Clock_getres 和内核 2.6

发布于 2024-11-18 10:23:07 字数 451 浏览 2 评论 0原文

我现在使用 ubuntu 11.04 并使用 v2lin 将我的程序从 vxWorks 移植到 Linux。我对clock_getres()有问题。

使用此代码：

struct timespec res;
clock_getres(CLOCK_REALTIME, &res);

我有 res.tv_nsec = 1 ，这在某种程度上不正确。

就像这个人展示的那样： http://forum.kernelnewbies.org/read.php?6,377,423 ，内核2.4和2.6之间存在差异。

那么内核 2.6 中时钟分辨率的正确值应该是多少

谢谢

原文

i'm using ubuntu 11.04 now and using v2lin to port my program from vxWorks tolinux. I have problem with clock_getres().

with this code:

struct timespec res;
clock_getres(CLOCK_REALTIME, &res);

i have res.tv_nsec = 1 , which is somehow not correct.

Like this guy showed: http://forum.kernelnewbies.org/read.php?6,377,423 , there is difference between kernel 2.4 and 2.6.

So what should be the correct value for the clock resolution in kernel 2.6

Thanks

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烟花易冷人易散 2024-11-25 10:23:07

根据内核源代码中的“include/linux/hrtimer.h”文件，对于高分辨率定时器，clock_getres() 将始终返回 1ns（一纳秒）（如果系统中存在此类定时器）。该值是硬编码的，它意味着：“定时器的值将四舍五入到它”

http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/include/linux/hrtimer.h

269 /*
270  * The resolution of the clocks. The resolution value is returned in
271  * the clock_getres() system call to give application programmers an
272  * idea of the (in)accuracy of timers. Timer values are rounded up to
273  * this resolution values.
274  */
275 # define HIGH_RES_NSEC          1
276 # define KTIME_HIGH_RES         (ktime_t) { .tv64 = HIGH_RES_NSEC }
277 # define MONOTONIC_RES_NSEC     HIGH_RES_NSEC
278 # define KTIME_MONOTONIC_RES    KTIME_HIGH_RES

对于低分辨率定时器（对于 MONOTONIC 和 REALTIME 时钟，如果没有 hrtimer 硬件），linux 将返回 1/HZ（典型的 HZ 是从 100 到 1000；所以值是从 1 到 10 ms）：

http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/include/linux/ktime.h#L321

321 #define LOW_RES_NSEC            TICK_NSEC
322 #define KTIME_LOW_RES           (ktime_t){ .tv64 = LOW_RES_NSEC }

低分辨率计时器的值可能会舍入到如此低的精度（实际上它们就像 jiffles，Linux 内核“滴答”）。

PS：这篇文章http://forum.kernelnewbies.org/read.php?6,377,423据我所知，将没有启用（实现） hrtimers 的 2.4 linux 与具有可用 hrtimers 的 2.6 内核进行比较。所以所有的值都是正确的。

According to "include/linux/hrtimer.h" file from kernel sources, clock_getres() will always return 1ns (one nanosecond) for high-resolution timers (if there are such timers in the system). This value is hardcoded and it means: "Timer's value will be rounded to it"

http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/include/linux/hrtimer.h

269 /*
270  * The resolution of the clocks. The resolution value is returned in
271  * the clock_getres() system call to give application programmers an
272  * idea of the (in)accuracy of timers. Timer values are rounded up to
273  * this resolution values.
274  */
275 # define HIGH_RES_NSEC          1
276 # define KTIME_HIGH_RES         (ktime_t) { .tv64 = HIGH_RES_NSEC }
277 # define MONOTONIC_RES_NSEC     HIGH_RES_NSEC
278 # define KTIME_MONOTONIC_RES    KTIME_HIGH_RES

For low-resolution timers (and for MONOTONIC and REALTIME clocks if there is no hrtimer hardware), linux will return 1/HZ (typical HZ is from 100 to 1000; so value will be from 1 to 10 ms):

http://www.cs.fsu.edu/~baker/devices/lxr/http/source/linux/include/linux/ktime.h#L321

321 #define LOW_RES_NSEC            TICK_NSEC
322 #define KTIME_LOW_RES           (ktime_t){ .tv64 = LOW_RES_NSEC }

Values from low-resolution timers may be rounded to such low precision (effectively they are like jiffles, the linux kernel "ticks").

PS: This post http://forum.kernelnewbies.org/read.php?6,377,423 as I can understand, compares 2.4 linux without hrtimers enabled (implemented) with 2.6 kernel with hrtimers available. So all values are correct.

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