1. 根目录:
2. kernel
3. time
4. timekeeping_internal.h

#ifndef _TIMEKEEPING_INTERNAL_H
#define _TIMEKEEPING_INTERNAL_H
/*
 * timekeeping debug functions
 */
#include <linux/clocksource.h>
#include <linux/time.h>

#ifdef CONFIG_DEBUG_FS
extern void tk_debug_account_sleep_time(struct timespec64 *t);
#else
#define tk_debug_account_sleep_time(x)
#endif

#ifdef CONFIG_CLOCKSOURCE_VALIDATE_LAST_CYCLE
static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask)
{
	cycle_t ret = (now - last) & mask;

	return (s64) ret > 0 ? ret : 0;
}
#else
static inline cycle_t clocksource_delta(cycle_t now, cycle_t last, cycle_t mask)
{
	return (now - last) & mask;
}
#endif

#endif /* _TIMEKEEPING_INTERNAL_H */