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To: Scott Long <scottl@freebsd.org>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Thu, 04 Nov 2004 09:36:02 MST."
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Date: Thu, 04 Nov 2004 17:36:53 +0100
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cc: =?ISO-8859-1?Q?Dag-Erling_Sm=F8rgrav?= <des@des.no>
cc: arch@freebsd.org
Subject: Re: HEADSUP: HZ=1000 by default on i386 
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In message <418A5A72.6020700@freebsd.org>, Scott Long writes:

>>> 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
>
>What timing hardware is used on amd64?  Would it suffer there too?

I only tested on i386, but any platform would suffer from this kind
of syncronism/syntonism. 

-- 
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.