Re: Why HZ on i386 is 100 ?

J. Dow
2002-04-17T00:35:13Z

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.)