linux-kernel - Re: Question about not saving power

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Date:	Thu, 25 Dec 2008 12:07:38 +0500
From:	"Alexander E. Patrakov" <patrakov@...il.com>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	linux-kernel@...r.kernel.org, intel-gfx@...ts.freedesktop.org
Subject: Re: Question about not saving power

On Wednesday 24 December 2008 12:02:53 Robert Hancock wrote:
> Alexander E. Patrakov wrote:
> > Hello.
> >
> > I tried playing with some audio apps like JACK and fluidsynth, and
> > noticed the following. If I set the parameters in JACK so that the
> > latency becomes less than ~10 milliseconds, a faint tone appears in the
> > headphones connected to the onboard sound card.
> >
> > I guess that its frequency is the tone is the same as that of the
> > interrupts generated by the sound card. The tone disappears if I run
> > something like "while : ; do : ; done" that consumes CPU time
> > continuously, so I guess this has something to do with the power-saving
> > features and less-than-perfect PSU.
> >
> > My question is: what are my options (like kernel parameters) to disable
> > power- saving features, other than running such CPU-eating process
> > continuously?
>
> You can try booting with idle=poll on kernel command line, so the CPU
> will not enter halt states..

This mostly helped. Now the tone disappeared, but there are noises (not 
xruns!) caused by the onboard graphics card when KDE4 draws something. I 
disabled the effects to reduce the noise, but it didn't fully help (there is 
still some "zzzzz" when I move the mouse over the taskbar so that different 
window buttons are highlighted). The noise exists both in the connector for 
headphones on the front panel, and in the green connector at the back of the 
computer, but in the second connector, it is much softer.

The board is Intel DG965SS, and the graphics ship is:

00:02.0 0300: 8086:29a2 (rev 02)
00:02.1 0380: 8086:29a3 (rev 02)

or, with names instead of the numbers,

00:02.0 VGA compatible controller: Intel Corporation 82G965 Integrated 
Graphics Controller (rev 02)
00:02.1 Display controller: Intel Corporation 82G965 Integrated Graphics 
Controller (rev 02)

Intel developers: could you please add some workaround to the "intel" driver, 
so that the GPU always stays busy (and thus draws the constant amount of 
power)? And please tell the hardware designers so that for the future boards, 
this interference between graphics and audio should not happen. Add separate 
stabilizers and filters for the power supply of the audio chip, carefully 
design the wiring so that the "noisy" lines don't get near anything related to 
audio.

-- 
Alexander E. Patrakov
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