Date: Sat, 27 Mar 2004 23:11:35 +0200
From: Micha Feigin <michf@post.tau.ac.il>
To: lkml <linux-kernel@vger.kernel.org>
Subject: Re: finding out the value of HZ from userspace
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On Tue, Mar 23, 2004 at 10:04:22AM +1100, Peter Williams wrote:
> Micha Feigin wrote:
> >On Sat, Mar 20, 2004 at 12:28:00PM +0100, Stefan Smietanowski wrote:
> >
> >>>>>there is one. Nothing uses it
> >>>>>(sysconf() provides this info)
> >>>>
> >>>>Seems to me that it would be fairly trivial to modify those programs 
> >>>>(that should use this mechanism but don't) to use it?  So why should 
> >>>>they be allowed to dictate kernel behaviour?
> >>>
> >>>
> >>>quality of implementation; for example shell scripts that want to do
> >>>echo 500 > /proc/sys/foo/bar/something_in_HZ
> >>>...
> >>>or /etc/sysctl.conf or ...
> >>>
> >>
> >>Then write a simple program already. How hard is it to write a program
> >>that does a sysconf() and returns (as ascii of course) just the
> >>value of HZ? Then do some trivial calculation off of that.
> >>
> >>HZ=$(gethz)
> >>
> >>If your 500 was 5 seconds, do
> >>
> >>TIME=$[HZ*5]
> >>echo $TIME > /proc/sys/foo/bar/something_in_HZ
> >>
> >
> >
> >Will this be USER_HZ or kernel HZ?
> >Someone earlier suggested it would be USER_HZ which would make it
> >pointless.
> 
> It has to be whatever enables user space to correctly interpret values 
> sent to user space as "ticks".  That means USER_HZ and it's not useless 
> as it enables USER_HZ to be different and/or change without breaking 
> programs that use values expressed in "ticks".
> 

Unless the kernel is converted to make that conversion possible then it
is useless at the moment since userspace gets USER_HZ and the kernel
proc interface speaks (KERNEL) HZ so userspace really has no idea how
to speak to kernel space with 2.6.

> >
> >
> >>I mean, come on.
> >>
> >>Then you include it in the default distro of choice so that
> >>everybody can use it and there you are.
> >>
> >>If someone doesn't have "gethz" then they can download it.
> >>
> >>// Stefan
> >>
> >
> >-
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> >Please read the FAQ at  http://www.tux.org/lkml/
> 
> 
> -- 
> Dr Peter Williams, Chief Scientist                peterw@aurema.com
> Aurema Pty Limited                                Tel:+61 2 9698 2322
> PO Box 305, Strawberry Hills NSW 2012, Australia  Fax:+61 2 9699 9174
> 79 Myrtle Street, Chippendale NSW 2008, Australia http://www.aurema.com
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