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I have been doing some profiling of a physics application I wrote, and I've noticed when I profile it, it runs faster and perhaps smoother than without the profiler. Note that I am NOT running the program in the debug configuration or with the debugger attached.

I measured the difference, and I found program runs ~50% faster under the profiler. I don't consider this a duplicate because the other question doesn't make it clear whether he/she was running it with the debugger attached, and the top answer assumes that's the case (And the 20x speedup strongly indicates it would be the correct answer in most cases).

Another answer suggests a "heisenburg" bug, but that's kind of a catchall hypothesis (I'm still going to investigate down this line).

Is it possible that Visual Studio does something that prevents other applications from interfering with my application's compute or memory resources (in order to get a "fairer" result)?

user2345397
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  • Is this a multithreaded program? Can you pinpoint some specific part that gets faster (perhaps by just timing it manually at different points)? – Dan Mašek Apr 05 '16 at 23:47

2 Answers2

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Visual Studio's "CPU Usage" profiler appears to disregard laptop power usage settings, so if you run an application on a laptop that is trying to conserve battery power, it will run slower than if you run the profiler on it.

I discovered this when I got home from work- I noticed the speed difference had disappeared. On a hunch, I unplugged my laptop and tried the test several more times. The speed difference returned. What's more, under the profiler, the application runs at about the same speed plugged in or not.

I was not able to find any sources on this, but I'll be happy to edit them in if someone can find some.

user2345397
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If you use threading in your code, this can be caused due to the System Timer Resolution in Windows.

Default windows timer resolution is 15.6ms

When you are running the profiler, this is reduced to 1ms and your program run fast. Checkout this answer

Kusal Dissanayake
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    Very interesting. I wonder whether windows decreases timer resolution when on battery power? A quick google search was not able to confirm this. I'm not sure this was the problem I was experiencing because my application did not alwaus speed up in the profiler - only when I wasn't plugged in. – user2345397 May 03 '20 at 14:42