[BugFix] Fix Eagle `IndexError: list index out of range` for even `num_speculative_tokens` (#29102)

Signed-off-by: Lucas Wilkinson <lwilkins@redhat.com>

tests/conftest.py

@@ -748,6 +748,14 @@ class VllmRunner:
             # being captured which can trigger edge cases that we don't handle yet.
             kwargs["compilation_config"] = {"cudagraph_capture_sizes": [4]}
 
+            # Make sure we have atleast one cudagraph large enough for a single decode.
+            if (speculative_config := kwargs.get("speculative_config")) and (
+                num_speculative_tokens := speculative_config["num_speculative_tokens"]
+            ):
+                kwargs["compilation_config"]["cudagraph_capture_sizes"].append(
+                    num_speculative_tokens + 1
+                )
+
         with init_ctx:
             self.llm = LLM(
                 model=model_name,

vllm/config/compilation.py

@@ -950,14 +950,18 @@ class CompilationConfig:
             )
         )
 
+        if len(rounded_sizes) == 0 and multiple_of <= self.max_cudagraph_capture_size:
+            # if one valid but would be round_down use that
+            rounded_sizes = [multiple_of]
+
         if len(rounded_sizes) == 0:
-            logger.warning(
-                "No valid cudagraph sizes after rounding to multiple of "
-                " num_speculative_tokens + 1 (%d); please adjust num_speculative_tokens"
-                " or max_cudagraph_capture_size (or cudagraph_capture_sizes)",
-                multiple_of,
+            raise ValueError(
+                f"No valid cudagraph sizes after rounding to multiple of {multiple_of} "
+                f"(num_speculative_tokens + 1 or tp if sequence parallelism is enabled)"
+                f" please adjust num_speculative_tokens ({uniform_decode_query_len - 1}"
+                f") or max_cudagraph_capture_size ({self.max_cudagraph_capture_size})"
+                f" or cudagraph_capture_sizes ({self.cudagraph_capture_sizes})"
             )
-            return
 
         self.max_cudagraph_capture_size = rounded_sizes[-1]
         self.cudagraph_capture_sizes = rounded_sizes

vllm/v1/spec_decode/eagle.py

@@ -86,9 +86,9 @@ class EagleProposer:
 
         self.use_cuda_graph = False
 
-        compilation_config = self.vllm_config.compilation_config
-        if compilation_config.mode == CompilationMode.VLLM_COMPILE:
-            cudagraph_mode = compilation_config.cudagraph_mode
+        self.compilation_config = self.vllm_config.compilation_config
+        if self.compilation_config.mode == CompilationMode.VLLM_COMPILE:
+            cudagraph_mode = self.compilation_config.cudagraph_mode
             if cudagraph_mode != CUDAGraphMode.NONE and not cudagraph_mode.has_mode(
                 CUDAGraphMode.PIECEWISE
             ):
@@ -103,13 +103,6 @@ class EagleProposer:
                 and not self.speculative_config.enforce_eager
             )
 
-        self.cudagraph_batch_sizes = (
-            (sorted(self.vllm_config.compilation_config.cudagraph_capture_sizes))
-            if self.use_cuda_graph
-            else []
-        )
-
-        self.use_cuda_graph = self.use_cuda_graph and bool(self.cudagraph_batch_sizes)
         # persistent buffers for cuda graph
         self.input_ids = torch.zeros(
             self.max_num_tokens, dtype=torch.int32, device=device
@@ -276,7 +269,10 @@ class EagleProposer:
             per_layer_attn_metadata[layer_name] = draft_indexer_metadata
 
         cudagraph_runtime_mode = CUDAGraphMode.NONE
-        if self.use_cuda_graph and num_tokens <= self.cudagraph_batch_sizes[-1]:
+        if (
+            self.use_cuda_graph
+            and num_tokens <= self.compilation_config.max_cudagraph_capture_size
+        ):
             num_input_tokens = self.vllm_config.pad_for_cudagraph(num_tokens)
             cudagraph_runtime_mode = CUDAGraphMode.PIECEWISE
         else:
@@ -366,7 +362,10 @@ class EagleProposer:
         # Generate the remaining draft tokens.
         draft_token_ids_list = [draft_token_ids]
 
-        if self.use_cuda_graph and batch_size <= self.cudagraph_batch_sizes[-1]:
+        if (
+            self.use_cuda_graph
+            and batch_size <= self.compilation_config.max_cudagraph_capture_size
+        ):
             input_batch_size = self.vllm_config.pad_for_cudagraph(batch_size)
             cudagraph_runtime_mode = CUDAGraphMode.PIECEWISE
         else:
@@ -777,7 +776,10 @@ class EagleProposer:
             self.positions[:num_tokens] = tree_positions.view(-1)
             self.hidden_states[:num_tokens] = tree_hidden_states.view(num_tokens, -1)
 
-            if self.use_cuda_graph and num_tokens <= self.cudagraph_batch_sizes[-1]:
+            if (
+                self.use_cuda_graph
+                and num_tokens <= self.compilation_config.max_cudagraph_capture_size
+            ):
                 num_input_tokens = self.vllm_config.pad_for_cudagraph(num_tokens)
                 cudagraph_runtime_mode = CUDAGraphMode.PIECEWISE
             else:
@@ -1114,7 +1116,10 @@ class EagleProposer:
     ) -> None:
         # Determine if CUDA graphs should be used for this run.
         cudagraphs_enabled = use_cudagraphs and self.use_cuda_graph
-        if cudagraphs_enabled and num_tokens <= self.cudagraph_batch_sizes[-1]:
+        if (
+            cudagraphs_enabled
+            and num_tokens <= self.compilation_config.max_cudagraph_capture_size
+        ):
             num_tokens = self.vllm_config.pad_for_cudagraph(num_tokens)
 
         with set_forward_context(