Re: [RFC PATCH V1 0/2] cpuidle: global registration of idle stateswith per-cpu statistics
From: Len Brown
Date: Fri Mar 25 2011 - 03:29:14 EST
On Tue, 22 Mar 2011, Trinabh Gupta wrote:
> This patch series is an early RFC to discuss the feasibility of
> avoiding registering of idle states from each cpu.
>
> The core change is to split the cpuidle_device structure into parts
> that can be global and parts that has to remain per-cpu. The per-cpu
> pieces are mostly generic statistics that can be independent of
> current running driver.
>
> Motivation:
> * Simplify the cpuidle subsystem framework and have
> registration/unregistration done by single cpu.
>
> * Minimise the data structure that needs to be maintained for multiple
> cpuidle drivers
>
> * Reference: https://lkml.org/lkml/2011/2/10/37
>
> Advantages:
> * Make the cpuidle framework simple for most use cases where C-States
> are symmetric. In case there are asymmetric C-States detected,
> fallback mechanism should be incorporated to maintain the system
> functional
> https://lkml.org/lkml/2011/2/10/257
> https://lkml.org/lkml/2011/2/10/37
>
> * Non x86 archs that does not have asymmetric C-States like POWER, may
> not need the fallback mechanism and hence the framework will be
> simple for most use cases.
>
> Disadvantages:
> * Asymmetric C-States are part of x86 ACPI specification. Incorrect
> handling may functionally affect the system
I think this is a non-issue.
> * Incorporating per-cpu masks for each state to allow/dis-allow global
> states on subset of CPUs may result in an implementation that is
> not better than current solution of having per-cpu states.
I don't think this is needed.
> This patch series applies on top of the pm_idle cleanup patch
> https://lkml.org/lkml/2011/3/22/150 (cpuidle: Cleanup pm_idle and
> include driver/cpuidle.c in-kernel)
>
> This patch series is tested on x86 Nehalem system with multiple ACPI
> C-States.
>
> This patch series has limitations of not handling multiple driver
> registration and switching between drivers on all CPUs mainly due to
> incomplete handling of per-cpu enable/disable and driver_data.
I think this series is more important than the feature of multiple
driver/system support, and thus should come first.
thanks,
Len Brown, Intel Open Source Technology Center
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