(Reply comes after ChangeLog and Signed-off-by.)

This patch creates a new LED trigger that triggers whenever the CPU is
active.  It can be configured with module parameters to trigger on any
combination of user, nice, system, or iowait time, and defaults to
including user and system time but not nice or iowait time.  I've tested
it a bit, and it seems to work, but no guarantees.  It's diffed against
2.6.17-git25.

Signed-off-by: Thomas Tuttle <thinkinginbinary@gmail.com>

On July 06 at 19:52 EDT, Pavel Machek hastily scribbled:
> Please don't include changelogs in sources.
Okay.  I've attached an updated patch.

> > +#define UPDATE_INTERVAL (5) /* delay between updates, in ms */
> Polling every 5 msec is going to cost _lot_ of juice. Is there a
> better way?
This is a sticky issue.  My first idea was to wire something into
schedule() so that when the idle process was selected, it would switch
the LED off, and when another process was selected, it would switch it
on, but that would have been really hairy.  In addition, it wouldn't
allow the trigger to differentiate between user, system, nice, and
iowait time, which it can now.

I don't think it's that much of a performance hit (the calculations are
fairly short, and a trigger event isn't sent unless the LED state
changed), but if you disagree, I can do a couple of things:

  * Lower the frequency to every 10ms (100Hz) or 40ms (25Hz).  This will
	  reduce the performance hit, but also reduce the accuracy of the LED.
		Right now, it flickers nicely when the CPU is somewhat busy, but if
		I lower the frequency, it will more often stay on rather than
		flickering.  I guess it's a matter of taste.

	* Make the frequency configurable by a module parameter.  This way,
	  users who don't mind the performance hit can increase the speed, and
		those who do mind can lower it.
	
	* Try to hook it in to the scheduler, so it actually knows the moment
	  the CPU idles or starts doing something.  This will make it
		impossible to differentiate user/system time, and hard to
		differentiate user/nice time.

I personally think it's okay as it is, but I'm willing to make changes
if you prefer.

--Thomas Tuttle