This utility probes GPUs and RDMA NICs over PCIe to estimate the system interconnect topology. This is for use in sitations where virtualization obscures information that would normally be reported by topology query tools like lstopo. This is true for some Azure GPU SKUs.

The goal is to answer these questions:

• which socket is each RDMA NIC connected to?
• which socket is each GPU connected to?
• which NICs and GPUs share a PCIe switch, and thus share bandwidth to the CPU?

This is a work in progress!

The tool currently depends on these libraries:

• ibverbs (specifically libibverbs-dev on Ubuntu, but if it's not already installed you probably have IB/RDMA driver problems)
• numa (specifically libnuma-dev)

On Ubuntu, you can install them like this:

sudo apt install libnuma-dev

Just run make.

Run make install to place the inspector-topo binary in /usr/local/bin.

GPU IDs are not yet handled in a smart way. You MUST set CUDA_VISIBLE_DEVICES before running to get results that make sense. For now on the 8-GPU ND40v2 nodes, use a command like this:

CUDA_VISIBLE_DEVICES=0,1,2,3,4,5,6,7 ./inspector-topo

For the GPU bandwidth tests, the tool defaults to copying a 1 GB buffer 10 times. This is probably fine, but you can change the buffer size with the --length flag and the GPU bandwidth iteration count with the --bw_iters flag if you want.

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