On Sat, 1 Aug 2009, Greg KH wrote:
> On Fri, Jul 31, 2009 at 11:23:15AM +0700, Mulyadi Santosa wrote:
> > On Fri, Jul 31, 2009 at 6:52 AM, Karel Zak<[email protected]> 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;
> }
i already knew about sysconf. so i'm going to assume there's no
simpler way to get the current HZ (either command line or /proc
based).
rday
p.s. is there any reason why one couldn't submit a patch to add that
value to /proc? surely the addition of, say, /proc/hz wouldn't be
ridiculously disruptive.
--
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Robert P. J. Day Waterloo, Ontario, CANADA
Linux Consulting, Training and Annoying Kernel Pedantry.
Web page: http://crashcourse.ca
Twitter: http://twitter.com/rpjday
"Kernel Newbie Corner" column @ linux.com: http://cli.gs/WG6WYX
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