[https://nvbugs/5498967][fix] Downgrade NCCL (#7556)

Signed-off-by: yizhang-nv <187001205+yizhang-nv@users.noreply.github.com>

cpp/tensorrt_llm/kernels/userbuffers/ub_allocator.cpp

@@ -83,6 +83,8 @@ communicator* UserBufferAllocator::comm()
     return mUbComm;
 }
 
+#if NCCL_VERSION_CODE >= NCCL_VERSION(2, 27, 0)
+
 void NCCLUserBufferAllocator::initialize(tensorrt_llm::runtime::WorldConfig const& worldConfig)
 {
     if (!isInitialized())
@@ -244,6 +246,18 @@ bool NCCLHelper::isLoaded() const
     return mIsLoaded;
 }
 
+#else
+
+void NCCLUserBufferAllocator::initialize(tensorrt_llm::runtime::WorldConfig const& worldConfig)
+{
+    TLLM_CHECK_WITH_INFO(false,
+        "NCCL symmetric is not supported for nccl version < 2.27. Please upgrade nccl to 2.27 or higher and rebuild "
+        "tensorrt_llm or disable nccl symmetric");
+    return;
+}
+
+#endif
+
 bool UserBufferAllocator::use_nccl_symmetric = false;
 
 }; // namespace tensorrt_llm::runtime::ub

cpp/tensorrt_llm/kernels/userbuffers/ub_allocator.h

@@ -35,13 +35,22 @@ struct UBBuffer
     void* addr;
     int handle;
     size_t size;
+#if NCCL_VERSION_CODE >= NCCL_VERSION(2, 27, 0)
     ncclWindow_t window;
+#endif
 
-    UBBuffer(void* a = nullptr, int h = -1, size_t s = 0, ncclWindow_t w = nullptr)
+    UBBuffer(void* a = nullptr, int h = -1, size_t s = 0
+#if NCCL_VERSION_CODE >= NCCL_VERSION(2, 27, 0)
+        ,
+        ncclWindow_t w = nullptr
+#endif
+        )
         : addr(a)
         , handle(h)
         , size(s)
+#if NCCL_VERSION_CODE >= NCCL_VERSION(2, 27, 0)
         , window(w)
+#endif
     {
     }
 
@@ -77,6 +86,8 @@ protected:
     tensorrt_llm::runtime::WorldConfig mWorldConfig;
 };
 
+#if NCCL_VERSION_CODE >= NCCL_VERSION(2, 27, 0)
+
 class NCCLHelper
 {
 public:
@@ -125,6 +136,13 @@ private:
     std::shared_ptr<ncclComm_t> mComm;
     static std::unique_ptr<NCCLHelper> mNCCLHelper;
 };
+#else
+class NCCLUserBufferAllocator : public UserBufferAllocator
+{
+public:
+    void initialize(tensorrt_llm::runtime::WorldConfig const& world_config) override;
+};
+#endif
 
 #else
 using communicator = void;

docker/common/install_tensorrt.sh

@@ -9,9 +9,8 @@ CUDA_VER="12.9" # 12.9.1
 # Keep the installation for cuDNN if users want to install PyTorch with source codes.
 # PyTorch 2.x can compile with cuDNN v9.
 CUDNN_VER="9.10.2.21-1"
-# NGC PyTorch 25.06 image uses NCCL 2.27.3, while NCCL 2.27.5 resolves a perf regression issue.
-# Use NCCL version 2.27.5 instead.
-NCCL_VER="2.27.5-1+cuda12.9"
+# Downgrade NCCL version to 2.25.1 temporarily
+NCCL_VER="2.25.1-1+cuda12.8"
 CUBLAS_VER="12.9.1.4-1"
 # Align with the pre-installed CUDA / NVCC / NVRTC versions from
 # https://docs.nvidia.com/cuda/cuda-toolkit-release-notes/index.html

jenkins/current_image_tags.properties

@@ -12,7 +12,7 @@
 # NB: Typically, the suffix indicates the PR whose CI pipeline generated the images. In case that
 #     images are adopted from PostMerge pipelines, the abbreviated commit hash is used instead.
 IMAGE_NAME=urm.nvidia.com/sw-tensorrt-docker/tensorrt-llm
-LLM_DOCKER_IMAGE=urm.nvidia.com/sw-tensorrt-docker/tensorrt-llm:pytorch-25.06-py3-x86_64-ubuntu24.04-trt10.11.0.33-skip-tritondevel-202508201630-pre-test
-LLM_SBSA_DOCKER_IMAGE=urm.nvidia.com/sw-tensorrt-docker/tensorrt-llm:pytorch-25.06-py3-aarch64-ubuntu24.04-trt10.11.0.33-skip-tritondevel-202508201630-pre-test
-LLM_ROCKYLINUX8_PY310_DOCKER_IMAGE=urm.nvidia.com/sw-tensorrt-docker/tensorrt-llm:cuda-12.9.1-devel-rocky8-x86_64-rocky8-py310-trt10.11.0.33-skip-tritondevel-202508201630-pre-test
-LLM_ROCKYLINUX8_PY312_DOCKER_IMAGE=urm.nvidia.com/sw-tensorrt-docker/tensorrt-llm:cuda-12.9.1-devel-rocky8-x86_64-rocky8-py312-trt10.11.0.33-skip-tritondevel-202508201630-pre-test
+LLM_DOCKER_IMAGE=urm.nvidia.com/sw-tensorrt-docker/tensorrt-llm:pytorch-25.06-py3-x86_64-ubuntu24.04-trt10.11.0.33-skip-tritondevel-202509051530-7556
+LLM_SBSA_DOCKER_IMAGE=urm.nvidia.com/sw-tensorrt-docker/tensorrt-llm:pytorch-25.06-py3-aarch64-ubuntu24.04-trt10.11.0.33-skip-tritondevel-202509051530-7556
+LLM_ROCKYLINUX8_PY310_DOCKER_IMAGE=urm.nvidia.com/sw-tensorrt-docker/tensorrt-llm:cuda-12.9.1-devel-rocky8-x86_64-rocky8-py310-trt10.11.0.33-skip-tritondevel-202509051530-7556
+LLM_ROCKYLINUX8_PY312_DOCKER_IMAGE=urm.nvidia.com/sw-tensorrt-docker/tensorrt-llm:cuda-12.9.1-devel-rocky8-x86_64-rocky8-py312-trt10.11.0.33-skip-tritondevel-202509051530-7556

tensorrt_llm/_torch/pyexecutor/model_engine.py

@@ -2334,6 +2334,8 @@ class PyTorchModelEngine(ModelEngine):
         if not ub.ub_supported():
             return False
         use_nccl_symmetric = self.pytorch_backend_config.allreduce_strategy == "NCCL_SYMMETRIC"
+        if use_nccl_symmetric:
+            return False
         ub.initialize_userbuffers_manager(
             self.mapping.tp_size, self.mapping.pp_size, self.mapping.cp_size,
             self.mapping.rank, self.mapping.gpus_per_node,

tests/unittest/_torch/multi_gpu/test_mnnvl_allreduce.py

@@ -184,6 +184,9 @@ def row_linear_residual_norm_fusion_forward(
 def test_row_linear_residual_norm_fusion(seq_len, hidden_size, dtype, strategy,
                                          fusion):
 
+    if strategy == AllReduceStrategy.NCCL_SYMMETRIC:
+        pytest.skip("NCCL symmetric is not supported for nccl version < 2.27.")
+
     torch.manual_seed(42)
     tensor_parallel_size = 2