linux-kernel - Re: [v8 PATCH 2/8]: cpuidle: implement a list based approach to register a set of idle routines.

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Message-ID: <20091015060651.GA4569@linux.vnet.ibm.com>
Date:	Thu, 15 Oct 2009 11:36:52 +0530
From:	Arun R Bharadwaj <arun@...ux.vnet.ibm.com>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ingo Molnar <mingo@...e.hu>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Balbir Singh <balbir@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-arch@...r.kernel.org, linux-acpi@...r.kernel.org,
	Arun Bharadwaj <arun@...ux.vnet.ibm.com>
Subject: Re: [v8 PATCH 2/8]: cpuidle: implement a list based approach to
	register a set of idle routines.

* Andi Kleen <andi@...stfloor.org> [2009-10-14 09:18:38]:

> > How about something like this..
> > If the arch does not enable CONFIG_CPU_IDLE, the cpuidle_idle_call
> > which is called from cpu_idle() should call default_idle without
> > involving the registering cpuidle steps. This should prevent bloating
> > up of the kernel for archs which dont want to use cpuidle.
> 
> On x86 some people want small kernel too, so selecting it on a architecture
> granuality is not good. Also you can make it default, you just need
> to slim it down first.
> 

No, I dont mean selecting it on an architecture granularity.

At compile time, if CONFIG_CPU_IDLE is disabled, the arch can redefine
cpuidle_idle_call. For e.g. in arch/x86/kernel/process.c

#ifndef CONFIG_CPU_IDLE
void cpuidle_idle_call(void)
{
	if (local_idle)
		local_idle();
	else
		default_idle();
}
#endif

where local_idle points to the idle routine selected using
select_idle_routine() which can be poll, mwait, c1e.

So this way, we still preserve the exact same functionality as before
and we also remove the ugly pm_idle exported function pointer and we
avoid unnecessary code bloat for platforms who do not want to use
cpuidle.

--arun
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