Electricity
[Sat Dec 1 15:05:36 2007] completed event "ac_adapter AC 00000080 00000000"
My power went out today at about 3 pm. It snowed, and apparently something in the Seattle City Light distribution grid broke. My brothers heard four bangs and saw some flashes. I didn't, but that's probably because I was listening to music. :)
I'm on battery power now. ACPI tends to estimate my battery life at something like three to four hours. That's apparently pretty damn good, but it seems low to me. Maybe I'm just picky? Anyway, I opened up powertop, a tool from Intel that attempts to figure out what percentage of battery usage each running program contributes. It's pretty good at that. It also shows you a gauge of the current battery usage, in watts. My idle power usage was something like 13W, which isn't bad.
It has a "wakeups per second" meter, which shows how many times per second the processor is being pulled from a low-power state into a doing-stuff state. This is a useful metric. You want this number to be as low as possible. Do note, however, that not all interrupts are equal. Mouse interrupts are very frequent, but not too expensive to service.
First, turn down the backlight. All the way. Really. With my backlight on full-bright, the system uses 4 W more than with it on full-dim. Full-dim appears to take something like 1 W, but I can't tell for sure.
Nobody uses runlevel four. Edit your runlevel four to have as few daemons as possible running. Each daemon contributes a few wakeups per second, and they add up! And don't forget to go into runlevel four when you're on battery power.
Don't play music. MPD, even idle, interrupts the processor something like 100 times per second. That's two watts on my laptop. MPD doesn't seem to make a difference when it's playing versus paused (or stopped). Maybe I should look into improving MPD's idle processor usage.
As an interesting comparison ogg123 on the same file increased power usage by 2 W without increasing the interrupt count much above 70.
I managed to drop my power usage to around 10 W while typing, with an idle interrupt count of 50 interrupts per second. This brought my predicted battery life to seven hours. (!)
Glory be, just as I finished editing this, the power is back. That was only three hours; not bad.
[Sat Dec 1 18:16:39 2007] completed event "ac_adapter AC 00000080 00000001"