.

syspread_test.go

@@ -4,13 +4,14 @@ import (
 	"crypto/rand"
 	"fmt"
 	"os"
+	"syscall"
 	"testing"
 )
 
 
 // xpread is pread(2) but aborts on an error or when fewer bytes was read
-func xpread(f *os.File, buf []byte, offset int64) {
-	n, err := f.ReadAt(buf, offset)
+func xpread(fd int, buf []byte, offset int64) {
+	n, err := syscall.Pread(fd, buf, offset)
 	if err != nil {
 		panic(err)
 	}
@@ -19,38 +20,77 @@ func xpread(f *os.File, buf []byte, offset int64) {
 	}
 }
 
-// BenchmarkPread1 benchmarks pread syscall when reading 1 byte from a file on tmpfs
-func BenchmarkPread1(b *testing.B) {
+// xreadat is ReadAt but aborts on an error or when fewer bytes was read
+func xreadat(f *os.File, buf []byte, offset int64) {
+	n, err := f.ReadAt(buf, offset)
+	if err != nil {
+		panic(err)
+	}
+	if n != len(buf) {
+		panic(fmt.Errorf("readat(%v) -> %v", len(buf), n))
+	}
+}
+
+// setupXdat4K setups /dev/shm/x.dat with 4K content
+func setupXdat4K(t testing.TB) *os.File {
 	// setup 4K file on a tmpfs
 	f, err := os.Create("/dev/shm/x.dat")
 	if err != nil {
-		b.Fatal(err)
+		t.Fatal(err)
 	}
 
 	buf4K := make([]byte, 4096)
 	_, err = rand.Read(buf4K)
 	if err != nil {
 		// rand promises n = len(buf) <=> err == nil
-		b.Fatal(err)
+		t.Fatal(err)
 	}
 
 	_, err = f.Write(buf4K)
 	if err != nil {
-		b.Fatal(err)
+		t.Fatal(err)
+	}
+
+	return f
+}
+
+
+// BenchmarkReadAt benchmarks os.File.ReadAt when reading 1 byte from a file on tmpfs
+func BenchmarkReadAt1(b *testing.B) {
+	f := setupXdat4K(b)
+	buf1B := make([]byte, 1)
+
+	// warm up
+	xreadat(f, buf1B, 0)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		xreadat(f, buf1B, 0)
+	}
+	b.StopTimer()
+
+	err := f.Close()
+	if err != nil {
+		b.Fatal(f)
 	}
+}
 
+// BenchmarkPread1 benchmarks pread syscall when reading 1 byte from a file on tmpfs
+func BenchmarkPread1(b *testing.B) {
+	f := setupXdat4K(b)
+	fd := int(f.Fd())	// syscall wants fd as int, not uintptr
 	buf1B := make([]byte, 1)
 
 	// warm up
-	xpread(f, buf1B, 0)
+	xpread(fd, buf1B, 0)
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		xpread(f, buf1B, 0)
+		xpread(fd, buf1B, 0)
 	}
 	b.StopTimer()
 
-	err = f.Close()
+	err := f.Close()
 	if err != nil {
 		b.Fatal(f)
 	}