Re: apmd and other archs

On Fri, 24 Nov 2000, Benjamin Herrenschmidt wrote:

Yup. Almost all Apple recent machines can do power management in various
ways. Some can deep sleep (not only portables), all can switch off power
to some PCI devices & ASICs, some support turning off the CPU...

Ok, I don't see very much the point of saving fractions of watt on a
desktop but...

quoted

BTW: I dislike any idea of playing with the scheduler.

Me too. The problem is that the IDE layer will always schedule if you do
something more complex that setting a few registers. scheduling in the
middle of putting things to sleep is bad, except is drivers that have
already been put to sleep can cope with it by just blocking userland IOs
or returning errors.

Returning errors to user mode looks like a bad idea, it should be
absolutely transparent to applications.

For other CPUs, I beleive we can go with a cross-CPU function call, the
called function putting the other CPU in a spin-loop. My problem with
that is that it happens all at interrupt time, which may not be the best
place to put the CPU to sleep. Maybe I can manage to schedule a bottom
half or soemthing like that.

I'm lost. Can't power management be done by the idle task ? There is one
per CPU but it can't handle signala AFAIR. After all power management
seems better handled by a task which never does I/O and whose only purpose
is to sleep...

Apple's code is smarter in that sense that they can apparently easily
turn CPUs on/off (putting them in sleep loops when they are off), causing
all processes to migrate to the still running CPU. However, AFAIK, their
current Darwin kernel cannot sleep on SMP machines properly neither yet.

What do you call a sleep loop ?

	Gabriel.


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