Slow argmin?

General Usage
1

Hi,

I come across the following performance gap and I am not sure I understand why.

function my_min(a)
    val = a[begin]
    ind = 0
    @inbounds for i in eachindex(a)
        if a[i]>val
            val = a[i]
            ind = i
        end
    end
    ind
end

a = rand(1000)
julia> @btime argmin(a)
  4.554 μs (0 allocations: 0 bytes)
325

julia> @btime my_min(a)
  1.113 μs (0 allocations: 0 bytes)
325
2

is it Performance Difference between argmin and minimum · Issue #41963 · JuliaLang/julia · GitHub ?

3

On recent nightly it seems to be improved compared to 1.11.1

EDIT: Apparently just benchmark noise, seems to be roughly the same.

julia> @benchmark argmin($a)
BenchmarkTools.Trial: 10000 samples with 10 evaluations.
 Range (min … max):  1.336 μs …   9.966 μs  ┊ GC (min … max): 0.00% … 0.00%
 Time  (median):     1.956 μs               ┊ GC (median):    0.00%
 Time  (mean ± σ):   2.066 μs ± 614.355 ns  ┊ GC (mean ± σ):  0.00% ± 0.00%

  █ ▄▁       ▁   ▁  ▂ ▁       ▂ ▃  ▄                           
  █▇███▇███████▄▇██▄█▃█▇▆█▄▆▆▂█▂█▂▂█▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▂▁▂▁▁▁▇ ▄
  1.34 μs         Histogram: frequency by time        3.94 μs <

 Memory estimate: 0 bytes, allocs estimate: 0.

julia> @benchmark my_min($a)
BenchmarkTools.Trial: 10000 samples with 84 evaluations.
 Range (min … max):  818.464 ns …   6.910 μs  ┊ GC (min … max): 0.00% … 0.00%
 Time  (median):     824.762 ns               ┊ GC (median):    0.00%
 Time  (mean ± σ):   876.617 ns ± 154.231 ns  ┊ GC (mean ± σ):  0.00% ± 0.00%

  █▄▂▁▁▁                                                        ▁
  ██████▇█▇█▆█▆█▅▆█▅█▄▆▇▅▇▄▄█▅▄▇▅▆█▆▃▇█▄▄█▅▅▇█▄▃▇█▄▃▃█▇▃▃▆█▅▅▃▄ █
  818 ns        Histogram: log(frequency) by time       1.46 μs <

 Memory estimate: 0 bytes, allocs estimate: 0.


julia> versioninfo()
Julia Version 1.12.0-DEV.1613
Commit 366a38e6ed6 (2024-11-12 01:41 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 14 × Intel(R) Core(TM) Ultra 7 155U
  WORD_SIZE: 64
  LLVM: libLLVM-18.1.7 (ORCJIT, alderlake)
Threads: 14 default, 0 interactive, 14 GC (on 14 virtual cores)
Environment:
  JULIA_MAX_NUM_PRECOMPILE_FILES = 100
  JULIA_NUM_THREADS = 14
  JULIA_PKG_PRESERVE_TIERED_INSTALLED = true

Vs

julia> @benchmark argmin($a) evals=100000
BenchmarkTools.Trial: 32 samples with 100000 evaluations.
 Range (min … max):  1.118 μs …   3.082 μs  ┊ GC (min … max): 0.00% … 0.00%
 Time  (median):     1.164 μs               ┊ GC (median):    0.00%
 Time  (mean ± σ):   1.559 μs ± 691.308 ns  ┊ GC (mean ± σ):  0.00% ± 0.00%

  █                                                            
  ██▄▃▄▃▁▁▁▁▁▁▁▁▁▃▁▁▁▁▁▁▁▃▁▁▁▁▁▃▁▁▁▁▁▁▃▁▁▁▁▁▁▁▁▁▁▁▃▁▁▁▁▁▁▁▃▁▆ ▁
  1.12 μs         Histogram: frequency by time        3.08 μs <

 Memory estimate: 0 bytes, allocs estimate: 0.

julia> @benchmark my_min($a) evals=100000
BenchmarkTools.Trial: 42 samples with 100000 evaluations.
 Range (min … max):  823.790 ns …   2.346 μs  ┊ GC (min … max): 0.00% … 0.00%
 Time  (median):     828.805 ns               ┊ GC (median):    0.00%
 Time  (mean ± σ):     1.194 μs ± 602.326 ns  ┊ GC (mean ± σ):  0.00% ± 0.00%

  █                                                           ▁  
  █▁▁▁▁▁▁▇▁▁▁▁▁▁▁▁▅▁▁▁▁▁▅▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▁▅▅▅▁▁▁▁▁▁▇▁▅█ ▁
  824 ns        Histogram: log(frequency) by time       2.35 μs <

 Memory estimate: 0 bytes, allocs estimate: 0.

julia> versioninfo()
Julia Version 1.11.1
Commit 8f5b7ca12ad (2024-10-16 10:53 UTC)
Build Info:
  Official https://julialang.org/ release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 14 × Intel(R) Core(TM) Ultra 7 155U
  WORD_SIZE: 64
  LLVM: libLLVM-16.0.6 (ORCJIT, alderlake)
Threads: 14 default, 0 interactive, 7 GC (on 14 virtual cores)
Environment:
  JULIA_MAX_NUM_PRECOMPILE_FILES = 100
  JULIA_NUM_THREADS = 14
  JULIA_PKG_PRESERVE_TIERED_INSTALLED = true
4

probably