linux-kernel - Re: [RFC V1] cpuidle: add idle routine registration and cleanup pm

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Message-ID: <4CBDE5AB.4040401@linux.intel.com>
Date:	Tue, 19 Oct 2010 11:38:35 -0700
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	Trinabh Gupta <trinabh@...ux.vnet.ibm.com>
CC:	peterz@...radead.org, lenb@...nel.org, suresh.b.siddha@...el.com,
	benh@...nel.crashing.org, venki@...gle.com,
	linux-kernel@...r.kernel.org, g.trinabh@...il.com
Subject: Re: [RFC V1] cpuidle: add idle routine registration and cleanup pm_idle
 pointer

  On 10/19/2010 11:36 AM, Trinabh Gupta wrote:
> The core of the kernel's idle routine on x86 presently depends on an
> exported pm_idle function pointer that is unmanaged and causing
> hazard to various subsystems when they save and restore it.
> The first problem is that this exported pointer can be modified/flipped
> by any subsystem. There is no tracking or notification mechanism.
> Secondly and more importantly, various subsystems save the value of
> this pointer, flip it and later restore to the saved value. There is
> no guarantee that the saved value is still valid. The problem has
> been discussed in [2,3] and Peter Zijlstra suggested removing pm_idle
> and implementing a list based registration [1].
>
> This patch is an initial RFC implementation for x86 architecture
> only. This framework can be generalised for other archs and also
> include the current cpuidle framework for managing multiple idle
> routines.
>
> Tests done with the patch:
> ------------------------
> 1. Build (on 2.6.36-rc7) and booted on x86 with C1E as deepest idle
>     state and current_idle was selected to be mwait_idle.
>
> 2. Build (on 2.5.36-rc8) and booted on x86 (Nehalem) with ACPI C3 as
>     deepest sleep state.  The current_idle was selected to be
>     cpuidle_idle_call which is the cpuidle subsystem that will further
>     select idle routines from {C1,C2,C3}.
>
> Future implementation will try to eliminate this hirearchy and have
> a single registration and menu/idle cpuidle governor for selection
> of idle routine.


looks like you're duplicating the cpuidle subsystem

how about biting the bullet and just always and only use the cpuidle 
subsystem for all idle on x86 ?

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