i see no mention of "concurrency" in that article. i see that the go programs make heavy use of goroutines so why were they run in "single threaded" mode? just testing their mqttsrv with various levels of GOMAXPROCS rewards with immediate benefits. here are some numbers for pingtest and loadtest in Go for varying levels of GOMAXPROCS for them and the server:

(pingtest/mqtt gomaxprocs) vs pingtest, reporting "elapsed time":

  1x1  5.8s
  2x1  6.0s
  4x1  6.0s
  8x1  6.1s
  16x1 6.1s

  1x2  5.5s
  2x2  3.5s
  4x2  3.4s
  8x2  3.5s
  16x2 3.5s

  1x4  5.4s
  2x4  3.6s
  4x4  3.3s
  8x4  3.4s
  16x4 3.7s

same thing but for loadtest, reported value is "messages/sec":

  1x1  75521
  2x1  76523
  4x1  77477
  8x1  74613
  16x1 73678

  1x2   71439
  2x2  100571
  4x2   93426
  8x2  108938
  16x2  97593

  1x4   71390
  2x4   87426
  4x4   98746
  8x4   99320
  16x4 119692

  1x8   64413
  2x8   87445
  4x8  102953
  8x8  120720
  16x8 106842

(note that the loadtest doesn't look like it takes long enough to be meaningful in its default)

as always with benchmarks, caveat emptor, but in my opinion go does just fine.