refactor(sim/compute): Move interference logic into VmInterferenceMember

This change updates the design of the VM interference model, where we
move more of the logic into the `VmInterferenceMember` interface. This
removes the dependency on the `VmInterferenceModel` for the hypervisor
interface.

12 files changed, 144 insertions, 206 deletions

diff --git a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt
index 908353f0..628f324b 100644
--- a/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt
+++ b/opendc-compute/opendc-compute-simulator/src/main/kotlin/org/opendc/compute/simulator/SimHost.kt
@@ -92,7 +92,7 @@ public class SimHost(
      * The hypervisor to run multiple workloads.
      */
     private val hypervisor: SimHypervisor = hypervisorProvider
-        .create(engine, scalingGovernor = scalingGovernor, interferenceDomain = interferenceDomain)
+        .create(engine, scalingGovernor = scalingGovernor)
 
     /**
      * The virtual machines running on the hypervisor.
@@ -144,7 +144,7 @@ public class SimHost(
         val guest = guests.computeIfAbsent(server) { key ->
             require(canFit(key)) { "Server does not fit" }
 
-            val interferenceKey = interferenceDomain?.createKey(key.name)
+            val interferenceKey = interferenceDomain?.getMember(key.name)
             val machine = hypervisor.newMachine(key.flavor.toMachineModel(), interferenceKey)
             val newGuest = Guest(
                 scope.coroutineContext,
diff --git a/opendc-simulator/opendc-simulator-compute/src/jmh/kotlin/org/opendc/simulator/compute/SimMachineBenchmarks.kt b/opendc-simulator/opendc-simulator-compute/src/jmh/kotlin/org/opendc/simulator/compute/SimMachineBenchmarks.kt
index fbcc99c3..02b48fa7 100644
--- a/opendc-simulator/opendc-simulator-compute/src/jmh/kotlin/org/opendc/simulator/compute/SimMachineBenchmarks.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/jmh/kotlin/org/opendc/simulator/compute/SimMachineBenchmarks.kt
@@ -107,7 +107,7 @@ class SimMachineBenchmarks {
             val machine = SimBareMetalMachine(
                 engine, machineModel, SimplePowerDriver(ConstantPowerModel(0.0))
             )
-            val hypervisor = SimFairShareHypervisor(engine, null, null)
+            val hypervisor = SimFairShareHypervisor(engine, null)
 
             launch { machine.runWorkload(hypervisor) }
 
@@ -129,7 +129,7 @@ class SimMachineBenchmarks {
             val machine = SimBareMetalMachine(
                 engine, machineModel, SimplePowerDriver(ConstantPowerModel(0.0))
             )
-            val hypervisor = SimFairShareHypervisor(engine, null, null)
+            val hypervisor = SimFairShareHypervisor(engine, null)
 
             launch { machine.runWorkload(hypervisor) }
 
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimAbstractHypervisor.kt b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimAbstractHypervisor.kt
index b3898004..98dab28f 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimAbstractHypervisor.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimAbstractHypervisor.kt
@@ -25,8 +25,7 @@ package org.opendc.simulator.compute.kernel
 import org.opendc.simulator.compute.*
 import org.opendc.simulator.compute.kernel.cpufreq.ScalingGovernor
 import org.opendc.simulator.compute.kernel.cpufreq.ScalingPolicy
-import org.opendc.simulator.compute.kernel.interference.VmInterferenceDomain
-import org.opendc.simulator.compute.kernel.interference.VmInterferenceKey
+import org.opendc.simulator.compute.kernel.interference.VmInterferenceMember
 import org.opendc.simulator.compute.model.MachineModel
 import org.opendc.simulator.compute.model.ProcessingUnit
 import org.opendc.simulator.compute.workload.SimWorkload
@@ -42,8 +41,7 @@ import kotlin.math.roundToLong
  */
 public abstract class SimAbstractHypervisor(
     protected val engine: FlowEngine,
-    private val scalingGovernor: ScalingGovernor?,
-    protected val interferenceDomain: VmInterferenceDomain? = null
+    private val scalingGovernor: ScalingGovernor?
 ) : SimHypervisor, FlowConvergenceListener {
     /**
      * The machine on which the hypervisor runs.
@@ -93,7 +91,7 @@ public abstract class SimAbstractHypervisor(
     private val governors = mutableListOf<ScalingGovernor.Logic>()
 
