# Multithreaded computation significantly slower

**URL:** https://discourse.julialang.org/t/multithreaded-computation-significantly-slower/47474
**Category:** Performance
**Tags:** question
**Created:** [September 29, 2020, 8:05am UTC](https://discourse.julialang.org/t/multithreaded-computation-significantly-slower/47474 "2020-09-29T08:05:58Z")
**Posts on this page:** 1
**Showing post:** 5

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### Author: ![cgeoga](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/cgeoga/32/216186_2.png) [@cgeoga](https://discourse.julialang.org/u/cgeoga)
#### Post date: [September 29, 2020, 1:16pm UTC](https://discourse.julialang.org/t/multithreaded-computation-significantly-slower/47474/5 "2020-09-29T13:16:52Z")

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Another thought: are you using BLAS at all? In my experience, Julia multi-threading does not play nice with BLAS multithreading, although I have never experienced it working that much worse than a single-thread performance ([ref](https://discourse.julialang.org/t/why-doesnt-multithreading-help-here/45286)). I’m always sure to use `BLAS.set_num_threads(1)` when I want thread-parallel _and_ linear algebra (thanks again, @Elrod).

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