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    SubjectRe: finding out the value of HZ from userspace
    On Sat, Mar 13, 2004 at 08:38:52PM +0100, Arjan van de Ven wrote:
    > On Sat, Mar 13, 2004 at 11:34:37AM -0800, John Reiser wrote:
    > > Arjan van de Ven wrote:
    > > >On Thu, 2004-03-11 at 15:17, Micha Feigin wrote:
    > > >
    > > >>Is it possible to find out what the kernel's notion of HZ is from user
    > > >>space?
    > > >>It seem to change from system to system and between 2.4 (100 on i386)
    > > >>to 2.6 (1000 on i386).
    > > >
    > > >
    > > >if you can see 1000 from userspace that is a bad kernel bug; can you say
    > > >where you find something in units of 1000 ?
    > >
    > > create_elf_tables() in fs/binfmt_elf.c tells every ELF execve():
    > > NEW_AUX_ENT(AT_CLKTCK, CLOCKS_PER_SEC);
    > > which can be found by crawling through the stack above the pointer
    > > to the last environment variable.
    >
    > Ugh that should say 100 on x86....
    > but..
    > param.h:# define USER_HZ 100 /* .. some user interfaces are in "ticks" */
    > param.h:# define CLOCKS_PER_SEC (USER_HZ) /* like times() */
    > .....
    > that looks like 100 to me.
    >

    When dealing with bdflush and a few other interfaces the values need to
    be in jiffies which requires knowledge of the kernels notion of HZ not
    userspace.

    The other option is to try to push a change to make the interface in
    centisecs instead of jiffies, question is if it will catch.

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