Fix System.Diagnostics.Process.[x]ProcessorTime on macOS

src/System.Diagnostics.Process/src/System/Diagnostics/Process.OSX.cs

@@ -9,14 +9,16 @@ namespace System.Diagnostics
 {
     public partial class Process
     {
+        private const int NanoSecondsTo100NanosecondsFactor = 100;
+
         /// <summary>Gets the amount of time the process has spent running code inside the operating system core.</summary>
         public TimeSpan PrivilegedProcessorTime
         {
             get
             {
                 EnsureState(State.HaveNonExitedId);
                 Interop.libproc.rusage_info_v3 info = Interop.libproc.proc_pid_rusage(_processId);
-                return new TimeSpan(Convert.ToInt64(info.ri_system_time));
+                return new TimeSpan(Convert.ToInt64(info.ri_system_time / NanoSecondsTo100NanosecondsFactor));
             }
         }
 
@@ -76,7 +78,7 @@ public TimeSpan TotalProcessorTime
             {
                 EnsureState(State.HaveNonExitedId);
                 Interop.libproc.rusage_info_v3 info = Interop.libproc.proc_pid_rusage(_processId);
-                return new TimeSpan(Convert.ToInt64(info.ri_system_time + info.ri_user_time));
+                return new TimeSpan(Convert.ToInt64((info.ri_system_time + info.ri_user_time) / NanoSecondsTo100NanosecondsFactor));
             }
         }
 
@@ -90,7 +92,7 @@ public TimeSpan UserProcessorTime
             {
                 EnsureState(State.HaveNonExitedId);
                 Interop.libproc.rusage_info_v3 info = Interop.libproc.proc_pid_rusage(_processId);
-                return new TimeSpan(Convert.ToInt64(info.ri_user_time));
+                return new TimeSpan(Convert.ToInt64(info.ri_user_time / NanoSecondsTo100NanosecondsFactor));
             }
         }
 

src/System.Diagnostics.Process/tests/ProcessTests.cs

@@ -754,6 +754,33 @@ public void TestProcessorTime()
             Assert.InRange(processorTimeAtHalfSpin, processorTimeBeforeSpin, Process.GetCurrentProcess().TotalProcessorTime.TotalSeconds);
         }
 
+        [Fact]
+        [ActiveIssue(31908, TargetFrameworkMonikers.Uap)]
+        public void TotalProcessorTime_PerformLoop_TotalProcessorTimeValid()
+        {
+            CreateDefaultProcess();
+
+            DateTime startTime = DateTime.UtcNow;
+            TimeSpan processorTimeBeforeSpin = Process.GetCurrentProcess().TotalProcessorTime;
+
+            // Perform loop to occupy cpu, takes less than a second.
+            int i = int.MaxValue / 16;
+            while (i > 0)
+            {
+                i--;
+            }
+
+            TimeSpan processorTimeAfterSpin = Process.GetCurrentProcess().TotalProcessorTime;
+            DateTime endTime = DateTime.UtcNow;
+
+            double timeDiff = (endTime - startTime).TotalMilliseconds;
+            double cpuTimeDiff = (processorTimeAfterSpin - processorTimeBeforeSpin).TotalMilliseconds;
+
+            double cpuUsage = cpuTimeDiff / (timeDiff * Environment.ProcessorCount);
+
+            Assert.InRange(cpuUsage, 0, 1);
+        }
+
         [Fact]
         public void UserProcessorTime_GetNotStarted_ThrowsInvalidOperationException()
         {