feat(vm): support live change of cpu fractions

build/components/versions.yml

@@ -3,7 +3,7 @@ firmware:
   libvirt: v10.9.0
   edk2: stable202411
 core:
-  3p-kubevirt: v1.6.2-v12n.28
+  3p-kubevirt: v1.6.2-v12n.30
   3p-containerized-data-importer: v1.60.3-v12n.18
   distribution: 2.8.3
 package:

images/virtualization-artifact/pkg/controller/kvbuilder/kvvm.go

@@ -318,7 +318,7 @@ func (b *KVVM) setCPUHotpluggable(cores int, coreFraction string) error {
 		domainSpec.CPU = &virtv1.CPU{}
 	}
 
-	fraction, err := GetCPUFraction(coreFraction)
+	fraction, err := ParseCPUCoreFraction(coreFraction)
 	if err != nil {
 		return err
 	}
@@ -440,14 +440,14 @@ func shouldKeepMemoryNonHotpluggable(kvvm *virtv1.VirtualMachine) bool {
 	return false
 }
 
-func GetCPUFraction(cpuFraction string) (int, error) {
+func ParseCPUCoreFraction(cpuFraction string) (int, error) {
 	if cpuFraction == "" {
 		return 100, nil
 	}
 	fraction := intstr.FromString(cpuFraction)
 	value, _, err := getIntOrPercentValueSafely(&fraction)
 	if err != nil {
-		return 0, fmt.Errorf("invalid value for cpu fraction: %w", err)
+		return 0, fmt.Errorf("invalid value for cpu core fraction: %w", err)
 	}
 	return value, nil
 }

images/virtualization-artifact/pkg/controller/vmchange/comparator_cpu.go

@@ -35,8 +35,8 @@ func NewComparatorCPU(featureGate featuregate.FeatureGate) VMSpecFieldComparator
 }
 
 // Compare returns changes in the cpu section.
-// // It supports CPU hotplug mechanism for cores changes.
-// // It requires reboot if cpu fraction is changed or if COU hotplug is disabled.
+// It returns "apply immediate" when cpu core fraction is changed or
+// CPU cores change is compatible with hotplug.
 func (c *comparatorCPU) Compare(current, desired *v1alpha2.VirtualMachineSpec) []FieldChange {
 	coresRestartMsg := ""
 
@@ -50,26 +50,29 @@ func (c *comparatorCPU) Compare(current, desired *v1alpha2.VirtualMachineSpec) [
 		coresChangedAction = ActionRestart
 	}
 
+	fractionChangedAction := ActionApplyImmediate
+
 	// Require reboot if CPU hotplug is not enabled.
 	if !c.featureGate.Enabled(featuregates.HotplugCPUWithLiveMigration) {
 		coresChangedAction = ActionRestart
+		fractionChangedAction = ActionRestart
 	}
 
 	coresChanges := compareInts("cpu.cores", current.CPU.Cores, desired.CPU.Cores, 0, coresChangedAction)
 	if HasChanges(coresChanges) && coresRestartMsg != "" {
 		coresChanges[0].RestartMessage = coresRestartMsg
 	}
-	fractionChanges := compareStrings("cpu.coreFraction", current.CPU.CoreFraction, desired.CPU.CoreFraction, DefaultCPUCoreFraction, ActionRestart)
+	fractionChanges := compareStrings("cpu.coreFraction", current.CPU.CoreFraction, desired.CPU.CoreFraction, DefaultCPUCoreFraction, fractionChangedAction)
 
-	// Yield full replace if both fields changed.
+	// Yield a full replace for cpu section if both fields are changed.
 	if HasChanges(coresChanges) && HasChanges(fractionChanges) {
 		return []FieldChange{
 			{
 				Operation:      ChangeReplace,
 				Path:           "cpu",
 				CurrentValue:   current.CPU,
 				DesiredValue:   desired.CPU,
-				ActionRequired: ActionRestart,
+				ActionRequired: MostDisruptiveAction(coresChangedAction, fractionChangedAction),
 				RestartMessage: coresRestartMsg,
 			},
 		}

images/virtualization-artifact/pkg/controller/vmchange/compare_test.go

@@ -71,7 +71,7 @@ cpu:
 			),
 		},
 		{
-			"restart on cpu section change",
+			"restart on cpu section change when hotplug is disabled",
 			`
 cpu:
   cores: 2
@@ -88,6 +88,24 @@ cpu:
 				requirePathOperation("cpu", ChangeReplace),
 			),
 		},
+		{
+			"immediate apply on cpu section change when hotplug is enabled",
+			`
+cpu:
+  cores: 2
+  coreFraction: 60%
+`,
+			`
+cpu:
+  cores: 6
+  coreFraction: 40%
+`,
+			[]featuregate.Feature{featuregates.HotplugCPUWithLiveMigration},
+			assertChanges(
+				actionRequired(ActionApplyImmediate),
+				requirePathOperation("cpu", ChangeReplace),
+			),
+		},
 		{
 			"no restart cpu.coreFraction from empty to default value",
 			`

images/virtualization-artifact/pkg/controller/vmchange/field_change.go

@@ -16,6 +16,8 @@ limitations under the License.
 
 package vmchange
 
+import "cmp"
+
 type ChangeOperation string
 
 const (
@@ -33,6 +35,12 @@ const (
 	ActionApplyImmediate ActionType = "ApplyImmediate"
 )
 
+var actionDisruptionOrder = map[ActionType]int{
+	ActionNone:           0,
+	ActionApplyImmediate: 1,
+	ActionRestart:        2,
+}
+
 type FieldChange struct {
 	Operation    ChangeOperation `json:"operation,omitempty"`
 	Path         string          `json:"path,omitempty"`
@@ -51,3 +59,31 @@ func HasChanges(changes []FieldChange) bool {
 	}
 	return false
 }
+
+// MostDisruptiveAction returns a most dangerous action from the list.
+func MostDisruptiveAction(actions ...ActionType) ActionType {
+	result := ActionNone
+	for _, action := range actions {
+		// Break immediately if 'action' is the most disruptive action.
+		if action == ActionRestart {
+			return action
+		}
+		if action.Cmp(result) == 1 {
+			result = action
+		}
+	}
+	return result
+}
+
+// Cmp returns 0 if the action is equal to 'other', -1 if the action is less harmless than 'other',
+// or 1 if the action is more disruptive than 'other'.
+func (a ActionType) Cmp(other ActionType) int {
+	aOrder, hasA := actionDisruptionOrder[a]
+	otherOrder, hasOther := actionDisruptionOrder[other]
+	if hasA && hasOther {
+		return cmp.Compare(aOrder, otherOrder)
+	}
+
+	// Should not reach here, but equal is safe.
+	return 0
+}

images/virtualization-artifact/pkg/controller/workload-updater/internal/handler/hotplug.go

@@ -82,5 +82,5 @@ func (h *HotplugHandler) Name() string {
 }
 
 func getHotplugResourcesSum(vm *v1alpha2.VirtualMachine) string {
-	return fmt.Sprintf("cpu.cores=%d,memory.size=%s", vm.Spec.CPU.Cores, vm.Spec.Memory.Size.String())
+	return fmt.Sprintf("cpu.cores=%d,cpu.coreFraction=%s,memory.size=%s", vm.Spec.CPU.Cores, vm.Spec.CPU.CoreFraction, vm.Spec.Memory.Size.String())
 }