Are you passing messages on the same host? When doing message passing between processes on the same machine, memory mapping and shared memory will be your friends. Check this architecture out for intra-host message passing: https://lmax-exchange.github.io/disruptor/

If you are doing tcp over loopback, the MTU is 64K, IIRC. You should be able to pack more messages per packet. Since you aren't CPU bound, you are probably memory bound.

Also if you on a non-kernelbypass accelerated host, wire-to-application memory takes about 10 micros, so wire-to-memory-to-wire will probably land somewhere around 20 microseconds.

> When I ran this I gave the server and client 2 cores each. Neither were maxing out the cores.

grep for GOMAXPROCS didn't turn up anything so not sure what you mean by that. This may help with core utilization.

   func init() {
       // 
       runtime.GOMAXPROCS(runtime.NumCPU())
       // …
   }