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Hi PETSc community, I've been looking at using Spack to build PETSc, in particular I need to disable the default metis/parmetis dependencies and use PTScotch instead, for our software. I've had quite a bit of trouble with this - it
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<div dir="ltr"><div>Hi PETSc community,</div><div><br></div><div>I've been looking at using Spack to build PETSc, in particular I need to disable the default metis/parmetis dependencies and use PTScotch instead, for our software.</div><div>I've had quite a bit of trouble with this - it seems like something in the resulting build of our simulator ends up badly optimised and an mpi bottleneck, when I build against </div><div>PETSc built with Spack.</div><div><br></div><div>I've been trying to track this down, and noticed this in the PETSc Spack build recipe:</div><div><br></div><div> # PTScotch: Currently disable Parmetis wrapper, this means<br> # nested disection won't be available thought PTScotch<br> depends_on("scotch+esmumps~metis+mpi", when="+ptscotch")<br> depends_on("scotch+int64", when="+ptscotch+int64")</div><div><br></div><div><br></div><div>Sure enough - when I compare the build with Spack and a traditional build with ./configure etc, I see that, in the traditional build, Scotch is always built with the parmetis wrapper,</div><div>but not in the Scotch build. In fact, I'm not sure how to turn off the parmetis wrapper option for scotch, in the case of a traditional build (i.e. there doesn't seem to be a flag in the <br></div><div>configure script for it) - which would be a very useful test for me (I can of course do similar experiments by doing a classical build of petsc against ptscotch built separately without the</div><div>wrappers, etc - will try that).</div><div><br></div><div>Does anyone know why the parmetis wrapper is always disabled in the spack build options? Is there something about Spack that would prevent it from working? It's notable - but I might <br></div><div>be missing it - that there's no warning that there's a difference in the way ptscotch is built between the spack and classical builds:</div><div>- classical: ptscotch will always be built with parmetis wrappers, can't seem to turn off</div><div>- spack: ptscotch will always be built without parmetis wrappers, can't turn on</div><div><br></div><div>Any insight at all would be great, I'm new to Spack and am not super familiar with the logic that goes into setting up builds for the system.<br></div><div><br></div><div>Here is the kind of command I give to Spack for PETSc builds, which may well be less than ideal:</div><div><br></div><div>spack install petsc@3.19.1 ~metis +ptscotch ^hdf5 +fortran +hl</div><div><br></div><div>Separate tiny note: when building with hdf5, I have to ensure that the fortran flag is set for it, as above. There's a fortran flag for the petsc module, default true, and a fortran flag for the hdf5</div><div>module, default false. A naive user (i.e. me), will see the fortran flag for the petsc module, and assume that all dependencies will correspondingly be built with fortran capability - then see that</div><div>hdf5.mod is missing when trying to build their software against petsc. It's the old "did you forget --with-hdf5-fortran-bindings?" issue, resurrected for a new build system.</div><div><br></div><div>Thanks,</div><div><br></div><div>Daniel<br></div></div>