do CUDA events time cudaMalloc and cudaMemcpy executions?

Question

I am using the following code to time calls to cudaMalloc(). I am curious: Do CUDA events only time our kernels, or they also time the "in-built kernels". In other words, is the following method for timing cudaMalloc() valid?

cudaEvent_t start, stop;
cudaEventCreate(&start);
cudaEventCreate(&stop);
cudaEventRecord(start, 0);
for(int t =0 ; t < 100 ; t++){
    float* test;
    cudaMalloc((void**)&test, 3000000 * sizeof(float));
    cudaFree(test);
}
cudaEventRecord(stop, 0);
cudaEventSynchronize(stop);
float elapsedTime; 
cudaEventElapsedTime(&elapsedTime , start, stop);
printf("time elapsed on the GPU: %f ms", elapsedTime/100);

Answer 1

cu(da)EventRecord() does nothing more than submit a command to the GPU that tells the GPU to write a timestamp when the GPU processes the command. The timestamp is just an onboard high-resolution counter. So CUDA events are most useful when used as an asynchronous mechanism for timing on-GPU events, like how long a specific kernel takes to run. CUDA memory management mostly happens on the CPU, so CUDA events are not ideal for timing CUDA allocation and free operations.

In short: You're better off using CPU-based timing like gettimeofday().