Yeah, that's what I thought about interrupt handlers. (Also if you're allocating in your interrupt handler, your background thread can't allocate without either disabling interrupts or using some kind of lock-free synchronization.)

I still haven't read the Metronome paper.

I don't know if I'd go so far as to say GC is usually faster than manual memory management, even if we measure by throughput, but at least "often faster" is justifiable. I think usually you can find a way for manual memory management to be faster.