Re: PowerOP, Intro 0/3

[Matthew Locke <matt@nomadgs.com>]

Scott, Pavel,


On Aug 28, 2006, at 9:59 AM, Preece Scott-PREECE wrote:

> Hi, Matt,
>
> Can you (and David, if his thoughts are different) clarify for me the
> scope of the "arbitrary subset of power parameters" managed by PowerOP?

Scott does a pretty good job of clarifying, so my comments are below.

>
> I had visualized this as managing CPU speed, voltage, and some
> associated clock and bus speeds and voltages, as opposed to "devices",
> though there would be some interaction with devices indirectly through
> dependencies on specific speeds and voltages. I put "devices" in quotes
> because it's a somewhat ambiguous - it covers both things that you 
> would
> normally think of as devices (like disk drives) and things that are
> modeled by device drivers but are actually just part of the system
> infrastructure (like the power management IC).
>
> Put another way, I had been thinking of PowerOP as managing 
> system-level
> power control, but that device-level controls would still be layered on
> that. Pavel's comments suggest that he thinks it would be managing
> devices as well (thereby creating a state explosion).

> What model did you have in mind?
>

Basically, PowerOP is a building block for managing system-level power 
control as you describe.  Its for controlling bus, clocks, and voltages 
that affect the entire system.  Devices are not controlled directly by 
PowerOP.   Device state should be managed by the devices themselves and 
some other higher level software.  The connection between devices and 
powerop is not device state control; it is notification and 
constraints.

PowerOP does not automatically lead to an explosion of states/points.  
As you can see from the cpufreq patches, PowerOP provides the same 
number points currently available in cpufreq.  It gives the kernel 
developer and/or system designer the choice how to define the operating 
points.

> Thanks,
> scott
>
>> -----Original Message-----
>> From: linux-pm-bounces@lists.osdl.org
>> [mailto:linux-pm-bounces@lists.osdl.org] On Behalf Of Matthew Locke
>> Sent: Monday, August 28, 2006 2:38 AM
>> To: Pavel Machek
>> Cc: pm list
>> Subject: Re: [linux-pm] PowerOP, Intro 0/3
>>
>>
>> On Aug 26, 2006, at 1:38 PM, Pavel Machek wrote:
>>
>>> Hi!
>>>
>>>>>> PowerOP Core upper layer interface provides the following
>>>>>> capabilities:
>>>>>> - to register an operating point by passing an
>> idenificator of the
>>>>>> point represened by a string and arbitrary substet of power
>>>>>> paremeters available on a certain platform by a string
>> (parameter
>>>>>> name) and value pairs.
>>>>>> - to unregister operating point by name
>>>>>> - to set operating point by name
>>>>>> - to get values of arbitrary subset of platform power parameters
>>>>>> associated this  a point (point is passed by name or NULL to get
>>>>>> current parameter values from hw)
>>>>>
>>>>> I do not think this can work in notebook world, sorry.
>>>>> You'll just get
>>>>> way too many operating points.
>>>> The only feature for notebook world currently presented in
>> the kernel
>>>> is CPUFreq. CPUFreq PowerOP integration
>>>
>>> Actually no. In the notebook world, we do cpufreq,
>> selective powerdown
>>> of devices (/sys/**/power/state), and suspend-to-ram/disk
>> (not sure if
>>> it applies to you, but at least some powerop versions wanted to
>>> replace that).
>>
>>
>> The main point is that you won't get too many operating
>> points.  You will get the number of operating points the x86
>> port of PowerOP chooses to have.  In the cpufreq/PowerOP
>> integration patches you get the same
>> number of operating points you have today in cpufreq.   We query ACPI
>> for the list or use the hardcoded table.  Also, if we provide
>> a userspace API for creating operating points,  distro's can
>> create additional operating points that make sense for some
>> specific use cases they would like to optimize around.
>>
>>
>> Matt
>>
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>