# Julia not using full CPU when running inside a GNU Screen session (edit: not a Julia isse

**URL:** <https://discourse.julialang.org/t/julia-not-using-full-cpu-when-running-inside-a-gnu-screen-session-edit-not-a-julia-isse/10430>\
**Category:** Performance\
**Created:** [April 19, 2018, 11:58am UTC](https://discourse.julialang.org/t/julia-not-using-full-cpu-when-running-inside-a-gnu-screen-session-edit-not-a-julia-isse/10430 "2018-04-19T11:58:18Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Axel\_Gagge](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/axel_gagge/32/859_2.png) [@Axel\_Gagge](https://discourse.julialang.org/u/Axel_Gagge)\
**Post date:** [April 19, 2018, 11:58am UTC](https://discourse.julialang.org/t/julia-not-using-full-cpu-when-running-inside-a-gnu-screen-session-edit-not-a-julia-isse/10430/1 "2018-04-19T11:58:18Z")

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**EDIT: the following is not a Julia issue, I notice exactly the same problem using Numpy.**

The following code:

```julia
x=rand(10000,10000);
x*x

```

shows ~800% CPU usage according to `top` (I have 8 cores). When running Julia within a GNU Screen session however, I see only ~100% usage. I am running on Ubuntu 16.04, installed Julia by downloading from the web page and my `versioninfo()` is

```julia
Julia Version 0.6.2
Commit d386e40c17 (2017-12-13 18:08 UTC)
Platform Info:
  OS: Linux (x86_64-pc-linux-gnu)
  CPU: Intel(R) Core(TM) i7-2600 CPU @ 3.40GHz
  WORD_SIZE: 64
  BLAS: libopenblas (USE64BITINT DYNAMIC_ARCH NO_AFFINITY Sandybridge)
  LAPACK: libopenblas64_
  LIBM: libopenlibm
  LLVM: libLLVM-3.9.1 (ORCJIT, sandybridge)

```

Screen:

```julia
Screen version 4.03.01 (GNU) 28-Jun-15

```

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**Author:** ![johnh](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/johnh/32/3615_2.png) [@johnh](https://discourse.julialang.org/u/johnh)\
**Post date:** [April 19, 2018, 12:31pm UTC](https://discourse.julialang.org/t/julia-not-using-full-cpu-when-running-inside-a-gnu-screen-session-edit-not-a-julia-isse/10430/2 "2018-04-19T12:31:42Z")

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Axel, stupid question. How exactly do you know the amount of cores in use?

I am sure I am going to be laughed at, but is screen somehow being put into a cgroup on your system?

---

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**Author:** ![Axel\_Gagge](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/axel_gagge/32/859_2.png) [@Axel\_Gagge](https://discourse.julialang.org/u/Axel_Gagge)\
**Post date:** [April 19, 2018, 12:57pm UTC](https://discourse.julialang.org/t/julia-not-using-full-cpu-when-running-inside-a-gnu-screen-session-edit-not-a-julia-isse/10430/3 "2018-04-19T12:57:38Z")

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I didn’t: I just see that `top` shows ~100% CPU usage when running inside screen, while 800% (I have 8 cores) is used when running without screen. Thanks for pointing this out, I don’t have any proof that only 1 core is used.

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**Author:** ![avik](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/avik/32/17_2.png) [@avik](https://discourse.julialang.org/u/avik)\
**Post date:** [April 19, 2018, 1:00pm UTC](https://discourse.julialang.org/t/julia-not-using-full-cpu-when-running-inside-a-gnu-screen-session-edit-not-a-julia-isse/10430/4 "2018-04-19T13:00:48Z")

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`htop` will you show you individual core usage.