     /* SimHypervisor */
-    override fun newMachine(model: MachineModel, interferenceKey: VmInterferenceKey?): SimVirtualMachine {
+    override fun newMachine(model: MachineModel, interferenceKey: VmInterferenceMember?): SimVirtualMachine {
         require(canFit(model)) { "Machine does not fit" }
         val vm = VirtualMachine(model, interferenceKey)
         _vms.add(vm)
@@ -163,7 +161,7 @@ public abstract class SimAbstractHypervisor(
      */
     private inner class VirtualMachine(
         model: MachineModel,
-        private val interferenceKey: VmInterferenceKey? = null
+        private val interferenceKey: VmInterferenceMember? = null
     ) : SimAbstractMachine(engine, model), SimVirtualMachine, AutoCloseable {
         /**
          * A flag to indicate that the machine is closed.
@@ -180,7 +178,7 @@ public abstract class SimAbstractHypervisor(
          */
         override val counters: SimHypervisorCounters
             get() = _counters
-        @JvmField val _counters = VmCountersImpl(cpus, interferenceDomain, interferenceKey)
+        @JvmField val _counters = VmCountersImpl(cpus, interferenceKey)
 
         /**
          * The CPU capacity of the hypervisor in MHz.
@@ -206,17 +204,18 @@ public abstract class SimAbstractHypervisor(
             return super.startWorkload(
                 object : SimWorkload {
                     override fun onStart(ctx: SimMachineContext) {
+                        val interferenceKey = interferenceKey
                         try {
-                            joinInterferenceDomain()
+                            interferenceKey?.activate()
                             workload.onStart(ctx)
                         } catch (cause: Throwable) {
-                            leaveInterferenceDomain()
+                            interferenceKey?.deactivate()
                             throw cause
                         }
                     }
 
                     override fun onStop(ctx: SimMachineContext) {
-                        leaveInterferenceDomain()
+                        interferenceKey?.deactivate()
                         workload.onStop(ctx)
                     }
                 },
@@ -236,26 +235,6 @@ public abstract class SimAbstractHypervisor(
                 cpu.close()
             }
         }
-
-        /**
-         * Join the interference domain of the hypervisor.
-         */
-        private fun joinInterferenceDomain() {
-            val interferenceKey = interferenceKey
-            if (interferenceKey != null) {
-                interferenceDomain?.join(interferenceKey)
-            }
-        }
-
-        /**
-         * Leave the interference domain of the hypervisor.
-         */
-        private fun leaveInterferenceDomain() {
-            val interferenceKey = interferenceKey
-            if (interferenceKey != null) {
-                interferenceDomain?.leave(interferenceKey)
-            }
-        }
     }
 
     /**
@@ -353,8 +332,7 @@ public abstract class SimAbstractHypervisor(
      */
     private inner class VmCountersImpl(
         private val cpus: List<VCpu>,
-        private val interferenceDomain: VmInterferenceDomain?,
-        private val key: VmInterferenceKey?
+        private val key: VmInterferenceMember?
     ) : SimHypervisorCounters {
         private val d = cpus.size / cpus.sumOf { it.model.frequency } * 1000
 
@@ -403,11 +381,11 @@ public abstract class SimAbstractHypervisor(
             cpuTime[2] += ((demandDelta - actualDelta) * d).roundToLong()
 
