Yeah, sorry, forgot I had changed the group size to 512, though it only impacts the initial time to compute the kangaroos, not the kernel performance. Some people here claim to get to 4 Gk/s on a RTX 4090, I did not investigate too much what the best grid size would actually be, I gave up trying as soon as the GPU -check flag was filling the stdout with "warning: xxxxx DPs were lost" and "item not found"...