[petsc-dev] PETSc optimization

Satish Balay balay at mcs.anl.gov
Tue Aug 8 12:24:03 CDT 2023

Well in spack world - the idea is to get flags from spack and use it in petsc build. Its possible that there are issues in this implementation.

Something spack does is - it internally adds in flags (to the compiler - via its compiler wrapper) - that petsc configure doesn't see.

I see 'spack install cflags=-O3' is working - but not spack install cflags='-O3 -g' [something to debug]

[there is also the alternative of adding flags to compiler spec file]

The other issue is mapping cflags from spack to CFLAGS/COPTFLAGS - in some cases petsc build requires some default CLFAGS to work - and overriding them from spack might cause issues. [again this part is not properly handed]..


On Tue, 8 Aug 2023, Liu Wei   AWE via petsc-dev wrote:

> Hi all
> I am currently building a large software stack using Spack with PETSc 3.19 as part of the dependency library.
> Spotted the following message during the build process
> Using default optimization C flags "-g -O". You might consider manually setting optimal optimization flags for your system with
> COPTFLAGS="optimization flags" see config/examples/arch-*-opt.py for examples
> Previously when we install PETSc manually, optimisation flags are enforced via configure script e.g.
> COPTFLAGS="-g -O3 -march=native"
> CXXOPTFLAGS="-g -O3 -march=native"
> ...
> (or "-g -O3 -xhost" for intel compiler)
> Whilst spack spec syntax allows compiler parameters via cflags/cxxflags/fflags
> https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/petsc/package.py<https://github.com/spack/spack/blob/develop/var/spack/repos/builtin/packages/petsc/package.py#L400>
> the requirement is not obvious, especially in a long build process.
> The question is should optimisation be amended at spack recipe stage or should PETSc configure enforce some compiler optimisation (if -with-debugging=0 is set) ?
> Regards
> Dr Wei Liu
> High Performance Computing
> To chat with me on Teams click here<https://teams.microsoft.com/l/chat/0/0?users=wei.liu@awe.co.uk>
> T: +44 01189 856209
> M: wei.liu at awe.co.uk<mailto:wei.liu at awe.co.uk>
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