Question 2
UnclassifiedWhich NCCL environment variable can help debug communication hangs?
Correct answer: D
Explanation
NCCL provides several environment variables that can aid debugging communication hangs, so choosing "All of the above" fits when the listed options are all valid debug aids. In practice, NCCL debug settings are used to increase logging and expose where communication is stalling.
Why each option is right or wrong
A. NCCL_DEBUG=INFO
B. NCCL_DEBUG_SUBSYS=ALL
C. NCCL_ASYNC_ERROR_HANDLING=1
D. All of the above
NCCL exposes multiple debug-oriented environment variables that are used together to diagnose stalled collectives, including NCCL_DEBUG (with levels such as INFO or TRACE), NCCL_DEBUG_SUBSYS, and NCCL_DEBUG_FILE for directing logs. Because each of the listed variables can contribute to identifying where the communication is hanging, the inclusive choice is the only one that matches the NCCL debugging controls available.