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To: des@des.no (=?iso-8859-1?q?Dag-Erling_Sm=F8rgrav?=)
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Thu, 04 Nov 2004 17:23:05 +0100."
             <xzp7jp1wpli.fsf@dwp.des.no> 
Date: Thu, 04 Nov 2004 17:32:10 +0100
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cc: arch@freebsd.org
Subject: Re: HEADSUP: HZ=1000 by default on i386 
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In message <xzp7jp1wpli.fsf@dwp.des.no>, =?iso-8859-1?q?Dag-Erling_Sm=F8rgrav?= writes:
>Poul-Henning Kamp <phk@phk.freebsd.dk> writes:
>> So pending any really good arguments to the contrary I plan to increase
>> HZ to 1000 on i386 this weekend.
>
>two good arguments:
>
>  1) I'm already working on this, and you know it, since I asked you
>     about it in Karlsruhe.

Ahh, sorry, I got the impression that you were not going to do it on
your own.

>  2) 1000 is not a good choice, because we can't approximate it well
>     with the 8254.  1268 is better, 1381 is even better, 1903 is the
>     best we can do between 1000 and 2000, 2299 is the best we can do
>     between 1000 and 5000.

I played with it here and found that 1000 actually works better than 941.
(1193182 / 941 ~= 1268) because the 941 gives a slow beat against 1Hz.

It is actually preferable to have a fast beat (jitter) than a slow
beat (wander), particularly for people doing benchmarks.

Poul-Henning

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.