Runtime dispatch for plan_fft

General Usage Performance
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1

Hi,

I am learning about JET.jl while optimizing a function that involves FFT. I happened to find that JET.jl detected a runtime dispatch for plan_fft or plan_fft!:

using JET
using FFTW

julia> @report_opt plan_fft!(zeros(ComplexF64, 8))
═════ 1 possible error found ═════
┌ plan_fft!(X::Vector{ComplexF64}) @ FFTW C:\Users\hyzho\.julia\packages\FFTW\mFpUb\src\fft.jl:805
│┌ plan_fft!(X::Vector{ComplexF64}; kws::@Kwargs{}) @ FFTW C:\Users\hyzho\.julia\packages\FFTW\mFpUb\src\fft.jl:805
││┌ plan_fft!(X::Vector{ComplexF64}, region::Tuple{Int64}) @ FFTW C:\Users\hyzho\.julia\packages\FFTW\mFpUb\src\fft.jl:791
│││┌ plan_fft!(X::Vector{ComplexF64}, region::Tuple{Int64}; flags::UInt32, timelimit::Float64, num_threads::Nothing) @ FFTW C:\Users\hyzho\.julia\packages\FFTW\mFpUb\src\fft.jl:801
││││┌ (FFTW.cFFTWPlan{…})(X::Vector{…}, Y::Vector{…}, region::Tuple{…}, flags::UInt32, timelimit::Float64) @ FFTW C:\Users\hyzho\.julia\packages\FFTW\mFpUb\src\FFTW.jl:52
│││││┌ destroy_deferred() @ FFTW C:\Users\hyzho\.julia\packages\FFTW\mFpUb\src\fft.jl:339
││││││┌ foreach(f::typeof(FFTW.unsafe_destroy_plan), itr::Vector{FFTW.FFTWPlan}) @ Base ./abstractarray.jl:3187
│││││││ runtime dispatch detected: f::typeof(FFTW.unsafe_destroy_plan)(%36::FFTW.FFTWPlan)::Any

Is this a performance issue that I should care about?

2

No, because it only affects garbage collection of plans (and only in relatively rare cases where there was thread contention when the initial deallocation was attempted).

Also, the plan_fft call itself shouldn’t be in a performance-critical path — the intended usage of FFTW is that, if performance matters, you should create plans once and then re-use them many times.

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