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/*
* kernel/trace/trace-clock.c
*
* (C) Copyright 2008 -
* Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca)
*
* Generic kernel tracing clock for architectures without TSC.
*/
#include <linux/module.h>
#include <linux/init.h>
#include <linux/delay.h>
#include <linux/timer.h>
#include <linux/workqueue.h>
#include <linux/cpu.h>
#include <linux/timex.h>
#include <linux/bitops.h>
#include <linux/trace-clock.h>
#include <linux/jiffies.h>
static int trace_clock_refcount;
static DEFINE_MUTEX(trace_clock_mutex);
static struct timer_list trace_clock_timer;
/*
* bits 0..12 : counter, atomically incremented
* bits 13..{32,64} : time counter, incremented each jiffy.
*/
atomic_long_t trace_clock_var;
EXPORT_SYMBOL(trace_clock_var);
static void trace_clock_update(void)
{
long old_clock, new_clock;
unsigned long ticks;
/*
* Make sure we keep track of delayed timer.
*/
ticks = jiffies - trace_clock_timer.expires + 1;
/* Don't update if ticks is zero, time would go backward. */
if (unlikely(!ticks))
return;
do {
old_clock = atomic_long_read(&trace_clock_var);
new_clock = (old_clock + (ticks << TRACE_CLOCK_SHIFT))
& (~((1 << TRACE_CLOCK_SHIFT) - 1));
} while (atomic_long_cmpxchg(&trace_clock_var, old_clock, new_clock)
!= old_clock);
}
static void trace_clock_timer_fct(unsigned long data)
{
trace_clock_update();
trace_clock_timer.expires = jiffies + 1;
add_timer(&trace_clock_timer);
}
static void enable_trace_clock(void)
{
init_timer(&trace_clock_timer);
/* trace_clock_update() reads expires */
trace_clock_timer.function = trace_clock_timer_fct;
trace_clock_timer.expires = jiffies + 1;
trace_clock_update();
add_timer(&trace_clock_timer);
}
static void disable_trace_clock(void)
{
del_timer_sync(&trace_clock_timer);
}
void get_trace_clock(void)
{
get_synthetic_tsc();
mutex_lock(&trace_clock_mutex);
if (trace_clock_refcount++)
goto end;
enable_trace_clock();
end:
mutex_unlock(&trace_clock_mutex);
}
EXPORT_SYMBOL_GPL(get_trace_clock);
void put_trace_clock(void)
{
mutex_lock(&trace_clock_mutex);
WARN_ON(trace_clock_refcount <= 0);
if (trace_clock_refcount != 1)
goto end;
disable_trace_clock();
end:
trace_clock_refcount--;
mutex_unlock(&trace_clock_mutex);
put_synthetic_tsc();
}
EXPORT_SYMBOL_GPL(put_trace_clock);
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