Reduce CPU consumption and heap allocations of SubsystemMountpoints()

metric/system/cgroup/bytesutil/bytesutil.go

@@ -0,0 +1,70 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package bytesutil
+
+import (
+	"iter"
+)
+
+var asciiSpace = [256]bool{'\t': true, '\n': true, '\v': true, '\f': true, '\r': true, ' ': true}
+
+// Fields returns an iterator that yields the fields of byte array b split around each single
+// ASCII white space character (space, tab, newline, vertical tab, form feed, carriage return).
+// It can be used with range loops like this:
+//
+//	for i, field := range stringutil.Fields(b) {
+//	    fmt.Printf("Field %d: %v\n", i, field)
+//	}
+func Fields(b []byte) iter.Seq2[int, []byte] {
+	return func(yield func(int, []byte) bool) {
+		for i, bi := 0, 0; bi < len(b); i++ {
+			fieldStart := bi
+			// Find the end of the field
+			for bi < len(b) && !asciiSpace[b[bi]] {
+				bi++
+			}
+			if !yield(i, b[fieldStart:bi]) {
+				return
+			}
+			bi++
+		}
+	}
+}
+
+// Split returns an iterator that yields the fields of byte array b split around
+// the given character.
+// It can be used with range loops like this:
+//
+//	for i, field := range stringutil.Split(b, ',') {
+//	    fmt.Printf("Field %d: %v\n", i, field)
+//	}
+func Split(b []byte, sep byte) iter.Seq2[int, []byte] {
+	return func(yield func(int, []byte) bool) {
+		for i, bi := 0, 0; bi < len(b); i++ {
+			fieldStart := bi
+			// Find the end of the field
+			for bi < len(b) && b[bi] != sep {
+				bi++
+			}
+			if !yield(i, b[fieldStart:bi]) {
+				return
+			}
+			bi++
+		}
+	}
+}

metric/system/cgroup/bytesutil/bytesutil_test.go

@@ -0,0 +1,96 @@
+// Licensed to Elasticsearch B.V. under one or more contributor
+// license agreements. See the NOTICE file distributed with
+// this work for additional information regarding copyright
+// ownership. Elasticsearch B.V. licenses this file to you under
+// the Apache License, Version 2.0 (the "License"); you may
+// not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package bytesutil
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestFields(t *testing.T) {
+	tests := []struct {
+		name  string
+		input []byte
+		want  []string
+	}{
+		{
+			name:  "empty array",
+			input: []byte(""),
+			want:  []string{},
+		},
+		{
+			name:  "single white space",
+			input: []byte(" "),
+			want:  []string{"", ""},
+		},
+		{
+			name:  "single word",
+			input: []byte("hello"),
+			want:  []string{"hello"},
+		},
+		{
+			name:  "multiple words",
+			input: []byte("hello world this is a test"),
+			want:  []string{"hello", "world", "this", "is", "a", "test"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			for i, f := range Fields(tt.input) {
+				require.Equal(t, tt.want[i], string(f), "Fields() mismatch at index %d", i)
+			}
+		})
+	}
+}
+
+func TestSplit(t *testing.T) {
+	tests := []struct {
+		name  string
+		input []byte
+		want  []string
+	}{
+		{
+			name:  "empty array",
+			input: []byte(""),
+			want:  []string{},
+		},
+		{
+			name:  "single separator",
+			input: []byte(","),
+			want:  []string{"", ""},
+		},
+		{
+			name:  "single word",
+			input: []byte("hello"),
+			want:  []string{"hello"},
+		},
+		{
+			name:  "multiple words",
+			input: []byte("hello,world,this,is,a,test"),
+			want:  []string{"hello", "world", "this", "is", "a", "test"},
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			for i, f := range Split(tt.input, ',') {
+				require.Equal(t, tt.want[i], string(f), "Split() mismatch at index %d", i)
+			}
+		})
+	}
+}

metric/system/cgroup/reader.go

@@ -27,6 +27,7 @@ import (
 	"time"
 
 	"github.com/elastic/elastic-agent-libs/logp"
+
 	"github.com/elastic/elastic-agent-system-metrics/metric/system/cgroup/cgv1"
 	"github.com/elastic/elastic-agent-system-metrics/metric/system/cgroup/cgv2"
 	"github.com/elastic/elastic-agent-system-metrics/metric/system/resolve"
@@ -361,6 +362,7 @@ func (r *Reader) readControllerList(cgroupsFile string) ([]string, error) {
 	controllers := strings.Split(cgroupsFile, "\n")
 	var cgpath string
 	for _, controller := range controllers {
+		logp.L().Infof("controller: %s", controller)
 		if strings.Contains(controller, "0::/") {
 			fields := strings.Split(controller, ":")
 			cgpath = fields[2]
@@ -370,16 +372,22 @@ func (r *Reader) readControllerList(cgroupsFile string) ([]string, error) {
 	if cgpath == "" {
 		return []string{}, nil
 	}
+	cgpath = filepath.Clean(cgpath) // The path may have a relative prefix like "/../..`, which effectively is "/".
 	cgFilePath := filepath.Join(r.cgroupMountpoints.V2Loc, cgpath, "cgroup.controllers")
 	if cgroupNSStateFetch() && r.rootfsMountpoint.IsSet() {
+		logp.L().Infof("a) V2Loc: %s, ContainerizedRootMount %s", r.cgroupMountpoints.V2Loc, r.cgroupMountpoints.ContainerizedRootMount)
 		cgFilePath = filepath.Join(r.cgroupMountpoints.V2Loc, r.cgroupMountpoints.ContainerizedRootMount, cgpath, "cgroup.controllers")
+	} else {
+		logp.L().Infof("b) V2Loc: %s, ContainerizedRootMount %s", r.cgroupMountpoints.V2Loc, r.cgroupMountpoints.ContainerizedRootMount)
 	}
 
+	logp.L().Infof("reading %s", cgFilePath)
 	controllersRaw, err := os.ReadFile(cgFilePath)
 	if err != nil {
 		return nil, fmt.Errorf("error reading cgroup '%s': file %s: %w", cgpath, cgFilePath, err)
 	}
 
+	logp.L().Infof("controllersRaw: %s", controllersRaw)
 	if len(controllersRaw) == 0 {
 		return []string{}, nil
 	}