Linux 将 jiffies 转换为毫秒
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Converting jiffies to milli seconds
提问by EpsilonVector
How do I manually convert jiffies to milliseconds and vice versa in Linux? I know kernel 2.6 has a function for this, but I'm working on 2.4 (homework) and though I looked at the code it uses lots of macro constants which I have no idea if they're defined in 2.4.
如何在 Linux 中手动将 jiffies 转换为毫秒，反之亦然？我知道内核 2.6 对此有一个函数，但我正在研究 2.4（作业），尽管我查看了代码，但它使用了很多宏常量，我不知道它们是否在 2.4 中定义。
采纳答案by Eric Seppanen
As a previous answer said, the rate at which jiffiesincrements is fixed.
正如之前的答案所说，jiffies增量的速率是固定的。
The standard way of specifying time for a function that accepts jiffiesis using the constant HZ.
为接受的函数指定时间的标准方法jiffies是使用常量HZ。
That's the abbreviation for Hertz, or the number of ticks per second. On a system with a timer tick set to 1ms, HZ=1000. Some distributions or architectures may use another number (100 used to be common).
那是赫兹的缩写，或每秒滴答数。在定时器刻度设置为 1ms 的系统上，HZ=1000。某些发行版或体系结构可能使用另一个数字（过去通常为 100）。
The standard way of specifying a jiffiescount for a function is using HZ, like this:
jiffies为函数指定计数的标准方法是使用HZ，如下所示：
schedule_timeout(HZ / 10); /* Timeout after 1/10 second */
In most simple cases, this works fine.
在大多数简单的情况下，这可以正常工作。
2*HZ /* 2 seconds in jiffies */
HZ /* 1 second in jiffies */
foo * HZ /* foo seconds in jiffies */
HZ/10 /* 100 milliseconds in jiffies */
HZ/100 /* 10 milliseconds in jiffies */
bar*HZ/1000 /* bar milliseconds in jiffies */
Those last two have a bit of a problem, however, as on a system with a 10 ms timer tick, HZ/100is 1, and the precision starts to suffer. You may get a delay anywhere between 0.0001 and 1.999 timer ticks (0-2 ms, essentially). If you tried to use HZ/200on a 10ms tick system, the integer division gives you 0 jiffies!
然而，最后两个有一些问题，因为在一个具有 10 ms 计时器滴答的系统上，它HZ/100是 1，并且精度开始受到影响。您可能会在 0.0001 和 1.999 计时器滴答之间的任何地方延迟（本质上是 0-2 毫秒）。如果您尝试HZ/200在 10ms 滴答系统上使用，整数除法会给您 0 jiffies！
So the rule of thumb is, be very careful using HZ for tiny values (those approaching 1 jiffie).
所以经验法则是，对微小值（接近 1 jiffie 的值）使用 HZ 时要非常小心。
To convert the other way, you would use:
要以另一种方式转换，您可以使用：
jiffies / HZ /* jiffies to seconds */
jiffies * 1000 / HZ /* jiffies to milliseconds */
You shouldn't expect anything better than millisecond precision.
您不应该期望比毫秒精度更好的东西。
回答by indiv
Jiffies are hard-coded in Linux 2.4. Check the definition of HZ, which is defined in the architecture-specific param.h. It's often 100 Hz, which is one tick every (1 sec/100 ticks * 1000 ms/sec) 10 ms.
Jiffies 在 Linux 2.4 中是硬编码的。检查 的定义HZ，该定义在特定于体系结构的 中定义param.h。它通常是 100 Hz，即每（1 秒/100 滴答声 * 1000 毫秒/秒）10 毫秒一个滴答声。
This holds true for i386, and HZ is defined in include/asm-i386/param.h.
这适用于 i386，HZ 定义在include/asm-i386/param.h.
There are functions in include/linux/time.hcalled timespec_to_jiffiesand jiffies_to_timespecwhere you can convert back and forth between a struct timespecand jiffies:
有函数include/linux/time.h称为timespec_to_jiffies和jiffies_to_timespec在那里你可以来回转换之间struct timespec和jiffies：
#define MAX_JIFFY_OFFSET ((~0UL >> 1)-1)
static __inline__ unsigned long
timespec_to_jiffies(struct timespec *value)
{
unsigned long sec = value->tv_sec;
long nsec = value->tv_nsec;
if (sec >= (MAX_JIFFY_OFFSET / HZ))
return MAX_JIFFY_OFFSET;
nsec += 1000000000L / HZ - 1;
nsec /= 1000000000L / HZ;
return HZ * sec + nsec;
}
static __inline__ void
jiffies_to_timespec(unsigned long jiffies, struct timespec *value)
{
value->tv_nsec = (jiffies % HZ) * (1000000000L / HZ);
value->tv_sec = jiffies / HZ;
}
Note:I checked this info in version 2.4.22.
注意：我在 2.4.22 版中检查了此信息。
回答by Anthony Giorgio
I found this sample code on kernelnewbies. Make sure you link with -lrt
我在kernelnewbies上找到了这个示例代码。确保您链接到-lrt
#include <unistd.h>
#include <time.h>
#include <stdio.h>
int main()
{
struct timespec res;
double resolution;
printf("UserHZ %ld\n", sysconf(_SC_CLK_TCK));
clock_getres(CLOCK_REALTIME, &res);
resolution = res.tv_sec + (((double)res.tv_nsec)/1.0e9);
printf("SystemHZ %ld\n", (unsigned long)(1/resolution + 0.5));
return 0;
}
回答by P. Cahyna
To obtain the USER_HZ value (see the comments under the accepted answer) using CLI:
要使用 CLI 获取 USER_HZ 值（请参阅已接受答案下的评论）：
getconf CLK_TCK
