power management experiences with joyride-1572

[Chris Ball]

Hi Frank,

   > Hi - I've been dabbling with joyride-1572 on a g1g1 laptop for a
   > day or few, and have noticed the suspend feature kick in after a
   > few seconds of apparent inactivity.  I have some questions about
   > whether some specific experiences with this are expected:

   > - that a resume operation begins only with a keyboard/touchpad
   > input, and takes 1-2 seconds for interactiveness to return?

Yes, the resume operation is triggered by user input, or a wireless
packet addressed to the host (or some battery-related events).  It
can't be triggered by anything in software unless that's organized
ahead of time; the CPU is turned off completely in the suspend mode.

We're going to be spending a lot of effort on decreasing that resume
time.  We've measured it at 280ms with USB and some other drivers turned
off, but as you say we're above 1 second with the current setup.  We
need to perform a mix of:

   * optimizing driver resume
   * parallelizing driver resume
   * delaying driver resume until the device is needed

wherever possible until we're back around the first number.  So far
we've been working on making it work rather than making it fast; that
will start to change with our next release.

   > - that running programs such as the sugar clock widget, or programs
   > running in the sugar terminal, all freeze during the suspend?

Correct.  Note that if a program running in the sugar terminal is using
non-trivial CPU, it will inhibit suspend by doing so; an automatic
suspend should never happen while a compile is underway, for example.
When in suspend, (approximately) everything except the screen/wireless
is turned off, hence the freeze.  This is why we avoid such
constantly-updating applets on the sugar home screen.

   > - that if one switches to the text console (C-A-F1), one observes
   > the backlight intensity oscillate up & down with about a 10s
   > interval, despite ongoing keyboard input?

That's a bug, since fixed in later builds.

   > - that power consumption during the "awake" mode has not
   > significantly fallen since build-650 or -653, leading to a ~3 hour
   > battery endurance for light continuous web browsing / terminal
   > usage?

Correct, we haven't changed power consumption while everything is turned
on.  We're working instead on turning a lot of things off where possible.
I'd be very interested to hear real-life experiences of battery life
with the mix of awake and asleep modes currently present in the Joyride
build.  I'd also be interested in opinions on the timeouts I've chosen
for the idle-suspend mode -- currently we suspend after 30 seconds of
user input idleness, if the CPU is also idle.

Thanks,

- Chris.
-- 
Chris Ball   <cjb at laptop.org>