atomicMax equivalent (and other atomics)

[ascheinb]

Hi all, I'm trying to convert a cuda atomicMax to Kokkos. In general, I see that there are a number of cuda atomics that do not have kokkos equivalents. I think that there is a way to effectively do an atomic max with the available kokkos atomics? In general, it would be nice to have guidance/documentation for the most efficient kokkos equivalent to the various cuda atomics.

[crtrott]

Which other ones are you looking for? AtomicMax and Min is certainly one we should add. Probably we should have all of the ones we also support for reducers.

[ascheinb]

Those are the only ones I need, and it looks like I can use the atomic CAS to get around it. I also had to convert an atomicInc before, which I replaced with a fetch add. It works fine, I was just thinking it might be nice to have a conversion chart in the docs.

[crtrott]

atomic increment should actually be there, but lets make this into a request for min and max.

[DavidPoliakoff]

@crtrott, I actually think this is a good idea more generally, cheat sheets for

"I use Programming Model and am looking to switch to Kokkos, how do I translate Feature into it"

Where Feature might be Parallelism Patterns, Data Placement, Atomics... anything else?

[ascheinb]

Hello all - Did atomic max and min ever get implemented? I was looking through https://github.com/kokkos/kokkos/wiki/Atomic-Operations and didn't see a way to construct an equivalent to atomic max from the existing listed operations.

[mhoemmen]

@ascheinb Here's how Tpetra does atomic max(abs(x), abs(y)) using Kokkos::Impl::atomic_fetch_oper: https://github.com/trilinos/Trilinos/blob/54bc582188ae18a3ef117c4c1ca2d1b3c030cd81/packages/tpetra/core/src/kokkos_refactor/Tpetra_KokkosRefactor_Details_MultiVectorDistObjectKernels.hpp#L768

[crtrott]

@janciesko You wanna do this? Or maybe @jrmadsen ?

[dalg24]

@janciesko will look into this