[Wien] FFTW and ifx/icx issue relevant to WIEN2k
Peter Blaha
peter.blaha at tuwien.ac.at
Wed Sep 10 15:06:00 CEST 2025
I recently tried it. Intels fft in the mkl is even a bit faster than
fftw3 and it works fine in the sequential code, probably except 3ddens !
But because there is no mpi-fftw with Intel, one needs to have the fftw3
anyway.
The intel fftw (cdftlib) is maybe an alternative for a stand-alone
PC/laptop compilation (if you don't need 3ddens).
Am 10.09.2025 um 14:28 schrieb Laurence Marks:
> Just to clarify one statement I made: linking against both your own fftw
> & Intel's is very dangerous. It may be that some subroutines will come
> from your library, some from Intel's and there is no reason they should
> be compatible. Only use one of the two.
>
> N.B., I am not certain that the Intel fftw is compatible with W2k. I
> tried some years ago and decided I was wasting time on non-critical
> code, so only use fftw3. If someone is using cdft please post here.
>
> ___
> Emeritus Professor Laurence Marks (Laurie)
> Department of Materials Science and Engineering, Northwestern University
> www.numis.northwestern.edu <http://www.numis.northwestern.edu>
> "Research is to see what everybody else has seen, and to think what
> nobody else has thought" Albert Szent-Györgyi
>
> On Wed, Sep 10, 2025, 01:51 Fecher, Gerhard <fecher at uni-mainz.de
> <mailto:fecher at uni-mainz.de>> wrote:
>
> more comments
> I could not find that zenver5 is a valid CPU architecture for ixc or
> ifx on https://www.intel.com/content/www/us/en/docs/fortran-
> compiler/developer-guide-reference/2025-2/march.html <https://
> www.intel.com/content/www/us/en/docs/fortran-compiler/developer-
> guide-reference/2025-2/march.html>
> (this concerns also other CPU dependent compiler switches -x, -ax, -
> arch, there is no zenverX)
> It seems it was just used by a "beginner" hoshi on https://
> community.intel.com/t5/Intel-Fortran-Compiler/Compilation-error-
> with-fast-on-AMD-Ryzen-9-9900X-using-ifx/td-p/1712241 <https://
> community.intel.com/t5/Intel-Fortran-Compiler/Compilation-error-
> with-fast-on-AMD-Ryzen-9-9900X-using-ifx/td-p/1712241>
> I would guess -march=znver5 (because it can be used with the GNU
> compilers) is just ignored why should Intel be interested to write
> an optimized comnpiler for AMD CPU's ?
> Did you ever test whether -march=znver5 changes anything ?
> As mentioned earlier -axCORE-AVX512, -axCORE-AVX2 or a combination
> of both may work on AMD processors (at least they don't slow the
> programm seriuously, and I didn't find dead electrons)
>
> There was already a lot of discussion on FFTW3 and ELPA at the
> beginning of the year
>
> Ciao
> Gerhard
>
> DEEP THOUGHT in D. Adams; Hitchhikers Guide to the Galaxy:
> "I think the problem, to be quite honest with you,
> is that you have never actually known what the question is."
>
> ====================================
> Dr. Gerhard H. Fecher
> Institut of Physics
> Johannes Gutenberg - University
> 55099 Mainz
> ________________________________________
> Von: Wien [wien-bounces at zeus.theochem.tuwien.ac.at <mailto:wien-
> bounces at zeus.theochem.tuwien.ac.at>] im Auftrag von Laurence Marks
> [laurence.marks at gmail.com <mailto:laurence.marks at gmail.com>]
> Gesendet: Dienstag, 9. September 2025 23:20
> An: A Mailing list for WIEN2k users
> Betreff: Re: [Wien] FFTW and ifx/icx issue relevant to WIEN2k
>
> Comments.
>
> 1. I have never seen -O3 do anything with icc/ifort except kill
> defenceless electrons and make the code slower. I will be happy to
> be proved wrong with ifx/icx.
> 2. I always use -mkl, rather than making mistakes chasing how
> intel changes its libraries.
> 3. I think you might have issues with -mkl_cdft (intel's version
> of fftw) and FFTW3
>
> On Tue, Sep 9, 2025 at 4:10 PM Straus, Daniel B <dstraus at tulane.edu
> <mailto:dstraus at tulane.edu><mailto:dstraus at tulane.edu
> <mailto:dstraus at tulane.edu>>> wrote:
> Sorry for the long delay in responding—I was set to receive a digest
> of list messages, and it only comes once every couple of weeks.
>
> Yes, this is on a Zen 5 computer, and it is running Rocky Linux 10.
> I am using the Intel compiler and MKL, rather than the one AMD
> provides. IFX and ICX support the march=znver5 flag. All the WIEN2k
> 24.1 patches available as of 9/1 were installed.
>
> To be clear, on my workstation, FFTW still will work with WIEN2k
> even if the autoconf script is not regenerated, but there may be a
> performance impact as it is not using the proper Intel libraries for
> Fortran calls to FFTW. However, 3ddens would then not compile, and
> if I also attempted to use ELPA, then parallel LAPW1 would not
> compile. Regenerating the autoconf script for FFTW and recompiling
> it solved both problems. You should check the config.log for your
> FFTW compilation to see if there is a line such as “ld: cannot find
> -loopopt=0” to see if this error is occurring. For me, the configure
> script continued even after this error, but it was using GNU default
> libraries rather than the Intel provided libraries.
