c# - What is the resolution of the CPU time value in ants or dotTrace profiler?

Question

As I understand from my previous research the resolution timer if we want to measure CPU time of a function is ~15.6ms mean we can get value like 0,15.6,32.2 ms

int a=Process.getCurrentProcess.UserProcessTime;
functionTest();
int b=Process.getCurrentProcess.UserProcessTime;
(b-a) //value like 0,15.6,32.2 ms

But using performance profiler like dotTrace or ant I see in time column where timing option is "CPU Time" value like 4.129; 1.032 ms So it's a high resolution.

What is the method to get this resolution by coding?

functionTest is ==>

    private long FindPrimeNumber(int n)
    {
        int count = 0;
        long a = 2;
        while (count < n)
        {
            long b = 2;
            int prime = 1;// to check if found a prime
            while (b * b <= a)
            {
                if (a % b == 0)
                {
                    prime = 0;
                    break;
                }
                b++;
            }
            if (prime > 0)
                count++;
            a++;
        }
        return (--a);
    }

Answer 1

It's native methods in WinAPI most likely, you can invoke them from C# via DLLImport. But for simplicity you could try use third party wrapper from here.

But you should clearly understand what you are doing. Between first call of your function and the second one will be difference because of JITting time. And if your method allocates memory - GC might occur any time while calling your method and it will be reflected in measurement.