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/*
* sched_clock.c: support for extending counters to full 64-bit ns counter
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License version 2 as
* published by the Free Software Foundation.
*/
#include <linux/clocksource.h>
#include <linux/init.h>
#include <linux/jiffies.h>
#include <linux/ktime.h>
#include <linux/kernel.h>
#include <linux/moduleparam.h>
#include <linux/sched.h>
#include <linux/syscore_ops.h>
#include <linux/hrtimer.h>
#include <linux/sched_clock.h>
#include <linux/seqlock.h>
#include <linux/bitops.h>
struct clock_data {
ktime_t wrap_kt;
u64 epoch_ns;
u64 epoch_cyc;
seqcount_t seq;
unsigned long rate;
u32 mult;
u32 shift;
bool suspended;
};
static struct hrtimer sched_clock_timer;
static int irqtime = -1;
core_param(irqtime, irqtime, int, 0400);
static struct clock_data cd = {
.mult = NSEC_PER_SEC / HZ,
};
static u64 __read_mostly sched_clock_mask;
static u64 notrace jiffy_sched_clock_read(void)
{
/*
* We don't need to use get_jiffies_64 on 32-bit arches here
* because we register with BITS_PER_LONG
*/
return (u64)(jiffies - INITIAL_JIFFIES);
}
static u64 __read_mostly (*read_sched_clock)(void) = jiffy_sched_clock_read;
static inline u64 notrace cyc_to_ns(u64 cyc, u32 mult, u32 shift)
{
return (cyc * mult) >> shift;
}
unsigned long long notrace sched_clock(void)
{
u64 epoch_ns;
u64 epoch_cyc;
u64 cyc;
unsigned long seq;
if (cd.suspended)
return cd.epoch_ns;
do {
seq = raw_read_seqcount_begin(&cd.seq);
epoch_cyc = cd.epoch_cyc;
epoch_ns = cd.epoch_ns;
} while (read_seqcount_retry(&cd.seq, seq));
cyc = read_sched_clock();
cyc = (cyc - epoch_cyc) & sched_clock_mask;
return epoch_ns + cyc_to_ns(cyc, cd.mult, cd.shift);
}
/*
* Atomically update the sched_clock epoch.
*/
static void notrace update_sched_clock(void)
{
unsigned long flags;
u64 cyc;
u64 ns;
cyc = read_sched_clock();
ns = cd.epoch_ns +
cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
cd.mult, cd.shift);
raw_local_irq_save(flags);
raw_write_seqcount_begin(&cd.seq);
cd.epoch_ns = ns;
cd.epoch_cyc = cyc;
raw_write_seqcount_end(&cd.seq);
raw_local_irq_restore(flags);
}
static enum hrtimer_restart sched_clock_poll(struct hrtimer *hrt)
{
update_sched_clock();
hrtimer_forward_now(hrt, cd.wrap_kt);
return HRTIMER_RESTART;
}
void __init sched_clock_register(u64 (*read)(void), int bits,
unsigned long rate)
{
u64 res, wrap, new_mask, new_epoch, cyc, ns;
u32 new_mult, new_shift;
ktime_t new_wrap_kt;
unsigned long r;
char r_unit;
if (cd.rate > rate)
return;
WARN_ON(!irqs_disabled());
/* calculate the mult/shift to convert counter ticks to ns. */
clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
new_mask = CLOCKSOURCE_MASK(bits);
/* calculate how many ns until we wrap */
wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask);
new_wrap_kt = ns_to_ktime(wrap - (wrap >> 3));
/* update epoch for new counter and update epoch_ns from old counter*/
new_epoch = read();
cyc = read_sched_clock();
ns = cd.epoch_ns + cyc_to_ns((cyc - cd.epoch_cyc) & sched_clock_mask,
cd.mult, cd.shift);
raw_write_seqcount_begin(&cd.seq);
read_sched_clock = read;
sched_clock_mask = new_mask;
cd.rate = rate;
cd.wrap_kt = new_wrap_kt;
cd.mult = new_mult;
cd.shift = new_shift;
cd.epoch_cyc = new_epoch;
cd.epoch_ns = ns;
raw_write_seqcount_end(&cd.seq);
r = rate;
if (r >= 4000000) {
r /= 1000000;
r_unit = 'M';
} else if (r >= 1000) {
r /= 1000;
r_unit = 'k';
} else
r_unit = ' ';
/* calculate the ns resolution of this counter */
res = cyc_to_ns(1ULL, new_mult, new_shift);
pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
bits, r, r_unit, res, wrap);
/* Enable IRQ time accounting if we have a fast enough sched_clock */
if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
enable_sched_clock_irqtime();
pr_debug("Registered %pF as sched_clock source\n", read);
}
void __init sched_clock_postinit(void)
{
/*
* If no sched_clock function has been provided at that point,
* make it the final one one.
*/
if (read_sched_clock == jiffy_sched_clock_read)
sched_clock_register(jiffy_sched_clock_read, BITS_PER_LONG, HZ);
update_sched_clock();
/*
* Start the timer to keep sched_clock() properly updated and
* sets the initial epoch.
*/
hrtimer_init(&sched_clock_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
sched_clock_timer.function = sched_clock_poll;
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
}
static int sched_clock_suspend(void)
{
update_sched_clock();
hrtimer_cancel(&sched_clock_timer);
cd.suspended = true;
return 0;
}
static void sched_clock_resume(void)
{
cd.epoch_cyc = read_sched_clock();
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
cd.suspended = false;
}
static struct syscore_ops sched_clock_ops = {
.suspend = sched_clock_suspend,
.resume = sched_clock_resume,
};
static int __init sched_clock_syscore_init(void)
{
register_syscore_ops(&sched_clock_ops);
return 0;
}
device_initcall(sched_clock_syscore_init);
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