runtime: implement procyield properly for ppc64x
The procyield() function should yield the processor as in other
architectures. On ppc64x, this is achieved by setting the Program
Priority Register to 'low priority' prior to the spin loop, and
setting it back to 'medium-low priority' afterwards.
benchmark old ns/op new ns/op delta
BenchmarkMakeChan/Byte-8 87.7 86.6 -1.25%
BenchmarkMakeChan/Int-8 107 106 -0.93%
BenchmarkMakeChan/Ptr-8 201 204 +1.49%
BenchmarkMakeChan/Struct/0-8 78.2 79.7 +1.92%
BenchmarkMakeChan/Struct/32-8 196 200 +2.04%
BenchmarkMakeChan/Struct/40-8 236 230 -2.54%
BenchmarkChanNonblocking-8 8.64 8.85 +2.43%
BenchmarkChanUncontended-8 5577 5598 +0.38%
BenchmarkChanContended-8 66106 51529 -22.05%
BenchmarkChanSync-8 451 441 -2.22%
BenchmarkChanSyncWork-8 9155 9170 +0.16%
BenchmarkChanProdCons0-8 1585 1083 -31.67%
BenchmarkChanProdCons10-8 1094 838 -23.40%
BenchmarkChanProdCons100-8 831 657 -20.94%
BenchmarkChanProdConsWork0-8 1471 941 -36.03%
BenchmarkChanProdConsWork10-8 1033 721 -30.20%
BenchmarkChanProdConsWork100-8 730 511 -30.00%
BenchmarkChanCreation-8 135 128 -5.19%
BenchmarkChanSem-8 602 463 -23.09%
BenchmarkChanPopular-8
3017466 2188441 -27.47%
Fixes #25625
Change-Id: Iacb1c888d3c066902152b8367500348fb631c5f9
Reviewed-on: https://go-review.googlesource.com/115376
Run-TryBot: Lynn Boger <laboger@linux.vnet.ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>