I implemented a RNS Montgomery exponentiation in Cuda and on cpu for comparison.

Everything nice everything fine. It runs on just one SM.

However I am going to tell you some strange regression in both cpu/gpu performances.

During the devoloping, about two month ago, I was using Cuda 5 preview on Ubuntu 11.04 64b.

In this time, I reach the following performances:

cpu 460ms gpu 120ms

Then one day when I turn on the pc, the graphical environment didnt start. I dont know which was the problem, however I switched to the console and installed again the Cuda driver. At the following boot performances changed:

cpu 310ms gpu 80ms

I was like Q.Q...uhm ok, nice to see this, but I was wondering how that could be possible

However, I went then in holiday for 10 days and I continued developing and optimizing on my notebook (but not the same part of the code, some additional stuff)

When I was back, I just updated the source files, and performances came back to 460/120ms..

I couldnt believe it, I tried to install Cuda 5 RC, updating the video driver too... nothing changed...

I checked Debug/Release, Cuda computability, but the problem seems being somewhere else..

Looking around the net I found this, I am pretty sure it must have something to do with the driver, because the performance change affected both cpu and gpu

Do you have some tips/ideas/suggestions?