minor: zero workspace buffer init for flashinfer trtllm-gen attn (vllm-project#22603)

Author: yyihuang

tests/kernels/attention/test_flashinfer_trtllm_attention.py

@@ -113,7 +113,7 @@ def test_flashinfer_trtllm_decode_with_baseline(
     kv_indices = torch.tensor(kv_indices, dtype=torch.int32)
     kv_last_page_lens = torch.tensor(kv_last_page_lens, dtype=torch.int32)
 
-    workspace_buffer = torch.empty(128 * 1024 * 1024, dtype=torch.int8)
+    workspace_buffer = torch.zeros(128 * 1024 * 1024, dtype=torch.int8)
     wrapper = flashinfer.BatchDecodeWithPagedKVCacheWrapper(
         workspace_buffer,
         kv_layout,
@@ -247,7 +247,7 @@ def test_flashinfer_trtllm_prefill_with_baseline(
     kv_indices = torch.tensor(kv_indices, dtype=torch.int32)
     kv_last_page_lens = torch.tensor(kv_last_page_lens, dtype=torch.int32)
 
-    workspace_buffer = torch.empty(128 * 1024 * 1024, dtype=torch.int8)
+    workspace_buffer = torch.zeros(128 * 1024 * 1024, dtype=torch.int8)
     wrapper = flashinfer.BatchPrefillWithPagedKVCacheWrapper(
         workspace_buffer, kv_layout)
     wrapper.plan(q_indptr,

vllm/attention/backends/flashinfer.py

@@ -203,7 +203,7 @@ def __init__(self, runner):
 
     def _get_workspace_buffer(self):
         if self._workspace_buffer is None:
-            self._workspace_buffer = torch.empty(
+            self._workspace_buffer = torch.zeros(
                 FLASHINFER_WORKSPACE_BUFFER_SIZE,
                 dtype=torch.uint8,
                 device=self.runner.device)

vllm/v1/attention/backends/flashinfer.py

@@ -252,7 +252,7 @@ def __init__(self, kv_cache_spec: AttentionSpec, layer_names: list[str],
 
     def _get_workspace_buffer(self):
         if self._workspace_buffer is None:
-            self._workspace_buffer = torch.empty(
+            self._workspace_buffer = torch.zeros(
                 FLASHINFER_WORKSPACE_BUFFER_SIZE,
                 dtype=torch.uint8,
                 device=self.device)