LWN: Comments on "How fast should HZ be?"

How fast should HZ be?

rlrevell — Mon, 29 Aug 2005 20:22:15 +0000

This is called a "singing capacitor". It happens because the greed of OEMs drives them to use increasingly cheap components. Windows uses a base timer frequency of 100HZ and that's all the OEMs test with so the problem isn't apparent under that OS.

How fast should HZ be?

mikec — Sun, 14 Aug 2005 21:52:59 +0000

There is another issue at work here which I have never taken the time to fully understand, but google tells me I am far from alone...

1000Hz Kernels make my laptop sound card whine!

100Hz whine far less if at all...

I found this little gem a few years ago and various laptops I have had whine more or less with default kernels and changing this setting always seems to help.

It makes some "seat of the pants" sense that the frequency of interrupts when the system is "idle" could interact with a poorly isolated sound card and cause undesired analog results...

In the case of my current computer (dell 8600) it occurs:
a. running under windows
b. with the sound "muted" (under linux)

The system whines when idle and quiets down when busy...

I'd love to take the time to fully understand this some day, but in the mean time, I just change Hz and off I go computing quietly...

/mike

How fast should HZ be?

xorbe — Thu, 11 Aug 2005 05:33:08 +0000

Certainly such a setup would be hand-tuned hopefully...

How fast should HZ be?

tres — Fri, 05 Aug 2005 09:33:50 +0000

Another reason to reduce the frequency is for servers with many virtual machines running since each one needs to service the interrupt and a machine with a thousand virtual machines running has to service ((1000 + 1) * Hz) timer interrupts. That is excessive when most of the virtual machines might be idle.

How fast should HZ be?

jrigg — Thu, 04 Aug 2005 21:40:24 +0000

Reducing HZ from 1000 to 100 gives around 7% power saving. That could be significant on a laptop, but presumably 250 will save less. Perhaps a simpler way of saving power would be to use less bloated software ;)