RE: Why HZ on i386 is 100 ?

Liam Girdwood
2002-04-16T09:31:39Z

On Tue, 2002-04-16 at 09:18, BALBIR SINGH wrote:
> I remember seeing somewhere unix system VII used to have HZ set to 60
> for the machines built in the 70's. I wonder if todays pentium iiis and ivs
> should still use HZ of 100, though their internal clock is in GHz.
>
> I think somethings in the kernel may be tuned for the value of HZ, these
> things would be arch specific.
>
> Increasing the HZ on your system should change the scheduling behaviour,
> it could lead to more aggresive scheduling and could affect the
> behaviour of the VM subsystem if scheduling happens more frequently. I am
> just guessing, I do not know.
>

I remember reading that a higher HZ value will make your machine more
responsive, but will also mean that each running process will have a
smaller CPU time slice and that the kernel will spend more CPU time
scheduling at the expense of processes.

HTH

Liam Girdwood

> Changing though trivial would require a good look at all the code that
> uses HZ.
>
> Comments,
> Balbir
>
> |-----Original Message-----
> |From: linux-kernel-owner@vger.kernel.org
> |[mailto:linux-kernel-owner@vger.kernel.org]On Behalf Of William Lee
> |Irwin III
> |Sent: Tuesday, April 16, 2002 1:45 PM
> |To: Olaf Fraczyk
> |Cc: linux-kernel@vger.kernel.org
> |Subject: Re: Why HZ on i386 is 100 ?
> |
> |
> |On Tue, Apr 16, 2002 at 09:47:48AM +0200, Olaf Fraczyk wrote:
> |> Hi,
> |> I would like to know why exactly this value was choosen.
> |> Is it safe to change it to eg. 1024? Will it break anything?
> |> What else should I change to get it working:
> |> CLOCKS_PER_SEC?
> |> Please CC me.
> |> Regards,
> |> Olaf Fraczyk
> |
> |I tried a few times running with HZ == 1024 for some testing (or I guess
> |just to see what happened). I didn't see any problems, even without the
> |obscure CLOCKS_PER_SEC ELF business.
> |
> |
> |Cheers,
> |Bill
> |-
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Liam Girdwood
l_girdwood@bitwise.co.uk (Work)
liam@nova-ioe.org (Home)