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

From: Andi Kleen <andi@firstfloor.org>
To: Pierre Ossman <drzeus-list@drzeus.cx>
Cc: Andi Kleen <andi@firstfloor.org>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>,
	Dave Jones <davej@codemonkey.org.uk>,
	Alan Stern <stern@rowland.harvard.edu>,
	LKML <linux-kernel@vger.kernel.org>,
	Adam Belay <abelay@novell.com>, Lee Revell <rlrevell@joe-job.com>,
	linux-pm@lists.linux-foundation.org, Pavel Machek <pavel@ucw.cz>
Subject: Re: [linux-pm] [PATCH] cpuidle: avoid singing capacitors
Date: Wed, 5 Mar 2008 16:48:56 +0100	[thread overview]
Message-ID: <20080305154856.GC553@one.firstfloor.org> (raw)
In-Reply-To: <20080305070454.3df78593@mjolnir.drzeus.cx>

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