Intel® oneAPI Math Kernel Library Developer Reference - C

Multi-threaded FFTW

This section discusses multi-threaded FFTW wrappers only. MPI FFTW wrappers, available only with Intel® oneAPI Math Kernel Library for the Linux* and Windows* operating systems, are described ina separate section.

Unlike the original FFTW interface, every computational function in the FFTW2 interface to Intel® oneAPI Math Kernel Library provides multithreaded computation by default, with the maximum number of threads permitted in FFT functions (see "Techniques to Set the Number of Threads" inIntel® oneAPI Math Kernel Library Developer Guide). To limit the number of threads, call the threaded FFTW computational functions:

void fftw_threads(int nthreads, fftw_plan plan, int howmany, fftw_complex *in, int istride, int idist, fftw_complex *out, int ostride, int odist);

void fftw_threads_one(int nthreads, rfftwnd_plan plan, fftw_complex *in, fftw_complex *out);

...

void rfftwnd_threads_real_to_complex( int nthreads, rfftwnd_plan plan, int howmany, fftw_real *in, int istride, int idist, fftw_complex *out, int ostride, int odist);

Compared to its non-threaded counterpart, every threaded computational function has threads_ as the second part of its name and additional first parameter nthreads. Set the nthreads parameter to the thread limit to ensure that the computation requires at most that number of threads.

Optimization Notice

Intel's compilers may or may not optimize to the same degree for non-Intel microprocessors for optimizations that are not unique to Intel microprocessors. These optimizations include SSE2, SSE3, and SSSE3 instruction sets and other optimizations. Intel does not guarantee the availability, functionality, or effectiveness of any optimization on microprocessors not manufactured by Intel. Microprocessor-dependent optimizations in this product are intended for use with Intel microprocessors. Certain optimizations not specific to Intel microarchitecture are reserved for Intel microprocessors. Please refer to the applicable product User and Reference Guides for more information regarding the specific instruction sets covered by this notice.

Notice revision #20110804

This notice covers the following instruction sets: SSE2, SSE4.2, AVX2, AVX-512.