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

[Abdullah Ibn Hamad Al-Marri]

On 7/2/07, Jack Stone <antennex at hotmail.com> wrote:
> >From: Chuck Swiger <cswiger at mac.com>
> >To: cpghost <cpghost at cordula.ws>
> >CC: questions <freebsd-questions at freebsd.org>
> >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.
> >
> >--
> >-Chuck
>
> A while ago, I noticed someone's kernel config that included:
> hertz=2000
> 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?
>
> Thanks,
> Jack

I don't know if the info is correct up to now or not, but I use pf
firewall, and I run IRC servers, I saw it in NOTES.

#####################################################################
# NETWORKING OPTIONS

#
# DEVICE_POLLING adds support for mixed interrupt-polling handling
# of network device drivers, which has significant benefits in terms
# of robustness to overloads and responsivity, as well as permitting
# accurate scheduling of the CPU time between kernel network processing
# and other activities.  The drawback is a moderate (up to 1/HZ seconds)
# potential increase in response times.
# It is strongly recommended to use HZ=1000 or 2000 with DEVICE_POLLING
# to achieve smoother behaviour.
# Additionally, you can enable/disable polling at runtime with help of
# the ifconfig(8) utility, and select the CPU fraction reserved to
# userland with the sysctl variable kern.polling.user_frac
# (default 50, range 0..100).
#
# Not all device drivers support this mode of operation at the time of
# this writing.  See polling(4) for more details.

options         DEVICE_POLLING

--

Maybe it's out of date now for 2000?

-- 
Regards,

-Abdullah Ibn Hamad Al-Marri
Arab Portal
http://www.WeArab.Net/