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

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Message-ID: <20080305154856.GC553@one.firstfloor.org>
Date:	Wed, 5 Mar 2008 16:48:56 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Pierre Ossman <drzeus-list@...eus.cx>
Cc:	Andi Kleen <andi@...stfloor.org>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	Dave Jones <davej@...emonkey.org.uk>,
	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, Mar 05, 2008 at 07:04:54AM +0100, Pierre Ossman wrote:
> I still don't follow. Perhaps you can express it in pseudo code? If I have a stale value that I cannot refresh, knowing that it is stale doesn't change anything.

Start: You discovered at some point where you currently have code a variable 
is not updated yet.
Fact: You have some new code that runs before that point
Information: The variable is updated later eventually in the idle exit path.
Fact II: You require the variable to be updated in your new code
Possible solutions: 
(1) you move your new code in a point of the idle exit path after the variable 
is updated 
(2) you move the code that updates the variable earlier before your code
Solution: I described the first variant which is likely easier.
How: I told you where it is updated, so that shouldn't be too difficult. 
Action: Implement solution (1) or (2) 
Action: Test if it works
Check: If test succeeded exit 
Otherwise: Restart at Start

-Andi
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