             // Compute the performance penalty due to flow interference
-            val interferenceDomain = interferenceDomain
-            if (interferenceDomain != null) {
+            val key = key
+            if (key != null) {
                 val mux = mux
                 val load = mux.rate / mux.capacity.coerceAtLeast(1.0)
-                val penalty = 1 - interferenceDomain.apply(key, load)
+                val penalty = 1 - key.apply(load)
                 val interference = (actualDelta * d * penalty).roundToLong()
 
                 if (interference > 0) {
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisor.kt b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisor.kt
index a12c5517..66453835 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisor.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisor.kt
@@ -24,7 +24,6 @@ package org.opendc.simulator.compute.kernel
 
 import org.opendc.simulator.compute.SimMachine
 import org.opendc.simulator.compute.kernel.cpufreq.ScalingGovernor
-import org.opendc.simulator.compute.kernel.interference.VmInterferenceDomain
 import org.opendc.simulator.compute.model.MachineModel
 import org.opendc.simulator.compute.workload.SimWorkload
 import org.opendc.simulator.flow.FlowEngine
@@ -36,15 +35,12 @@ import org.opendc.simulator.flow.mux.MaxMinFlowMultiplexer
  * concurrently using weighted fair sharing.
  *
  * @param engine The [FlowEngine] to manage the machine's resources.
- * @param listener The listener for the convergence of the system.
  * @param scalingGovernor The CPU frequency scaling governor to use for the hypervisor.
- * @param interferenceDomain The resource interference domain to which the hypervisor belongs.
  */
 public class SimFairShareHypervisor(
     engine: FlowEngine,
-    scalingGovernor: ScalingGovernor?,
-    interferenceDomain: VmInterferenceDomain?,
-) : SimAbstractHypervisor(engine, scalingGovernor, interferenceDomain) {
+    scalingGovernor: ScalingGovernor?
+) : SimAbstractHypervisor(engine, scalingGovernor) {
     /**
      * The multiplexer that distributes the computing capacity.
      */
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisorProvider.kt b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisorProvider.kt
index 204b4860..ad8177d3 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisorProvider.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisorProvider.kt
@@ -23,7 +23,6 @@
 package org.opendc.simulator.compute.kernel
 
 import org.opendc.simulator.compute.kernel.cpufreq.ScalingGovernor
-import org.opendc.simulator.compute.kernel.interference.VmInterferenceDomain
 import org.opendc.simulator.flow.FlowEngine
 
 /**
@@ -35,6 +34,5 @@ public class SimFairShareHypervisorProvider : SimHypervisorProvider {
     override fun create(
         engine: FlowEngine,
         scalingGovernor: ScalingGovernor?,
-        interferenceDomain: VmInterferenceDomain?,
-    ): SimHypervisor = SimFairShareHypervisor(engine, scalingGovernor, interferenceDomain)
+    ): SimHypervisor = SimFairShareHypervisor(engine, scalingGovernor)
 }
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimHypervisor.kt b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimHypervisor.kt
index 229e569c..f53d0c5d 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimHypervisor.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimHypervisor.kt
@@ -23,7 +23,7 @@
 package org.opendc.simulator.compute.kernel
 
 import org.opendc.simulator.compute.SimMachine
-import org.opendc.simulator.compute.kernel.interference.VmInterferenceKey
+import org.opendc.simulator.compute.kernel.interference.VmInterferenceMember
 import org.opendc.simulator.compute.model.MachineModel
 import org.opendc.simulator.compute.workload.SimWorkload
 
@@ -68,7 +68,7 @@ public interface SimHypervisor : SimWorkload {
      * @param model The machine to create.
      * @param interferenceKey The key of the machine in the interference model.
      */
-    public fun newMachine(model: MachineModel, interferenceKey: VmInterferenceKey? = null): SimVirtualMachine
+    public fun newMachine(model: MachineModel, interferenceKey: VmInterferenceMember? = null): SimVirtualMachine
 
     /**
      * Remove the specified [machine] from the hypervisor.
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimHypervisorProvider.kt b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimHypervisorProvider.kt
index b7e8760a..6ee523fd 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimHypervisorProvider.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimHypervisorProvider.kt
@@ -23,7 +23,6 @@
 package org.opendc.simulator.compute.kernel
 
 import org.opendc.simulator.compute.kernel.cpufreq.ScalingGovernor
-import org.opendc.simulator.compute.kernel.interference.VmInterferenceDomain
 import org.opendc.simulator.flow.FlowEngine
 
 /**
@@ -41,9 +40,5 @@ public interface SimHypervisorProvider {
     /**
      * Create a new [SimHypervisor] instance.
      */
-    public fun create(
-        engine: FlowEngine,
-        scalingGovernor: ScalingGovernor? = null,
-        interferenceDomain: VmInterferenceDomain? = null,
-    ): SimHypervisor
+    public fun create(engine: FlowEngine, scalingGovernor: ScalingGovernor? = null): SimHypervisor
 }
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimSpaceSharedHypervisorProvider.kt b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimSpaceSharedHypervisorProvider.kt
index 96b73e69..f7456797 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimSpaceSharedHypervisorProvider.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/SimSpaceSharedHypervisorProvider.kt
@@ -23,7 +23,6 @@
 package org.opendc.simulator.compute.kernel
 
 import org.opendc.simulator.compute.kernel.cpufreq.ScalingGovernor
-import org.opendc.simulator.compute.kernel.interference.VmInterferenceDomain
 import org.opendc.simulator.flow.FlowEngine
 
 /**
@@ -35,6 +34,5 @@ public class SimSpaceSharedHypervisorProvider : SimHypervisorProvider {
     override fun create(
         engine: FlowEngine,
         scalingGovernor: ScalingGovernor?,
-        interferenceDomain: VmInterferenceDomain?,
     ): SimHypervisor = SimSpaceSharedHypervisor(engine, scalingGovernor)
 }
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceDomain.kt b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceDomain.kt
index 5220fa2d..3b355f1e 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceDomain.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceDomain.kt
@@ -27,40 +27,11 @@ package org.opendc.simulator.compute.kernel.interference
  */
 public interface VmInterferenceDomain {
     /**
-     * Compute the performance score of a participant in this interference domain.
-     *
-     * @param key The participant to obtain the score of or `null` if the participant has no key.
-     * @param load The overall load on the interference domain.
-     * @return A score representing the performance score to be applied to the resource consumer, with 1
-     * meaning no influence, <1 means that performance degrades, and >1 means that performance improves.
-     */
-    public fun apply(key: VmInterferenceKey?, load: Double): Double
-
-    /**
-     * Construct an [VmInterferenceKey] for the specified [id].
+     * Return the [VmInterferenceMember] associated with the specified [id].
      *
      * @param id The identifier of the virtual machine.
-     * @return A key identifying the virtual machine as part of the interference domain. `null` if the virtual machine
-     * does not participate in the domain.
-     */
-    public fun createKey(id: String): VmInterferenceKey?
-
-    /**
-     * Remove the specified [key] from this domain.
-     */
-    public fun removeKey(key: VmInterferenceKey)
-
-    /**
-     * Mark the specified [key] as active in this interference domain.
-     *
-     * @param key The key to join the interference domain with.
-     */
-    public fun join(key: VmInterferenceKey)
-
-    /**
-     * Mark the specified [key] as inactive in this interference domain.
-     *
-     * @param key The key of the virtual machine that wants to leave the domain.
+     * @return A [VmInterferenceMember] representing the virtual machine as part of the interference domain. `null` if
+     * the virtual machine does not participate in the domain.
      */
-    public fun leave(key: VmInterferenceKey)
+    public fun getMember(id: String): VmInterferenceMember?
 }
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceKey.kt b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceMember.kt
index 8d720ea9..2f3dd74b 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceKey.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceMember.kt
@@ -23,6 +23,25 @@
 package org.opendc.simulator.compute.kernel.interference
 
