On Sun 2006-09-03 16:21:34, Scott E. Preece wrote: > | From: Pavel Machek<pavel at ucw.cz> > | On Thu 2006-08-31 16:44:12, Amit Kucheria wrote: > | > On Thu, 2006-08-31 at 00:36 +0200, ext Pavel Machek wrote: > | > > On Wed 2006-08-30 14:00:53, Amit Kucheria wrote: > | > > > But PowerOP would allow SoC-based systems to tune the operating points > | > > > to get the most out of their top-10 use-cases and sleep modes. > | > > > | > > Question is: can we get similar savings without ugly interface powerop > | > > presents? > | > > | > If I have understood correctly, your main objection is to defining new > | > operating points from userspace? > | > | Well, that is big objection, but not my main one. I believe that "new > | operating points from userspace" are non-starter. "So obviously wrong > | that noone would merge that". > --- > > Why? Are you interpreting "from user space" as "under user control"? A > lot of us have been taught for some time that it's a good thing to move > stuff out of the kernel, unless it really needs to be there. Is > there Moving stuff out of kernel is one important design principe. Keeping user<->kernel interface reasonably clean is another one. > some reason, in your perception, why definition of operating points > really needs to be in the kernel? Definition of the operating points, > as opposed to changing from one OP to another, shouldn't have any timing > issues, so why isn't a privileged user-space manager a reasonable > approach? For one thing, is not powerop needed for boot? You need to boot in some operating point after all :-). Yes, I see having points defined in userspace is useful for debugging, but having kernel depend on external daemon for its proper operation is not nice. > | > The only other interface is the actually setting of a (named) operating > | > point and that is _required_ to do anything useful. > | > | No, they are not. > | > | We already have interface for selecting cpu frequency. Lets keep it. > > As noted previously, OPs bundle together more than just the > frequency. Those of us supporting the OP model believe that you can't > intelligently change CPU frequency in isolation and you can't change > some of those parameters independently, because only certain > combinations work. That's okay. User gives you combination he wants, and you select "next higher" working operating point. > | Now, it should be up-to the powerop framework to select best operating > | point given "cpu speed, dsp speed, usb on/off" state. But I argue that > | this should be done in-kernel and hidden from user. > > Well, I agree with hiding it from the user, but there's no particular > reason that means it needs to be done in the kernel. Again, we like to > have it run from user-space, so we can replace it easily (without > recompiling/restarting the kernel) in development. Do whatever you want for development (that includes patching your kernel). For production, nice interface is more important. Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
