Go 1.12 network slowdown on Darwin

main.go

package main

import (
	"fmt"
	"io"
	"log"
	"net"
	"os"
	"sync"
	"sync/atomic"
	"time"
)

func main() {
	switch {
	case len(os.Args) > 1 && os.Args[1] == "bench":
		bench()
	case len(os.Args) > 1 && os.Args[1] == "server":
		server()
	default:
		fmt.Fprintf(os.Stderr, "usage: <command> server|bench\n")
		os.Exit(1)
	}
}

func server() {
	log.Printf("echo server started\n")
	os.RemoveAll("socket")
	ln, err := net.Listen("unix", "socket")
	if err != nil {
		log.Fatal(err)
	}
	defer ln.Close()
	for {
		conn, err := ln.Accept()
		if err != nil {
			log.Fatal(err)
		}
		go func(conn net.Conn) {
			defer conn.Close()
			var packet [256]byte
			for {
				n, err := conn.Read(packet[:])
				if err != nil {
					return
				}
				conn.Write(packet[:n])
			}
		}(conn)
	}
}

func bench() {
	c := 50
	n := 100000
	log.Printf("echo benchmark connecting %d clients\n", c)
	start := time.Now()
	var total int32
	var wg sync.WaitGroup
	wg.Add(c)
	for i := 0; i < c; i++ {
		go func() {
			defer wg.Done()
			conn, err := net.Dial("unix", "socket")
			if err != nil {
				log.Fatal(err)
			}
			defer conn.Close()
			packet := []byte("ping\n")
			for i := 0; i < n/c; i++ {
				conn.Write(packet)
				if _, err := io.ReadFull(conn, packet); err != nil {
					log.Fatal(err)
				}
				if atomic.AddInt32(&total, 1)%3131 == 0 {
					fmt.Printf("\r%.0f ops/sec ",
						float64(total)/time.Since(start).Seconds())
				}
			}
		}()
	}
	wg.Wait()
	fmt.Printf("\r%.0f ops/sec\n",
		float64(total)/time.Since(start).Seconds())
}

Basic networking is a lot slower on Go 1.12 Darwin

go version	arch	op/sec
1.11.5	darwin	265,409
1.12	darwin	16,509
1.11.5	linux	331,180
1.12	linux	359,625

Reproduce

Download go1.11.5 and go1.12

$ go get golang.org/dl/go1.11.5
$ go1.11.5 download
$ go get golang.org/dl/go1.12
$ go1.12 download

go1.11.5-darwin

Open terminal #1 (server)

$ go1.11.5 run main.go server
2019/03/13 10:50:02 echo server started

Open terminal #2 (bench)

$ go1.11.5 run main.go bench
2019/03/13 10:50:51 echo benchmark using 50 clients
265409 ops/sec

go1.12-darwin

Open terminal #1 (server)

$ go1.12 run main.go server
2019/03/13 10:50:02 echo server started

Open terminal #2 (bench)

$ go1.12 run main.go bench
2019/03/13 10:50:51 echo benchmark using 50 clients
16509 ops/sec

go1.11.5-linux

Open terminal #1 (server)

$ go1.11.5 run main.go server
2019/03/13 10:50:02 echo server started

Open terminal #2 (bench)

$ go1.11.5 run main.go bench
2019/03/13 10:50:51 echo benchmark using 50 clients
331180 ops/sec

go1.12-linux

Open terminal #1 (server)

$ go1.12 run main.go server
2019/03/13 11:17:30 echo server started

Open terminal #2 (bench)

$ go1.12 run main.go bench
2019/03/13 11:17:37 echo benchmark using 50 clients
359625 ops/sec

$ go1.11.5 run main.go bench
2019/03/13 11:33:42 echo benchmark connecting 50 clients
267517 ops/sec

$ go1.12 run main.go bench
2019/03/13 11:33:55 echo benchmark connecting 50 clients
95068 ops/sec

Just tested with Go 1.12.1 on macOS Mojave 10.14.3.

