# SVectors + @reset from Accessors: Strange Benchmarks

**URL:** <https://discourse.julialang.org/t/svectors-reset-from-accessors-strange-benchmarks/119201>\
**Category:** General Usage\
**Tags:** benchmarktools, staticarrays, setfield, accessors\
**Created:** [September 9, 2024, 2:50am UTC](https://discourse.julialang.org/t/svectors-reset-from-accessors-strange-benchmarks/119201 "2024-09-09T02:50:02Z")\
**Posts on this page:** 1\
**Showing post:** 24

<div class="post-metadata">

**Author:** ![Tetrakai](https://avatars.discourse-cdn.com/v4/letter/t/4da419/32.png) [@Tetrakai](https://discourse.julialang.org/u/Tetrakai)\
**Post date:** [September 10, 2024, 2:22pm UTC](https://discourse.julialang.org/t/svectors-reset-from-accessors-strange-benchmarks/119201/24 "2024-09-10T14:22:40Z")

</div>

If we get rid of the random number, can’t the compiler just calculate the result? I think that is what I am seeing when I make it simpler.

Results differ on my PC vs laptop (which are also different Julia versions…) and depending on the optimization flag.

> **Slimmed MWE**
>
> ```julia
> using Parameters, StaticArrays, Accessors, BenchmarkTools
> using Distributions, Random 
> 
> @with_kw struct Str00{N}
> fat :: SVector{N, Float64}
> sh_c0 :: SVector{N, Float64}
> sh_cm :: SVector{N, Float64}
> end
> 
> Random.seed!(1234)
> bg1 = Str00(fat = SVector{16}(fill(Float64(1.0), 16)),
> sh_c0 = SVector{16}(rand(Uniform(4, 25), 16)),
> sh_cm = SVector{16}(rand(Uniform(4, 25), 16)))
> 
> bg2 = Str00(fat = SVector{16}(fill(Float64(1.0), 16)),
> sh_c0 = SVector{16}(rand(Uniform(4, 25), 16)),
> sh_cm = SVector{16}(rand(Uniform(4, 25), 16)))
> 
> gt = (bg1, bg2)
> 
> function test1(gt)
> for t in 1:100
> @reset gt[1].sh_cm .= gt[1].sh_c0 .* gt[1].fat
> @reset gt[2].sh_cm .= gt[2].sh_c0 .* gt[2].fat
> end
> return gt
> end
> 
> function test2(gt)
> for t in 1:100
> gt = map(gt) do x
> @reset x.sh_cm .= x.sh_c0 .* x.fat
> return x
> end
> end
> return gt
> end
> 
> @btime test1($gt);
> @btime test2($gt);
> 
> res1 = test1(gt);
> res2 = test2(gt);
> 
> res1 == res2
> 
> ```

System info

```julia
Laptop (i5-6300u Julia 1.10.4)
PC (2990wx Julia 1.11.0-rc-1)

```

**Laptop**

- No flag, does not depend on outer loop length

```julia
julia> @btime test1($gt);
  23.730 ns (0 allocations: 0 bytes)

julia> @btime test2($gt);
  24.456 ns (0 allocations: 0 bytes)

```

Unless the -O1 optimization flag is used (but not -O2/-O3):

```julia
julia> @btime test1($gt);
  12.909 μs (0 allocations: 0 bytes)

julia> @btime test2($gt);
  12.497 μs (0 allocations: 0 bytes)

```

**PC**

- No flag, test2 depends on outer loop

```julia
julia> @btime test1($gt);
  24.407 ns (0 allocations: 0 bytes)

julia> @btime test2($gt);
  6.592 μs (0 allocations: 0 bytes)

```

PC -O1 flag

```julia
julia> @btime test1($gt);
  8.403 μs (0 allocations: 0 bytes)

julia> @btime test2($gt);
  9.490 μs (0 allocations: 0 bytes)

```

PC -O2 (or -03) flag

```julia
julia> @btime test1($gt);
  25.980 ns (0 allocations: 0 bytes)

julia> @btime test2($gt);
  6.594 μs (0 allocations: 0 bytes)

```

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