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

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Date:	Wed, 5 Mar 2008 10:03:04 +0100
From:	Pavel Machek <pavel@....cz>
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
Subject: Re: [linux-pm] [PATCH] cpuidle: avoid singing capacitors

On Wed 2008-03-05 09:40:23, Pierre Ossman wrote:
> 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.
> 

Actually, there are more uncertaininties. Suspecting some machines
seemed to produce noise whenever they were in low-power state. Not
with fluctuations: when I forced them to low-power, it just produced
steady beep.

(Thinkpad 560X and toshiba 4030cdt, IIRC).
									Pavel
-- 
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