AoS vs SoA particle data and GPU memory coalescing

[BenWibking]

Hi,

I am reading the Particles documentation (https://amrex-codes.github.io/amrex/docs_html/Particle.html#arrays-of-structs-and-structs-of-arrays) and it looks like some data is always stored in array-of-structs form.

Based on how memory coalescing works, I would have expected structs-of-arrays form to be generically more efficient. Is this not the case in practice? Or are there other reasons to store it this way?

Thanks,
Ben

[atmyers]

Hi Ben,

Yes, in my experience the SoA format is generally more efficient. Originally, all particle data was stored in AoS form, and the fact the positions and ids still are is a remnant of that history. There are plans to relax this constraint this summer with @ax3l and @Thierry992.

[BenWibking]

Ok, thanks. We'll keep that in mind when working on the particles implementation in Quokka.