[ohm] OHM vs. PPM

[Rob Taylor]

Holger Macht wrote:
> Hi,

Hi Holger, sorry for taking so long to reply.

> might be a quite provoking subject, however, I like to attract some
> responses... ;-)
> 
> For quite some while now, I'm looking into finding a replacement (and
> starting to become active in the development for it), for the powersave
> daemon we use on openSUSE based distributions. Actually it's about the
> question: "Who does the power management job when there's no desktop
> applet?"
> 
> Obviously, two frameworks caught my eye... open-hardware-manager (OHM [1])
> and the power-policy-manager (PPM [2]). So I have a couple of questions:
> 
>  1. Is OHM aught to be used on usual desktop/laptop systems? I mean, it
>     would be a valid target to define that OHM is "just" meant for
>     embedded devices and thus, development wouldn't consider
>     problems/drawbacks on the desktop side.

OHM needs some work before its usable on a desktop system, mainly in 
that it should become a session daemon rather than a system daemon - 
connecting up to X from the system is not ideal.

>  2. Are you guys in contact in any kind with the PPM Intel developers?

Not particularly. I've tried to get a discussion going, but haven't had 
much luck. It maybe that I've just not managed to reach the right people.

>  3. As I understand it, OHM is more than PPM. It doesn't exclusively look
>     at power management, but also on other aspects. Due to it's plugin
>     system, it could be used for any kind of things. Same plugin system in
>     PPM, but with the difference that PPM's defined target is just power
>     management AFAICT. So, at first glance, there are duplicate
>     development efforts. Again ;-) I mean, we had so many different
>     implementations (scripts, C++ daemons, etc..) in the past, so I think
>     it's time to agree on one single framework. At least I have to choose
>     one :-) Any statement about that?

Yep, OHM is more about generic policy management and allowing an easy 
way to define behaviour. I'd hoped that starting a fd.o project might 
encourage people to come in and discuss the various viewpoints, but 
that's not happened hugely. I should note that OHM was started before 
PPM became public.

I guess the main difference between OHM and PPM at this point is that 
PPM is much more structured, with a langauge for policy definition. OHM 
at this point is really little more than a key/value state store, an 
event transition system and plugins that can respond to events and 
modify the store.

I talked to David Zeuthen about both frameworks a while back at the 
GNOME Boston summit, his take was that both were wrong for running at 
the system level as policy can often be user and desktop specific.

> I already checked out both frameworks and gave them a quick try, both
> seemed to work, at least to a certain extend. But "remaining issues" which
> can be fixed are not a problem here.

How's your investigation gone so far?

Thanks,
Rob

> Thanks,
> 	Holger
> 
> [1] http://ohm.freedesktop.org/wiki/
> [2] http://www.lesswatts.org/projects/power-policy/index.php
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