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author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
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committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-04-27 10:05:51 +0000 |
commit | 5d1646d90e1f2cceb9f0828f4b28318cd0ec7744 (patch) | |
tree | a94efe259b9009378be6d90eb30d2b019d95c194 /kernel/time/jiffies.c | |
parent | Initial commit. (diff) | |
download | linux-5d1646d90e1f2cceb9f0828f4b28318cd0ec7744.tar.xz linux-5d1646d90e1f2cceb9f0828f4b28318cd0ec7744.zip |
Adding upstream version 5.10.209.upstream/5.10.209upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'kernel/time/jiffies.c')
-rw-r--r-- | kernel/time/jiffies.c | 122 |
1 files changed, 122 insertions, 0 deletions
diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c new file mode 100644 index 000000000..65409abcc --- /dev/null +++ b/kernel/time/jiffies.c @@ -0,0 +1,122 @@ +// 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" + + +/* Since jiffies uses a simple TICK_NSEC 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. TICK_NSEC 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 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 accuratly 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_t jiffies_seq; + +#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; +} |