> On Aug 11, 2020, at 6:58 AM, Bastian Löhrer <[email protected]>
> wrote:
>
> Dear PETSc users,
>
> we use PETSc in our code.
> Therefore, we have multiple PETSc compilations lying around, each compiled
> differently,
> e.g debug build using an Intel-compiler, optimized build for Intel-CPUs using
> an Intel-compiler, optimized build for AMD-Rome-CPUs using an Intel-compiler,
> several builds using GNU-compilers ...
>
> Prior to compiling our code, we essentially set $PETSC_DIR and $PETSC_ARCH to
> point to a suitable PETSc build.
>
> When I compile such an optimized PETSc build aimed at Intel-CPUs and using an
> Intel-compiler I do so with
>
> COPTFLAGS="-axCOMMON-AVX512,CORE-AVX2,AVX ..."
>
> to address all Intel processors available on our cluster.
>
> However, I recently noticed that the PETSc compilation provided by our
> HPC-administrators was compiled with -march=native.
> Does that make sense? If so this implies that my optimization flags are
> unnecessary, does it not?
>
> I imagine that when using a PETSc previously compiled with march=native and I
> compile that into my code on a CPU different from the one that has been used
> when compiling PETSc, I end up without optimizations of PETSc. Is that
> correct?
This is a good question that suggests maybe we should add a check in PETSc.
At runtime could we compare the options used for the compile (and what was
built in the .o) to the hardware it is being run on and produce a warning if
they are out of wack or one could do better? Presumably one could also do this
with non-Intel hardware and GPUs also? Then at least users would know when they
copied excutables to other hardware that they are not the best possible
optimization for what they are running on.
Barry
>
> Best,
> Bastian
>