 /**
- * A key that uniquely identifies a participant of an interference domain.
+ * A participant of an interference domain.
  */
-public interface VmInterferenceKey
+public interface VmInterferenceMember {
+    /**
+     * Mark this member as active in this interference domain.
+     */
+    public fun activate()
+
+    /**
+     * Mark this member as inactive in this interference domain.
+     */
+    public fun deactivate()
+
+    /**
+     * Compute the performance score of the member in this interference domain.
+     *
+     * @param load The overall load on the interference domain.
+     * @return A score representing the performance score to be applied to the member, with 1
+     * meaning no influence, <1 means that performance degrades, and >1 means that performance improves.
+     */
+    public fun apply(load: Double): Double
+}
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceModel.kt b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceModel.kt
index 7cc545c8..bfda3121 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceModel.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/kernel/interference/VmInterferenceModel.kt
@@ -35,11 +35,11 @@ import java.util.*
  * @param seed The seed to use for randomly selecting the virtual machines that are affected.
  */
 public class VmInterferenceModel private constructor(
-    private val targets: DoubleArray,
-    private val scores: DoubleArray,
     private val idMapping: Map<String, Int>,
     private val members: Array<IntArray>,
     private val membership: Array<IntArray>,
+    private val targets: DoubleArray,
+    private val scores: DoubleArray,
     private val size: Int,
     seed: Long,
 ) {
@@ -51,13 +51,13 @@ public class VmInterferenceModel private constructor(
     /**
      * Construct a new [VmInterferenceDomain].
      */
-    public fun newDomain(): VmInterferenceDomain = InterferenceDomainImpl(targets, scores, idMapping, members, membership, random)
+    public fun newDomain(): VmInterferenceDomain = InterferenceDomainImpl(idMapping, members, membership, targets, scores, random)
 
     /**
      * Create a copy of this model with a different seed.
      */
     public fun withSeed(seed: Long): VmInterferenceModel {
-        return VmInterferenceModel(targets, scores, idMapping, members, membership, size, seed)
+        return VmInterferenceModel(idMapping, members, membership, targets, scores, size, seed)
     }
 
     public companion object {
@@ -171,11 +171,11 @@ public class VmInterferenceModel private constructor(
 
             @Suppress("UNCHECKED_CAST")
             return VmInterferenceModel(
-                newTargets,
-                newScores,
                 idMapping,
                 newMembers as Array<IntArray>,
                 membership.map { it.value.toIntArray() }.toTypedArray(),
+                newTargets,
+                newScores,
                 size,
                 seed
             )
@@ -197,127 +197,62 @@ public class VmInterferenceModel private constructor(
      * Internal implementation of [VmInterferenceDomain].
      */
     private class InterferenceDomainImpl(
-        private val targets: DoubleArray,
-        private val scores: DoubleArray,
         private val idMapping: Map<String, Int>,
         private val members: Array<IntArray>,
         private val membership: Array<IntArray>,
+        private val targets: DoubleArray,
+        private val scores: DoubleArray,
         private val random: SplittableRandom
     ) : VmInterferenceDomain {
         /**
          * Keys registered with this domain.
          */
-        private val keys = HashMap<Int, InterferenceKeyImpl>()
+        private val keys = HashMap<Int, InterferenceMemberImpl>()
 
         /**
          * The set of keys active in this domain.
          */
-        private val activeKeys = ArrayList<InterferenceKeyImpl>()
-
-        override fun createKey(id: String): VmInterferenceKey? {
-            val intId = idMapping[id] ?: return null
-            return keys.computeIfAbsent(intId) { InterferenceKeyImpl(intId) }
-        }
-
-        override fun removeKey(key: VmInterferenceKey) {
-            if (key !is InterferenceKeyImpl) {
-                return
-            }
+        private val activeKeys = ArrayList<InterferenceMemberImpl>()
 
-            if (activeKeys.remove(key)) {
-                computeActiveGroups(key.id)
-            }
+        /**
+         * Queue of participants that will be removed or added to the active groups.
+         */
+        private val participants = ArrayDeque<InterferenceMemberImpl>()
 
-            keys.remove(key.id)
+        override fun getMember(id: String): VmInterferenceMember? {
+            val intId = idMapping[id] ?: return null
+            return keys.computeIfAbsent(intId) { InterferenceMemberImpl(it, this, members, targets, scores, random) }
         }
 
-        override fun join(key: VmInterferenceKey) {
-            if (key !is InterferenceKeyImpl) {
-                return
-            }
+        override fun toString(): String = "VmInterferenceDomain"
 
