fix import flashinfer error on AMD GPUs

[akaitsuki-ii]

Getting CUDA arch flags raises error during importing flashinfer on AMD GPUs. As flashinfer is not officially supported on AMD platform, just disable it when flashinfer is not installed.

[eppaneamd]

@akaitsuki-ii I think this fix needs to be revisited, due to:

• When flashinfer is installed on AMD GPUs, HAS_FLASHINFER gets set to True in globals when e.g. MI300X returns (9, 4) from torch.cuda.get_device_capability()
  • (TORCH_CUDA_ARCH_LIST is NVIDIA specific envvar)
• torch_cpp_ext._get_cuda_arch_flags() function is NVIDIA specific so that will crash on AMD GPUs when HAS_FLASHINFER = True
  • (There exists a rocm counterpart called _get_rocm_arch_flags)

If disabling flashinfer is desired on AMD GPUs, then the HAS_FLASHINFER check at globals could be augmented with torch.version.hip, so something like:

try:
    from flashinfer.prefill import single_prefill_with_kv_cache
    
    if torch.version.hip:
        raise ImportError("FlashInfer not supported on AMD GPUs")

    HAS_FLASHINFER = True
    def get_cuda_arch():
        major, minor = torch.cuda.get_device_capability()
        return f"{major}.{minor}"

    cuda_arch = get_cuda_arch()
    os.environ['TORCH_CUDA_ARCH_LIST'] = cuda_arch
    print(f"Set TORCH_CUDA_ARCH_LIST to {cuda_arch}")
except ImportError as e:
    print("Warning: ", type(e).__name__, "–", e)
    HAS_FLASHINFER = False

And the suggested

if HAS_FLASHINFER:
    torch_cpp_ext._get_cuda_arch_flags()

Can be added/kept (as the purpose of that function is to raise an error if unknown CUDA arch is detected).

[feifeibear]

Hi dose this #150 PR solve the problem.

[akaitsuki-ii]

@feifeibear Yes, LGTM. Thank you and let me close this PR.