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[PATCH] Time: Clocksource Infrastructure

Browse source 
This introduces the clocksource management infrastructure.  A clocksource is a
driver-like architecture generic abstraction of a free-running counter.  This
code defines the clocksource structure, and provides management code for
registering, selecting, accessing and scaling clocksources.

Additionally, this includes the trivial jiffies clocksource, a lowest common
denominator clocksource, provided mainly for use as an example.

[hirofumi@mail.parknet.co.jp: Don't enable IRQ too early]
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: John Stultz <johnstul@us.ibm.com>
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This commit is contained in:
john stultz 2006-06-26 00:25:05 -07:00 committed by Linus Torvalds
parent ade1a29e16
commit 734efb467b
5 changed files with 609 additions and 4 deletions
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14
Documentation/kernel-parameters.txt
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@ -61,6 +61,7 @@ parameter is applicable:
MTD MTD support is enabled.
NET Appropriate network support is enabled.
NUMA NUMA support is enabled.
GENERIC_TIME The generic timeofday code is enabled.
NFS Appropriate NFS support is enabled.
OSS OSS sound support is enabled.
PARIDE The ParIDE subsystem is enabled.
@ -341,10 +342,11 @@ running once the system is up.
Value can be changed at runtime via
/selinux/checkreqprot.
clock= [BUGS=IA-32,HW] gettimeofday timesource override.
Forces specified timesource (if avaliable) to be used
when calculating gettimeofday(). If specicified
timesource is not avalible, it defaults to PIT.
clock= [BUGS=IA-32, HW] gettimeofday clocksource override.
[Deprecated]
Forces specified clocksource (if avaliable) to be used
when calculating gettimeofday(). If specified
clocksource is not avalible, it defaults to PIT.
Format: { pit | tsc | cyclone | pmtmr }
disable_8254_timer
@ -1617,6 +1619,10 @@ running once the system is up.
time Show timing data prefixed to each printk message line
clocksource= [GENERIC_TIME] Override the default clocksource
Override the default clocksource and use the clocksource
with the name specified.
tipar.timeout= [HW,PPT]
Set communications timeout in tenths of a second
(default 15).

