confuse about wakep?

[xie cui]

https://github.com/golang/go/blob/master/src/runtime/proc.go#L2441

why not  change to if !atomic.Cas(&sched.nmspinning, 0, 1),  it seems check sched.nmspinning no zero is unneccessary in logic,

i am not sure, i guess it's about performence issue?

[Ian Lance Taylor]

An atomic load is faster than an atomic compare-and-swap. In
particular, on amd64, an atomic load is just an ordinary load
instruction.

Ian