kern.hz="100" stops high-pitched whine

Jack Stone antennex at
Mon Jul 2 12:43:50 UTC 2007

>From: Chuck Swiger <cswiger at>
>To: cpghost <cpghost at>
>CC: questions <freebsd-questions at>
>Subject: Re: kern.hz="100" stops high-pitched whine
>Date: Sun, 01 Jul 2007 09:46:19 -0400
>cpghost wrote:
>>Are there any reasons NOT changing kern.hz from the
>>default 1000 back to 100? With my typical mix of
>>desktop apps (EPIA) and networking / server (Soekris),
>>everything seems to be running just as smoothly with
>>100 Hz than with 1000 Hz (testing now for two weeks
>>without problems). Even playing videos with mplayer
>>on the EPIA doesn't look different in any way.
>>Is it okay to stay with 100 Hz with this type of
>>low-speed CPU/boards? Or are there some compelling
>>reasons not to?
>Actually, many Unix systems ran with HZ=100 until a few years ago, about 
>when Gb ethernet and CPUs became common.  A slower machine like the EPIA 
>boxes do quite well with HZ=100/200/250 or so...HZ=1000 is better if you 
>have a fast box running lots of concurrent processes, and/or are proxying 
>or routing network traffic where the difference between 10 ms and 1ms of 
>latency adds up and/or effects other systems.

A while ago, I noticed someone's kernel config that included:
which made me wonder where this setting info comes from?

I've been using hertz=1000 however, with my much faster boxes, is this 
appropriate now?


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