ThinkPad T400 switched into integrated gpu mode – running Intel GM45 eats ~12W of power.
ThinkPad T400 switched into discrete gpu mode – running Radeon HD 3400 eats … ~28W of power!
Which means that radeon itself eats more than 16W of power (meausred with powertop). That’s more than whole notebook in integrated gpu mode. Nightmare!
Note that HD 3400 was driven by open source radeon driver which doesn’t have any power management support at this moment.
200904 update: ati driver in git contains updated power management and it’s eating ~16W here instead of ~28W now with DynamicPM turned on.