# Sys.CPU\_THREADS doesn't appear to get all my threads on Mac

**URL:** <https://discourse.julialang.org/t/sys-cpu-threads-doesnt-appear-to-get-all-my-threads-on-mac/115613>\
**Category:** Julia at Scale\
**Tags:** question\
**Created:** [June 13, 2024, 5:22pm UTC](https://discourse.julialang.org/t/sys-cpu-threads-doesnt-appear-to-get-all-my-threads-on-mac/115613 "2024-06-13T17:22:28Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![schwob](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/schwob/32/49423_2.png) [@schwob](https://discourse.julialang.org/u/schwob)\
**Post date:** [June 13, 2024, 5:22pm UTC](https://discourse.julialang.org/t/sys-cpu-threads-doesnt-appear-to-get-all-my-threads-on-mac/115613/1 "2024-06-13T17:22:28Z")

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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!

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**Author:** ![Oscar\_Smith](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oscar_smith/32/25343_2.png) [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)\
**Post date:** [June 13, 2024, 5:24pm UTC](https://discourse.julialang.org/t/sys-cpu-threads-doesnt-appear-to-get-all-my-threads-on-mac/115613/2 "2024-06-13T17:24:05Z")

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What CPU do you have?

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**Author:** ![schwob](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/schwob/32/49423_2.png) [@schwob](https://discourse.julialang.org/u/schwob)\
**Post date:** [June 13, 2024, 6:16pm UTC](https://discourse.julialang.org/t/sys-cpu-threads-doesnt-appear-to-get-all-my-threads-on-mac/115613/3 "2024-06-13T18:16:20Z")

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I have the M2 Ultra.

From `sysctl -a | grep machdep.cpu`:

```julia
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

```

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<div class="post-metadata">

**Author:** ![Oscar\_Smith](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/oscar_smith/32/25343_2.png) [@Oscar\_Smith](https://discourse.julialang.org/u/Oscar_Smith)\
**Post date:** [June 13, 2024, 6:38pm UTC](https://discourse.julialang.org/t/sys-cpu-threads-doesnt-appear-to-get-all-my-threads-on-mac/115613/4 "2024-06-13T18:38:55Z")

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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](https://github.com/JuliaLang/julia/pull/42099)

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<div class="post-metadata">

**Author:** ![schwob](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/schwob/32/49423_2.png) [@schwob](https://discourse.julialang.org/u/schwob)\
**Post date:** [June 13, 2024, 6:57pm UTC](https://discourse.julialang.org/t/sys-cpu-threads-doesnt-appear-to-get-all-my-threads-on-mac/115613/5 "2024-06-13T18:57:10Z")

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