Go to

/home/ubuntu/NVIDIA_CUDA-8.0_Samples/0_Simple/simpleP2P

run make and then execute

./simpleP2P

[./simpleP2P] – Starting…
Checking for multiple GPUs…
CUDA-capable device count: 4
> GPU0 = ” GRID K520″ IS capable of Peer-to-Peer (P2P)
> GPU1 = ” GRID K520″ IS capable of Peer-to-Peer (P2P)
> GPU2 = ” GRID K520″ IS capable of Peer-to-Peer (P2P)
> GPU3 = ” GRID K520″ IS capable of Peer-to-Peer (P2P)

Checking GPU(s) for support of peer to peer memory access…
> Peer access from GRID K520 (GPU0) -> GRID K520 (GPU1) : No
> Peer access from GRID K520 (GPU0) -> GRID K520 (GPU2) : No
> Peer access from GRID K520 (GPU0) -> GRID K520 (GPU3) : No
> Peer access from GRID K520 (GPU1) -> GRID K520 (GPU0) : No
> Peer access from GRID K520 (GPU1) -> GRID K520 (GPU2) : No
> Peer access from GRID K520 (GPU1) -> GRID K520 (GPU3) : No
> Peer access from GRID K520 (GPU2) -> GRID K520 (GPU0) : No
> Peer access from GRID K520 (GPU2) -> GRID K520 (GPU1) : No
> Peer access from GRID K520 (GPU2) -> GRID K520 (GPU3) : No
> Peer access from GRID K520 (GPU3) -> GRID K520 (GPU0) : No
> Peer access from GRID K520 (GPU3) -> GRID K520 (GPU1) : No
> Peer access from GRID K520 (GPU3) -> GRID K520 (GPU2) : No
Two or more GPUs with SM 2.0 or higher capability are required for ./simpleP2P.
Peer to Peer access is not available amongst GPUs in the system, waiving test.

As you can see, g2.8xlarge does not support NVIDIA GPUDirect peer to peer transfers. Only P2 instances have the support.