I'm currently living in performance-testing land for a distributed application. This time, it's not enough to merely know the time it takes to execute certain functionality, but I also need to know which toll a certain feature has on all machines involved (client, server, DB server).

I've therefore created another small helper class which can be used to report the exact CPU usage ("% Processor Time" in perfmon.exe) between two points in time for your process.

Usage

static void Main(string[] args)
{
   CPUMeter mtr = new CPUMeter();

   // do some heavy stuff
   double result = 0;
   for (int i = 0;i<100000000; i++)
   {
      result = result+Math.Sin(i);
   }

   double usage = mtr.GetCpuUtilization();

   Console.WriteLine("Done. CPU Usage {0:#00.00} %", usage);
   Console.ReadLine();
}

Source

using System.Diagnostics;

public class CPUMeter: IDisposable
{
   CounterSample _startSample;
   PerformanceCounter _cnt;

   /// Creates a per-process CPU meter instance tied to the current process.
   public CPUMeter()
   {
      String instancename = GetCurrentProcessInstanceName();
      _cnt = new PerformanceCounter("Process","% Processor Time", instancename, true);
      ResetCounter();
   }

   /// Creates a per-process CPU meter instance tied to a specific process.
   public CPUMeter(int pid)
   {
      String instancename = GetProcessInstanceName(pid);
      _cnt = new PerformanceCounter("Process","% Processor Time", instancename, true);
      ResetCounter();
   }

   /// Resets the internal counter. All subsequent calls to GetCpuUtilization() will 
   /// be relative to the point in time when you called ResetCounter(). This 
   /// method can be call as often as necessary to get a new baseline for 
   /// CPU utilization measurements.
   public void ResetCounter()
   {
      _startSample = _cnt.NextSample();
   }

   /// Returns this process's CPU utilization since the last call to ResetCounter().
   public double GetCpuUtilization()
   {
      CounterSample curr = _cnt.NextSample();

      double diffValue = curr.RawValue - _startSample.RawValue;
      double diffTimestamp = curr.TimeStamp100nSec - _startSample.TimeStamp100nSec;

      double usage = (diffValue / diffTimestamp) * 100;
      return usage;
   }

   private static string GetCurrentProcessInstanceName()
   {
      Process proc = Process.GetCurrentProcess();
      int pid = proc.Id;
      return GetProcessInstanceName(pid);
   }

   private static string GetProcessInstanceName(int pid)
   {
      PerformanceCounterCategory cat = new PerformanceCounterCategory("Process");

      string[] instances = cat.GetInstanceNames();
      foreach (string instance in instances)
      {
         
         using (PerformanceCounter cnt = new PerformanceCounter("Process",  
              "ID Process", instance, true))
         {
            int val = (int) cnt.RawValue;
            if (val == pid)
            {
               return instance;
            }
         }
      }
      throw new Exception("Could not find performance counter " + 
          "instance name for current process. This is truly strange ...");
   }

   public void Dispose()
   {
      if (_cnt!=null) _cnt.Dispose();
   }
}

Have fun!