[Bugfix] Resolve MTP > 1 issue when lm head tp > 1 (#4254)

### What this PR does / why we need it?

Previously, the dummy run executed compute_logits only once, regardless
of num_speculative_tokens. This caused execute_model to hang on
compute_logits when lm head tensor parallelism exceeded 1. The fix
ensures compute_logits executes correctly during dummy run, matching
num_speculative_tokens.

I set the `non_blocking` argument to False when moving
`exceeds_max_model_len` to the CPU. From what I understand, using
`non_blocking=True` and immediately accessing the tensor on the CPU can
cause accuracy problems. However, this issue doesn't happen when
transferring data to a device. ref:
https://discuss.pytorch.org/t/should-we-set-non-blocking-to-true/38234/18

- vLLM version: v0.11.0
- vLLM main:
2918c1b49c

---------

Signed-off-by: Jade Zheng <zheng.shoujian@outlook.com>

vllm_ascend/spec_decode/eagle_proposer.py

@@ -123,7 +123,8 @@ class EagleProposer(Proposer):
                   num_reqs: int = 0,
                   num_tokens_across_dp: Optional[torch.Tensor] = None,
                   aclgraph_runtime_mode: CUDAGraphMode = CUDAGraphMode.NONE,
-                  batch_descriptor=None):
+                  batch_descriptor=None,
+                  dummy_compute_logits=lambda hidden_states: None):
         moe_comm_type = self.runner._select_moe_comm_method(num_tokens)
         with set_ascend_forward_context(None,
                                         self.vllm_config,
@@ -134,6 +135,7 @@ class EagleProposer(Proposer):
                 positions=self.positions[:num_tokens],
                 hidden_states=self.hidden_states[:num_tokens],
             )
+            dummy_compute_logits(self.hidden_states)
 
     def generate_token_ids(self,
                            valid_sampled_token_ids: list[np.ndarray],

vllm_ascend/spec_decode/mtp_proposer.py

@@ -213,7 +213,8 @@ class MtpProposer(Proposer):
                   num_reqs: int = 0,
                   num_tokens_across_dp=None,
                   aclgraph_runtime_mode: CUDAGraphMode = CUDAGraphMode.NONE,
-                  batch_descriptor=None) -> None:
+                  batch_descriptor=None,
+                  dummy_compute_logits=lambda hidden_states: None) -> None:
 
         (
             num_tokens,
@@ -296,6 +297,7 @@ class MtpProposer(Proposer):
                             self.update_stream, forward_context,
                             positions.shape[0],
                             self.vllm_config.speculative_config)
+                dummy_compute_logits(previous_hidden_states)
             if with_prefill:
                 break
 
@@ -756,6 +758,7 @@ class MtpProposer(Proposer):
             logits = self.model.compute_logits(sample_hidden_states)
             if lmhead_tp_enable() and num_indices < logits.shape[0]:
                 logits = logits[:num_indices]
+                last_token_indices = last_token_indices[:num_indices]
             draft_token_ids = logits.argmax(dim=-1)
 
             if self.num_speculative_tokens == 1:
@@ -821,7 +824,7 @@ class MtpProposer(Proposer):
             # For the requests that exceed the max model length, we set the
             # sequence length to 1 to minimize their overheads in attention.
             exceeds_max_model_len_cpu = exceeds_max_model_len.to(
-                attn_metadata_i.seq_lens.device, non_blocking=True)
+                attn_metadata_i.seq_lens.device, non_blocking=False)
             attn_metadata_i.seq_lens[:batch_size].masked_fill_(
                 exceeds_max_model_len_cpu, 1)
             # Mask out the slot mappings that exceed the max model length.

vllm_ascend/spec_decode/ngram_proposer.py

@@ -27,7 +27,8 @@ class NgramProposer(VllmNgramProposer, Proposer):
                   num_reqs=None,
                   num_tokens_across_dp=None,
                   aclgraph_runtime_mode: CUDAGraphMode = CUDAGraphMode.NONE,
-                  batch_descriptor=None):
+                  batch_descriptor=None,
+                  dummy_compute_logits=lambda hidden_states: None):
         pass
 
     def generate_token_ids(self,

vllm_ascend/torchair/torchair_mtp_proposer.py

@@ -81,7 +81,8 @@ class TorchairMtpProposer(MtpProposer):
                   num_reqs: int = 0,
                   num_tokens_across_dp=None,
                   aclgraph_runtime_mode: CUDAGraphMode = CUDAGraphMode.NONE,
-                  batch_descriptor=None) -> None:
+                  batch_descriptor=None,
+                  dummy_compute_logits=lambda hidden_states: None) -> None:
         moe_comm_type = self.runner._select_moe_comm_method(num_tokens)
 
         if not with_prefill:
@@ -143,6 +144,7 @@ class TorchairMtpProposer(MtpProposer):
                     self.model(input_ids=input_ids,
                                positions=positions,
                                hidden_states=previous_hidden_states)
+                dummy_compute_logits(previous_hidden_states)
             if with_prefill:
                 break
 

vllm_ascend/worker/model_runner_v1.py

@@ -3003,14 +3003,21 @@ class NPUModelRunner(LoRAModelRunnerMixin):
 
             need_dummy_logits = (not self.in_profile_run
                                  and lmhead_tp_enable())
-
-            if need_dummy_logits:
             max_num_reqs_across_dp = num_tokens if not with_prefill else max_num_reqs
             dummy_indices = torch.zeros(max_num_reqs_across_dp,
                                         dtype=torch.int32)
 
             def dummy_compute_logits(hidden_states):
-                    return self.model.compute_logits(
+                if not need_dummy_logits:
+                    return None
+                return self.model.compute_logits(hidden_states[dummy_indices])
+
+            def dummy_drafter_compute_logits(hidden_states):
+                if not need_dummy_logits or self.drafter is None:
+                    return
+                if hasattr(self.drafter, "model") and hasattr(
+                        self.drafter.model, "compute_logits"):
+                    return self.drafter.model.compute_logits(
                         hidden_states[dummy_indices])
 
             with set_ascend_forward_context(
@@ -3032,7 +3039,6 @@ class NPUModelRunner(LoRAModelRunnerMixin):
                     with_prefill, is_torchair_compile, input_ids, positions,
                     attn_metadata, num_tokens, intermediate_tensors,
                     inputs_embeds)
-                if need_dummy_logits:
                 dummy_compute_logits(hidden_states)
 
             if self.drafter:
@@ -3042,10 +3048,8 @@ class NPUModelRunner(LoRAModelRunnerMixin):
                     num_reqs=num_reqs,
                     num_tokens_across_dp=num_tokens_across_dp,
                     aclgraph_runtime_mode=aclgraph_runtime_mode,
-                    batch_descriptor=batch_descriptor)
+                    batch_descriptor=batch_descriptor,
-                if need_dummy_logits:
+                    dummy_compute_logits=dummy_drafter_compute_logits)
-                    self.drafter.model.compute_logits(
-                        hidden_states[dummy_indices])
             if self.in_profile_run and self.dynamic_eplb:
                 self.model.clear_all_moe_loads()
             if not self.in_profile_run and self.dynamic_eplb: