Dear Community Members!

I have written a program in plain C to carry out some mathematical calculations. Now I am trying to identify bottlenecks using a profiler (IDE: Open Watcom 1.8). I find that a very large portion (60-79%) of the running time is used by ntdll.dll. The core program and the few called dlls consume just a smaller portion. The profiler does not show anything inside ntdll.

As I am not a programmer (just an olap developer doing some programming on my own) I do not fully understand what this means. Google has told me it is some very basic windows dll. But why does it take so much time? First I thought it is becaue I printed some information on the screen for testing purposes but commenting out the printf-s and leaving just the calculations has not changed the situation.

Is there a possibility to improve the performance of my program somehow? Or is it normal? What does ntdll.dll do?

Thanks, S.

This page says that ntdll.dll is "a Native API file of Microsoft operating systems and it contains NT kernel functions". Kind of vague, but perhaps if the code is doing any system calls (accessing files, perhaps), that may account for it. Or perhaps if your program uses a lot of memory, some virtual memory software may be kicking in to move your data from disk to RAM periodically.

Does your hard disk get much usage while the program is running?

This page says that ntdll.dll is "a Native API file of Microsoft operating systems and it contains NT kernel functions". Kind of vague, but perhaps if the code is doing any system calls (accessing files, perhaps), that may account for it. Or perhaps if your program uses a lot of memory, some virtual memory software may be kicking in to move your data from disk to RAM periodically.

Does your hard disk get much usage while the program is running?

Hello DWKS! Thank You for your answer.

You have the point. I watched Process Explorer during a long series of repeated running of my program. I saw a lot of page faults. So that slowed down my program.
It turned out that the lpsolve 5.5 's dll, more exactly the solution of the linear programming model produced the large number of page faults. Putting that line into comment dropped the % portion of the ntdll in the running time. So my original problem is solved, but I am not so happy having found that an outer party dll causes everything. I do not see yet how it can be influenced.

Anyway, you showed the right way, thanks again.

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