oneAPI & FFTW

Specific Domains GPU
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1

I’m trying oneAPI.jl with FFTW and I get an error when trying to use complex arrays in the GPU.

using oneAPI
using FFTW
a = randn(1024) .+ im*randn(1024);
b = oneArray(a);

fft(a);
fft(b);

For the oneArray case I get

julia> fft(b);
ERROR: ArgumentError: cannot take the host address of a oneArray{ComplexF64, 1}
Stacktrace:
 [1] unsafe_convert(#unused#::Type{Ptr{ComplexF64}}, x::oneArray{ComplexF64, 1})
   @ oneAPI ~/.julia/packages/oneAPI/zydrg/src/array.jl:176
 [2] macro expansion
   @ ~/.julia/packages/FFTW/G3lSO/src/fft.jl:564 [inlined]
 [3] (FFTW.cFFTWPlan{ComplexF64, -1, false, 1, G} where G)(X::oneArray{ComplexF64, 1}, Y::FFTW.FakeArray{ComplexF64, 1}, region::UnitRange{Int64}, flags::UInt32, timelimit::Float64)
   @ FFTW ~/.julia/packages/FFTW/G3lSO/src/FFTW.jl:71
 [4] plan_fft(X::oneArray{ComplexF64, 1}, region::UnitRange{Int64}; flags::UInt32, timelimit::Float64)
   @ FFTW ~/.julia/packages/FFTW/G3lSO/src/fft.jl:684
 [5] plan_fft(X::oneArray{ComplexF64, 1}, region::UnitRange{Int64})
   @ FFTW ~/.julia/packages/FFTW/G3lSO/src/fft.jl:684
 [6] plan_fft(X::oneArray{ComplexF64, 1}; kws::Base.Iterators.Pairs{Union{}, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
   @ FFTW ~/.julia/packages/FFTW/G3lSO/src/fft.jl:693
 [7] plan_fft(X::oneArray{ComplexF64, 1})
   @ FFTW ~/.julia/packages/FFTW/G3lSO/src/fft.jl:693
 [8] fft(x::oneArray{ComplexF64, 1})
   @ AbstractFFTs ~/.julia/packages/AbstractFFTs/JebmH/src/definitions.jl:50
 [9] top-level scope
   @ REPL[15]:1

This error doesn’t happen if oneArray is real. Am I combining FFTW and oneAPI in the right way?
At the end I would like to find out if there is any speedup, but for the moment I’m just trying to see it working.

2

FFTW only works with in-memory arrays. It won’t work arrays that reside on a GPU.

3

oneMKL does have FFT routines, but we don’t have that library wrapped, let alone integrated with AbstractFFTs such that the fft method would just work (as it does with CUDA.jl).