Messages in this thread | | | Date | Sun, 14 Mar 2004 00:14:19 +0200 | From | Micha Feigin <> | Subject | Re: finding out the value of HZ from userspace |
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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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