5% seems like a surprisingly large overhead. What is k8s doing in this situation that would have that kind of impact?
We haven’t yet evolved Kubernetes services to prefer specific cores and avoid app workloads quite yet (although cpu management is getting closer).
Docker is also somewhat hefty memory wise and you may contend on disk if not careful.
5% seems pretty reasonable to me in general, just as a consequence of having something heavier weight on the same node managing workloads.
I'll note, though, that the 5% number is when using host networking for both Cockroach and the client load generator. Using GKE's default cluster networking through the Docker bridge is closer to 15% worse than running directly on equivalent non-Kubernetes VMs.