181
include/linux/clocksource.h Normal file
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@ -0,0 +1,181 @@
/* linux/include/linux/clocksource.h
*
* This file contains the structure definitions for clocksources.
*
* If you are not a clocksource, or timekeeping code, you should
* not be including this file!
*/
#ifndef _LINUX_CLOCKSOURCE_H
#define _LINUX_CLOCKSOURCE_H
#include <linux/types.h>
#include <linux/timex.h>
#include <linux/time.h>
#include <linux/list.h>
#include <asm/div64.h>
#include <asm/io.h>
/* clocksource cycle base type */
typedef u64 cycle_t;
/**
* struct clocksource - hardware abstraction for a free running counter
* Provides mostly state-free accessors to the underlying hardware.
*
* @name: ptr to clocksource name
* @list: list head for registration
* @rating: rating value for selection (higher is better)
* To avoid rating inflation the following
* list should give you a guide as to how
* to assign your clocksource a rating
* 1-99: Unfit for real use
* Only available for bootup and testing purposes.
* 100-199: Base level usability.
* Functional for real use, but not desired.
* 200-299: Good.
* A correct and usable clocksource.
* 300-399: Desired.
* A reasonably fast and accurate clocksource.
* 400-499: Perfect
* The ideal clocksource. A must-use where
* available.
* @read: returns a cycle value
* @mask: bitmask for two's complement
* subtraction of non 64 bit counters
* @mult: cycle to nanosecond multiplier
* @shift: cycle to nanosecond divisor (power of two)
* @update_callback: called when safe to alter clocksource values
* @is_continuous: defines if clocksource is free-running.
* @interval_cycles: Used internally by timekeeping core, please ignore.
* @interval_snsecs: Used internally by timekeeping core, please ignore.
*/
struct clocksource {
char *name;
struct list_head list;
int rating;
cycle_t (*read)(void);
cycle_t mask;
u32 mult;
u32 shift;
int (*update_callback)(void);
int is_continuous;
/* timekeeping specific data, ignore */
cycle_t interval_cycles;
u64 interval_snsecs;
};
/**
* clocksource_khz2mult - calculates mult from khz and shift
* @khz: Clocksource frequency in KHz
* @shift_constant: Clocksource shift factor
*
* Helper functions that converts a khz counter frequency to a timsource
* multiplier, given the clocksource shift value
*/
static inline u32 clocksource_khz2mult(u32 khz, u32 shift_constant)
{
/* khz = cyc/(Million ns)
* mult/2^shift = ns/cyc
* mult = ns/cyc * 2^shift
* mult = 1Million/khz * 2^shift
* mult = 1000000 * 2^shift / khz
* mult = (1000000<<shift) / khz
*/
u64 tmp = ((u64)1000000) << shift_constant;
tmp += khz/2; /* round for do_div */
do_div(tmp, khz);
return (u32)tmp;
}
/**
* clocksource_hz2mult - calculates mult from hz and shift
* @hz: Clocksource frequency in Hz
* @shift_constant: Clocksource shift factor
*
* Helper functions that converts a hz counter
* frequency to a timsource multiplier, given the
* clocksource shift value
*/
static inline u32 clocksource_hz2mult(u32 hz, u32 shift_constant)
{
/* hz = cyc/(Billion ns)
* mult/2^shift = ns/cyc
* mult = ns/cyc * 2^shift
* mult = 1Billion/hz * 2^shift
* mult = 1000000000 * 2^shift / hz
* mult = (1000000000<<shift) / hz
*/
u64 tmp = ((u64)1000000000) << shift_constant;
tmp += hz/2; /* round for do_div */
do_div(tmp, hz);
return (u32)tmp;
}
/**
* read_clocksource: - Access the clocksource's current cycle value
* @cs: pointer to clocksource being read
*
* Uses the clocksource to return the current cycle_t value
*/
static inline cycle_t read_clocksource(struct clocksource *cs)
{
return cs->read();
}
/**
* cyc2ns - converts clocksource cycles to nanoseconds
* @cs: Pointer to clocksource
* @cycles: Cycles
*
* Uses the clocksource and ntp ajdustment to convert cycle_ts to nanoseconds.
*
* XXX - This could use some mult_lxl_ll() asm optimization
*/
static inline s64 cyc2ns(struct clocksource *cs, cycle_t cycles)
{
u64 ret = (u64)cycles;
ret = (ret * cs->mult) >> cs->shift;
return ret;
}
/**
* calculate_clocksource_interval - Calculates a clocksource interval struct
*
* @c: Pointer to clocksource.
* @length_nsec: Desired interval length in nanoseconds.
*
* Calculates a fixed cycle/nsec interval for a given clocksource/adjustment
* pair and interval request.
*
* Unless you're the timekeeping code, you should not be using this!
*/
static inline void calculate_clocksource_interval(struct clocksource *c,
unsigned long length_nsec)
{
u64 tmp;
/* XXX - All of this could use a whole lot of optimization */
tmp = length_nsec;
tmp <<= c->shift;
tmp += c->mult/2;
do_div(tmp, c->mult);
c->interval_cycles = (cycle_t)tmp;
if(c->interval_cycles == 0)
c->interval_cycles = 1;
c->interval_snsecs = (u64)c->interval_cycles * c->mult;
}
/* used to install a new clocksource */
int register_clocksource(struct clocksource*);
void reselect_clocksource(void);
struct clocksource* get_next_clocksource(void);
#endif /* _LINUX_CLOCKSOURCE_H */

1
kernel/time/Makefile Normal file
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@ -0,0 +1 @@
obj-y += clocksource.o jiffies.o

