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

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Date:	Mon, 10 Mar 2008 13:49:15 +0100
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	Pavel Machek <pavel@....cz>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	linux-pm@...ts.linux-foundation.org,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Dave Jones <davej@...emonkey.org.uk>,
	Andi Kleen <andi@...stfloor.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Adam Belay <abelay@...ell.com>,
	Lee Revell <rlrevell@...-job.com>
Subject: Re: [linux-pm] [PATCH] cpuidle: avoid singing capacitors

On Mon, 10 Mar 2008 11:00:08 +0100
Pavel Machek <pavel@....cz> wrote:

> On Sun 2008-03-09 15:16:59, Pierre Ossman wrote:
> > 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.
> 
> USB keeps processor out of C3 in many cases.
> 

I figured that was the case. But I did not see any difference in powertop.

> > 4. Battery and AC
> > 
> > The noise increases with the battery present and also when the AC supply is removed.
> >
> 
> On battery, some machines swap C3 for "secret" C4, which is slower but
> saves power.

I guess the only way to find out is to disassemble the DSDT. Exposing myself to such concentrations of ACPI is not an appealing project. :/

-- 
     -- Pierre Ossman

  Linux kernel, MMC maintainer        http://www.kernel.org
  PulseAudio, core developer          http://pulseaudio.org
  rdesktop, core developer          http://www.rdesktop.org
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