On Fri, Jul 31, 2009 at 11:23:15AM +0700, Mulyadi Santosa wrote:
> On Fri, Jul 31, 2009 at 6:52 AM, Karel Zak<kzak@xxxxxxxxxx> wrote:
> > Linux exports HZ to userspace via AT_CLKTCK auxiliary vector entry,
> > for more details see include/linux/auxvec.h.
> >
> > The vector is area between process's environ[] and argv[]. I guess glibc
> > reads the vector for the sysconf() call.
> >
> > Karel
>
> Hi Karel...
>
> I checked that using the following command:
> $ LD_SHOW_AUXV=1 sleep 1
> AT_SYSINFO: 0xb7fed414
> AT_SYSINFO_EHDR: 0xb7fed000
> AT_HWCAP: fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca
> cmov clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe
> AT_PAGESZ: 4096
> AT_CLKTCK: 100
> AT_PHDR: 0x8048034
> AT_PHENT: 32
> AT_PHNUM: 8
> AT_BASE: 0x0
> AT_FLAGS: 0x0
> AT_ENTRY: 0x8048c50
> AT_UID: 500
> AT_EUID: 500
> AT_GID: 500
> AT_EGID: 500
> AT_SECURE: 0
> AT_??? (0x19): 0xbf84ba4b
> AT_??? (0x1f): 0xbf84cff1
> AT_PLATFORM: i686
>
> It seems that user space sees HZ as 100, while in fact my current
> running kernel is compiled with HZ=300. What do you think about it? Or
> is there something wrong with my conclusion?
The following C program should properly show you the kernel HZ.
thanks,
greg k-h
--------------
#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;
}
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