Go Benchmark

Printing

Compare fmt's Print, Printf, and Println variants, with and without a target writer.

fmtprintio

The Go fmt package provides several functions for printing output. This benchmark compares Print, Println, and Printf (which write to stdout) against their Fprint, Fprintln, and Fprintf counterparts (which write to an io.Writer, here io.Discard). The Fprint variants avoid the overhead of going through os.Stdout, making them noticeably faster.

linux/amd64AMD Ryzen 9 9950X3D 16-Core Processorbenchmarks/printing

Compare atCPUs

1 CPU

Fastest

Fprintln

16.83 ns/op

Slowest

108.4 ns/op · 6.4x slower

32 CPUs

Fastest

Fprintln

18.35 ns/op

Slowest

112.33 ns/op · 6.1x slower

Performance Comparison (lower is better)

CPU:

Fprintln #

Fastest

Uses fmt.Fprintln to write a string followed by a newline directly to io.Discard, bypassing stdout entirely.

CPU Scaling (lower is better)

const s = "Hello, World!"

// Fprintln writes to an io.Writer with a trailing newline.
func BenchmarkFprintln_run(b *testing.B) {
	for i := 0; i < b.N; i++ {
		fmt.Fprintln(io.Discard, s)
	}
}

1 CPU

1.1xfaster(6%)thanFprint

1.2xfaster(21%)thanFprintf

6.4xfaster(544%)thanPrint

6.3xfaster(534%)thanPrintf

6.2xfaster(521%)thanPrintln

32 CPUs

1xfaster(4%)thanFprint

1.2xfaster(20%)thanFprintf

6.1xfaster(512%)thanPrint

6.1xfaster(512%)thanPrintf

6.1xfaster(507%)thanPrintln

Fprint #

Uses fmt.Fprint to write a string directly to io.Discard, bypassing stdout entirely.

CPU Scaling (lower is better)

const s = "Hello, World!"

// Fprint writes to an io.Writer.
func BenchmarkFprint_run(b *testing.B) {
	for i := 0; i < b.N; i++ {
		fmt.Fprint(io.Discard, s)
	}
}

1 CPU

1.1xfaster(14%)thanFprintf

1.1xslower(6%)thanFprintln

6.1xfaster(507%)thanPrint

6xfaster(497%)thanPrintf

5.8xfaster(485%)thanPrintln

32 CPUs

1.2xfaster(16%)thanFprintf

1xslower(4%)thanFprintln

5.9xfaster(489%)thanPrint

5.9xfaster(488%)thanPrintf

5.8xfaster(484%)thanPrintln

Fprintf #

Uses fmt.Fprintf with a %s verb to write a formatted string directly to io.Discard, bypassing stdout entirely.

CPU Scaling (lower is better)

const s = "Hello, World!"

// Fprintf writes a formatted string to an io.Writer.
func BenchmarkFprintf_run(b *testing.B) {
	for i := 0; i < b.N; i++ {
		fmt.Fprintf(io.Discard, "%s\n", s)
	}
}

1 CPU

1.1xslower(14%)thanFprint

1.2xslower(21%)thanFprintln

5.3xfaster(434%)thanPrint

5.3xfaster(425%)thanPrintf

5.1xfaster(414%)thanPrintln

32 CPUs

1.2xslower(16%)thanFprint

1.2xslower(20%)thanFprintln

5.1xfaster(409%)thanPrint

5.1xfaster(409%)thanPrintf

5xfaster(405%)thanPrintln

Println #

Uses fmt.Println to write a string followed by a newline to stdout (redirected to /dev/null).

CPU Scaling (lower is better)

const s = "Hello, World!"

// Println writes to stdout with a trailing newline.
func BenchmarkPrintln_run(b *testing.B) {
	os.Stdout, _ = os.Open(os.DevNull)

	for i := 0; i < b.N; i++ {
		fmt.Println(s)
	}
}

1 CPU

5.8xslower(485%)thanFprint

5.1xslower(414%)thanFprintf

6.2xslower(521%)thanFprintln

1xfaster(4%)thanPrint

1xfaster(2%)thanPrintf

32 CPUs

5.8xslower(484%)thanFprint

5xslower(405%)thanFprintf

6.1xslower(507%)thanFprintln

1xfaster(1%)thanPrint

1xfaster(1%)thanPrintf

Printf #

Uses fmt.Printf with a %s verb to write a formatted string to stdout (redirected to /dev/null).

CPU Scaling (lower is better)

const s = "Hello, World!"

// Printf writes a formatted string to stdout.
func BenchmarkPrintf_run(b *testing.B) {
	os.Stdout, _ = os.Open(os.DevNull)

	for i := 0; i < b.N; i++ {
		fmt.Printf("%s\n", s)
	}
}

1 CPU

6xslower(497%)thanFprint

5.3xslower(425%)thanFprintf

6.3xslower(534%)thanFprintln

1xfaster(2%)thanPrint

1xslower(2%)thanPrintln

32 CPUs

5.9xslower(488%)thanFprint

5.1xslower(409%)thanFprintf

6.1xslower(512%)thanFprintln

Same speed asPrint

1xslower(1%)thanPrintln

Print #

Slowest

Uses fmt.Print to write a string to stdout (redirected to /dev/null).

CPU Scaling (lower is better)

const s = "Hello, World!"

// Print writes to stdout.
func BenchmarkPrint_run(b *testing.B) {
	os.Stdout, _ = os.Open(os.DevNull)

	for i := 0; i < b.N; i++ {
		fmt.Print(s)
	}
}

1 CPU

6.1xslower(507%)thanFprint

5.3xslower(434%)thanFprintf

6.4xslower(544%)thanFprintln

1xslower(2%)thanPrintf

1xslower(4%)thanPrintln

32 CPUs

5.9xslower(489%)thanFprint

5.1xslower(409%)thanFprintf

6.1xslower(512%)thanFprintln

Same speed asPrintf

1xslower(1%)thanPrintln

Contributors

MarvinJWendt