On Fri, 24 Nov 2000, Benjamin Herrenschmidt wrote:

quoted

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

It can be more than fraction of watts when you put it all together, especially
in deep sleep. And multiply that by the number of machines out there...

Also, the Cube is sensitive to heat problems, having some power
management (and CPU temp control, but that's another issue) helps.

That's what I call `solving hardware problems by software'. Gives some bonus
points in the old Hackers' Test :-)

quoted

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...

That could be done this way too. Are there any guarantees that the idle
task will run at all, however, if a process is using all the available
CPU time ? If we need all processors to stop scheduling userland code and
wait in a sleep loop (not doze nor nap in this case), we need to have a
way to let the idle task know that we need it to enter this special sleep
stage ASAP. It will have to flush all caches properly and go to sleep. On
some boxes, the CPU(s) will be shut down and revived via ROM hooks.

quoted

What do you call a sleep loop ?

An infinite loop where the CPU goes to sleep mode. It exists via an
external reset or CPU shut down.

What about putting all CPUs except one to sleep at night?

Gr{oetje,eeting}s,

						Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
							    -- Linus Torvalds


** Sent via the linuxppc-dev mail list. See http://lists.linuxppc.org/