c# - Get CPU and RAM usage

Question

I need to get the ram memory and CPU usage during execution of a process (the process can run sometimes and over 30 minutes). I am able to get the free RAM but the CPU usage it's not correct, compared with the value from task manager. Am I doing something wrong? Here is my code:

class Program
{
    static List<float> AvailableCPU = new List<float>();
    static List<float> AvailableRAM = new List<float>();

    protected static PerformanceCounter cpuCounter;
    protected static PerformanceCounter ramCounter;
    static void Main(string[] args)
    {
        cpuCounter = new PerformanceCounter();
        cpuCounter.CategoryName = "Processor";
        cpuCounter.CounterName = "% Processor Time";
        cpuCounter.InstanceName = "_Total";

        ramCounter = new PerformanceCounter("Memory", "Available MBytes");

        try
        {
            System.Timers.Timer t = new System.Timers.Timer(1200);
            t.Elapsed += new ElapsedEventHandler(TimerElapsed);
            t.Start();
            Thread.Sleep(10000);
        }
        catch (Exception e)
        {
            Console.WriteLine("catched exception");
        }
        Console.ReadLine();

    }

    public static void TimerElapsed(object source, ElapsedEventArgs e)
    {
        float cpu = cpuCounter.NextValue();
        float ram = ramCounter.NextValue();
        Console.WriteLine(string.Format("CPU Value: {0}, ram value: {1}", cpu, ram));
        AvailableCPU.Add(cpu);
        AvailableRAM.Add(ram);
    }

}

But when I run the program, here is what it's printed to the console, compared with values from task manager:

What am I doing wrong?

Answer 1

There is nothing wrong with your values.

The reason you see differences with what task manager returns is that the "CPU usage" value is something computed for a given interval, i.e. between two NextValue() calls. If task manager "doesn't call its own NextValue" (if we simplify how it works) at the same time you do, you won't return the same results.

Imagine the following scenario:

Time 0: 0% actual CPU usage
Time 1: 50% actual CPU usage
Time 2: 70% actual CPU usage
Time 3: 2% actual CPU usage
Time 4: 100% actual CPU usage

• If you check the value between Time 1 and Time 3, you'll return something based on "50% and 2%".
• If task manager checks the value between Time 2 and Time 4, it'll return something different, i.e. a value based on "70% and 100%".

You could try to spawn multiple processes of your own application, you should also see different results.