RE: Why HZ on i386 is 100 ?

Chen, Kenneth W
2002-04-17T00:33:25Z

If you change HZ to 1000, you need to change PROC_CHANGE_PENALTY
accordingly. Otherwise, process would get preempted before its time slice
gets expired. The net effect is more context switch than necessary, which
could explain the 10% difference.

-----Original Message-----
From: Davide Libenzi [mailto:davidel@xmailserver.org]
Sent: Tuesday, April 16, 2002 11:10 AM
To: davidm@hpl.hp.com
Cc: Linus Torvalds; Linux Kernel Mailing List
Subject: Re: Why HZ on i386 is 100 ?

On Tue, 16 Apr 2002, David Mosberger wrote:

> >>>>> On Tue, 16 Apr 2002 10:18:18 -0700 (PDT), Davide Libenzi
<davidel@xmailserver.org> said:
>
> Davide> i still have pieces of paper on my desk about tests done on
> Davide> my dual piii where by hacking HZ to 1000 the kernel build
> Davide> time went from an average of 2min:30sec to an average
> Davide> 2min:43sec. that is pretty close to 10%
>
> Did you keep the timeslice roughly constant?

it was 2.5.1 time and it was still ruled by TICK_SCALE that made the
timeslice to drop from 60ms ( 100HZ ) to 21ms ( 1000HZ ).

- Davide

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