fix(simulator): Compute energy usage in absence of convergence

This change addresses an issue where energy usage was not computed
correctly if the machine performed no work in between collection cycles.

2 files changed, 20 insertions, 4 deletions

diff --git a/opendc-experiments/opendc-experiments-capelin/src/test/kotlin/org/opendc/experiments/capelin/CapelinIntegrationTest.kt b/opendc-experiments/opendc-experiments-capelin/src/test/kotlin/org/opendc/experiments/capelin/CapelinIntegrationTest.kt
index e34c5bdc..94e92c1b 100644
--- a/opendc-experiments/opendc-experiments-capelin/src/test/kotlin/org/opendc/experiments/capelin/CapelinIntegrationTest.kt
+++ b/opendc-experiments/opendc-experiments-capelin/src/test/kotlin/org/opendc/experiments/capelin/CapelinIntegrationTest.kt
@@ -120,7 +120,7 @@ class CapelinIntegrationTest {
             { assertEquals(67006560, this@CapelinIntegrationTest.exporter.activeTime) { "Incorrect active time" } },
             { assertEquals(3159377, this@CapelinIntegrationTest.exporter.stealTime) { "Incorrect steal time" } },
             { assertEquals(0, this@CapelinIntegrationTest.exporter.lostTime) { "Incorrect lost time" } },
-            { assertEquals(5.840212485920686E9, this@CapelinIntegrationTest.exporter.energyUsage, 0.01) { "Incorrect power draw" } },
+            { assertEquals(5.840862926294953E9, this@CapelinIntegrationTest.exporter.energyUsage, 0.01) { "Incorrect power draw" } },
         )
     }
 
@@ -164,7 +164,7 @@ class CapelinIntegrationTest {
             { assertEquals(9740289, this@CapelinIntegrationTest.exporter.activeTime) { "Active time incorrect" } },
             { assertEquals(0, this@CapelinIntegrationTest.exporter.stealTime) { "Steal time incorrect" } },
             { assertEquals(0, this@CapelinIntegrationTest.exporter.lostTime) { "Lost time incorrect" } },
-            { assertEquals(7.0099453912813E8, this@CapelinIntegrationTest.exporter.energyUsage, 0.01) { "Incorrect power draw" } }
+            { assertEquals(7.010642279990053E8, this@CapelinIntegrationTest.exporter.energyUsage, 0.01) { "Incorrect power draw" } }
         )
     }
 
diff --git a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimBareMetalMachine.kt b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimBareMetalMachine.kt
index 9140d31b..5df03d45 100644
--- a/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimBareMetalMachine.kt
+++ b/opendc-simulator/opendc-simulator-compute/src/main/kotlin/org/opendc/simulator/compute/SimBareMetalMachine.kt
@@ -60,8 +60,12 @@ public class SimBareMetalMachine(
      * The total energy usage of the machine (without PSU loss) in Joules.
      */
     public val energyUsage: Double
-        get() = _energyUsage
+        get() {
+            computeEnergyUsage(engine.clock.millis())
+            return _energyUsage
+        }
     private var _energyUsage = 0.0
+    private var _energyLastComputation = 0L
 
     /**
      * The processing units of the machine.
@@ -86,13 +90,25 @@ public class SimBareMetalMachine(
         val duration = max(0, now - lastConverge)
         if (duration > 0) {
             // Compute the power and energy usage of the machine
-            _energyUsage += _powerUsage * (duration / 1000.0)
+            computeEnergyUsage(now)
             _powerUsage = powerDriverLogic.computePower()
         }
     }
 
     init {
         psu.connect(powerDriverLogic)
+        _powerUsage = powerDriverLogic.computePower()
+    }
+
+    /**
+     * Helper method to compute total energy usage.
+     */
+    private fun computeEnergyUsage(now: Long) {
+        val duration = max(0, now - _energyLastComputation)
+        _energyLastComputation = now
+
+        // Compute the energy usage of the machine
+        _energyUsage += _powerUsage * (duration / 1000.0)
     }
 
     /**