Fix torch.compile issue of dispatch key set mismatch

[yuwenzho]

Issue:

torch.compile recompiles after warmup because tensor 'L['input_ids']' dispatch key set mismatch. expected DispatchKeySet(HPU, BackendSelect), actual DispatchKeySet(HPU, BackendSelect, ADInplaceOrView).

Detail:

Run script with TORCH_LOGS="guards" and get different dispatch key set info:

• warmup:

TENSOR_MATCH: check_tensor(L['input_ids'], Tensor, DispatchKeySet(HPU, BackendSelect), torch.int64, device=0, requires_grad=False, size=[2, 1], stride=[1, 1])  # masked_input = input_  # ome/zyuwen/workspace/vllm/habana_main_g3_v2/vllm/model_executor/layers/vocab_parallel_embedding.py:358 in forward

• after warmup:

TENSOR_MATCH: check_tensor(L['input_ids'], Tensor, DispatchKeySet(HPU, BackendSelect, ADInplaceOrView), torch.int64, device=0, requires_grad=False, size=[2, 1], stride=[1, 1])  # masked_input = input_  # ome/zyuwen/workspace/vllm/habana_main_g3_v2/vllm/model_executor/layers/vocab_parallel_embedding.py:358 in forward 

Solution:

The difference in dispatch key set is caused by the 'torch.inference_mode()' decoration, and here is a simple example:

import torch
import habana_frameworks.torch as htorch

@torch.inference_mode()
def func():    
    x = torch.rand(3, 3).to("hpu")    
    print(torch._C._dispatch_key_set(x))
func() 
# output: DispatchKeySet(HPU, AutocastHPU)

import torch
import habana_frameworks.torch as htorch 

def func():    
    x = torch.rand(3, 3).to("hpu")    
    print(torch._C._dispatch_key_set(x)) 
func() 
# output: DispatchKeySet(HPU, ADInplaceOrView, AutogradHPU, AutocastHPU) 

In vllm-fork, the warmup phase is decorated with torch.inference_mode() in habana_model_runner.py#L1487-L1488, but the after-warmup phase is not.

So in this PR I add the decorator to prepare_input_tensors function to keep the dispatch key set the same.

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