Automated adoption of devkit-power latencies

Phil Knirsch pknirsch at
Tue Nov 11 09:41:36 PST 2008

Richard Hughes wrote:
>>>> I'd personally like to use devkit-power and it's API as a service, as 
>>>> overloading it with such functionality might very quickly lead to the 
>>>> problems we've seen in the past with HAL where everything was put into
>>>> a single service.
>>> No, I think it's 100% on topic for DK-p. Powersaving is inextricably
>>> linked to latency in my opinion.
>> What about cases where you want to completely shut down a device though 
>> as you know it's not used?
> Well, I think for the sort of latencies we are talking about (us and low
> order ms) we need to do this in the kernel driver by default. The logic
> goes like this: If the device isn't being used, power it down _UNLESS_
> it takes more time than $CURRENT_LATENCY_SETTING to wakeup.
> This way everything sleeps by default.

Yep, absolutely agree. But even there wouldn't it be nice if e.g. during 
the day that server would have a 10us latency for CPU and during the 
night automatically transition to higher and higher latencies, up to 
even 100ms or so? Or a desktop system that has a screenlock running 
overnight, the user forgot to close his firefox window with a flash 
plugin running in it. Thats what i'm thinking about at least. Not to 
have a fixed latency but a dynamic one that, depending on whats going on 
on the system adapts those.

And devices that take a lot longer to power down resp. up e.g. harddisks 
aren't addresses by the latency changes yet if i remember correctly?

Regards, Phil

Philipp Knirsch              | Tel.:  +49-711-96437-470
Team Lead Core Services      | Fax.:  +49-711-96437-111
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