mirror of
https://github.com/torvalds/linux.git
synced 2024-12-11 05:33:09 +00:00
d25a025201
The clocksource watchdog test sets a local JIFFIES_SHIFT macro and assumes that HZ is >= 100. For smaller HZ values this shift value is too large and causes undefined behaviour. Move the HZ-based definitions of JIFFIES_SHIFT from kernel/time/jiffies.c to kernel/time/tick-internal.h so the clocksource watchdog test can utilize them, which makes it work correctly with all HZ values. [ tglx: Resolved conflicts and massaged changelog ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/lkml/20210812000133.GA402890@paulmck-ThinkPad-P17-Gen-1/
105 lines
2.6 KiB
C
105 lines
2.6 KiB
C
// SPDX-License-Identifier: GPL-2.0+
|
|
/*
|
|
* This file contains the jiffies based clocksource.
|
|
*
|
|
* Copyright (C) 2004, 2005 IBM, John Stultz (johnstul@us.ibm.com)
|
|
*/
|
|
#include <linux/clocksource.h>
|
|
#include <linux/jiffies.h>
|
|
#include <linux/module.h>
|
|
#include <linux/init.h>
|
|
|
|
#include "timekeeping.h"
|
|
#include "tick-internal.h"
|
|
|
|
|
|
static u64 jiffies_read(struct clocksource *cs)
|
|
{
|
|
return (u64) jiffies;
|
|
}
|
|
|
|
/*
|
|
* 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 accurately tick at the
|
|
* requested HZ value. It is also not recommended
|
|
* for "tick-less" systems.
|
|
*/
|
|
static struct clocksource clocksource_jiffies = {
|
|
.name = "jiffies",
|
|
.rating = 1, /* lowest valid rating*/
|
|
.uncertainty_margin = 32 * NSEC_PER_MSEC,
|
|
.read = jiffies_read,
|
|
.mask = CLOCKSOURCE_MASK(32),
|
|
.mult = TICK_NSEC << JIFFIES_SHIFT, /* details above */
|
|
.shift = JIFFIES_SHIFT,
|
|
.max_cycles = 10,
|
|
};
|
|
|
|
__cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(jiffies_lock);
|
|
__cacheline_aligned_in_smp seqcount_raw_spinlock_t jiffies_seq =
|
|
SEQCNT_RAW_SPINLOCK_ZERO(jiffies_seq, &jiffies_lock);
|
|
|
|
#if (BITS_PER_LONG < 64)
|
|
u64 get_jiffies_64(void)
|
|
{
|
|
unsigned int seq;
|
|
u64 ret;
|
|
|
|
do {
|
|
seq = read_seqcount_begin(&jiffies_seq);
|
|
ret = jiffies_64;
|
|
} while (read_seqcount_retry(&jiffies_seq, 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;
|
|
}
|
|
|
|
static 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;
|
|
}
|