[petsc-users] configure error with fftw and without mpi

[Matthew Knepley]

On Thu, Nov 25, 2021 at 2:29 PM Fabio Rossi via petsc-users <
petsc-users at mcs.anl.gov> wrote:

> Thanks for the reply.
>
> I am using the system fftw which is provided by the distribution so I am
> not going to install it by using PETSC's install scripts.
>
> I am sorry but I am not confident with the PETSC building system. What
> happens if mpi is installed but the user prefers to compile PETSC with
> --with-mpi=0 configure option? In that case self.mpi.found would be true?
>
> Regarding fftw.c, basically the functions to modify are:
>
> extern PetscErrorCode MatMult_SeqFFTW(Mat,Vec,Vec);
> extern PetscErrorCode MatMultTranspose_SeqFFTW(Mat,Vec,Vec);
> extern PetscErrorCode MatMult_MPIFFTW(Mat,Vec,Vec);
> extern PetscErrorCode MatMultTranspose_MPIFFTW(Mat,Vec,Vec);
> extern PetscErrorCode MatDestroy_FFTW(Mat);
> extern PetscErrorCode VecDestroy_MPIFFTW(Vec);
> extern PetscErrorCode MatCreateVecsFFTW_FFTW(Mat,Vec*,Vec*,Vec*);
> PETSC_EXTERN PetscErrorCode MatCreate_FFTW(Mat A)
>
> The *MPI* function should exist only with PETSC_HAVE_MPI true while inside
> the other functions the number of processors (detected inside the variable
> "size") should be initialized to 1 and support the parallel case only when
> PETSC_HAVE_MPI is true.
>
> As a user of the PETSC library and not programmer (I need to build another
> library which requires it), I want to put your attention to the
> documentation at
>
> https://petsc.org/release/install/install/#doc-config-externalpack
>
> where it's written "PETSc may be built and run without MPI support if
> processing only in serial."
>

This is true, but we cannot control our dependencies.

  Thanks,

    Matt


> which then seems to be true for PETSc itself but not for its dependencies
> because the interface to fftw, right now, depends on MPI. That's the reason
> of this new thread in the mailing list :-)
>
> Fabio
>
> > Il 25/11/2021 17:27 Barry Smith <bsmith at petsc.dev> ha scritto:
> >
> >
> > PETSc's install and use of fftw always requires MPI.
> >
> >   The code in config/BuildSystem/config/packages/fftw.py and
> src/mat/impls/fft/fftw/fftw.c could relatively easily be "fixed" to also
> support building and using FFTW without MPI.
> >
> >    Just change the fftw.py to conditionally pass in
> args.append('--enable-mpi') if self.mpi.found and change
> >
> >  self.deps = [self.mpi,self.blasLapack]
> >
> >  to
> >
> >  self.deps = [self.blasLapack]
> >  self.odeps = [self.mpi]
> >
> > and in fftw.c add #if defined(PETSC_HAVE_MPI) around the parts of the
> code that depend on MPI.
> >
> > We'd welcome a merge request with these enhancements.
> >
> > Barry
> >
> >
> > > On Nov 25, 2021, at 5:15 AM, Fabio Rossi via petsc-users <
> petsc-users at mcs.anl.gov> wrote:
> > >
> > > I am trying to compile petsc with the following options (Gentoo build
> system):
> > >
> > > ./configure --prefix=/usr --build=x86_64-pc-linux-gnu
> --host=x86_64-pc-linux-gnu --mandir=/usr/share/man
> --infodir=/usr/share/info --datadir=/usr/share --sysconfdir=/etc
> --localstatedir=/var/lib --libdir=/usr/lib64/petsc/lib64 scrollOutput=1
> FFLAGS=-O2 -pipe -fPIC CFLAGS=-march=core2 -O2 -pipe -fPIC
> CXXFLAGS=-march=core2 -O2 -pipe -fPIC LDFLAGS=-Wl,-O1 -Wl,--as-needed
> --prefix=/usr/lib64/petsc --with-shared-libraries --with-single-library
> --with-clanguage=c --with-petsc-arch=linux-gnu-c-opt
> --with-precision=double --with-gnu-compilers --with-blas-lapack-lib=-lblas
> -llapack  --with-debugging=0 --with-mpi=0 --with-cc=x86_64-pc-linux-gnu-gcc
> --with-cxx=x86_64-pc-linux-gnu-g++ --with-fortran=1
> --with-fc=x86_64-pc-linux-gnu-gfortran --with-mpi-compilers=0
> --with-scalar-type=real --with-windows-graphics=0 --with-matlab=0
> --with-cmake:BOOL=1 --with-pthread=1 --with-afterimage=0 --without-hdf5
> --with-hypre=0 --without-suitesparse --with-superlu=0 --with-x --with-x11
> --with-ptscot
>  ch=0
> > >  --with-
> > > scalapack=0 --without-mumps --with-imagemagick=0 --with-python=0
> --with-boost --with-fftw
> > >
> > > so MPI support is disabled, and I get the following configure error:
> > >
> > > TESTING: consistencyChecks from
> config.packages.fftw(/var/tmp/portage/sci-mathematics/petsc-3.15.0/work/petsc-3.15.0/config/BuildSystem/config/package.py:963)
> > > TESTING: checkDependencies from
> config.packages.fftw(/var/tmp/portage/sci-mathematics/petsc-3.15.0/work/petsc-3.15.0/config/BuildSystem/config/package.py:872)
> > >
> *******************************************************************************
> > >         UNABLE to CONFIGURE with GIVEN OPTIONS    (see configure.log
> for details):
> > >
> -------------------------------------------------------------------------------
> > > Did not find package MPI needed by fftw.
> > > Enable the package using --with-mpi
> > >
> > > Isn't MPI optional? Where is the error coming from?
> > >
> > > If I disable fftw then it compiles successfully.
> > >
> > > Fabio
>


-- 
What most experimenters take for granted before they begin their
experiments is infinitely more interesting than any results to which their
experiments lead.
-- Norbert Wiener

https://www.cse.buffalo.edu/~knepley/ <http://www.cse.buffalo.edu/~knepley/>
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