Subject: Re: finding out the value of HZ from userspace
From: Arjan van de Ven <arjanv@redhat.com>
Reply-To: arjanv@redhat.com
To: Micha Feigin <michf@post.tau.ac.il>
Cc: lkml <linux-kernel@vger.kernel.org>
In-Reply-To: <20040313221018.GE5960@luna.mooo.com>
References: <20040311141703.GE3053@luna.mooo.com>
	 <1079198671.4446.3.camel@laptop.fenrus.com>
	 <20040313221018.GE5960@luna.mooo.com>
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Organization: Red Hat, Inc.
Message-Id: <1079217685.4915.2.camel@laptop.fenrus.com>
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Date: Sat, 13 Mar 2004 23:41:25 +0100
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On Sat, 2004-03-13 at 23:10, Micha Feigin wrote:
> On Sat, Mar 13, 2004 at 06:24:31PM +0100, 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 use=
r
> > > space?
> > > It seem to change from system to system and between 2.4 (100 on i386)
> > > to 2.6 (1000 on i386).
> >=20
> > if you can see 1000 from userspace that is a bad kernel bug; can you sa=
y
> > where you find something in units of 1000 ?
>=20
> I can't see it from user space. Its in the kernel headers. The thing is
> I am working on fixes to laptop mode. The problem is it requires
> changing bdflush and journaled file systems journal flush times. The
> problem is that some of these (bdflush, xfs) expect the value in jiffies
> and not seconds or milliseconds so making the initiation script portable
> requires knowing the value of HZ.

the kernel side is supposed to use clock_t_to_jiffies() and co for this
to present a unified HZ to userspace. The internal kernel HZ should
*NOT* leak out to usespace. Heck it's quite thinkable that in the future
there will be no such HZ.
=20


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