go version	arch	op/sec
1.12.1	darwin	15,590

Have same issue

go version	arch	op/sec
both go1.12.4	darwin	63431 ops/sec
both go1.11.5	darwin	204351 ops/sec
server 1.11.5 + client 1.12.4	darwin	114049 ops/sec
server 1.12.4 + client 1.11.5	darwin	115997 ops/sec

Looks like in 1.12.4 runtime spent much time to scheduling and less for networking

top20 from pprof for 1.11.5

Showing top 20 nodes out of 32
      flat  flat%   sum%        cum   cum%
     0.88s 74.58% 74.58%      0.88s 74.58%  syscall.Syscall
     0.10s  8.47% 83.05%      0.10s  8.47%  runtime.pthread_cond_signal
     0.08s  6.78% 89.83%      0.08s  6.78%  runtime.kevent
     0.05s  4.24% 94.07%      0.05s  4.24%  runtime.pthread_cond_wait
     0.03s  2.54% 96.61%      0.03s  2.54%  runtime.freedefer
     0.02s  1.69% 98.31%      0.10s  8.47%  runtime.netpoll
     0.01s  0.85% 99.15%      0.01s  0.85%  runtime.kevent_trampoline
     0.01s  0.85%   100%      0.01s  0.85%  runtime.nanotime
         0     0%   100%      0.68s 57.63%  internal/poll.(*FD).Read
         0     0%   100%      0.23s 19.49%  internal/poll.(*FD).Write
         0     0%   100%      0.91s 77.12%  main.server.func2
         0     0%   100%      0.68s 57.63%  net.(*conn).Read
         0     0%   100%      0.23s 19.49%  net.(*conn).Write
         0     0%   100%      0.68s 57.63%  net.(*netFD).Read
         0     0%   100%      0.23s 19.49%  net.(*netFD).Write
         0     0%   100%      0.01s  0.85%  runtime.asmcgocall
         0     0%   100%      0.03s  2.54%  runtime.deferreturn
         0     0%   100%      0.26s 22.03%  runtime.findrunnable
         0     0%   100%      0.10s  8.47%  runtime.injectglist
         0     0%   100%      0.26s 22.03%  runtime.mcall

same for 1.12.4

Showing top 20 nodes out of 39
      flat  flat%   sum%        cum   cum%
     1.93s 39.55% 39.55%      1.93s 39.55%  runtime.pthread_cond_wait
     0.97s 19.88% 59.43%         1s 20.49%  syscall.syscall
     0.76s 15.57% 75.00%      0.76s 15.57%  runtime.pthread_cond_signal
     0.69s 14.14% 89.14%      0.69s 14.14%  runtime.freedefer
     0.13s  2.66% 91.80%      0.13s  2.66%  runtime.pthread_mutex_unlock
     0.12s  2.46% 94.26%      0.22s  4.51%  runtime.netpoll
     0.09s  1.84% 96.11%      0.09s  1.84%  runtime.kevent
     0.04s  0.82% 96.93%      0.04s  0.82%  runtime.usleep
     0.02s  0.41% 97.34%      1.72s 35.25%  main.server.func2
     0.01s   0.2% 97.54%      0.03s  0.61%  runtime.exitsyscall
     0.01s   0.2% 97.75%      1.95s 39.96%  runtime.semasleep
     0.01s   0.2% 97.95%      0.60s 12.30%  syscall.read
         0     0% 97.95%      0.98s 20.08%  internal/poll.(*FD).Read
         0     0% 97.95%      0.71s 14.55%  internal/poll.(*FD).Write
         0     0% 97.95%      0.98s 20.08%  net.(*conn).Read
         0     0% 97.95%      0.71s 14.55%  net.(*conn).Write
         0     0% 97.95%      0.98s 20.08%  net.(*netFD).Read
         0     0% 97.95%      0.71s 14.55%  net.(*netFD).Write
         0     0% 97.95%      0.69s 14.14%  runtime.deferreturn
         0     0% 97.95%      0.85s 17.42%  runtime.entersyscallblock_handoff

Still continue in 1.12.5

go 1.11     darwin  268.093 ops/sec
go 1.12.5   darwin  71.273 ops/sec