136 lines
3.9 KiB
C
136 lines
3.9 KiB
C
/***********************************************************************
|
|
* 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/module.h>
|
|
#include <linux/init.h>
|
|
|
|
#include "tick-internal.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 recommended
|
|
* for "tick-less" systems.
|
|
*/
|
|
#define NSEC_PER_JIFFY ((NSEC_PER_SEC+HZ/2)/HZ)
|
|
|
|
/* 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 than 8 overflow 32bits when
|
|
* HZ=100.
|
|
*/
|
|
#if HZ < 34
|
|
#define JIFFIES_SHIFT 6
|
|
#elif HZ < 67
|
|
#define JIFFIES_SHIFT 7
|
|
#else
|
|
#define JIFFIES_SHIFT 8
|
|
#endif
|
|
|
|
static cycle_t jiffies_read(struct clocksource *cs)
|
|
{
|
|
return (cycle_t) jiffies;
|
|
}
|
|
|
|
static struct clocksource clocksource_jiffies = {
|
|
.name = "jiffies",
|
|
.rating = 1, /* lowest valid rating*/
|
|
.read = jiffies_read,
|
|
.mask = 0xffffffff, /*32bits*/
|
|
.mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */
|
|
.shift = JIFFIES_SHIFT,
|
|
};
|
|
|
|
__cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock);
|
|
|
|
#if (BITS_PER_LONG < 64)
|
|
u64 get_jiffies_64(void)
|
|
{
|
|
unsigned long seq;
|
|
u64 ret;
|
|
|
|
do {
|
|
seq = read_seqbegin(&jiffies_lock);
|
|
ret = jiffies_64;
|
|
} while (read_seqretry(&jiffies_lock, seq));
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL(get_jiffies_64);
|
|
#endif
|
|
|
|
EXPORT_SYMBOL(jiffies);
|
|
|
|
static int __init init_jiffies_clocksource(void)
|
|
{
|
|
return clocksource_register(&clocksource_jiffies);
|
|
}
|
|
|
|
core_initcall(init_jiffies_clocksource);
|
|
|
|
struct clocksource * __init __weak clocksource_default_clock(void)
|
|
{
|
|
return &clocksource_jiffies;
|
|
}
|
|
|
|
struct clocksource refined_jiffies;
|
|
|
|
int register_refined_jiffies(long cycles_per_second)
|
|
{
|
|
u64 nsec_per_tick, shift_hz;
|
|
long cycles_per_tick;
|
|
|
|
|
|
|
|
refined_jiffies = clocksource_jiffies;
|
|
refined_jiffies.name = "refined-jiffies";
|
|
refined_jiffies.rating++;
|
|
|
|
/* Calc cycles per tick */
|
|
cycles_per_tick = (cycles_per_second + HZ/2)/HZ;
|
|
/* shift_hz stores hz<<8 for extra accuracy */
|
|
shift_hz = (u64)cycles_per_second << 8;
|
|
shift_hz += cycles_per_tick/2;
|
|
do_div(shift_hz, cycles_per_tick);
|
|
/* Calculate nsec_per_tick using shift_hz */
|
|
nsec_per_tick = (u64)NSEC_PER_SEC << 8;
|
|
nsec_per_tick += (u32)shift_hz/2;
|
|
do_div(nsec_per_tick, (u32)shift_hz);
|
|
|
|
refined_jiffies.mult = ((u32)nsec_per_tick) << JIFFIES_SHIFT;
|
|
|
|
clocksource_register(&refined_jiffies);
|
|
return 0;
|
|
}
|