linux内核：时间与jiffes互相转换前言一 ms转jiffies二 jiffies转毫秒三微秒转jiffiestimespec_to_jiffiesjiffies_to_timespectimeval_to_jiffiesjiffies_to_timevaljiffies_to_clock_tclock_t_to_jiffiesnsecs_to_jiffiesnsec_to_clock_t

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我是靠谱客的博主闪闪酸奶，最近开发中收集的这篇文章主要介绍linux内核：时间与jiffes互相转换前言一 ms转jiffies二 jiffies转毫秒三微秒转jiffiestimespec_to_jiffiesjiffies_to_timespectimeval_to_jiffiesjiffies_to_timevaljiffies_to_clock_tclock_t_to_jiffiesnsecs_to_jiffiesnsec_to_clock_t，觉得挺不错的，现在分享给大家，希望可以做个参考。

概述

前言

内核中有一个神奇的全局变量jiffies。

本篇介绍的内容全部位于文件kernel/time/time.c

一 ms转jiffies

msecs_to_jiffies

/*
 * When we convert to jiffies then we interpret incoming values
 * the following way:
 *
 * - negative values mean 'infinite timeout' (MAX_JIFFY_OFFSET)
 *
 * - 'too large' values [that would result in larger than
 *   MAX_JIFFY_OFFSET values] mean 'infinite timeout' too.
 *
 * - all other values are converted to jiffies by either multiplying
 *   the input value by a factor or dividing it with a factor
 *
 * We must also be careful about 32-bit overflows.
 */
unsigned long msecs_to_jiffies(const unsigned int m)
{
	/*
	 * Negative value, means infinite timeout:
	 */
	if ((int)m < 0)
		return MAX_JIFFY_OFFSET;

#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
	/*
	 * HZ is equal to or smaller than 1000, and 1000 is a nice
	 * round multiple of HZ, divide with the factor between them,
	 * but round upwards:
	 */
	return (m + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ);
#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
	/*
	 * HZ is larger than 1000, and HZ is a nice round multiple of
	 * 1000 - simply multiply with the factor between them.
	 *
	 * But first make sure the multiplication result cannot
	 * overflow:
	 */
	if (m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
		return MAX_JIFFY_OFFSET;

	return m * (HZ / MSEC_PER_SEC);
#else
	/*
	 * Generic case - multiply, round and divide. But first
	 * check that if we are doing a net multiplication, that
	 * we wouldn't overflow:
	 */
	if (HZ > MSEC_PER_SEC && m > jiffies_to_msecs(MAX_JIFFY_OFFSET))
		return MAX_JIFFY_OFFSET;

	return (MSEC_TO_HZ_MUL32 * m + MSEC_TO_HZ_ADJ32)
		>> MSEC_TO_HZ_SHR32;
#endif
}
EXPORT_SYMBOL(msecs_to_jiffies);

二 jiffies转毫秒

jiffies_to_msecs

/*
 * Convert jiffies to milliseconds and back.
 *
 * Avoid unnecessary multiplications/divisions in the
 * two most common HZ cases:
 */
unsigned int jiffies_to_msecs(const unsigned long j)
{
#if HZ <= MSEC_PER_SEC && !(MSEC_PER_SEC % HZ)
	return (MSEC_PER_SEC / HZ) * j;
#elif HZ > MSEC_PER_SEC && !(HZ % MSEC_PER_SEC)
	return (j + (HZ / MSEC_PER_SEC) - 1)/(HZ / MSEC_PER_SEC);
#else
# if BITS_PER_LONG == 32
	return (HZ_TO_MSEC_MUL32 * j) >> HZ_TO_MSEC_SHR32;
# else
	return (j * HZ_TO_MSEC_NUM) / HZ_TO_MSEC_DEN;
# endif
#endif
}

三微秒转jiffies

usecs_to_jiffies

unsigned long usecs_to_jiffies(const unsigned int u)
{
	if (u > jiffies_to_usecs(MAX_JIFFY_OFFSET))
		return MAX_JIFFY_OFFSET;
#if HZ <= USEC_PER_SEC && !(USEC_PER_SEC % HZ)
	return (u + (USEC_PER_SEC / HZ) - 1) / (USEC_PER_SEC / HZ);
#elif HZ > USEC_PER_SEC && !(HZ % USEC_PER_SEC)
	return u * (HZ / USEC_PER_SEC);
#else
	return (USEC_TO_HZ_MUL32 * u + USEC_TO_HZ_ADJ32)
		>> USEC_TO_HZ_SHR32;
#endif
}
EXPORT_SYMBOL(usecs_to_jiffies);

timespec_to_jiffies

unsigned long
timespec_to_jiffies(const struct timespec *value)
{
	return __timespec_to_jiffies(value->tv_sec, value->tv_nsec);
}

jiffies_to_timespec

void
jiffies_to_timespec(const unsigned long jiffies, struct timespec *value)
{
	/*
	 * Convert jiffies to nanoseconds and separate with
	 * one divide.
	 */
	u32 rem;
	value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
				    NSEC_PER_SEC, &rem);
	value->tv_nsec = rem;
}
EXPORT_SYMBOL(jiffies_to_timespec);

timeval_to_jiffies

unsigned long
timeval_to_jiffies(const struct timeval *value)
{
	return __timespec_to_jiffies(value->tv_sec,
				     value->tv_usec * NSEC_PER_USEC);
}

jiffies_to_timeval

void jiffies_to_timeval(const unsigned long jiffies, struct timeval *value)
{
	/*
	 * Convert jiffies to nanoseconds and separate with
	 * one divide.
	 */
	u32 rem;

	value->tv_sec = div_u64_rem((u64)jiffies * TICK_NSEC,
				    NSEC_PER_SEC, &rem);
	value->tv_usec = rem / NSEC_PER_USEC;
}

jiffies_to_clock_t

clock_t jiffies_to_clock_t(unsigned long x)
{
#if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
# if HZ < USER_HZ
	return x * (USER_HZ / HZ);
# else
	return x / (HZ / USER_HZ);
# endif
#else
	return div_u64((u64)x * TICK_NSEC, NSEC_PER_SEC / USER_HZ);
#endif
}

clock_t_to_jiffies

unsigned long clock_t_to_jiffies(unsigned long x)
{
#if (HZ % USER_HZ)==0
	if (x >= ~0UL / (HZ / USER_HZ))
		return ~0UL;
	return x * (HZ / USER_HZ);
#else
	/* Don't worry about loss of precision here .. */
	if (x >= ~0UL / HZ * USER_HZ)
		return ~0UL;

	/* .. but do try to contain it here */
	return div_u64((u64)x * HZ, USER_HZ);
#endif
}

nsecs_to_jiffies

unsigned long nsecs_to_jiffies(u64 n)
{
	return (unsigned long)nsecs_to_jiffies64(n);
}

nsec_to_clock_t

u64 nsec_to_clock_t(u64 x)
{
#if (NSEC_PER_SEC % USER_HZ) == 0
	return div_u64(x, NSEC_PER_SEC / USER_HZ);
#elif (USER_HZ % 512) == 0
	return div_u64(x * USER_HZ / 512, NSEC_PER_SEC / 512);
#else
	/*
         * max relative error 5.7e-8 (1.8s per year) for USER_HZ <= 1024,
         * overflow after 64.99 years.
         * exact for HZ=60, 72, 90, 120, 144, 180, 300, 600, 900, ...
         */
	return div_u64(x * 9, (9ull * NSEC_PER_SEC + (USER_HZ / 2)) / USER_HZ);
#endif
}