[https://nvbugs/5485325][fix] Add a postprocess to the model engine to fix the CUDA graph warmup issue when using speculative decoding

tensorrt_llm/_torch/pyexecutor/cuda_graph_runner.py

@@ -136,8 +136,11 @@ def maybe_get_cuda_graph(self, batch: ScheduledRequests):
     def needs_capture(self, batch_size: int):
         return (batch_size, self.draft_len) not in self.graph_outputs
 
-    def capture(self, batch_size: int, forward_fn: Callable,
-                initial_inputs: Dict[str, Any]):
+    def capture(self,
+                batch_size: int,
+                forward_fn: Callable,
+                initial_inputs: Dict[str, Any],
+                postprocess_fn: Optional[Callable] = None):
         """Captures the forward pass for a given batch size."""
         engine = self._get_engine()
         key = (batch_size, self.draft_len)
@@ -181,8 +184,12 @@ def capture(self, batch_size: int, forward_fn: Callable,
         with with_multi_stream(True), piecewise_cuda_graph(False):
             for _ in range(self.WARMUP_STEPS):
                 forward_fn(capture_inputs)
+                if postprocess_fn is not None:
+                    postprocess_fn(capture_inputs)
             with torch.cuda.graph(graph, pool=self.memory_pool):
                 output = forward_fn(capture_inputs)
+            if postprocess_fn is not None:
+                postprocess_fn(capture_inputs)
 
         self.graphs[key] = graph
         self.graph_outputs[key] = make_weak_ref(output)

tensorrt_llm/_torch/pyexecutor/model_engine.py

@@ -1133,6 +1133,26 @@ def _preprocess_inputs(self, inputs: Dict[str, Any]):
                         self.previous_kv_lens_offsets_cuda[:num_gen_requests])
         return inputs
 
+    def _postprocess_inputs(self, inputs: Dict[str, Any]):
+        """
+        Postprocess to make sure model forward doesn't change the inputs.
+        It is only used in cuda graph capture, because other cases will prepare
+        new inputs before the model forward.
+        """
+        if self.enable_spec_decode and not self._disable_overlap_scheduler:
+            if inputs['attn_metadata'].kv_cache_manager is not None:
+                num_seqs = inputs['attn_metadata'].num_seqs
+                num_ctx_requests = inputs['attn_metadata'].num_contexts
+                num_gen_requests = inputs['attn_metadata'].num_generations
+                num_ctx_tokens = inputs['attn_metadata'].num_ctx_tokens
+                previous_batch_tokens = inputs['input_ids'].shape[
+                    0] - num_ctx_tokens
+                inputs['position_ids'][0, num_ctx_tokens:] -= (
+                    self.previous_pos_id_offsets_cuda[:previous_batch_tokens])
+                inputs['attn_metadata'].kv_lens_cuda[
+                    num_ctx_requests:num_seqs] -= (
+                        self.previous_kv_lens_offsets_cuda[:num_gen_requests])
+
     def _get_all_rank_num_tokens(self, attn_metadata: AttentionMetadata):
         if self.enable_attention_dp:
             return list(self.dist.tp_allgather(attn_metadata.num_tokens))
@@ -2206,8 +2226,12 @@ def capture_forward_fn(inputs: Dict[str, Any]):
                                 gather_ids=gather_ids,
                                 gather_context_logits=gather_context_logits)
 
+                    def capture_postprocess_fn(inputs: Dict[str, Any]):
+                        self._postprocess_inputs(inputs)
+
                     self.cuda_graph_runner.capture(batch_size,
-                                                   capture_forward_fn, inputs)
+                                                   capture_forward_fn, inputs,
+                                                   capture_postprocess_fn)
 
                     # here we don't need to use context since cuda graph capture didn't run kernel.
                     # maybe we need a cleaner way to do this.

tests/integration/defs/accuracy/test_llm_api_pytorch.py

@@ -1871,6 +1871,42 @@ def test_nvfp4_multi_gpus(self, tp_size, pp_size, ep_size, mtp_nextn, fp8kv,
             # task.evaluate(llm,
             #               extra_evaluator_kwargs=dict(apply_chat_template=True))
 
