VASP Forum

Hi VASP developers,

I hope you are doing well.

I have installed the GPU version of VASP, and I got a speedup of 12x for my system with 82 atoms compared to the CPU-only version. I would like to optimize some settings to fully utilize my cluster’s capabilities, especially as I plan to scale to larger systems with more atoms (100 Pt atoms).

Currently, I have access to 2 GPUs and 40 CPU cores per node, and 4 nodes in total. I am running a geometry optimization on a single node using the two GPUs, with NTASKS=2 and 16 CPUs per task. I use k-point parallelization with KPAR=2 and didn't specify NPAR (default). Given this setup, is there a way to further increase the per-node performance with the resources available? Which parameters (e.g., NCORE, NPAR, or others) should I prioritize adjusting first for benchmarking and improved scaling?

Thank you for your guidance, and happy to provide more info if needed.

Hi Karianaandrea,

Setting KPAR is a good start. Depending on the number of k-points you have, it may be worth increasing this further to increase savings. The other tag that you can test is NSIM, which sets the number of bands that are simultaneously optimised by the RMM-DIIS algorithm. You cannot modify NCORE to optimised CPUS when usign GPUS, as you would normally do, as this would adversely affect performance. There is more information about GPUs using VASP in the OpenACC GPU port of VASP wiki page.

Does this answer your question?

Best wishes,

Chris

Hi Christopher,

This is great—thanks! I’ll give it a try with a higher KPAR. I read somewhere that the number of k-points should be divisible by KPAR. Does it cause any issues if it's not? I assume I’d just incur a performance penalty due to load imbalance and less efficient use of resources, but I’m not sure if there’s any further impact on convergence or results in general

Thanks a lot

Hi Kariana-Andrea,

Sorry for my slow reply, I'd missed your message among the other posts. You are correct, the number of k-points must be divisible by KPAR. If it is not, it can make the calculation unstable.

Best wishes,

Chris