock);
-
- /* copy the name given: */
- memcpy(override_name, buf, count);
- override_name[count] = 0;
-
- /* try to select it: */
- next_clocksource = select_clocksource();
-
- spin_unlock_irq(&clocksource_lock);
-
- return ret;
-}
-
-/**
* sysfs_show_available_clocksources - sysfs interface for listing clocksource
* @dev: unused
* @buf: char buffer to be filled with clocksource list
@@ -322,11 +199,8 @@ sysfs_show_available_clocksources(struct
}

/*
- * Sysfs setup bits:
+ * Generic sysfs setup bits:
*/
-static SYSDEV_ATTR(current_clocksource, 0600, sysfs_show_current_clocksources,
- sysfs_override_clocksource);
-
static SYSDEV_ATTR(available_clocksource, 0600,
sysfs_show_available_clocksources, NULL);

@@ -339,6 +213,21 @@ static struct sys_device device_clocksou
.cls = &clocksource_sysclass,
};

+/**
+ * clocksource_sysfs_register - interface to register a sysfs
+ * hook under the clocksource sys_device.
+ * @attr: sysdev_attribute created with the SYSDEV_ATTR macro.
+ *
+ * This functions should be used to create a sysfs file under
+ * the clocksource directory which will be used to show the current
+ * clock used by the code calling clocksource_sysfs_register(), and
+ * set a specific overide when written to.
+ */
+int clocksource_sysfs_register(struct sysdev_attribute * attr)
+{
+ return sysdev_create_file(&device_clocksource, attr);
+}
+
static int __init init_clocksource_sysfs(void)
{
int error = sysdev_class_register(&clocksource_sysclass);
@@ -348,52 +237,7 @@ static int __init init_clocksource_sysfs
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);
-
-/**
- * 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)
-{
- unsigned long flags;
- spin_lock_irqsave(&clocksource_lock, flags);
- if (str)
- strlcpy(override_name, str, sizeof(override_name));
- spin_unlock_irqrestore(&clocksource_lock, flags);
- 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);
+postcore_initcall(init_clocksource_sysfs);
Index: linux-2.6.18/kernel/timer.c
===================================================================
--- linux-2.6.18.orig/kernel/timer.c
+++ linux-2.6.18/kernel/timer.c
@@ -17,6 +17,8 @@
* 2000-10-05 Implemented scalable SMP per-CPU timer handling.
* Copyright (C) 2000, 2001, 2002 Ingo Molnar
* Designed by David S. Miller, Alexey Kuznetsov and Ingo Molnar
+ * 2006-08-03 Added usage of the generic clocksource API
+ * Copyright (C) 2006 MontaVista, Daniel Walker
*/

#include <linux/kernel_stat.h>
@@ -578,9 +580,15 @@ EXPORT_SYMBOL(xtime);

/* XXX - all of this timekeeping code should be later moved to time.c */
#include <linux/clocksource.h>
-static struct clocksource *clock; /* pointer to current clocksource */
+/* pointer to current clocksource */
+static struct clocksource *clock = &clocksource_jiffies;
+static char clock_override_name[32];
+
+/* Interrupt update singaling variables */
+static atomic_t clock_check = ATOMIC_INIT(0);