+    def test_nvfp4_multi_gpus_corner_case(self):
+        """
+        This test is used to test the corner case of the NVFP4 model.
+        When using the same value for max_seq_len and max_num_tokens, there will be no
+        enough kv block for the dummy requests in CUDA graph warmup when creating
+        the py_executor before estimating kv cache. Then CUDA graph capture will be
+        triggered when estimating kv cache. This may cause some errors.
+        More info in https://nvbugs/5485325.
+        """
+        kv_cache_config = KvCacheConfig(free_gpu_memory_fraction=0.80,
+                                        dtype="fp8",
+                                        enable_block_reuse=False)
+        pytorch_config = dict(disable_overlap_scheduler=False,
+                              cuda_graph_config=CudaGraphConfig(
+                                  enable_padding=True, max_batch_size=1024),
+                              moe_config=MoeConfig(backend="TRTLLM"))
+
+        mtp_config = MTPDecodingConfig(num_nextn_predict_layers=1)
+        with LLM(f"{llm_models_root()}/DeepSeek-R1/DeepSeek-R1-FP4",
+                 tensor_parallel_size=8,
+                 pipeline_parallel_size=1,
+                 moe_expert_parallel_size=8,
+                 kv_cache_config=kv_cache_config,
+                 **pytorch_config,
+                 enable_attention_dp=False,
+                 speculative_config=mtp_config,
+                 max_seq_len=5120,
+                 max_num_tokens=5120) as llm:
+
+            assert llm.args.quant_config.quant_algo == QuantAlgo.NVFP4
+
+            task = MMLU(self.MODEL_NAME)
+            task.evaluate(llm)
+            task = GSM8K(self.MODEL_NAME)
+            task.evaluate(llm)
+
     @pytest.mark.skip_less_mpi_world_size(8)
     @skip_pre_hopper
     @pytest.mark.parametrize(

tests/integration/test_lists/qa/llm_function_full.txt

@@ -526,6 +526,7 @@ accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus[latency_
 accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus[throughput]
 accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus[throughput_tp8]
 accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus[throughput_tp4]
+accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus_corner_case
 accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_fp8_blockscale[throughput]
 accuracy/test_llm_api_pytorch.py::TestQwen3_8B::test_fp8_block_scales[latency]
 accuracy/test_llm_api_pytorch.py::TestQwen3_30B_A3B::test_fp8_block_scales[latency-torch_compile=False]

tests/integration/test_lists/qa/llm_function_sanity.txt

@@ -35,6 +35,7 @@ accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus[latency]
 accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus[throughput_tp4]
 accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus[throughput_tp8]
 accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus[throughput]
+accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus_corner_case
 accuracy/test_llm_api_pytorch.py::TestDeepSeekV3Lite::test_bfloat16_4gpus_online_eplb[mtp_nextn=0]
 accuracy/test_llm_api_pytorch.py::TestDeepSeekV3Lite::test_bfloat16_4gpus_online_eplb[mtp_nextn=2]
 accuracy/test_llm_api_pytorch.py::TestDeepSeekV3Lite::test_bfloat16[mtp_nextn=0-attention_dp=False-cuda_graph=False-overlap_scheduler=False-torch_compile=False-enable_chunked_prefill=False]

tests/integration/test_lists/test-db/l0_dgx_b200.yml

@@ -70,6 +70,21 @@ l0_dgx_b200:
   - accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus[throughput_mtp] TIMEOUT (180)
   - accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_fp8_blockscale[throughput] TIMEOUT (180)
   - accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_fp8_blockscale[throughput_mtp] TIMEOUT (180)
+- condition:
+    ranges:
+      system_gpu_count:
+        gte: 8
+        lte: 8
+    wildcards:
+      gpu:
+      - '*b200*'
+      linux_distribution_name: ubuntu*
+      cpu: x86_64
+    terms:
+      stage: post_merge
+      backend: pytorch
+  tests:
+  - accuracy/test_llm_api_pytorch.py::TestDeepSeekR1::test_nvfp4_multi_gpus_corner_case TIMEOUT (180)
 - condition:
     ranges:
       system_gpu_count: