Created
August 15, 2015 02:22
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Benchmarking Go Mutex overhead
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| package main | |
| import ( | |
| "fmt" | |
| "sync" | |
| ) | |
| type unlocked struct { | |
| i int | |
| } | |
| type locked struct { | |
| i int | |
| l sync.Mutex | |
| } | |
| func (c *unlocked) add() { | |
| c.i++ | |
| } | |
| func (c *locked) add() { | |
| c.l.Lock() | |
| defer c.l.Unlock() | |
| c.i++ | |
| } | |
| func main() { | |
| fmt.Println("ok") | |
| } |
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| package main | |
| import "testing" | |
| func TestLocked_add(t *testing.T) { | |
| c := locked{} | |
| c.add() | |
| if c.i != 1 { | |
| t.Errorf("Expected 1 but got %d", c.i) | |
| } | |
| } | |
| func BenchmarkLocked_add(t *testing.B) { | |
| c := locked{} | |
| for i := 0; i < t.N; i++ { | |
| c.add() | |
| } | |
| if c.i != t.N { | |
| t.Errorf("Expected %d, but got %d", t.N, c.i) | |
| } | |
| } | |
| func TestUnlocked_add(t *testing.T) { | |
| c := unlocked{} | |
| c.add() | |
| if c.i != 1 { | |
| t.Errorf("Expected 1 but got %d", c.i) | |
| } | |
| } | |
| func BenchmarkUnlocked_add(t *testing.B) { | |
| c := unlocked{} | |
| for i := 0; i < t.N; i++ { | |
| c.add() | |
| } | |
| if c.i != t.N { | |
| t.Errorf("Expected %d, but got %d", t.N, c.i) | |
| } | |
| } |
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| $ go test -v -bench . | |
| === RUN TestLocked_add | |
| --- PASS: TestLocked_add (0.00s) | |
| === RUN TestUnlocked_add | |
| --- PASS: TestUnlocked_add (0.00s) | |
| PASS | |
| BenchmarkLocked_add 10000000 143 ns/op | |
| BenchmarkUnlocked_add 1000000000 2.41 ns/op | |
| ok _/home/hippo/test/mutex-bench 4.226s |
Defer's performance was improved from Go 1.14 https://golang.org/doc/go1.14#runtime
go version go1.16.4 darwin/amd64
Code
func (c *locked) addWithoutDefer() {
c.l.Lock()
c.i++
c.l.Unlock()
}
func (c *locked) addWithDefer() {
c.l.Lock()
defer c.l.Unlock()
c.i++
}Result
goos: darwin
goarch: amd64
pkg: defer
cpu: Intel(R) Core(TM) i7-9750H CPU @ 2.60GHz
BenchmarkLocked_addWithoutDefer
BenchmarkLocked_addWithoutDefer-12 96066108 12.30 ns/op
BenchmarkLocked_addWithDefer
BenchmarkLocked_addWithDefer-12 92623209 12.95 ns/op
BenchmarkUnlocked_add
BenchmarkUnlocked_add-12 891768594 1.322 ns/op
go1.21.3 darwin/arm64
go test -v -bench .
=== RUN TestLocked_add
--- PASS: TestLocked_add (0.00s)
=== RUN TestUnlocked_add
--- PASS: TestUnlocked_add (0.00s)
goos: darwin
goarch: arm64
pkg: awesomeProject
BenchmarkLocked_add
BenchmarkLocked_add-12 87840225 13.77 ns/op
BenchmarkUnlocked_add
BenchmarkUnlocked_add-12 1000000000 0.3220 ns/op
PASS
ok awesomeProject 2.228s
For those coming from internet: this benchmarks nothing fastpath that is atomic CAS because benchmark does not access mutex in parallel.
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go version go1.11.2 darwin/amd64
Most of the slowdown comes from defer. When rewritten as
… then the numbers go down to: