[petsc-dev] PETSc optimization

[Liu Wei AWE]

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>
AWE Aldermaston,
Reading, Berkshire, RG7 4PR

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