message: use env variable TF_GPU_CUPTI_USE_ACTIVITY_API to control which device events tracking mechanism. true => cupti activity api, false => enclosing pair of cuda events.
diff: @@ -291,6 +291,12 @@ Status GpuTracer::DoStart() {
  CUPTI_DRIVER_TRACE_CBID_cuStreamSynchronize,
  };
  + bool use_cupti_activity_api = true;
  + ReadBoolFromEnvVar("TF_GPU_CUPTI_USE_ACTIVITY_API", true,
  + &use_cupti_activity_api)
  + .IgnoreError();
  + options_.enable_event_based_activity = !use_cupti_activity_api;
  +
  bool trace_concurrent_kernels = false;
  ReadBoolFromEnvVar("TF_GPU_CUPTI_FORCE_CONCURRENT_KERNEL", false,
  &trace_concurrent_kernels)
  