Sys.CPU_THREADS doesn't appear to get all my threads on Mac

On my Mac computer, Sys.CPU_THREADS=16, but in the terminal, sysctl -n hw.ncpu=24, which really implies I have 48 threads. I’m trying to use Distributed’s addprocs()=addprocs(Sys.CPU_THREADS) command, but it seems to not capture all available threads. I’m not pointing fingers at any package or bug, I’m just trying to find what I’m misunderstanding.

Thank you!

What CPU do you have?

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I have the M2 Ultra.

From sysctl -a | grep machdep.cpu:

machdep.cpu.cores_per_package: 24
machdep.cpu.core_count: 24
machdep.cpu.logical_per_package: 24
machdep.cpu.thread_count: 24
machdep.cpu.brand_string: Apple M2 Ultra

So the M2 ultra has 16 big cores and 8 small cores. Julia is only telling you about the big cores because generally putting work on the little cores slows things down a bunch. See also jl_cpu_threads: exclude big.LITTLE efficency cores by staticfloat · Pull Request #42099 · JuliaLang/julia · GitHub


I see. Thank you for the quick responses, Oscar!