344
kernel/time/clocksource.c Normal file
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@ -0,0 +1,344 @@
/*
* linux/kernel/time/clocksource.c
*
* This file contains the functions which manage clocksource drivers.
*
* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
*
* 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
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
* TODO WishList:
* o Allow clocksource drivers to be unregistered
* o get rid of clocksource_jiffies extern
*/
#include <linux/clocksource.h>
#include <linux/sysdev.h>
#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:
* linked 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.
*/
static struct clocksource *curr_clocksource = &clocksource_jiffies;
static struct clocksource *next_clocksource;
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 bootup
*
* Hack to avoid lots of clocksource churn at boot time
*/
static int clocksource_done_booting(void)
{
finished_booting = 1;
return 0;
}
late_initcall(clocksource_done_booting);
/**
* get_next_clocksource - Returns the selected clocksource
*
*/
struct clocksource *get_next_clocksource(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;
}
/**
* 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;
}
/**
* register_clocksource - Used to install new clocksources
* @t: clocksource to be registered
*
* Returns -EBUSY if registration fails, zero otherwise.
*/
int register_clocksource(struct clocksource *c)
{
int ret = 0;
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. "
"Already registered!", c->name);
ret = -EBUSY;
} else {
/* register it */
list_add(&c->list, &clocksource_list);
/* scan the registered clocksources, and pick the best one */
next_clocksource = select_clocksource();
}
spin_unlock_irqrestore(&clocksource_lock, flags);
return ret;
}
EXPORT_SYMBOL(register_clocksource);
/**
* reselect_clocksource - Rescan list for next clocksource
*
* A quick helper function to be used if a clocksource changes its
* rating. Forces the clocksource list to be re-scaned for the best
* clocksource.
*/
void reselect_clocksource(void)
{
unsigned long flags;
spin_lock_irqsave(&clocksource_lock, flags);
next_clocksource = select_clocksource();
spin_unlock_irqrestore(&clocksource_lock, flags);
}
/**
* 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
*
* Provides sysfs interface for listing registered clocksources
*/
static ssize_t
sysfs_show_available_clocksources(struct sys_device *dev, char *buf)
{
struct list_head *tmp;
char *curr = buf;
spin_lock_irq(&clocksource_lock);
list_for_each(tmp, &clocksource_list) {
struct clocksource *src;
src = list_entry(tmp, struct clocksource, list);
curr += sprintf(curr, "%s ", src->name);
}
spin_unlock_irq(&clocksource_lock);
curr += sprintf(curr, "\n");
return curr - buf;
}
/*
* 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);
static struct sysdev_class clocksource_sysclass = {
set_kset_name("clocksource"),
};
static struct sys_device device_clocksource = {
.id = 0,
.cls = &clocksource_sysclass,
};
static int init_clocksource_sysfs(void)
{
int error = sysdev_class_register(&clocksource_sysclass);
if (!error)
error = sysdev_register(&device_clocksource);
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)
{
printk("Warning! clock= boot option is deprecated.\n");
return boot_override_clocksource(str);
}
__setup("clock=", boot_override_clock);

73
kernel/time/jiffies.c Normal file
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@ -0,0 +1,73 @@
/***********************************************************************
* linux/kernel/time/jiffies.c
*
* This file contains the jiffies based clocksource.
*
* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
*
* 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
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*
************************************************************************/
#include <linux/clocksource.h>
#include <linux/jiffies.h>
#include <linux/init.h>
/* The Jiffies based clocksource is the lowest common
* denominator clock source which should function on
* all systems. It has the same coarse resolution as
* the timer interrupt frequency HZ and it suffers
* inaccuracies caused by missed or lost timer
* interrupts and the inability for the timer
* interrupt hardware to accuratly tick at the
* requested HZ value. It is also not reccomended
* for "tick-less" systems.
*/
#define NSEC_PER_JIFFY ((u32)((((u64)NSEC_PER_SEC)<<8)/ACTHZ))
/* Since jiffies uses a simple NSEC_PER_JIFFY multiplier
* conversion, the .shift value could be zero. However
* this would make NTP adjustments impossible as they are
* in units of 1/2^.shift. Thus we use JIFFIES_SHIFT to
* shift both the nominator and denominator the same
* amount, and give ntp adjustments in units of 1/2^8
*
* The value 8 is somewhat carefully chosen, as anything
* larger can result in overflows. NSEC_PER_JIFFY grows as
* HZ shrinks, so values greater then 8 overflow 32bits when
* HZ=100.
*/
#define JIFFIES_SHIFT 8
static cycle_t jiffies_read(void)
{
return (cycle_t) jiffies;
}
struct clocksource clocksource_jiffies = {
.name = "jiffies",
.rating = 0, /* lowest rating*/
.read = jiffies_read,
.mask = 0xffffffff, /*32bits*/
.mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
.shift = JIFFIES_SHIFT,
.is_continuous = 0, /* tick based, not free running */
};
static int __init init_jiffies_clocksource(void)
{
return register_clocksource(&clocksource_jiffies);
}
module_init(init_jiffies_clocksource);