> buttering the cost of switches [over the whole execution time]
The switches get cheaper but the rest of the code gets slower (because it has less flexibility in register allocation) so the cost of the switches is "buttered" (i.e. smeared) over the rest of the execution time.
But I don't think this argument holds water. The surrounding code can use whatever registers it wants. In the worst case it saves and restores all of them, which is what a standard context switch does anyway. In other words, this can be better and is never worse.
> buttering the cost of switches [over the whole execution time]
The switches get cheaper but the rest of the code gets slower (because it has less flexibility in register allocation) so the cost of the switches is "buttered" (i.e. smeared) over the rest of the execution time.
But I don't think this argument holds water. The surrounding code can use whatever registers it wants. In the worst case it saves and restores all of them, which is what a standard context switch does anyway. In other words, this can be better and is never worse.