# Distributed performance depends on the number of workers?

**URL:** <https://discourse.julialang.org/t/distributed-performance-depends-on-the-number-of-workers/115514>\
**Category:** General Usage\
**Tags:** package, parallel, cluster, distributed, slurm\
**Created:** [June 11, 2024, 9:01pm UTC](https://discourse.julialang.org/t/distributed-performance-depends-on-the-number-of-workers/115514 "2024-06-11T21:01:09Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![greivin](https://avatars.discourse-cdn.com/v4/letter/g/a6a055/32.png) [@greivin](https://discourse.julialang.org/u/greivin)\
**Post date:** [June 11, 2024, 9:01pm UTC](https://discourse.julialang.org/t/distributed-performance-depends-on-the-number-of-workers/115514/1 "2024-06-11T21:01:09Z")

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I’m executing a code that solves a linear system (Ax = b) for a fixed matrix A, and for several vectors `b_i` here i runs from 1 to N. I set N to match the number of available cores in my system, therefore I’ll be solving N = 32 (for example) linear systems in parallel.

I do this by putting @everywhere in front of every required function, defining the matrix of solutions as a SharedArray (that contains every vector solution (x1 x2 … x32)) and adding the tags @sync @distributed in front of the for that runs over the `i=1:N(=32)` vectors `b_i`.

However, when sent to the cluster using slurm, I noticed that the running time is larger than expected compared to a single run in my personal machine. In my personal machine all the code (for one vector b1) lasts ~500 s while in the cluster using N = 16 (and hence 16 workers with @sync @distributed) it is taking longer than 2700 s. Worst of all, when attempting to send more jobs than available workers (32 vectors `b_i` with @sync @distributed over 16 workers) for ~2700 s it was already done.

What could be going on? Is there a way to avoid this overhead and produce faster results?