[petsc-users] Spack build and ptscotch

[Satish Balay]

This is the complexity with maintaining dependencies (and dependencies
of dependencies), and different build systems

- Its not easy to keep the "defaults" in both builds exactly the same.
- And its not easy to expose all "variants" or keep the same variants in both builds.
- And each pkg has its own issues that prevents some combinations to
  work or not [or tested combinations vs untested].

This e-mail query has multiple things:

- understand "why" the current impl of [spack, petsc] build tools are the way they are.
- if they can be improved
- and build use cases that you need working
- [and subsequently your code working]

Addressing them all is not easy - so lets stick with what you need to make progress.

For one - we recommend using latest petsc version [i.e 3.21 - not 3.19] - any fixes we have will address the current release.

> - spack: ptscotch will always be built without parmetis wrappers, can't turn on

diff --git a/var/spack/repos/builtin/packages/petsc/package.py b/var/spack/repos/builtin/packages/petsc/package.py
index b7b1d86b15..ae27ba4c4e 100644
--- a/var/spack/repos/builtin/packages/petsc/package.py
+++ b/var/spack/repos/builtin/packages/petsc/package.py
@@ -268,9 +268,7 @@ def check_fortran_compiler(self):
     depends_on("metis at 5:~int64", when="@3.8:+metis~int64")
     depends_on("metis at 5:+int64", when="@3.8:+metis+int64")
 
-    # PTScotch: Currently disable Parmetis wrapper, this means
-    # nested disection won't be available thought PTScotch
-    depends_on("scotch+esmumps~metis+mpi", when="+ptscotch")
+    depends_on("scotch+esmumps+mpi", when="+ptscotch")
     depends_on("scotch+int64", when="+ptscotch+int64")
 
     depends_on("hdf5@:1.10+mpi", when="@:3.12+hdf5+mpi")

Now you can try:

spack install petsc~metis+ptscotch ^scotch+metis
vs
spack install petsc~metis+ptscotch ^scotch~metis [~metis is the default for scotch]

Note the following comment in spack/var/spack/repos/builtin/packages/scotch/package.py

>>>>
    # Vendored dependency of METIS/ParMETIS conflicts with standard
    # installations
    conflicts("metis", when="+metis")
    conflicts("parmetis", when="+metis")
<<<<<

> - classical: ptscotch will always be built with parmetis wrappers, can't seem to turn off

Looks like spack uses cmake build of ptscotch. PETSc uses Makefile interface. It likely doesn't support turning off metis wrappers [without hacks].

So you might either need to hack scotch build via petsc - or just install it separately - and use it with petsc.

I see  an effort to migrate scotch build in petsc to cmake

https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/merge_requests/7242/__;!!G_uCfscf7eWS!dL00pokNVI6oaNk_chaSyfI1zWFeTgYA9jbRW6n9YT73s51VwLBuXYc-MAJWEKXr8uBgEFrmhFQ_VJOSlvzW6OA$ 
https://urldefense.us/v3/__https://gitlab.com/petsc/petsc/-/merge_requests/7495/__;!!G_uCfscf7eWS!dL00pokNVI6oaNk_chaSyfI1zWFeTgYA9jbRW6n9YT73s51VwLBuXYc-MAJWEKXr8uBgEFrmhFQ_VJOS6OuSrPs$ 

Satish

On Wed, 24 Apr 2024, Daniel Stone wrote:

> 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 seems like something in the
> resulting build of our simulator ends up badly optimised and an mpi
> bottleneck, when I build against
> PETSc built with Spack.
> 
> I've been trying to track this down, and noticed this in the PETSc Spack
> build recipe:
> 
>     # PTScotch: Currently disable Parmetis wrapper, this means
>     # nested disection won't be available thought PTScotch
>     depends_on("scotch+esmumps~metis+mpi", when="+ptscotch")
>     depends_on("scotch+int64", when="+ptscotch+int64")
> 
> 
> 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,
> 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
> 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
> wrappers, etc - will try that).
> 
> 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
> 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:
> - classical: ptscotch will always be built with parmetis wrappers, can't
> seem to turn off
> - spack: ptscotch will always be built without parmetis wrappers, can't
> turn on
> 
> 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.
> 
> Here is the kind of command I give to Spack for PETSc builds, which may
> well be less than ideal:
> 
> spack install petsc at 3.19.1 ~metis +ptscotch ^hdf5 +fortran +hl
> 
> 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
> 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
> 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.
> 
> Thanks,
> 
> Daniel
>