CUDA code get slow in some time. NVIDIA geforce gtx card's performance varies time to time?

I developed a dll programmed with cuda code.
This dll’s speed performance get slow in some time.
Dll is running on DELL inspiron laptop equipped with NVIDIA Geforce gtx 850m.
So, I doubt whether NVIDIA Geforce gtx 850m’s performance varies time to time.
Please help me with why this happens.
Thanks in advance.

it could be anything, really

run memcheck and racecheck, to point to potential bugs, and to reduce the probability that a bug is causing this

if that does not solve the matter, timestamp sections of the program, to ring fence areas wherein the problem likely resides

otherwise, it is merely a case of: “i have a program with x lines of code, what could be the problem?”, which in truth is similar to asking: “what is the average traveling speed of santa’s sled?”

Thanks little_jimmy.
I could solve the problem. It was related to gpu’s clock balancing.
My laptop was controlling the gpu’s clock according to the power supply(battery mode or line mode),
So it happened.

Even independent of special power supply scenarios applicable to portable devices (such as lower clocks selected when running in battery mode as was the case here), clocks and thus performance can vary based on dynamic controls such as power capping (first introduced with Fermi-class GPUs) that reduces clocks, and clock boosting (first introduced with Kepler-class GPUs) that increases clocks. I have seen dynamic performance changes of up to 10% based on that, some GPUs may provide an even wider dynamic range.