GC occurs at the worst time in tight loop (Garbage Collection)

General Usage Performance
82 
Base.@ccallable function julia_set_dB_gain(dB_gain::Cdouble)::Cvoid 
    isCalculationValid[]=false  # Parameter Set, so invalidate current answer
    inputRef[].dB_gain = dB_gain
    return nothing
end

f(x) = ccall("extern julia_set_dB_gain", llvmcall, Cvoid, (Cdouble,), x)


using BenchmarkTools

julia> @benchmark f(1.0)
BenchmarkTools.Trial: 10000 samples with 998 evaluations.
 Range (min … max):  16.092 ns … 230.391 ns  ┊ GC (min … max): 0.00% … 83.13%
 Time  (median):     17.305 ns               ┊ GC (median):    0.00%
 Time  (mean ± σ):   18.390 ns ±   6.985 ns  ┊ GC (mean ± σ):  0.48% ±  2.21%

  ▂     ▆█▄▃▁▅                           ▁▃▂▁▁       ▁         ▂
  █▅▁▄▅▆███████▅▅▇▆▃▃▄▁▁▃▃▄▄▅▄▄▅▆█▇▇▆▅▅▄▄██████▇▆▅▄▅███▇▇▆▅▄▁▃ █
  16.1 ns       Histogram: log(frequency) by time      26.1 ns <

 Memory estimate: 16 bytes, allocs estimate: 1.

That surprised me, but it seems the argument passing is indeed the culprit…

1 Like