XPU and MPS support

[jatkinson1000]

@ElliottKasoar has done some work to use the MPS backend on apple silicon in #125

He has also started similar efforts to add XPU support on the intel GPU devices, but this may take more work if the backend isn't currently part of Torch.
@christopheredsall and @ma595 have offered to look at this on Dawn.

[jatkinson1000]

Looks like there is some XPU info in the C++ docs on pytorch: https://pytorch.org/cppdocs/api/dir_c10.html#dir-c10

[ElliottKasoar]

Sorry for not sharing more about what I've looked into on the XPU side. I would have liked to see if I could at least do something with the basic Intel extension that in theory I could run on CPU, which is probably a sensible first step, but I've had no time.

What I'd had found so far:

From PyTorch:

• PyTorch Tutorials for CPU and GPU via Python and CPU-only C++, including example CMakeLists.txt

From Intel:

• General Intel docs for CPU and GPU
  • The search doesn't seem to work for me, so it can be tricky to find things
  • XPU C++ API
• Intel C++ inference example with installation instructions (note the cppsdk package for installing)
  • Includes a useful link to a (CPU) example for C++, including an example app and CMakeLists.txt
  • Equivalent XPU example

The find_package and variables set differ between the PyTorch and Intel CMakeLists.txt examples, so I suspect the PyTorch example is slightly outdated.

My initial thoughts for changes we would need were something along the lines of an ENABLE_INTEL flag, which we could use both to change the find_package and what we link to:

if(ENABLE_INTEL)
  find_package(IPEX REQUIRED)
else()
  find_package(Torch REQUIRED)
endif()
...
...
-
if(ENABLE_INTEL)
  target_link_libraries(${LIB_NAME} PRIVATE ${TORCH_IPEX_LIBRARIES})
else()
  target_link_libraries(${LIB_NAME} PRIVATE ${TORCH_LIBRARIES})
endif()

I can't check right now, but I think finding the package worked ok, but I was getting errors linking, I think related to glibc versions.

[ElliottKasoar]

It's not immediately completely clear exactly how it fits in with ipex, but worth noting that it looks like Intel (Data Center, for now) GPUs should be supported natively as of PyTorch 2.4.

My initial reading is that ipex still should offer additional optimisation for CPU and/or GPU, and I think I saw a comment that there's "No change of the upstreaming goal", but this potentially simplifies immediate setup, with ipex potentially becoming more of a nice-to-have optimisation option instead of a requirement.

I may have misunderstood, though.