runtime: use vDSO for clock_gettime on linux/arm64
Use the __vdso_clock_gettime fast path via the vDSO on linux/arm64 to
speed up nanotime and walltime. This results in the following
performance improvement for time.Now on Cavium ThunderX:
name old time/op new time/op delta
TimeNow 442ns ± 0% 163ns ± 0% -63.16% (p=0.000 n=10+10)
And benchmarks on VDSO
BenchmarkClockVDSOAndFallbackPaths/vDSO
10000000 166 ns/op
BenchmarkClockVDSOAndFallbackPaths/Fallback
3000000 456 ns/op
Change-Id: I326118c6dff865eaa0569fc45d1fc1ff95cb74f6
Reviewed-on: https://go-review.googlesource.com/99855
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>