/*
* 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_read_data - data required to read from sched_clock
*
* @epoch_ns: sched_clock value at last update
* @epoch_cyc: Clock cycle value at last update
* @sched_clock_mask: Bitmask for two's complement subtraction of non 64bit
* clocks
* @read_sched_clock: Current clock source (or dummy source when suspended)
* @mult: Multipler for scaled math conversion
* @shift: Shift value for scaled math conversion
*
* Care must be taken when updating this structure; it is read by
* some very hot code paths. It occupies <=40 bytes and, when combined
* with the seqcount used to synchronize access, comfortably fits into
* a 64 byte cache line.
*/
struct clock_read_data {
u64 epoch_ns;
u64 epoch_cyc;
u64 sched_clock_mask;
u64 (*read_sched_clock)(void);
u32 mult;
u32 shift;
};
/**
* struct clock_data - all data needed for sched_clock (including
* registration of a new clock source)
*
* @seq: Sequence counter for protecting updates.
* @read_data: Data required to read from sched_clock.
* @wrap_kt: Duration for which clock can run before wrapping
* @rate: Tick rate of the registered clock
* @actual_read_sched_clock: Registered clock read function
*
* The ordering of this structure has been chosen to optimize cache
* performance. In particular seq and read_data (combined) should fit
* into a single 64 byte cache line.
*/
struct clock_data {
seqcount_t seq;
struct clock_read_data read_data;
ktime_t wrap_kt;
unsigned long rate;
u64 (*actual_read_sched_clock)(void);
};
static struct hrtimer sched_clock_timer;
static int irqtime = -1;
core_param(irqtime, irqtime, int, 0400);
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 struct clock_data cd ____cacheline_aligned = {
.read_data = { .mult = NSEC_PER_SEC / HZ,
.read_sched_clock = jiffy_sched_clock_read, },
.actual_read_sched_clock = 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 cyc, res;
unsigned long seq;
struct clock_read_data *rd = &cd.read_data;
do {
seq = raw_read_seqcount_begin(&cd.seq);
cyc = (rd->read_sched_clock() - rd->epoch_cyc) &
rd->sched_clock_mask;
res = rd->epoch_ns + cyc_to_ns(cyc, rd->mult, rd->shift);
} while (read_seqcount_retry(&cd.seq, seq));
return res;
}
/*
* Atomically update the sched_clock epoch.
*/
static void update_sched_clock(void)
{
unsigned long flags;
u64 cyc;
u64 ns;
struct clock_read_data *rd = &cd.read_data;
cyc = cd.actual_read_sched_clock();
ns = rd->epoch_ns +
cyc_to_ns((cyc - rd->epoch_cyc) & rd->sched_clock_mask,
rd->mult, rd->shift);
raw_local_irq_save(flags);
raw_write_seqcount_begin(&cd.seq);
rd->epoch_ns = ns;
rd->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;
unsigned long r;
char r_unit;
struct clock_read_data *rd = &cd.read_data;
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);
cd.rate = rate;
/* calculate how many nanosecs until we risk wrapping */
wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);
cd.wrap_kt = ns_to_ktime(wrap);
/* update epoch for new counter and update epoch_ns from old counter*/
new_epoch = read();
cyc = cd.actual_read_sched_clock();
ns = rd->epoch_ns +
cyc_to_ns((cyc - rd->epoch_cyc) & rd->sched_clock_mask,
rd->mult, rd->shift);
cd.actual_read_sched_clock = read;
raw_write_seqcount_begin(&cd.seq);
rd->read_sched_clock = read;
rd->sched_clock_mask = new_mask;
rd->mult = new_mult;
rd->shift = new_shift;
rd->epoch_cyc = new_epoch;
rd->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 (cd.actual_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);
}
/*
* Clock read function for use when the clock is suspended.
*
* This function makes it appear to sched_clock() as if the clock
* stopped counting at its last update.
*/
static u64 notrace suspended_sched_clock_read(void)
{
return cd.read_data.epoch_cyc;
}
static int sched_clock_suspend(void)
{
struct clock_read_data *rd = &cd.read_data;
update_sched_clock();
hrtimer_cancel(&sched_clock_timer);
rd->read_sched_clock = suspended_sched_clock_read;
return 0;
}
static void sched_clock_resume(void)
{
struct clock_read_data *rd = &cd.read_data;
rd->epoch_cyc = cd.actual_read_sched_clock();
hrtimer_start(&sched_clock_timer, cd.wrap_kt, HRTIMER_MODE_REL);
rd->read_sched_clock = cd.actual_read_sched_clock;
}
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);
