Incorrect CPU usage calculation using C # and WMI

Question

It is my function to list the processes in the window and calculate the percentage of CPU usage for each process, but the results are not correct.

CPU usage is not up to 100%, but more like 120% or 130%, and I don't know what I'm doing wrong. It looks like it is calculating the correct CPU usage for varoius applications like firefox, VS2010, office, .. but has problems with the System Idle Process.

public List<ProcInfo> GetRunningProcesses()
{
    List<ProcInfo> allProcesses = new List<ProcInfo>();
    UInt64 currentProcessCpuTime = 0;
    UInt64 allProcessCpuTime = 0;

    SelectQuery wmiQuery = new SelectQuery("SELECT Name, Description, ProcessId, KernelModeTime, UserModeTime FROM Win32_Process");
    ManagementObjectSearcher oSearcher = new ManagementObjectSearcher(connectionScope, wmiQuery);
    ManagementObjectCollection moc = oSearcher.Get();

    foreach (ManagementObject mo in moc)
    {
        allProcessCpuTime += (UInt64)mo["KernelModeTime"] + (UInt64)mo["UserModeTime"];
    }

    foreach (ManagementObject mo in moc)
    {
        currentProcessCpuTime = (UInt64)mo["KernelModeTime"] + (UInt64)mo["UserModeTime"];
        allProcesses.Add(new ProcInfo((string)mo["Name"], (string)mo["Description"], (UInt32)mo["ProcessId"], (currentProcessCpuTime / (double)allProcessCpuTime * 100));
    }

    return allProcesses;
}

EDIT:

I found that my function is wrong.

I begin generosity for the best working solution. The solution should work for the local and remote system and should be fast.

Answer 1

# :

public static void DumpProcessesCpu(string machineName)
{
    List<PerformanceCounter> counters = new List<PerformanceCounter>();

    foreach (Process process in Process.GetProcesses(machineName))
    {
        PerformanceCounter processorTimeCounter = new PerformanceCounter(
            "Process",
            "% Processor Time",
            process.ProcessName,
            machineName);

        processorTimeCounter.NextValue();
        counters.Add(processorTimeCounter);
    }

    Thread.Sleep(1000); // 1 second wait, needed to get a sample

    foreach (PerformanceCounter processorTimeCounter in counters)
    {
        Console.WriteLine("Process:{0} CPU% {1}",
            processorTimeCounter.InstanceName,
            processorTimeCounter.NextValue());
    }
}

: http://blogs.msdn.com/b/bclteam/archive/2006/06/02/618156.aspx , . , , , .

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Answer 2

        var mos = new ManagementObjectSearcher("SELECT * FROM Win32_PerfRawData_PerfProc_Process");
        var run1 = mos.Get().Cast<ManagementObject>().ToDictionary(mo => mo.Properties["Name"].Value, mo => (ulong)mo.Properties["PercentProcessorTime"].Value);
        Thread.Sleep(570); // can be an arbitrary number
        var run2 = mos.Get().Cast<ManagementObject>().ToDictionary(mo => mo.Properties["Name"].Value, mo => (ulong)mo.Properties["PercentProcessorTime"].Value);

        var total = run2["_Total"] - run1["_Total"];

        foreach (var kvp in run1)
        {
            var proc = kvp.Key;
            var p1 = kvp.Value;
            if (run2.ContainsKey(proc))
            {
                var p2 = run2[proc];
                Console.WriteLine("{0}: {1:P}", proc, (double)(p2 - p1) / total);
            }
        }

Answer 3

#, , fejesjoco , .

public class CPUUtilizationTests
{

    [Test]
    public void TestPercentProcessorTime()
    {
        Assert.That(PercentProcessorTime("Idle"), Is.Not.GreaterThan(100.0));
    }

    public float PercentProcessorTime(string processName)
    {
        var mos = new ManagementObjectSearcher("SELECT * FROM Win32_PerfRawData_PerfProc_Process");
        var run1 = mos.Get().Cast<ManagementObject>().ToDictionary(mo => mo.Properties["Name"].Value, mo => mo);
        System.Threading.Thread.Sleep(1000); // can be an arbitrary number
        var run2 = mos.Get().Cast<ManagementObject>().ToDictionary(mo => mo.Properties["Name"].Value, mo => mo);

        if (!run2.ContainsKey(processName)) throw new Exception(string.Format("Process not found: {0}", processName));

        string percentageProcessorTime = "PercentProcessorTime";
        string total = "_Total";

        ulong percentageDiff = (ulong)run2[processName][percentageProcessorTime] - (ulong)run1[processName][percentageProcessorTime];
        ulong totalDiff = (ulong)run2[total][percentageProcessorTime] - (ulong)run1[total][percentageProcessorTime];

        return ((float)percentageDiff / (float)totalDiff)*100.0f;
    }

}