I've been developing a small indie game in my spare time and have run across an inexplicable issue. Some builds of the game will randomly run several hundred frames per second slower than other builds. For example, when rendering some text and no 3D scene, I can achieve 1800FPS on my own hardware. Add one 3D sphere (10k verts, pixel shaded), achieve 1700 FPS. Add two more spheres, achieve 800 FPS. Remove all spheres, achieve 1100FPS- even though the code now renders the same scene as I previously achieved at 1800FPS, which is just the FPS counter being rendered. I've tried rebuilding and cleaning the project and rebooting the compiler. This is in Release mode and I turned on all the optimizations I could find. Any suggestions as to the cause?

I ran a quick profile, and Visual Studio seems to think that over 90% of my time was spent in D3D9_43.dll, suggesting that it's not a bug in my app, which doesn't explain why it manifests in only some builds.

I rebooted my machine and it's back up to 1800FPS. I think it's a bug in the DirectX SDK tools (amongst many others). Going to delete this question.