# Poor performance while multithreading (Julia 1.0)

**URL:** <https://discourse.julialang.org/t/poor-performance-while-multithreading-julia-1-0/20325>\
**Category:** Performance\
**Tags:** multithreading\
**Created:** [January 31, 2019, 5:14pm UTC](https://discourse.julialang.org/t/poor-performance-while-multithreading-julia-1-0/20325 "2019-01-31T17:14:02Z")\
**Posts on this page:** 1\
**Showing post:** 9

<div class="post-metadata">

**Author:** ![dkiese](https://avatars.discourse-cdn.com/v4/letter/d/71e660/32.png) [@dkiese](https://discourse.julialang.org/u/dkiese)\
**Post date:** [February 2, 2019, 11:00pm UTC](https://discourse.julialang.org/t/poor-performance-while-multithreading-julia-1-0/20325/9 "2019-02-02T23:00:13Z")

</div>

@foobar_lv2

Let me break my answer into pieces according to your questions.

For my test parameters `@btime` for no threads gives me 2.89 s, for 2 threads 4.11s, for 3 threads 3.92 s and for 4 threads 3.71 seconds (my machine has 4 physical cores). So although there seems to be some scaling with `Threads.nthreads()` I am not getting in range of the non-threaded loops.

The structs consist of 3 Arrays. Field1 has ~`10^2` entries atmost, in the tests it hast like 10 entries. The other contain up to `10^7` entries, in the test its roughly a thousand each.

```julia
struct MyStruct 
Field1 :: Vector{Float64}
Field2 :: Array{Float64, 4}
Field3 :: Array{Float64, 4}
end

```

The `computeKernel()` functions compute one dimensional integrals, so inside of these I define inner functions which are passed as kernels to some integration function. In that process I allocate memory temporarily for a buffer that saves intermediate results.

Within the calculation elements of one struct are used to compute elements of the other struct, so there is in fact quite a lot of data access (so cache might be a concern?! ).

Not sure how I test if two threads write into the same cache line… Only thing I can say that the loops are definitely threadsafe, in the sense that no chunck of memory is simultaneously accessed for both reading and writing.

---

_[View the full topic](https://discourse.julialang.org/t/poor-performance-while-multithreading-julia-1-0/20325)._