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

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Message-ID: <AANLkTi=cetw_mdp_3s+T4OxTfcMT2u4cdVPKxOp7jbVU@mail.gmail.com>
Date:	Tue, 19 Oct 2010 11:49:02 -0700
From:	Venkatesh Pallipadi <venki@...gle.com>
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	Trinabh Gupta <trinabh@...ux.vnet.ibm.com>, peterz@...radead.org,
	lenb@...nel.org, suresh.b.siddha@...el.com,
	benh@...nel.crashing.org, linux-kernel@...r.kernel.org,
	g.trinabh@...il.com
Subject: Re: [RFC V1] cpuidle: add idle routine registration and cleanup
 pm_idle pointer

On Tue, Oct 19, 2010 at 11:38 AM, Arjan van de Ven
<arjan@...ux.intel.com> wrote:
>  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 ?
>

I agree with Arjan.
If we have a default_cpuidle driver which parses idle= params, handles
various mwait quirks in x86 process*.c and registers with cpuidle, we
can then always call cpuidle idle routine on x86.

Thanks,
Venki
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