[Feature][Spec Decode] Simplify the use of Eagle Spec Decode (#12304)

Signed-off-by: Shangming Cai <caishangming@linux.alibaba.com>

tests/spec_decode/test_spec_decode_worker.py

@@ -13,15 +13,18 @@ from vllm.model_executor.layers.sampler import SamplerOutput
 from vllm.model_executor.utils import set_random_seed
 from vllm.sequence import ExecuteModelRequest, SequenceOutput
 from vllm.spec_decode.batch_expansion import BatchExpansionTop1Scorer
+from vllm.spec_decode.draft_model_runner import TP1DraftModelRunner
 from vllm.spec_decode.interfaces import SpeculativeProposals
 from vllm.spec_decode.metrics import (AsyncMetricsCollector,
                                       SpecDecodeWorkerMetrics)
 from vllm.spec_decode.multi_step_worker import MultiStepWorker
 from vllm.spec_decode.spec_decode_worker import (SpecDecodeWorker,
                                                  split_num_cache_blocks_evenly)
+from vllm.worker.worker import Worker
 
 from .test_utils import mock_spec_decode_sampler
-from .utils import create_batch, create_sampler_output_list, mock_worker
+from .utils import (create_batch, create_sampler_output_list, create_worker,
+                    mock_worker)
 
 
 @pytest.mark.parametrize('k', [1, 2, 6])
@@ -905,3 +908,38 @@ def test_chunked_prefill_flow(k: int, batch_size: int, batch_composition: str):
             worker.execute_model(execute_model_req=execute_model_req)
         # but first draft still counted
         assert draft_worker.get_spec_proposals.call_count == 1
+
+
+def test_correctly_load_weight_for_eagle():
+    """
+        Verify SpecDecodeWorker loads lm_head weight for eagle correctly.
+    """
+    seed = 100
+    block_size = 32
+    num_gpu_blocks = 8096 // block_size
+    target_worker = create_worker(
+        Worker,
+        "JackFram/llama-68m",
+        block_size,
+        num_gpu_blocks,
+        seed,
+    )
+    draft_worker = create_worker(
+        MultiStepWorker,
+        "abhigoyal/vllm-eagle-llama-68m-random",
+        block_size,
+        num_gpu_blocks,
+        seed,
+        model_runner_cls=TP1DraftModelRunner,
+    )
+
+    spec_decode_sampler = mock_spec_decode_sampler("rejection_sampler")
+    worker = SpecDecodeWorker(draft_worker,
+                              target_worker,
+                              spec_decode_sampler,
+                              disable_logprobs=False)
+    worker.proposer_worker.maybe_load_lm_head_weight(
+        target_worker.model_runner.model.lm_head.weight.data)
+    assert torch.allclose(
+        worker.proposer_worker.worker.model_runner.model.lm_head.weight.data,
+        worker.scorer_worker.model_runner.model.lm_head.weight.data)