Date: Sat, 13 Mar 2004 20:38:52 +0100
From: Arjan van de Ven <arjanv@redhat.com>
To: John Reiser <jreiser@BitWagon.com>
Cc: Micha Feigin <michf@post.tau.ac.il>, lkml <linux-kernel@vger.kernel.org>
Subject: Re: finding out the value of HZ from userspace
Message-ID: <20040313193852.GC12292@devserv.devel.redhat.com>
References: <20040311141703.GE3053@luna.mooo.com> <1079198671.4446.3.camel@laptop.fenrus.com> <4053624D.6080806@BitWagon.com>
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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.


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