>
> siteconfig_lapw is set to use the ifx and icx compilers, and here
> are the flags under “Options” in siteconfig_lapw I am using the
> following compiler options for WIEN2k with the IFX compiler.
> Current settings:
> M OpenMP switch: -qopenmp
> O Compiler options: -O3 -march=znver5 -traceback -assume
> buffered_io -FR -I$(MKLROOT)/include
> L Linker Flags: $(FOPT) -L$(MKLROOT)/lib -lpthread -
> lm -ldl -liomp5 -Wl,-rpath,$MKLROOT/lib
> P Preprocessor flags '-DParallel'
> R R_LIBS (LAPACK+BLAS): -lmkl_intel_lp64 -lmkl_intel_thread
> -lmkl_core
> F FFTW options: -DFFTW3 -DFFTW_OMP -I/home/software/
> fftw-3.3.10/include
> FFTW-LIBS: -L/home/software/fftw-3.3.10/lib -
> lfftw3 -lfftw3_omp
> X LIBX options:
> LIBXC-LIBS:
>
> For Parallel Options in siteconfig_lapw, here are the flags I am using:
> Your current parallel settings (options and libraries) are:
> C Parallel Compiler: mpiifx
> FP Parallel Compiler Options: -O3 -FR -march=znver5 -fc=ifx
> -traceback -assume buffered_io -I$(MKLROOT)/include
> MP MPIRUN command: mpirun -np _NP_ -machinefile
> _HOSTS_ _EXEC_
> O Parallel OpenMP switch: -qopenmp
> Additional setting for SLURM batch systems (is set to 1 otherwise):
> CN Number of Cores: 1
> Libraries:
> Sp SCALAPACK: -L$(MKLROOT)/lib
> -
> lmkl_scalapack_lp64
> -L$(MKLROOT)/
> lib -lmkl_blacs_intelmpi_lp64
> E ELPA options: -DELPA -I/home/software/
> elpa-2025.06.001/include/elpa-2025.06.001/elpa
> -I/home/
> software/elpa-2025.06.001/include/elpa-2025.06.001/modules
> ELPA-LIBS: -lelpa -L/home/software/
> elpa-2025.06.001/lib -Wl,-rpath=/home/software/elpa-2025.06.001/lib
> RP Parallel-Libs: $(R_LIBS) -lmkl_cdft_core
>
> In case it’s relevant here is what I passed to the configure script
> for FFTW3 (after regenerating the script with autoconf):
> module load oneapi/2025.2.0
> ./configure --prefix=/home/software/fftw-3.3.10 CC="mpiicx -cc=icx"
> MPICC="mpiicx -cc=icx" F77="mpiifx -fc=ifx" FFLAGS="-O3 -
> march=znver5 -I"${MKLROOT}/include"" CFLAGS="-O3 -march=znver5 -
> I"${MKLROOT}/include"" CXXFLAGS="-I"${MKLROOT}/include"" LDFLAGS="-
> L${MKLROOT}/lib -lmkl_scalapack_lp64 -lmkl_cdft_core -
> lmkl_intel_lp64 -lmkl_intel_thread -lmkl_core -
> lmkl_blacs_intelmpi_lp64 -liomp5 -lpthread -lm -ldl" --enable-
> option-checking=fatal --enable-avx512 --enable-avx2 --enable-mpi --
> enable-openmp --enable-threads
>
> And for ELPA:
> module load oneapi/2025.2.0
> ./configure --prefix=/home/software/elpa-2025.06.001 CC="mpiicx -
> cc=icx" CXX="mpiicpx -cxx=icpx" FC="mpiifx -fc=ifx" CFLAGS="-O3 -
> march=znver5 -I"${MKLROOT}/include"" FCFLAGS="-O3 -march=znver5 -
> I"${MKLROOT}/include"" CXXFLAGS="-O3 -march=znver5 -I"${MKLROOT}/
> include"" LDFLAGS="-L${MKLROOT}/lib -lmkl_scalapack_lp64 -
> lmkl_cdft_core -lmkl_intel_lp64 -lmkl_intel_thread -lmkl_core -
> lmkl_blacs_intelmpi_lp64 -liomp5 -lpthread -lm -ldl" --enable-
> option-checking=fatal --with-mpi=yes --enable-openmp=yes
>
> Hopefully this is helpful.
>
>
>
> Daniel Straus
> Assistant Professor
> Department of Chemistry
> Tulane University
> 5088 Percival Stern Hall
> 6400 Freret Street
> New Orleans, LA 70118
> (504) 862-3585
> http://straus.tulane.edu/ <http://straus.tulane.edu/>
>
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>
> --
> Emeritus Professor Laurence Marks (Laurie)
> Northwestern University
> Webpage<http://www.numis.northwestern.edu <http://
> www.numis.northwestern.edu>> and Google Scholar link<http://
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> "Research is to see what everybody else has seen, and to think what
> nobody else has thought", Albert Szent-Györgyi
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Peter Blaha, Inst. f. Materials Chemistry, TU Vienna, A-1060 Vienna
Phone: +43-158801165300
Email: peter.blaha at tuwien.ac.at
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