Enable CUPTI to measure kernel execution time instead of CUDA Events

[fbusato]

CUDA events suffer from low accuracy and include the kernel launch overhead. On the other hand, CUPTI provides a more reliable way to get consistent timing measurement.
This request asks to add an option to replace CUDA Events with CUPTI.

Details

CUDA events issues:

• Accuracy and Stability:
  • cudaEvent can fluctuate in the range of 10-30us, making measurements of small computations unreliable
  • cudaEvent take into account the kernel launch overhead that depends on host/CPU execution and/or driver version

CUPTI:

• ~0.5us granularity vs. 10-30us
• Not affected by kernel launch overhead
• Consistency: measurements close to the profiler (nsys)
• Efficiency: avoid using waiting/delay kernels to hide CPU overhead

[alliepiper]

We do mitigate a lot of the issues with events by using blocking_kernels, so it's not quite as bad as it seems. I think this would be a great addition, I'm curious how much this would improve the stability of our results, especially when sync tags are used.