[$] The long road to lazy preemption

The kernel's CPU scheduler currently offers several preemption modes thatimplement a range of tradeoffs between system throughput and response time.Back in September 2023, a discussionon scheduling led to the concept of "lazy preemption", which couldsimplify scheduling in the kernel while providing better results. Thingswent quiet for a while, but lazy preemption has returned in the form of this patch seriesfrom Peter Zijlstra. While the concept appears to work well, there isstill a fair amount of work to be done.