# FLoops ThreadedEx scheduling

**URL:** <https://discourse.julialang.org/t/floops-threadedex-scheduling/86024>\
**Category:** General Usage\
**Tags:** package\
**Created:** [August 19, 2022, 5:10pm UTC](https://discourse.julialang.org/t/floops-threadedex-scheduling/86024 "2022-08-19T17:10:28Z")\
**Posts on this page:** 1\
**Showing post:** 2

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**Author:** ![tkf](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/tkf/32/17635_2.png) [@tkf](https://discourse.julialang.org/u/tkf)\
**Post date:** [September 1, 2022, 5:03pm UTC](https://discourse.julialang.org/t/floops-threadedex-scheduling/86024/2 "2022-09-01T17:03:16Z")

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(Maybe aside: Typically, simple tweaking of `basesize` is the best “very cheap” way to get “good enough” performance. For load-balancing, simply reduce `basesize`. If the given computation is not big enough increase `basesize`. I should put this at more prominent location in the manual.)

What did you have in the `...`? It has to be sufficiently time-consuming in order to observe the Julia scheduler doing _something_. If it’s too short, the Julia scheduler may re-use the same worker thread to execute the given tasks.

The main difficulty here is that, if `...` is too long, any clever things that FoldsThreads can do will be negligible. This is why [[ANN] FoldsThreads.jl: A zoo of pluggable thread-based data-parallel execution mechanisms](https://discourse.julialang.org/t/ann-foldsthreads-jl-a-zoo-of-pluggable-thread-based-data-parallel-execution-mechanisms/54662) has a bit more elaborate examples to emphasize the differences of the schedulers.

Another difficulty is interaction with the GC. If the iteration space is not too large (`length(xs)` below is not too large), I’d simply preallocate a `record` array and record the thread id used in the loop

```julia
record = zeros(Int, length(xs))

@floop ... for (i, x) in enumerate(xs)
   ...
   record[i] = threadid()
end

```

where the loop body `...` should be some non-trivial computation. You’d also need to gather some samples of `record` data to get a “typical” picture of the execution.

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