SimpleP2P with Quadro P4000 and GeForce GTX 1080Ti not available?

Accelerated Computing CUDA CUDA Setup and Installation
1

I tried to use GPUDirect between Quadro p4000 and 1080 Ti, but SimpleP2P showed me p2p between these two GPUs is NO.

ubuntu@:~$ nvidia-smi topo -m
        GPU0    GPU1    GPU2    CPU Affinity
GPU0     X      PHB     SOC     0-31
GPU1    PHB      X      SOC     0-31
GPU2    SOC     SOC      X      0-31

Legend:

  X   = Self
  SOC  = Connection traversing PCIe as well as the SMP link between CPU sockets(e.g. QPI)
  PHB  = Connection traversing PCIe as well as a PCIe Host Bridge (typically the CPU)
  PXB  = Connection traversing multiple PCIe switches (without traversing the PCIe Host Bridge)
  PIX  = Connection traversing a single PCIe switch
  NV#  = Connection traversing a bonded set of # NVLinks

[./simpleP2P] - Starting...
Checking for multiple GPUs...
CUDA-capable device count: 3
> GPU0 = "GeForce GTX 1080 Ti" IS  capable of Peer-to-Peer (P2P)
> GPU1 = "   Quadro P4000" IS  capable of Peer-to-Peer (P2P)
> GPU2 = "   Quadro P4000" IS  capable of Peer-to-Peer (P2P)

Checking GPU(s) for support of peer to peer memory access...
> Peer access from GeForce GTX 1080 Ti (GPU0) -> Quadro P4000 (GPU1) : No
> Peer access from GeForce GTX 1080 Ti (GPU0) -> Quadro P4000 (GPU2) : No
> Peer access from Quadro P4000 (GPU1) -> GeForce GTX 1080 Ti (GPU0) : No
> Peer access from Quadro P4000 (GPU1) -> Quadro P4000 (GPU2) : No
> Peer access from Quadro P4000 (GPU2) -> GeForce GTX 1080 Ti (GPU0) : No
> Peer access from Quadro P4000 (GPU2) -> Quadro P4000 (GPU1) : 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.

# dmidecode 3.0
Getting SMBIOS data from sysfs.
SMBIOS 2.8 present.
2

If the test indicates it is not possible, then it is not possible for your setup.
P2P is not guaranteed to be supported in every scenario. If you desire P2P support, you should work with your system vendor to ensure that P2P support is available.

If this is a skylake CPU system, that may be one possible explanation.