[yuliyp]

If you have a single TCP connection, all the data flows through that connection, ultimately serializing at least some of the processing. Given that the workers are just responding with OK, no matter how many CPU cores you give to that you're still bound by the throughput of the IO thread (well by the minimum of the client and server IO thread). If you want more than 1 IO thread to share the load, you need more than one TCP connection.

[atombender]

When I started out using the gRPC SDK in Go, I was really surprised to find that it created just one connection per client. You'd think someone had made a multiplexing client wrapper, but I haven't been able to find one, so inevitably I've just written lightweight pooling myself. (Actually, I did come across one, but the code was very low quality.)