controlling CPU utilization

Question

how is it advisable to control the cpu utilization during run time ?

poll the cpu load and insert sleeps ?

Answer 1

I'd recommend OS functionality. There are performance counters and WinAPI functions for this on Windows.

Here is an example using performance counters from BCL Team Blog:

foreach (Process proc in Process.GetProcesses()) {
    using (PerformanceCounter pcProcess = new PerformanceCounter("Process", "% Processor Time", proc.ProcessName)) {
        pcProcess.NextValue();
        System.Threading.Thread.Sleep(1000);
        Console.WriteLine("Process:{0} CPU% {1}", proc.ProcessName, pcProcess.NextValue());   
    }
}

This code makes the same with WMI from CodeProject:

public string GetCPU()
{
    decimal PercentProcessorTime=0;
    mObject_CPU.Get();

    ulong  u_newCPU   = 
      (ulong)mObject_CPU.Properties["PercentProcessorTime"].Value;
    ulong u_newNano   = 
      (ulong)mObject_CPU.Properties["TimeStamp_Sys100NS"].Value;
    decimal d_newCPU  = Convert.ToDecimal(u_newCPU);
    decimal d_newNano = Convert.ToDecimal(u_newNano);
    decimal d_oldCPU  = Convert.ToDecimal(u_oldCPU);
    decimal d_oldNano = Convert.ToDecimal(u_oldNano);

    // Thanks to MSDN for giving me this formula !

    PercentProcessorTime = 
      (1 - ((d_newCPU-d_oldCPU)/(d_newNano - d_oldNano)))*100m;

    // Save the values for the next run

    u_oldCPU          = u_newCPU;
    u_oldNano         = u_newNano;

    return PercentProcessorTime.ToString("N",nfi);;
}

So you can query these OS providers (or others for your OS) and sleep your thread if processor utilization is high.

Answer 2

The easiest way would be to modify your main loop to either wait on input - the classic event driven model - or to periodically sleep for a short period of time.

If putting the application to sleep I would only use a very short timeout, somewhere within 10-100ms range as any more and some user input would be delayed, and any less would involve a lot more OS level overhead in switching your application.