runtime: native xadd for 386/amd64
benchmark old ns/op new ns/op delta
BenchmarkSemaUncontended 37.40 34.10 -8.82%
BenchmarkSemaUncontended-2 18.90 17.70 -6.35%
BenchmarkSemaUncontended-4 11.90 10.90 -8.40%
BenchmarkSemaUncontended-8 6.26 5.19 -17.09%
BenchmarkSemaUncontended-16 4.39 3.91 -10.93%
BenchmarkSemaSyntNonblock 38.00 35.30 -7.11%
BenchmarkSemaSyntNonblock-2 83.00 46.70 -43.73%
BenchmarkSemaSyntNonblock-4 124.00 101.00 -18.55%
BenchmarkSemaSyntNonblock-8 124.00 116.00 -6.45%
BenchmarkSemaSyntNonblock-16 148.00 114.00 -22.97%
(on HP Z600 2 x Xeon E5620, 8 HT cores, 2.40GHz)
R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/
4755041