-            if (key.acquire()) {
-                val pos = activeKeys.binarySearch(key)
-                if (pos < 0) {
-                    activeKeys.add(-pos - 1, key)
-                }
-                computeActiveGroups(key.id)
+        fun join(key: InterferenceMemberImpl) {
+            val activeKeys = activeKeys
+            val pos = activeKeys.binarySearch(key)
+            if (pos < 0) {
+                activeKeys.add(-pos - 1, key)
             }
-        }
 
-        override fun leave(key: VmInterferenceKey) {
-            if (key is InterferenceKeyImpl && key.release()) {
-                activeKeys.remove(key)
-                computeActiveGroups(key.id)
-            }
+            computeActiveGroups(activeKeys, key.id)
         }
 
-        override fun apply(key: VmInterferenceKey?, load: Double): Double {
-            if (key == null || key !is InterferenceKeyImpl) {
-                return 1.0
-            }
-
-            val groups = key.groups
-            val groupSize = groups.size
-
-            if (groupSize == 0) {
-                return 1.0
-            }
-
-            val targets = targets
-            val scores = scores
-            var low = 0
-            var high = groups.size - 1
-
-            var group = -1
-            var score = 1.0
-
-            // Perform binary search over the groups based on target load
-            while (low <= high) {
-                val mid = low + high ushr 1
-                val midGroup = groups[mid]
-                val target = targets[midGroup]
-
-                if (target < load) {
-                    low = mid + 1
-                    group = midGroup
-                    score = scores[midGroup]
-                } else if (target > load) {
-                    high = mid - 1
-                } else {
-                    group = midGroup
-                    score = scores[midGroup]
-                    break
-                }
-            }
-
-            return if (group >= 0 && random.nextInt(members[group].size) == 0) {
-                score
-            } else {
-                1.0
-            }
+        fun leave(key: InterferenceMemberImpl) {
+            val activeKeys = activeKeys
+            activeKeys.remove(key)
+            computeActiveGroups(activeKeys, key.id)
         }
 
-        override fun toString(): String = "VmInterferenceDomain"
-
-        /**
-         * Queue of participants that will be removed or added to the active groups.
-         */
-        private val _participants = ArrayDeque<InterferenceKeyImpl>()
-
         /**
-         * (Re-)Compute the active groups.
+         * (Re-)compute the active groups.
          */
-        private fun computeActiveGroups(id: Int) {
-            val activeKeys = activeKeys
-            val groups = membership[id]
-
+        private fun computeActiveGroups(activeKeys: ArrayList<InterferenceMemberImpl>, id: Int) {
             if (activeKeys.isEmpty()) {
                 return
             }
 
+            val groups = membership[id]
             val members = members
-            val participants = _participants
+            val participants = participants
 
             for (group in groups) {
                 val groupMembers = members[group]
@@ -366,7 +301,14 @@ public class VmInterferenceModel private constructor(
      *
      * @param id The identifier of the member.
      */
-    private class InterferenceKeyImpl(@JvmField val id: Int) : VmInterferenceKey, Comparable<InterferenceKeyImpl> {
+    private class InterferenceMemberImpl(
+        @JvmField val id: Int,
+        private val domain: InterferenceDomainImpl,
+        private val members: Array<IntArray>,
+        private val targets: DoubleArray,
+        private val scores: DoubleArray,
+        private val random: SplittableRandom
+    ) : VmInterferenceMember, Comparable<InterferenceMemberImpl> {
         /**
          * The active groups to which the key belongs.
          */
@@ -377,16 +319,57 @@ public class VmInterferenceModel private constructor(
          */
         private var refCount: Int = 0
 
-        /**
-         * Join the domain.
-         */
-        fun acquire(): Boolean = refCount++ <= 0
+        override fun activate() {
+            if (refCount++ <= 0) {
+                domain.join(this)
+            }
+        }
 
