OCPBUGS-44786: add support for the LLC alignment cpumanager policy option

pkg/kubelet/cm/cpumanager/policy_options.go

@@ -22,9 +22,11 @@ import (
 
 	"k8s.io/apimachinery/pkg/util/sets"
 	utilfeature "k8s.io/apiserver/pkg/util/feature"
+	"k8s.io/klog/v2"
 	kubefeatures "k8s.io/kubernetes/pkg/features"
 	"k8s.io/kubernetes/pkg/kubelet/cm/cpumanager/topology"
 	"k8s.io/kubernetes/pkg/kubelet/cm/topologymanager"
+	"k8s.io/kubernetes/pkg/kubelet/llcalign"
 )
 
 // Names of the options, as part of the user interface.
@@ -56,6 +58,14 @@ func CheckPolicyOptionAvailable(option string) error {
 		return fmt.Errorf("unknown CPU Manager Policy option: %q", option)
 	}
 
+	// must override the base feature gate check. Relevant only for alpha (disabled by default).
+	// for beta options are enabled by default and we totally want to keep the possibility to
+	// disable them explicitly.
+	if alphaOptions.Has(option) && checkPolicyOptionHasEnablementFile(option) {
+		// note that we override the decision and shortcut exit with success
+		// all other cases exit early with failure.
+		return nil
+	}
 	if alphaOptions.Has(option) && !utilfeature.DefaultFeatureGate.Enabled(kubefeatures.CPUManagerPolicyAlphaOptions) {
 		return fmt.Errorf("CPU Manager Policy Alpha-level Options not enabled, but option %q provided", option)
 	}
@@ -173,3 +183,13 @@ func ValidateStaticPolicyOptions(opts StaticPolicyOptions, topology *topology.CP
 	}
 	return nil
 }
+
+func checkPolicyOptionHasEnablementFile(option string) bool {
+	switch option {
+	case PreferAlignByUnCoreCacheOption:
+		val := llcalign.IsEnabled()
+		klog.InfoS("policy option enablement file check", "option", option, "enablementFile", val)
+		return val
+	}
+	return false
+}

pkg/kubelet/cm/cpumanager/policy_options_test.go

@@ -25,6 +25,7 @@ import (
 	pkgfeatures "k8s.io/kubernetes/pkg/features"
 	"k8s.io/kubernetes/pkg/kubelet/cm/cpumanager/topology"
 	"k8s.io/kubernetes/pkg/kubelet/cm/topologymanager"
+	"k8s.io/kubernetes/pkg/kubelet/llcalign"
 )
 
 type optionAvailTest struct {
@@ -246,3 +247,65 @@ func TestPolicyOptionsCompatibility(t *testing.T) {
 		})
 	}
 }
+
+func TestPolicyOptionsAvailableWithEnablement(t *testing.T) {
+
+	type optionAvailEnabTest struct {
+		name                  string
+		option                string
+		featureGate           featuregate.Feature
+		featureGateEnable     bool
+		featureEnablementFlag bool
+		expectedAvailable     bool
+	}
+
+	testCases := []optionAvailEnabTest{
+		{
+			name:                  "all disabled",
+			option:                PreferAlignByUnCoreCacheOption,
+			featureGate:           pkgfeatures.CPUManagerPolicyAlphaOptions,
+			featureGateEnable:     false, // expected standard case
+			featureEnablementFlag: false,
+			expectedAvailable:     false,
+		},
+		{
+			name:                  "all enabled",
+			option:                PreferAlignByUnCoreCacheOption,
+			featureGate:           pkgfeatures.CPUManagerPolicyAlphaOptions,
+			featureGateEnable:     true, // this should not be allowed by OCP profiles
+			featureEnablementFlag: true,
+			expectedAvailable:     true,
+		},
+		{
+			name:                  "enabled by feature gate",
+			option:                PreferAlignByUnCoreCacheOption,
+			featureGate:           pkgfeatures.CPUManagerPolicyAlphaOptions,
+			featureGateEnable:     true, // this should not be allowed by OCP profiles, makes no sense either
+			featureEnablementFlag: false,
+			expectedAvailable:     true,
+		},
+		{
+			name:                  "enabled by enablement file",
+			option:                PreferAlignByUnCoreCacheOption,
+			featureGate:           pkgfeatures.CPUManagerPolicyAlphaOptions,
+			featureGateEnable:     false,
+			featureEnablementFlag: true,
+			expectedAvailable:     true,
+		},
+	}
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			featuregatetesting.SetFeatureGateDuringTest(t, utilfeature.DefaultFeatureGate, testCase.featureGate, testCase.featureGateEnable)
+			oldEnablementFlag := llcalign.TestOnlySetEnabled(testCase.featureEnablementFlag)
+
+			err := CheckPolicyOptionAvailable(testCase.option)
+
+			_ = llcalign.TestOnlySetEnabled(oldEnablementFlag)
+
+			isEnabled := (err == nil)
+			if isEnabled != testCase.expectedAvailable {
+				t.Errorf("option %q available got=%v expected=%v", testCase.option, isEnabled, testCase.expectedAvailable)
+			}
+		})
+	}
+}

pkg/kubelet/llcalign/llcalign.go

@@ -0,0 +1,46 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed 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 llcalign
+
+import (
+	"os"
+)
+
+var (
+	llcAlignmentEnabled  bool
+	llcAlignmentFilename = "/etc/kubernetes/openshift-llc-alignment"
+)
+
+func init() {
+	readEnablementFile()
+}
+
+func readEnablementFile() {
+	if _, err := os.Stat(llcAlignmentFilename); err == nil {
+		llcAlignmentEnabled = true
+	}
+}
+
+func IsEnabled() bool {
+	return llcAlignmentEnabled
+}
+
+func TestOnlySetEnabled(enabled bool) bool {
+	oldEnabled := llcAlignmentEnabled
+	llcAlignmentEnabled = enabled
+	return oldEnabled
+}