[attn] fix device of tensors in attention (#25)

### What this PR does / why we need it?
Fix device of tensors created in `AscendAttentionBackendImpl`.

While specifying device to cards except card-0, there'll cause an
**device conflict** because the tensors (such as `attn_mask`) will be
put on card-0 by default.

This pr creates these tensors on the correct card corresponding to the
input.

### Does this PR introduce _any_ user-facing change?
User could specify device with local rank by this pr, and a modify on
vLLM is also needed, will related to this pr when created.

### How was this patch tested?
This is tested by the following code locally. Will add a test case when
the modify in vLLM is also completed.
```python
from vllm import LLM, SamplingParams

prompts = [
    "Hello, my name is",
    "The president of the United States is",
    "The capital of France is",
    "The future of AI is",
]

# Create a sampling params object.
sampling_params = SamplingParams(max_tokens=100, temperature=0.0)
# Create an LLM.
llm = LLM(model="~/.cache/modelscope/hub/Qwen/Qwen2___5-7B-Instruct", device="npu:1")

# Generate texts from the prompts.
outputs = llm.generate(prompts, sampling_params)
for output in outputs:
    prompt = output.prompt
    generated_text = output.outputs[0].text
    print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
```

Signed-off-by: MengqingCao <cmq0113@163.com>

examples/offline_distributed_inference_npu.py

@@ -29,11 +29,10 @@
 # Create a sampling params object.
 sampling_params = SamplingParams(max_tokens=100, temperature=0.0)
 # Create an LLM.
-# TODO (cmq): ray is not supported currently, need some fixes
 llm = LLM(
     model="facebook/opt-125m",
     tensor_parallel_size=2,
-    distributed_executor_backend="mp",
+    distributed_executor_backend="ray",
     trust_remote_code=True,
 )
 

vllm_ascend/attention.py

@@ -457,9 +457,7 @@ def __init__(
         self.kv_cache_dtype = kv_cache_dtype
         self.sliding_window = sliding_window
         if alibi_slopes is not None:
-            alibi_slopes = torch.tensor(alibi_slopes,
-                                        dtype=torch.float32,
-                                        device="npu")
+            alibi_slopes = torch.tensor(alibi_slopes, dtype=torch.float32)
         self.alibi_slopes = alibi_slopes
         self.attn_type = attn_type
 
@@ -520,7 +518,7 @@ def forward(
                     attn_metadata.sparse_mode = 2
                 attention_mask = gen_input_mask(
                     attn_metadata.max_prefill_seq_len, self.sliding_window,
-                    num_tokens)
+                    num_tokens, query.device)
                 attn_metadata.attn_mask = attention_mask
 
             if (self.alibi_slopes is not None
@@ -531,6 +529,7 @@ def forward(
                     dtype=query.dtype,
                     seq_len=attn_metadata.max_prefill_seq_len,
                     batch_size=num_tokens,
+                    device=query.device,
                 )
 
             if (len(kv_cache) == 0 or attn_metadata.block_tables is None
@@ -571,7 +570,7 @@ def forward(
                 query = query.view(query.shape[0], -1,
                                    self.num_heads * self.head_size)
                 output = torch.zeros(query.shape,
-                                     device="npu",
+                                     device=query.device,
                                      dtype=query.dtype)
                 # TODO (Mengqing Cao): torch_npu.npu_incre_flash_attention
                 # support only when `S == 1`, OPTIMIZE ME when prefix caching
@@ -621,7 +620,7 @@ def forward(
         return output
 
 
-def gen_input_mask(seq_len, sliding_window, len):
+def gen_input_mask(seq_len, sliding_window, len, device):
     """
     Generating lower triangular matrix
     """
@@ -630,15 +629,15 @@ def gen_input_mask(seq_len, sliding_window, len):
         global SHARE_MASK_TRIL_PREFIX_CACHE
         if SHARE_MASK_TRIL_PREFIX_CACHE is None:
             SHARE_MASK_TRIL_PREFIX_CACHE = torch.triu(
-                torch.ones(1, 1, 2048, 2048, dtype=bool, device="npu"),
+                torch.ones(1, 1, 2048, 2048, dtype=bool, device=device),
                 diagonal=1,
             )
         attention_mask = SHARE_MASK_TRIL_PREFIX_CACHE
     else:
         global SHARE_MASK_TRIL
         if SHARE_MASK_TRIL is None or SHARE_MASK_TRIL.shape[0] < seq_len:
             SHARE_MASK_TRIL = ~torch.tril(
-                torch.ones(seq_len, seq_len, dtype=bool, device="npu"))
+                torch.ones(seq_len, seq_len, dtype=bool, device=device))
 
         attention_mask = SHARE_MASK_TRIL
         if sliding_window is not None:
@@ -656,8 +655,10 @@ def _make_alibi_bias(
     dtype: torch.dtype,
     seq_len: int,
     batch_size: int,
+    device: torch.device,
 ):
-    bias = torch.arange(seq_len, dtype=dtype, device=alibi_slopes.device)
+    alibi_slopes = alibi_slopes.to(device)
+    bias = torch.arange(seq_len, dtype=dtype, device=device)
     # NOTE(zhuohan): HF uses
     #     `bias = bias[None, :].repeat(seq_len, 1)`
     # here. We find that both biases give the same results, but
@@ -674,7 +675,7 @@ def _make_alibi_bias(
         num_heads,
         seq_len,
         padded_len,
-        device=alibi_slopes.device,
+        device=device,
         dtype=dtype,
     )[:, :, :, :seq_len].copy_(bias)
     bias.mul_(alibi_slopes[:, None, None])