What did you do for timer coalescing? If every thread can request a custom wakeup time then power consumption goes up. If wakeups are coalesced then what algorithm do you use to coalesce them, and how much movement in wakeup times do you allow? Depending on how you coalesce timers you can very easily find yourself reinventing the basics of what Windows does.

The Windows system also gives you a very cheap to read timer counter which is a nice attribute.

The Windows system is frustrating, especially for those who don't understand it, but it does have some excellent attributes.