kern.hz="100" stops high-pitched whine
smithi at nimnet.asn.au
Sun Jul 1 14:16:19 UTC 2007
On Sun, 01 Jul 2007 13:12:28 +0200 cpghost <cpghost at cordula.ws> wrote:
> I'm using fan-less Soekris (266 MHz) and EPIA (500 MHz)
> boards with -STABLE. Those boards have been emitting a
> very high pitched annoying whine, similar to a dog
> whistle. Not everyone I asked could hear it, but I was,
> and it was driving me crazy for months.
> This whine stopped entirely the moment I put
> kern.hz="100" in /boot/loader.conf and rebooted.
> Quite relieving!
Possibly a beat frequency between the 1kHz default slicing and some
faster oscillator on board? You could play around with kern.clockrate,
sometimes quite small frequency changes make a difference, especially if
it's a harmonic. Default HZ jumped from 100 to 1000 probably around the
time when more servers were seen running at nearer 3000MHz than 300 :)
> 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.
No problem then, and a lighter interrupt load; probably enough to notice
in top. If you want to run dummynet or something else? wanting quicker
ticking you could try HZ=200 - 500. 200Hz on my Celeron 300 works well.
> Is it okay to stay with 100 Hz with this type of
> low-speed CPU/boards? Or are there some compelling
> reasons not to?
If it's happy, smooth and keeping up, it's fine.
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