On Fri, Feb 08, 2019 at 12:10:02AM -0500, Ted Unangst wrote:
> Go tries to use NCPU cpus. Unfortunately, half of them are turned off because
> hw.smt=0 by default, and then go spends a lot of time fighting against itself.
>
> The diff below, against go/src/runtime, changes to use the number of CPUs
> online. It's possible for this number to change, and thus become stale, but
> that's unlikely, and not the default.
>
> (This sysctl was added in 6.4.)
>
> --- os_openbsd.go.orig Fri Feb 8 00:02:27 2019
> +++ os_openbsd.go Fri Feb 8 00:06:21 2019
> @@ -85,8 +85,8 @@
> _KERN_OSREV = 3
>
> _CTL_HW = 6
> - _HW_NCPU = 3
> _HW_PAGESIZE = 7
> + _HW_NCPUONLINE = 25
> )
>
> func sysctlInt(mib []uint32) (int32, bool) {
> @@ -101,7 +101,7 @@
>
> func getncpu() int32 {
> // Fetch hw.ncpu via sysctl.
> - if ncpu, ok := sysctlInt([]uint32{_CTL_HW, _HW_NCPU}); ok {
> + if ncpu, ok := sysctlInt([]uint32{_CTL_HW, _HW_NCPUONLINE}); ok {
> return int32(ncpu)
> }
> return 1
Is there at least a knob to turn that off entirely ?
Like, specifically, when you are bulk-building ports, you do not want go
to hog on every cpu while it's not alone.
Parallelizing everything is not always (very often not actually) a win.
