It never happened to me. In Visual Studio, I have a part of code that is executed 300 times, I time it every iteration with the performance counter, and then average it.
If I'm running the code in the debugger I get an average of 1.01 ms if I run it without the debugger I get 1.8 ms.
I closed all other apps, I rebooted, I tried it many times: Always the same timing.
I'm trying to optimize my code, but before throwing me into changing the code, I want to be sure of my timings. To have something to compare with.
What can cause that strange behaviour?
Edit:
Some clarification:
I'm running the same compiled piece of code: the release build. The only difference is (F5 vs CTRL-F5)
So, the compiler optimization should not be invoved.
Since each calcuated times were verry small, I changed the way I benchmark: I'm now timing the 300 iterations and then divide by 300. I have the same result.
About caching: The code is doing some image cross correlation, with different images at each iterations. The steps of the processing are not modified by the data in the images. So, I think caching is not the problem.
Best Answer
I think I figured it out.
If I add a Sleep(3000) before running the tests, they give the same result.
I think it has something to do with the loading of misc. dlls. In the debugger, the dlls were loaded before any code was executed. Outside the debugger, the dlls were loaded on demand, and one or more were loaded after the timer was started.
Thanks all.