Fixes dotnet#2319

Author: MattFromRVA

src/BenchmarkDotNet/Running/PowerManagementApplier.cs

@@ -72,6 +72,14 @@ private void ApplyPlanByGuid(Guid guid)
                     isInitialized = true;
                 }
 
+                Guid ultimatePerformanceGuid = PowerPlansDict[PowerPlan.UltimatePerformance];
+                Guid highPerformanceGuid = PowerPlansDict[PowerPlan.HighPerformance];
+                if (userCurrentPowerPlan == ultimatePerformanceGuid && guid == highPerformanceGuid)
+                {
+                    logger.WriteLineInfo($"Current power plan is already Ultimate Performance. Not changing to High Performance.");
+                    return;
+                }
+
                 if (PowerManagementHelper.Set(guid))
                 {
                     powerPlanChanged = true;
@@ -87,4 +95,4 @@ private void ApplyPlanByGuid(Guid guid)
             }
         }
     }
-}
+}