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

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Message-ID: <20080305094023.6486ebdf@mjolnir.drzeus.cx>
Date:	Wed, 5 Mar 2008 09:40:23 +0100
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	Pierre Ossman <drzeus-list@...eus.cx>
Cc:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	"Dave Jones" <davej@...emonkey.org.uk>,
	"Andi Kleen" <andi@...stfloor.org>,
	"Alan Stern" <stern@...land.harvard.edu>,
	"LKML" <linux-kernel@...r.kernel.org>,
	"Adam Belay" <abelay@...ell.com>,
	"Lee Revell" <rlrevell@...-job.com>,
	linux-pm@...ts.linux-foundation.org, "Pavel  Machek" <pavel@....cz>
Subject: Re: [linux-pm] [PATCH] cpuidle: avoid singing capacitors

On Wed, 5 Mar 2008 07:02:01 +0100
Pierre Ossman <drzeus-list@...eus.cx> wrote:

> 
> I tried using predicted_us and last_measured_us, and those didn't work (see the #if 0 code in my last patch). And since cpuidle_get_last_residency() is part of predicted_us, I don't think it is reporting useful values.
> 

I take this back. They might be working just fine. It seems I've been looking at a too small piece of the puzzle. This machine has a dual core processor, and the governors control each core independently. Unfortunately it's the power fluctuations of the entire socket that causes noise, not just each processor.

So I need to build some global algorithm instead of one per core. Ideas are welcome.

>From what I can tell, disabling one core makes the noise go away. So I guess both cores need to go into C3 (or perhaps one C2 and one C3) at the same time to cause the problem. I'm not 100% sure of this as the damn noise comes and goes, but I've been running for an hour or so now with one core disabled and without my anti-noise patch.

Rgds
-- 
     -- 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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