-        /**
-         * Leave the domain.
-         */
-        fun release(): Boolean = --refCount <= 0
+        override fun deactivate() {
+            if (--refCount <= 0) {
+                domain.leave(this)
+            }
+        }
+
+        override fun apply(load: Double): Double {
+            val groups = groups
+            val groupSize = groups.size
+
+            if (groupSize == 0) {
+                return 1.0
+            }
+
+            val targets = targets
+            val scores = scores
+            var low = 0
+            var high = groups.size - 1
+
+            var group = -1
+
+            // Perform binary search over the groups based on target load
+            while (low <= high) {
+                val mid = low + high ushr 1
+                val midGroup = groups[mid]
+                val target = targets[midGroup]
+
+                if (target < load) {
+                    low = mid + 1
+                    group = midGroup
+                } else if (target > load) {
+                    high = mid - 1
+                } else {
+                    group = midGroup
+                    break
+                }
+            }
+
+            return if (group >= 0 && random.nextInt(members[group].size) == 0) {
+                scores[group]
+            } else {
+                1.0
+            }
+        }
 
-        override fun compareTo(other: InterferenceKeyImpl): Int = id.compareTo(other.id)
+        override fun compareTo(other: InterferenceMemberImpl): Int = id.compareTo(other.id)
     }
 }
diff --git a/opendc-simulator/opendc-simulator-compute/src/test/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisorTest.kt b/opendc-simulator/opendc-simulator-compute/src/test/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisorTest.kt
index ab2a6d76..15d32002 100644
--- a/opendc-simulator/opendc-simulator-compute/src/test/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisorTest.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/test/kotlin/org/opendc/simulator/compute/kernel/SimFairShareHypervisorTest.kt
@@ -77,7 +77,7 @@ internal class SimFairShareHypervisorTest {
 
         val platform = FlowEngine(coroutineContext, clock)
         val machine = SimBareMetalMachine(platform, model, SimplePowerDriver(ConstantPowerModel(0.0)))
-        val hypervisor = SimFairShareHypervisor(platform, PerformanceScalingGovernor(), null)
+        val hypervisor = SimFairShareHypervisor(platform, PerformanceScalingGovernor())
 
         launch {
             machine.runWorkload(hypervisor)
@@ -128,7 +128,7 @@ internal class SimFairShareHypervisorTest {
         val machine = SimBareMetalMachine(
             platform, model, SimplePowerDriver(ConstantPowerModel(0.0))
         )
-        val hypervisor = SimFairShareHypervisor(platform, null, null)
+        val hypervisor = SimFairShareHypervisor(platform, null)
 
         launch {
             machine.runWorkload(hypervisor)
@@ -167,7 +167,7 @@ internal class SimFairShareHypervisorTest {
 
         val platform = FlowEngine(coroutineContext, clock)
         val machine = SimBareMetalMachine(platform, model, SimplePowerDriver(ConstantPowerModel(0.0)))
-        val hypervisor = SimFairShareHypervisor(platform, null, null)
+        val hypervisor = SimFairShareHypervisor(platform, null)
 
         assertDoesNotThrow {
             launch {
@@ -197,7 +197,7 @@ internal class SimFairShareHypervisorTest {
         val machine = SimBareMetalMachine(
             platform, model, SimplePowerDriver(ConstantPowerModel(0.0))
         )
-        val hypervisor = SimFairShareHypervisor(platform, null, interferenceDomain)
+        val hypervisor = SimFairShareHypervisor(platform, null)
 
         val duration = 5 * 60L
         val workloadA =
@@ -225,11 +225,11 @@ internal class SimFairShareHypervisorTest {
 
         coroutineScope {
             launch {
-                val vm = hypervisor.newMachine(model, interferenceDomain.createKey("a"))
+                val vm = hypervisor.newMachine(model, interferenceDomain.getMember("a"))
                 vm.runWorkload(workloadA)
                 hypervisor.removeMachine(vm)
             }
-            val vm = hypervisor.newMachine(model, interferenceDomain.createKey("b"))
+            val vm = hypervisor.newMachine(model, interferenceDomain.getMember("b"))
             vm.runWorkload(workloadB)
             hypervisor.removeMachine(vm)
         }