linux-kernel - Re: [v4 PATCH 1/5]: cpuidle: Cleanup drivers/cpuidle/cpuidle.c

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Message-ID: <20090903044253.GA31928@linux.vnet.ibm.com>
Date:	Thu, 3 Sep 2009 10:12:53 +0530
From:	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Joel Schopp <jschopp@...tin.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	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@...ibm.com>,
	Gautham R Shenoy <ego@...ibm.com>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	Arun Bharadwaj <arun@...ux.vnet.ibm.com>
Subject: Re: [v4 PATCH 1/5]: cpuidle: Cleanup drivers/cpuidle/cpuidle.c

* Peter Zijlstra <a.p.zijlstra@...llo.nl> [2009-09-02 07:42:24]:

> On Tue, 2009-09-01 at 17:08 +0530, Arun R Bharadwaj wrote:
> > * Arun R Bharadwaj <arun@...ux.vnet.ibm.com> [2009-09-01 17:07:04]:
> > 
> > Cleanup drivers/cpuidle/cpuidle.c
> > 
> > Cpuidle maintains a pm_idle_old void pointer because, currently in x86
> > there is no clean way of registering and unregistering a idle function.
> 
> Right, and instead of fixing that, they build this cpuidle crap on top,
> instead of replacing the current crap with it.
> 
> > So remove pm_idle_old and leave the responsibility of maintaining the
> > list of registered idle loops to the architecture specific code. If the
> > architecture registers cpuidle_idle_call as its idle loop, only then
> > this loop is called.
> 
> OK, that's a start I guess. Best would be to replace all of pm_idle with
> cpuidle, which is what should have been done from the very start.
> 
> If cpuidle cannot fully replace the pm_idle functionality, then it needs
> to fix that. But having two layers of idle functions is just silly.
> 
> Looking at patch 2 and 3, you're making the same mistake on power, after
> those patches there are multiple ways of registering idle functions, one
> through some native interface and one through cpuidle, this strikes me
> as undesirable.
> 
> If cpuidle is a good idle function manager, then it should be good
> enough to be the sole one, if its not, then why bother with it at all.
> 

Okay, I'm giving this approach a shot now. i.e. trying to make cpuidle
as _the_ sole idle function manager. This would mean doing away with
pm_idle and ppc_md.power_save. And, cpuidle_idle_call() which is the
main idle loop of cpuidle, present in drivers/cpuidle/cpuidle.c will
have to be called from arch specific code of cpu_idle()

Also this would mean enabling cpuidle for all platforms, even if the
platform doesn't have multiple idle states. So suppose a platform doesnt
have multiple states, it wouldn't want the bloated code of cpuidle
governors, and would want just a simple cpuidle loop.

--arun
> 
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