Reuse OpenBLAS installation from Julia distribution

[jiahao]

Currently, PETSc.jl fails to build PETSc on a Linux system without a BLAS package installed at the system level.

Instead, it would be preferable to reuse the OpenBLAS or MKL BLAS installation that comes with Julia, especially if Julia is built from source.

It looks like the relevant ./configure options are

BLAS/LAPACK:
  --with-blas-lib=<libraries: e.g. [/Users/..../libblas.a,...]>
       Indicate the library(s) containing BLAS
  --known-64-bit-blas-indices=<bool>
       Indicate if using 64 bit integer BLAS  current: 0

[jiahao]

Although it looks like the name mangling we do on 64-bit platforms makes it impossible for PETSc to understand.

For reference, the Ubuntu packages needed are installed by apt-get install libopenblas-dev liblapack-dev

PETSc's ./configure script appears to know if it's being run from a script and emits no messages...

[stevengj]

@jedbrown, would PETSc be open to a patch to use a BLAS library with mangled names?

In particular, Julia compiles BLAS with a 64-bit integer interface (instead of the default 32-bit integer API), and to avoid conflicts with other BLAS libraries (when libraries using a 32-bit BLAS are loaded) we rename both the the library (to libopenblas64_.so) and the symbols (by appending 64_, e.g. dgemm64_).

It would be nice to be able to compile PETSc to use the 64-bit BLAS as well, and similarly to link the mangled symbols. This looks easy to do, since petscblaslapack_c.h already defines macros for all of the BLAS and LAPACK symbols.

[stevengj]

(See also OpenMathLib/OpenBLAS#646)

[jedbrown]

Yes, we can add this to PETSc. It'll be a good reason for us to clean up those macros somewhat (because I don't want a combinatorial expansion of that nasty code), but it doesn't look like much effort. Are your 64-bit conventions common or specific to Julia?

[stevengj]

They are specific to Julia. As far as we can tell, there are no common ABI conventions for the 64-bit BLAS, and the situation is something of a mess. (See the linked OpenBLAS discussion and also JuliaLang/julia#4923.)

Basically you should support adding an arbitrary suffix/prefix to the BLAS and LAPACK symbols, maybe as configure options, along with an arbitrary path to the libraries.

[stevengj]

Correction: the 64_ suffix is also used by the 64-bit SunPerf BLAS, apparently.

[nalimilan]

And now that 64_ suffix is also used by a Fedora/EPEL OpenBLAS package.

[stevengj]

I've started a PETSc PR: https://bitbucket.org/petsc/petsc/pull-requests/394