# Is back propagation in Flux alway run on a single cpu core?

**URL:** <https://discourse.julialang.org/t/is-back-propagation-in-flux-alway-run-on-a-single-cpu-core/91379>\
**Category:** Performance\
**Tags:** flux\
**Created:** [December 7, 2022, 6:07pm UTC](https://discourse.julialang.org/t/is-back-propagation-in-flux-alway-run-on-a-single-cpu-core/91379 "2022-12-07T18:07:08Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![tiZ](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tiz/32/211800_2.png) [@tiZ](https://discourse.julialang.org/u/tiZ)\
**Post date:** [December 7, 2022, 6:07pm UTC](https://discourse.julialang.org/t/is-back-propagation-in-flux-alway-run-on-a-single-cpu-core/91379/1 "2022-12-07T18:07:08Z")

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Hi, I am trainning a neural network with Flux on a machine with 56 cpu cores, but I found that it seems it is alway only one core working while `Flux.train!` is performed, and I can see multi cpu is running in the `forward` caculation step of my model.

so, is it normal or anything I missing?