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Message-ID: <053d01c1e5a7$b4121e70$1125a8c0@wednesday>
From: "J. Dow" <jdow@earthlink.net>
To: "Andreas Dilger" <adilger@clusterfs.com>,
        "Herbert Xu" <herbert@gondor.apana.org.au>
Cc: <linux-kernel@vger.kernel.org>
In-Reply-To: <20020416222156.GB20464@turbolinux.com> <E16xba3-0005tw-00@gondolin.me.apana.org.au> <20020416225631.GD20464@turbolinux.com>
Subject: Re: Why HZ on i386 is 100 ?
Date: Tue, 16 Apr 2002 17:34:58 -0700
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From: "Andreas Dilger" <adilger@clusterfs.com>

> On Apr 17, 2002  08:37 +1000, Herbert Xu wrote:
> > Why are we still measuring uptime using the tick variable? Ticks != time.
> > Surely we should be recording the boot time somewhere (probably on a
> > file system), and then comparing that with the current time?
> 
> Er, because the 'tick' is a valid count of the actual time that the
> system has been running, while the "boot time" is totally meaningless.
> What if the system has no RTC, or the RTC is wrong until later in the
> boot sequence when it can be set by the user/ntpd?  What if you pass
> daylight savings time?  Does your uptime increase/decrease by an hour?

Well, Andreas, it seems like a very simple thing to define the time
quantum, "tick", differently from the resolution of the count reported
by a call to get the tick counter value. If the latter maintains a
constant resolution even if the tick time changes then all utilities
should continue to work. Of course, with a tick time resolution of 10mS
it gets ugly when setting up a tick time of 1mS. Ideally reporting would
have an LSB of a microsecond or even a tenth microsecond while the
increment might still be a hundredth or thousandth of a second. Of course,
that blows anything that relies on the tick counter to smithereens, I fear.

{^_^}   Joanne "I STILL want a Linux suitable for multimedia applications" Dow.
        jdow@earthlink.net    (1mS ticks is a GREAT help for multimedia apps.)

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