Remove some useless code in ModelDrafter

Signed-off-by: ziyixiong-nv <fxiong@nvidia.com>

tensorrt_llm/_torch/speculative/model_drafter.py

@@ -47,14 +47,6 @@ def __init__(
         # Sampling
         self.sampler = sampler
 
-    def _should_process_request(self, request: LlmRequest) -> bool:
-        """Check if request should be processed for drafting."""
-        return request.py_draft_pages_allocated > 0  # type: ignore
-
-    def _exceeds_max_sequence_length(self, request: LlmRequest) -> bool:
-        """Check if the request exceeds maximum sequence length for drafting."""
-        return request.max_beam_num_tokens - 1 >= self.draft_model_engine.max_seq_len
-
     def _create_draft_request(self, request_id: int, max_new_tokens: int,
                               input_tokens: Optional[List],
                               sampling_config: SamplingConfig,
@@ -81,10 +73,6 @@ def _initialize_draft_tokens(self, request: LlmRequest) -> Tuple[int, int]:
 
         return num_draft_tokens, num_accepted_tokens
 
-    def _get_draft_model_input(self, request: LlmRequest) -> Any:
-        """Get input tokens for draft model."""
-        return self.spec_config.get_draft_model_prompt(request.get_tokens()[0])
-
     def _create_context_request(self, request: LlmRequest,
                                 input_tokens: Any) -> LlmRequest:
         """Create a context request for first-time drafting."""
@@ -116,10 +104,6 @@ def _create_chunked_context_request(self, request: LlmRequest,
                                                  request.sampling_config,
                                                  request.return_perf_metrics)
         new_request.context_chunk_size = num_accepted_tokens + 1
-        new_request.context_current_position = len(
-            input_tokens) - num_accepted_tokens - 1
-        # Note: Original code has duplicate assignment (appears to be a bug, but keeping it)
-        new_request.context_chunk_size = num_accepted_tokens + 1
         new_request.context_current_position = len(
             input_tokens) - num_accepted_tokens - 1
         return new_request
@@ -129,7 +113,8 @@ def _create_draft_request_for_request(
         """Create a draft request based on the original request state."""
         num_draft_tokens, num_accepted_tokens = self._initialize_draft_tokens(
             request)
-        input_tokens = self._get_draft_model_input(request)
+        input_tokens = self.spec_config.get_draft_model_prompt(
+            request.get_tokens()[0])
 
         # First time seeing this request - context request
         if request.max_beam_num_tokens - 1 == request.py_prompt_len:
@@ -184,11 +169,18 @@ def _prepare_draft_batch(
             draft_batch = ScheduledRequests()
 
             for request in scheduled_requests.generation_requests:
-                if not self._should_process_request(request):
+                if request.py_draft_pages_allocated == 0:
+                    # No space for draft tokens
                     continue
 
-                # Stop drafting when we hit the max seqlen
-                if self._exceeds_max_sequence_length(request):
+                # Stop drafting when we hit the max seqlen. We still need dummy draft
+                # tokens attached to the requests to make sure everything works properly
+                # with CUDA graph. These dummy tokens are already added by
+                # _prepare_draft_requests to make the KV cache/scheduler aware of the fact
+                # that we want to do spec decoding, so no need to do anything else here.
+                # This makes the perf for this case suboptimal, but that's OK - this is
+                # a corner case for weird models like the llama 3.1 8b EAGLE3 implementation.
+                if request.max_beam_num_tokens - 1 >= self.draft_model_engine.max_seq_len:
                     continue
 
                 draft_request = self._create_draft_request_for_request(request)
@@ -255,17 +247,8 @@ def _update_request_states(self,
 
     def _update_requests(self, sample_state: SampleState) -> None:
         """Update requests with sample state."""
-        try:
-            if self.sampler is not None:
-                self.sampler.update_requests(sample_state)
-        except Exception as e:
-            logger.error(f"Error updating requests: {str(e)}")
-
-    def _handle_errors(self, error_msg: str) -> None:
-        """Handle errors during draft token generation."""
-        logger.error(f"Draft token generation error: {error_msg}")
-        # For now, just log the error. In a full implementation, this could
-        # clean up resources, notify other components, etc.
+        if self.sampler is not None:
+            self.sampler.update_requests(sample_state)
 
     def _process_decoded_tokens(
             self, draft_batch: ScheduledRequests,
@@ -277,7 +260,7 @@ def _process_decoded_tokens(
             target_model_req.py_draft_tokens.append(req.get_last_tokens(0))
             if req.state != LlmRequestState.GENERATION_COMPLETE and len(
                     target_model_req.py_draft_tokens
-            ) < target_model_req.py_draft_pages_allocated:  # type: ignore
+            ) < target_model_req.py_draft_pages_allocated:
                 new_requests.append(req)
             else:
                 self.draft_seq_slot_manager.free_resources(req)