Linux內核中常用的延时方法

#ifndef _LINUX_DELAY_H
#define _LINUX_DELAY_H

/*
 * Copyright (C) 1993 Linus Torvalds
 *
 * Delay routines, using a pre-computed "loops_per_jiffy" value.
 */

#include <linux/kernel.h>

extern unsigned long loops_per_jiffy;

#include <asm/delay.h>

/*
 * Using udelay() for intervals greater than a few milliseconds can
 * risk overflow for high loops_per_jiffy (high bogomips) machines. The
 * mdelay() provides a wrapper to prevent this.  For delays greater
 * than MAX_UDELAY_MS milliseconds, the wrapper is used.  Architecture
 * specific values can be defined in asm-???/delay.h as an override.
 * The 2nd mdelay() definition ensures GCC will optimize away the 
 * while loop for the common cases where n <= MAX_UDELAY_MS  --  Paul G.
 */

#ifndef MAX_UDELAY_MS
#define MAX_UDELAY_MS	5
#endif

#ifndef mdelay
#define mdelay(n) (\
	(__builtin_constant_p(n) && (n)<=MAX_UDELAY_MS) ? udelay((n)*1000) : \
	({unsigned long __ms=(n); while (__ms--) udelay(1000);}))
#endif

#ifndef ndelay
static inline void ndelay(unsigned long x)
{
	udelay(DIV_ROUND_UP(x, 1000));
}
#define ndelay(x) ndelay(x)
#endif

extern unsigned long lpj_fine;
void calibrate_delay(void);
void msleep(unsigned int msecs);
unsigned long msleep_interruptible(unsigned int msecs);
void usleep_range(unsigned long min, unsigned long max);

static inline void ssleep(unsigned int seconds)
{
	msleep(seconds * 1000);
}

#endif /* defined(_LINUX_DELAY_H) */