bug#51536: openblas builds not reproducible on different x86_64 machines

[zimoun]

 Hi Maxim,

On Mon, 1 Nov 2021 at 04:08, Maxim Cournoyer <maxim.cournoyer@gmail.com> wrote:

> Our OpenBLAS package uses DYNAMIC_ARCH=1 to provide optimizations for
> all supported targets, at least of x86 and x86_64.  In theory that seems
> OK, but in practice the builds differ depending on the host CPU.
>
> I've made a build on an old Core2 CPU (Q6700), and another one on
> Berlin.  I've run diffoscope on the result, and got tons of differences;
> here's the tail of the diffoscope output:

Well, it rings this bell [1] and this one [2] too. ;-)

Maybe I am wrong, but speaking about HPC, it seems expected that the
builds differ depending on the host CPU and I am not convinced we can
do better than DYNAMIC_ARCH=1 for performances which somehow sacrifice
reproducibility, IIUC.

1: <https://hpc.guix.info/blog/2018/01/pre-built-binaries-vs-performance/>
2: 
<https://hpc.guix.info/blog/2019/12/optimized-and-portable-open-mpi-packaging/>


Cheers,
simon