kern.hz="100" stops high-pitched whine
cpghost at cordula.ws
Mon Jul 2 12:11:42 UTC 2007
Ian Smith wrote:
> 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 :)
Interesting! I've booted the EPIA with Hz=840 and Hz=1160,
and the whine was *considerably* quieter in both cases. It really
seemed to be some kind of harmonic oscillation at Hz=1000.
Now I'm back to HZ=100, which seems to be ideal.
> > 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.
> Cheers, Ian
I'll stay with 100 Hz for now. Should I need dummynet, I'll
crank it up slowly.
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