#ifdef CONFIG_GENERIC_TIME
+
/**
* __get_nsec_offset - Returns nanoseconds since last call to periodic_hook
*
@@ -700,29 +708,119 @@ EXPORT_SYMBOL(do_settimeofday);
*
* Accumulates current time interval and initializes new clocksource
*/
-static int change_clocksource(void)
+static int change_clocksource(char * override)
{
- struct clocksource *new;
- cycle_t now;
u64 nsec;
- new = clocksource_get_next();
- if (clock != new) {
- now = clocksource_read(new);
- nsec = __get_nsec_offset();
- timespec_add_ns(&xtime, nsec);
-
- clock = new;
- clock->cycle_last = now;
- printk(KERN_INFO "Time: %s clocksource has been installed.\n",
- clock->name);
- return 1;
- } else if (clock->update_callback) {
- return clock->update_callback();
+ cycle_t now;
+ struct clocksource *new = clocksource_get_clock(override);
+
+ now = clocksource_read(new);
+ nsec = __get_nsec_offset();
+ timespec_add_ns(&xtime, nsec);
+
+ clock = new;
+ clock->cycle_last = now;
+ printk(KERN_INFO "Time: %s clocksource has been installed.\n",
+ clock->name);
+
+ return 1;
+}
+
+/**
+ * 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 the current clocksource.
+ * Locking handled inside sysfs.
+ */
+static ssize_t
+sysfs_show_current_clocksources(struct sys_device *dev, char *buf)
+{
+ return sprintf(buf, "%s \n", clock->name);
+}
+
+/**
+ * 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. Locking handled inside sysfs
+ */
+static ssize_t sysfs_override_clocksource(struct sys_device *dev,
+ const char *buf, size_t count)
+{
+ size_t ret = count;
+
+ /*
+ * If there's already an update in progress then
+ * we can't proceed.
+ */
+ if (atomic_read(&clock_check))
+ return -EINVAL;
+
+ /* strings from sysfs write are not 0 terminated! */
+ if (count >= sizeof(clock_override_name))
+ return -EINVAL;
+
+ /* strip of \n: */
+ if (buf[count-1] == '\n')
+ count--;
+ if (count < 1)
+ return -EINVAL;
+
+ /* copy the name given: */
+ memcpy(clock_override_name, buf, count);
+ clock_override_name[count] = 0;
+
+ if (!clocksource_get_clock(clock_override_name)) {
+ clock_override_name[0] = 0;
+ return -EINVAL;
}
- return 0;
+
+ atomic_inc(&clock_check);
+
+ return ret;
+}
+
+/*
+ * Sysfs atrribure structure.
+ */
+static SYSDEV_ATTR(timeofday_clocksource, 0600, sysfs_show_current_clocksources,
+ sysfs_override_clocksource);
+
+/**
+ * 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)
+{
+ if (str) {
+ /*
+ * Make sure the clock exists.
+ */
+ if (clocksource_get_clock(str))
+ strlcpy(clock_override_name, str,
+ sizeof(clock_override_name));
+ else {
+ printk("Time: requested clock \"%s\" doesn't exist\n",
+ str);
+ return 0;
+ }
+
+ }
+
+ return 1;
}
+__setup("timeofday_clocksource=", boot_override_clocksource);
+
#else
-#define change_clocksource() do { 0; } while(0)
+#define change_clocksource(x) do { } while(0)
#endif

/**
@@ -754,7 +852,7 @@ void __init timekeeping_init(void)

ntp_clear();

- clock = clocksource_get_next();
+ clock = clocksource_get_best_clock();
clocksource_calculate_interval(clock, tick_nsec);
clock->cycle_last = clocksource_read(clock);

@@ -811,6 +909,17 @@ static int __init timekeeping_init_devic
int error = sysdev_class_register(&timekeeping_sysclass);
if (!error)
error = sysdev_register(&device_timer);
+
+#ifdef CONFIG_GENERIC_TIME
+ clocksource_sysfs_register(&attr_timeofday_clocksource);
+
+ /*
+ * All the clocks should be registered at this point,
+ * so it's safe to trigger a switch to a higher res
+ * clock.
+ */
+ atomic_inc(&clock_check);
+#endif
return error;
}

@@ -952,10 +1061,26 @@ static void update_wall_time(void)
clock->xtime_nsec -= (s64)xtime.tv_nsec << clock->shift;

/* check to see if there is a new clocksource to use */
- if (change_clocksource()) {
+ if (unlikely(atomic_read(&clock_check))) {
+
+ /*
+ * Switch to the new override clock, or the highest
+ * rated clock.
+ */
+ if (*clock_override_name)
+ change_clocksource(clock_override_name);
+ else
+ change_clocksource(NULL);
+
clock->error = 0;
clock->xtime_nsec = 0;
clocksource_calculate_interval(clock, tick_nsec);
+
+ /*
+ * Remove the change signal
+ */
+ atomic_dec(&clock_check);
+
}
}


--

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