linux-kernel - Re: [PATCH 2/4]: CPUIDLE: Introduce architecture independent cpuidle_pm

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Message-Id: <1251442872.18584.125.camel@twins>
Date:	Fri, 28 Aug 2009 09:01:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	arun@...ux.vnet.ibm.com
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Joel Schopp <jschopp@...tin.ibm.com>,
	Paul Mackerras <paulus@...ba.org>, Ingo Molnar <mingo@...e.hu>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ux.vnet.ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH 2/4]: CPUIDLE: Introduce architecture independent
 cpuidle_pm_idle in drivers/cpuidle/cpuidle.c

On Fri, 2009-08-28 at 08:48 +0200, Peter Zijlstra wrote:
> 
> > void cpuidle_install_idle_handler(void)
> > {
> >       .........
> >       .........
> >       cpuidle_pm_idle = cpuidle_idle_call;
> > }
> 
> All I'm seeing here is a frigging mess.
> 
> How on earths can something called: cpuidle_install_idle_handler() have
> a void argument, _WHAT_ handler is it going to install?

Argh, now I see, it installs itself as the platform idle handler.

so cpuidle_install_idle_handler() pokes at the unmanaged pm_idle pointer
to make cpuidle take control.

On module load it does:

 pm_idle_old = pm_idle;

then in the actual idle loop it does:

        if (!dev || !dev->enabled) {
                if (pm_idle_old)
                        pm_idle_old();

who is to say that the pointer stored at module init time is still
around at that time?

So cpuidle recognised the pm_idle stuff was a flaky, but instead of
fixing it, they build a whole new layer on top of it. Brilliant.

/me goes mark this whole thread read, I've got enough things to do.
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