Re: [sparta-users] [EXTERNAL] Kokkos limit on command instances

[Max A. <max...@gm...>]

Thank you Stan, indeed it did work.

I'll read a bit more into the resources you sent to better understand what
I'm doing hahah

El mié, 29 oct 2025 a las 21:32, Moore, Stan (<st...@sa...>)
escribió:

> If you want more details on the challenges of virtual functions on the
> GPU, see
> https://kokkos.org/kokkos-core-wiki/ProgrammingGuide/Kokkos-and-Virtual-Functions.html.
> Note that this isn't a Kokkos issue, but rather a GPU issue (we would have
> the same issue if using raw CUDA).
>
> Stan
> ------------------------------
> *From:* Moore, Stan <st...@sa...>
> *Sent:* Wednesday, October 29, 2025 2:27 PM
> *To:* Max Amer <max...@gm...>; SPARTA Mailing list <
> spa...@li...>
> *Subject:* Re: [EXTERNAL] [sparta-users] Kokkos limit on command instances
>
> Hi Max,
>
> The problem is that GPUs don't support virtual functions very well—it is a
> chore to get the vtable into GPU memory. And there can be a performance hit
> of using virtual functions on the device too, so the current workaround is
> to use a compile time limit instead.
>
> Yes you can change the limit in the code then recompile and it should
> work. If that doesn't work please let us know.
>
> Regards,
>
> Stan
> ------------------------------
> *From:* Max Amer <max...@gm...>
> *Sent:* Wednesday, October 29, 2025 6:36 AM
> *To:* SPARTA Mailing list <spa...@li...>
> *Subject:* [EXTERNAL] [sparta-users] Kokkos limit on command instances
>
> Dear developers,
>
> I have recently started using Kokkos for GPU acceleration, and in reusing
> the codes I have for mpi CPU computing I have come across an "issue" that
> is giving me some complications.
>
> I have noticed that there is a hard limit on the number of instances
> commands such as compute_surf or surf_collide have (i.e. I can only use two
> surf_collide diffuse commands, two surf_collide transparent commands, or
> two compute_surf commands). This is an issue when you have a simulation
> where you want to compute more than two surfaces (which is my case) and
> define different surf collide models conditions to each surface.
>
> The update_kokkos.cpp and .h have the variables
>
> #define KOKKOS_MAX_SURF_COLL_PER_TYPE 2
> #define KOKKOS_MAX_TOT_SURF_COLL 10
>
> which set the limit for surf_collide types and total count, I guess a
> similar variable is implemented for compute_surf.
>
> If I change those limits in the code and recompile would I be able to then
> run my simulations with Kokkos for more surfaces and collision models or
> would it not work due to other factors implicit in the structure of the
> code?
>
> GPU acceleration seems very useful but only if I have the same flexibility
> to play with multiple geometry configurations, and I need to know that for
> proper benchmarking.
>
> Thank you in advance for your attention.
> Max
>
> P.S. I sent a couple other emails in the past months that have gone
> unanswered and I don't know if it is because there's no clear or good
> response to them or if maybe they got lost inside a mailbox, but I think
> some points are worth looking over as they can add interesting features to
> SPARTA!
>
>