[Libguestfs] [PATCH libnbd v2 8/9] golang: aio_buffer.go: Benchmark copy flows

[Nir Soffer]

Add benchmark for coping a buffer using 3 strategies - reusing same
buffer, making a new uninitialized buffer per copy, and using a zeroed
buffer per copy. This benchmark is the worst possible case, copying a
buffer to memory. Any real I/O will be much slower, hiding the overhead
of allocating or zeroing buffers.

$ go test -run=AioBuffer -bench=Copy -benchtime=5s
goos: linux
goarch: amd64
pkg: libguestfs.org/libnbd
cpu: Intel(R) Core(TM) i7-10850H CPU @ 2.70GHz
BenchmarkAioBufferCopyBaseline-12    	 1142508	      4523 ns/op
BenchmarkAioBufferCopyMake-12        	 1000000	      5320 ns/op
BenchmarkAioBufferCopyMakeZero-12    	  728940	      8218 ns/op

Signed-off-by: Nir Soffer <nsoffer at redhat.com>
---
 golang/libnbd_020_aio_buffer_test.go | 32 ++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/golang/libnbd_020_aio_buffer_test.go b/golang/libnbd_020_aio_buffer_test.go
index e07f8973..f38866e7 100644
--- a/golang/libnbd_020_aio_buffer_test.go
+++ b/golang/libnbd_020_aio_buffer_test.go
@@ -195,10 +195,42 @@ func BenchmarkAioBufferBytes(b *testing.B) {
 func BenchmarkAioBufferSlice(b *testing.B) {
 	buf := MakeAioBuffer(bufferSize)
 	defer buf.Free()
 	var r int
 
 	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
 		r += len(buf.Slice())
 	}
 }
+
+var data = make([]byte, bufferSize)
+
+// Benchmark copying into same buffer, used as baseline for CopyMake and
+// CopyMakeZero benchmarks.
+func BenchmarkAioBufferCopyBaseline(b *testing.B) {
+	buf := MakeAioBufferZero(bufferSize)
+	defer buf.Free()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		copy(buf.Slice(), data)
+	}
+}
+
+// Benchmark overhead of making a new buffer per read.
+func BenchmarkAioBufferCopyMake(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		buf := MakeAioBuffer(bufferSize)
+		copy(buf.Slice(), data)
+		buf.Free()
+	}
+}
+
+// Benchmark overhead of making a new zero buffer per read.
+func BenchmarkAioBufferCopyMakeZero(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		buf := MakeAioBufferZero(bufferSize)
+		copy(buf.Slice(), data)
+		buf.Free()
+	}
+}
-- 
2.34.1