Clock ticks per second

[Archos]

Is there any function in syscall to get the number of clock ticks per
second?

[Brad Fitzpatrick]

This doesn't mean as much as it used to.  Lot of Linux machines now run tickless or with dynamic HZ.  Probably likewise on other platforms.

[Jessta]

On Tue, Sep 21, 2010 at 8:27 AM, Archos <raul...@sent.com> wrote:
> Is there any function in syscall to get the number of clock ticks per
> second?

What would you use it for?

-jessta
--
=====================
http://jessta.id.au

[ron minnich]

On Mon, Sep 20, 2010 at 5:11 PM, Jessta <jes...@jessta.id.au> wrote:
> On Tue, Sep 21, 2010 at 8:27 AM, Archos <raul...@sent.com> wrote:
>> Is there any function in syscall to get the number of clock ticks per
>> second?
>
> What would you use it for?

or, what's it even mean? The TSC is not really constant on most x86
boxes. So what does a "tick" mean here?

ron

[Archos]

It's to calculate the CPU usage from "/proc/stat".

The values that I need are expressed in units of 1/HZ seconds, where
HZ is the kernel clock tick rate. But, as Brad has said, the HZ value
used in the kernel may vary. Anyway, I can get it from
`gettimeofday` :)

On Sep 21, 12:11 am, Jessta <jes...@jessta.id.au> wrote:

[Archos]

gettimeofday(2) can be used to calculate the CPU usage from "/proc/
stat". But it isn't useful when you only want to calculate the CPU
usage of some processes.

* * *
#include <stdio.h>
#include <stdlib.h>
#include <sys/time.h>
#include <unistd.h>

double time_so_far()
{
struct timeval tp;

if (gettimeofday(&tp, (struct timezone *) NULL) == -1)
perror("gettimeofday");
return ((double) (tp.tv_sec)) +
(((double) tp.tv_usec) * 0.000001 );
}

int main() {
FILE *f1;
double ti, tf;
char c[10];
int i1,i2,i3,i4,i5,i6;

ti = time_so_far();
f1 = fopen("/proc/stat", "r");
fscanf(f1, "%s\t%d\t%d\t%d\n", c, &i1, &i2, &i3);
fclose(f1);

usleep(1000000);

tf = time_so_far();
f1 = fopen("/proc/stat", "r");
fscanf(f1, "%s\t%d\t%d\t%d\n", c, &i4, &i5, &i6);
fclose(f1);

int t = (i4+i5+i6)-(i1+i2+i3);
printf("cpu usage: %.1f%%\n", (t / ((tf-ti) * 100)) * 100);

return 0;
}
* * *

To calculate the CPU usage of some processes it's necessary to get
some fields expressed in number of CPU ticks. And as is said in
times(2) [2]:
"the number of clock ticks per second can be obtained using:
sysconf(_SC_CLK_TCK);"

So, can it get the value of "_SC_CLK_TCK" in package syscall? If no,
please add it, from it's necessary to read (interpret) values in /proc/
stat


[1]: http://www.linuxquestions.org/questions/programming-9/proc-stat-file-problem-for-cpu-usage-369302/
[2]: http://www.kernel.org/doc/man-pages/online/pages/man2/times.2.html

[cfsal...@gmail.com]

Looking the code at http://golang.org/src/pkg/os/user/lookup_unix.go I've found a way to do what you need:

package main

import (
    "fmt"
)

/*
#include <unistd.h>
#include <sys/types.h>
#include <pwd.h>
#include <stdlib.h>
*/
import "C"

func main() {
    var sc_clk_tck C.long
    sc_clk_tck = C.sysconf(C._SC_CLK_TCK)
    fmt.Printf("SysConf Clock Ticks: %d\n", sc_clk_tck)
}

[Dave Cheney]

Have a play with http://godoc.org/github.com/davecheney/junk/clock,
there might be a clock type in there that will do what you want.

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