This doesn't seem corroborated just from that chart. runtime.systemstack() is one of the calls that allows code to switch from the user stack to the system stac

This doesn't seem corroborated just from that chart. runtime.systemstack() is one of the calls that allows code to switch from the user stack to the system stack, so that non-preemptible (by the goroutine scheduler) code can run, but this doesn't only include garbage collection. It includes all system calls. The kubelet works by synchronizing node state with the definition retrieved from the apiserver across the network, so I would expect it spends a lot of time making system calls just to read from and write to whatever port and/or socket it uses to do that.