# Running in parallel slower than serial?

**URL:** <https://fenicsproject.discourse.group/t/running-in-parallel-slower-than-serial/1661>\
**Category:** Uncategorized\
**Created:** [October 3, 2019, 1:22pm UTC](https://fenicsproject.discourse.group/t/running-in-parallel-slower-than-serial/1661 "2019-10-03T13:22:59Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![kamensky](https://avatars.discourse-cdn.com/v4/letter/k/e95f7d/32.png) [@kamensky](https://fenicsproject.discourse.group/u/kamensky)\
**Post date:** [October 3, 2019, 1:47pm UTC](https://fenicsproject.discourse.group/t/running-in-parallel-slower-than-serial/1661/2 "2019-10-03T13:47:29Z")

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Maybe take a look at this tread:

> [@Mumps in parallel slower than in serial](https://fenicsproject.discourse.group/t/mumps-in-parallel-slower-than-in-serial/662/2):
>
> Hey, I had a similar problem which is due to petsc (or in particular its mumps solver) using thread parallelism via OpenMP. Let us say your PC has n threads available. Then, when you run your program in serial it already uses n threads (afaik this is the default). Using mpirun with m instances now lets each of these create another n openmp threads, so you have in total m\*n openmp threads, allthough your system can only support n. Therefore, you are slower. You can fix this behaviour setting …

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