Finding out the CPU clock frequency (per core, per processor)

Question

Programs like CPUz are very good at giving in depth information about the system (bus speed, memory timings, etc.)

However, is there a programmatic way of calculatin

Answer 1

I realise this has already been answered. I also realise this is basically a black art, so please take it or leave it - or offer feedback.

In a quest to find the clock rate on throttled (thanks microsft,hp, and dell) HyperV hosts (unreliable perf counter), and HyperV guests (can only get stock CPU speed, not current), I have managed, through trial error and fluke, to create a loop that loops exactly once per clock.

Code as follows - C# 5.0, SharpDev, 32bit, Target 3.5, Optimize on (crucial), no debuger active (crucial)

        long frequency, start, stop;
        double multiplier = 1000 * 1000 * 1000;//nano
        if (Win32.QueryPerformanceFrequency(out frequency) == false)
            throw new Win32Exception();

        Process.GetCurrentProcess().ProcessorAffinity = new IntPtr(1);
        const int gigahertz= 1000*1000*1000;
        const int known_instructions_per_loop = 1; 

        int iterations = int.MaxValue;
        int g = 0;

        Win32.QueryPerformanceCounter(out start);
        for( i = 0; i < iterations; i++)
        {
            g++;
            g++;
            g++;
            g++;
        }
        Win32.QueryPerformanceCounter(out stop);

        //normal ticks differs from the WMI data, i.e 3125, when WMI 3201, and CPUZ 3199
        var normal_ticks_per_second = frequency * 1000;
        var ticks = (double)(stop - start);
        var time = (ticks * multiplier) /frequency;
        var loops_per_sec = iterations / (time/multiplier);
        var instructions_per_loop = normal_ticks_per_second  / loops_per_sec;

        var ratio = (instructions_per_loop / known_instructions_per_loop);
        var actual_freq = normal_ticks_per_second / ratio;

        Console.WriteLine( String.Format("Perf counhter freq: {0:n}", normal_ticks_per_second));
        Console.WriteLine( String.Format("Loops per sec:      {0:n}", loops_per_sec));
        Console.WriteLine( String.Format("Perf counter freq div loops per sec: {0:n}", instructions_per_loop));
        Console.WriteLine( String.Format("Presumed freq: {0:n}", actual_freq));
        Console.WriteLine( String.Format("ratio: {0:n}", ratio));

Notes

• 25 instructions per loop if debugger is active
• Consider running a 2 or 3 seconds loop before hand to spin up the processor (or at least attempt to spin up, knowing how heavily servers are throttled these days)
• Tested on a 64bit Core2 and Haswell Pentium and compared against CPU-Z