ProcessExtension.cs

using System;
using System.Diagnostics;
using System.IO;
using System.Linq;

namespace MyProcessUsage
{
    internal static class ProcessExtension
    {
        public static string PerformanceCounterInstanceName(this Process process)
        {
            var matchesProcessId = new Func<string, bool>(instanceName =>
            {
                using (var pc = new PerformanceCounter("Process", "ID Process", instanceName, true))
                {
                    if ((int)pc.RawValue == process.Id)
                    {
                        return true;
                    }
                }

                return false;
            });

            string processName = Path.GetFileNameWithoutExtension(process.ProcessName);
            return new PerformanceCounterCategory("Process")
               .GetInstanceNames()
               .AsParallel()
               .FirstOrDefault(instanceName => instanceName.StartsWith(processName)
                                               && matchesProcessId(instanceName));
        }
    }
}