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

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Message-ID: <20080305070201.0d16cd40@mjolnir.drzeus.cx>
Date:	Wed, 5 Mar 2008 07:02:01 +0100
From:	Pierre Ossman <drzeus-list@...eus.cx>
To:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
Cc:	"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 Tue, 4 Mar 2008 11:01:28 -0800
"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com> wrote:

> >
> >(On that subject, does anyone except Adam understand that 
> >algorithm? Some comments wouldn't hurt...)
> 
> Prediction is based on cumulative time till "non expected wakeup". So,
> prediction will come into play only when there are very short wakeups
> due to "unexpected wakeups".
> 

Ah, so the measured_us and elapsed_us are trying to keep track of time between non-timer wakeups?

> >So for now, I'm back to thinking that measuring the interval 
> >between deep sleeps is the better approach. I could use some 
> >ideas for a good clock source though. I haven't dug much 
> >deeper than jiffies when it comes to kernel timekeeping.
> 
> I think best solution is to use get_last_residency that is already
> there. If the last residency or expected_us is very low, you can avoid
> deep idle states. That way you don't have to depend on jiffies being
> updated at the time you are checking it.
> 

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.

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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