Go context switching

main.go

package main

import (
	"fmt"
	"runtime"
	"sync"
	"time"
)

const iterations = 50000

func main() {
	single()

	for i := 2; i <= runtime.NumCPU(); i++ {
		multi(i)
	}
	multi(runtime.NumCPU() * 4)
	multi(runtime.NumCPU() * 16)
	multi(runtime.NumCPU() * 32)
	multi(runtime.NumCPU() * 64)
	multi(runtime.NumCPU() * 256)
}

func single() {
	single := time.Now()
	switcher()
	fmt.Printf("1 switcher: %.2f yields/sec\n", convertToRate(1, time.Since(single)))
}

func multi(switchers int) {
	wg := &sync.WaitGroup{}
	multi := time.Now()
	for proc := 0; proc < switchers; proc++ {
		wg.Add(1)
		go multi_switcher(wg)
	}
	wg.Wait()
	fmt.Printf("%d switchers: %.2f yields/sec\n", switchers, convertToRate(switchers, time.Since(multi)))
}

func multi_switcher(wg *sync.WaitGroup) {
	switcher()
	wg.Done()
}

func switcher() {
	for i := 0; i < iterations; i++ {
		runtime.Gosched()
	}
}

// converts a Duration into a float representing iterations/sec
func convertToRate(workers int, dur time.Duration) float64 {
	return float64(iterations*workers) / (float64(dur) / float64(time.Second))
}

output.txt

    1 switcher:    14_289_797.08 yields/sec
    2 switchers:    5_866_478.94 yields/sec
    3 switchers:    4_832_941.33 yields/sec
    4 switchers:    4_604_051.57 yields/sec
    5 switchers:    4_268_906.99 yields/sec
    6 switchers:    3_982_688.58 yields/sec
    7 switchers:    3_799_103.41 yields/sec
    8 switchers:    3_673_094.58 yields/sec
    9 switchers:    3_513_868.07 yields/sec
    10 switchers:   3_351_813.00 yields/sec
    11 switchers:   3_325_754.64 yields/sec
    12 switchers:   3_150_383.56 yields/sec
    13 switchers:   3_037_539.31 yields/sec
    14 switchers:   2_435_807.77 yields/sec
    15 switchers:   2_326_201.72 yields/sec
    16 switchers:   2_275_610.57 yields/sec
    64 switchers:   2_366_303.83 yields/sec
    256 switchers:  2_400_782.51 yields/sec
    512 switchers:  2_408_757.26 yields/sec
    1024 switchers: 2_418_661.29 yields/sec
    4096 switchers: 2_460_257.29 yields/sec