Timing Kernel Executions on CUDA

I've used code from CUDA C Best Practices to implement an execution timer. However their is something strange and I don't know if it's an anomaly or if that's normal. I get different read outs each time I run my CUDA app.

Could开发者_StackOverflow these readings by related to design or is that something I should expect.

I'm not running any graphic intensive applications on my machine, other than Windows 7.

Well it depends how big the differences are. One thing you can see anomalies caused by is the kernel scheduler. It may just happen that the scheduler is giving some extra timeslices to kernel functions (because graphics API calls have error checking involved) which shows more execution time. If the differences are very large I would say check your code but if it's very low in orders of milliseconds I wouldn't worry about it +- 10msecs is the usual for the timeslicing quantum in most OS's (windows probably included). Also Aero is kind of intensive so that may be adding to the discrepancies you are seeing.

I've used code from CUDA C Best Practices to implement an execution timer.

Yeah, well, that's not a "best practice" in my experience.

I suggest using the nvprof profiler instead for your device-side code and CUDA Runtime API calls (it also works relatively well, I think, for your own host-side code). It'll take you a bit of hassle to set up and figure out which options you want to use, but it's worth it.