Re: [linux-pm] [PATCH] cpuidle: avoid singing capacitors

I'm beginning to think this is a lost cause. I've tried several variants, all without satisfactory results.

In case anyone else has any more ideas, I'll detail what I've found influences the noise:

1. C state

This is the big one. There is no noise as long as C3 is avoided (processor.max_cstate).

2. uhci_hcd driver

USB is somehow involved in this problem. Unloading the uhci_hcd driver almost entirely kills the noise on a 1000 HZ NO_HZ kernel. On a 100 HZ, no NO_HZ kernel, the effect is very small, but still there.

3. Low speed USB devices

Related, the noise goes away if I insert a USB mouse (low speed). A high-speed device does not effect the noise, neither does the two built-in low speed devices (a fingerprint reader and a bluetooth host).

4. Battery and AC

The noise increases with the battery present and also when the AC supply is removed.

5. Second core

Disabling the second core makes the noise go away. This might be a subset of 1., as I've been told that a stopped core enters C1.


Changing HZ and NO_HZ has no noticeable effect on the problem (except the odd behaviour in 2.). This is further supported by the fact that Windows also has the problem (which should behave close to 100 HZ without NO_HZ).


So for now, the only viable workaround is processor.max_cstate....

--
-- Pierre Ossman

Linux kernel, MMC maintainer http://www.kernel.org
PulseAudio, core developer http://pulseaudio.org
rdesktop, core developer http://www.rdesktop.org
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Relevant Pages

  • Re: [linux-pm] [PATCH] cpuidle: avoid singing capacitors
    ... Unloading the uhci_hcd driver almost entirely kills the noise on a 1000 HZ NO_HZ kernel. ... USB keeps processor out of C3 in many cases. ... The noise increases with the battery present and also when the AC supply is removed. ...
    (Linux-Kernel)
  • Re: USB hum/noise isolation?
    ... OUTs, and a headphone jack. ... jack, I still get the noise, although very faintly. ... USB adaptor- solve anything? ... balance signals - therefore cannot be separated. ...
    (rec.audio.pro)
  • Re: USB hum/noise isolation?
    ... I have a high-pitched beeping/pulsing ... the noise somewhat by purchasing a simple Behringer 2-in/2-out USB ... USB audio always gives me a ground loop hum if I have any other soundcard ...
    (rec.audio.pro)
  • Re: USB 5V noise filtering
    ... with a USB sound adapter tapping its power from the USB +5V. ... noise of switching noise. ... I build a small filter with 22 ohms with bypass caps 15uF/0.01uF on the ...
    (sci.electronics.design)
  • USB hum/noise isolation?
    ... I'm looking for suggestions/insight into a sticky noise ... The problem is that the USB connection between my computer (AMD 64x2 ... on the same power bar -does anyone know if the HumX would sort out ...
    (rec.audio.pro)