[Kernel] Refactor FlashInfer allreduce for mnnvl backend (#34109)

Signed-off-by: hjjq <50634613+hjjq@users.noreply.github.com>
Signed-off-by: wzhao18 <wzhao18.sz@gmail.com>
Co-authored-by: wzhao18 <wzhao18.sz@gmail.com>
Co-authored-by: Wei Zhao <51183510+wzhao18@users.noreply.github.com>

benchmarks/kernels/benchmark_device_communicators.py

@@ -30,6 +30,9 @@ import torch.distributed as dist
 from torch.distributed import ProcessGroup
 
 from vllm.distributed.device_communicators.custom_all_reduce import CustomAllreduce
+from vllm.distributed.device_communicators.flashinfer_all_reduce import (
+    FlashInferAllReduce,
+)
 from vllm.distributed.device_communicators.pynccl import (
     PyNcclCommunicator,
     register_nccl_symmetric_ops,
@@ -44,7 +47,7 @@ from vllm.utils.argparse_utils import FlexibleArgumentParser
 logger = init_logger(__name__)
 
 # Default sequence lengths to benchmark
-DEFAULT_SEQUENCE_LENGTHS = [128, 512, 1024, 2048, 4096, 8192]
+DEFAULT_SEQUENCE_LENGTHS = [16, 64, 128, 512, 1024, 2048, 4096, 8192]
 
 # Fixed hidden size and dtype for all benchmarks
 HIDDEN_SIZE = 8192
@@ -81,6 +84,7 @@ class CommunicatorBenchmark:
         self.symm_mem_comm = None
         self.symm_mem_comm_multimem = None
         self.symm_mem_comm_two_shot = None
+        self.fi_ar_comm = None
 
         self._init_communicators()
 
@@ -161,6 +165,22 @@ class CommunicatorBenchmark:
             )
             self.symm_mem_comm_two_shot = None
 
+        try:
+            self.fi_ar_comm = FlashInferAllReduce(
+                group=self.cpu_group,
+                device=self.device,
+            )
+            if not self.fi_ar_comm.disabled:
+                logger.info("Rank %s: FlashInferAllReduce initialized", self.rank)
+            else:
+                logger.info("Rank %s: FlashInferAllReduce disabled", self.rank)
+                self.fi_ar_comm = None
+        except Exception as e:
+            logger.warning(
+                "Rank %s: Failed to initialize FlashInferAllReduce: %s", self.rank, e
+            )
+            self.fi_ar_comm = None
+
     def benchmark_allreduce(
         self, sequence_length: int, num_warmup: int, num_trials: int
     ) -> dict[str, float]:
@@ -180,7 +200,8 @@ class CommunicatorBenchmark:
                     lambda t, c=comm: c.custom_all_reduce(t),
                     lambda t, c=comm: c.should_custom_ar(t),
                     comm.capture(),
-                    "1stage",  # env variable value
+                    {"VLLM_CUSTOM_ALLREDUCE_ALGO": "1stage"},
+                    None,  # no destroy function
                 )
             )
             # CustomAllreduce two-shot
@@ -190,7 +211,8 @@ class CommunicatorBenchmark:
                     lambda t, c=comm: c.custom_all_reduce(t),
                     lambda t, c=comm: c.should_custom_ar(t),
                     comm.capture(),
-                    "2stage",  # env variable value
+                    {"VLLM_CUSTOM_ALLREDUCE_ALGO": "2stage"},
+                    None,  # no destroy function
                 )
             )
 
@@ -202,7 +224,8 @@ class CommunicatorBenchmark:
                     lambda t, c=comm: c.all_reduce(t),
                     lambda t: True,  # Always available if initialized
                     nullcontext(),
-                    None,  # no env variable needed
+                    {},  # no env variable needed
+                    None,  # no destroy function
                 )
             )
             communicators.append(
@@ -211,7 +234,8 @@ class CommunicatorBenchmark:
                     lambda t: torch.ops.vllm.all_reduce_symmetric_with_copy(t),
                     lambda t: True,  # Always available if initialized
                     nullcontext(),
-                    None,  # no env variable needed
+                    {},  # no env variable needed
+                    None,  # no destroy function
                 )
             )
 
@@ -223,7 +247,8 @@ class CommunicatorBenchmark:
                     lambda t, c=comm: c.all_reduce(t),
                     lambda t, c=comm: c.should_use_symm_mem(t),
                     nullcontext(),
-                    None,  # no env variable needed
+                    {},  # no env variable needed
+                    None,  # no destroy function
                 )
             )
 
@@ -235,29 +260,67 @@ class CommunicatorBenchmark:
                     lambda t, c=comm: c.all_reduce(t),
                     lambda t, c=comm: c.should_use_symm_mem(t),
                     nullcontext(),
-                    None,  # no env variable needed
+                    {},  # no env variable needed
+                    None,  # no destroy function needed
+                )
+            )
+
+        if self.fi_ar_comm is not None:
+            comm = self.fi_ar_comm
+            communicators.append(
+                (
+                    "flashinfer_trtllm",
+                    lambda t, c=comm: c.all_reduce(t),
+                    lambda t, c=comm: c.should_use_fi_ar(t),
+                    nullcontext(),
+                    {"VLLM_FLASHINFER_ALLREDUCE_BACKEND": "trtllm"},
+                    lambda c=comm: c.destroy(),
+                )
+            )
+            communicators.append(
+                (
+                    "flashinfer_mnnvl",
+                    lambda t, c=comm: c.all_reduce(t),
+                    lambda t, c=comm: c.should_use_fi_ar(t),
+                    nullcontext(),
+                    {"VLLM_FLASHINFER_ALLREDUCE_BACKEND": "mnnvl"},
+                    lambda c=comm: c.destroy(),
                 )
             )
 
         # Benchmark each communicator
-        for name, allreduce_fn, should_use_fn, context, env_var in communicators:
-            # Set environment variable if needed
-            if env_var is not None:
-                os.environ["VLLM_CUSTOM_ALLREDUCE_ALGO"] = env_var
-            else:
-                # Clear the environment variable to avoid interference
-                os.environ.pop("VLLM_CUSTOM_ALLREDUCE_ALGO", None)
-
-            latency = self.benchmark_allreduce_single(
-                sequence_length,
-                allreduce_fn,
-                should_use_fn,
-                context,
-                num_warmup,
-                num_trials,
-            )
-            if latency is not None:
-                results[name] = latency
+        for (
+            name,
+            allreduce_fn,
+            should_use_fn,
+            context,
+            env_dict,
+            destroy_fn,
+        ) in communicators:
+            # Save original values and apply new environment variables
+            saved_env = {key: os.environ.get(key) for key in env_dict}
+            for key, value in env_dict.items():
+                os.environ[key] = value
+            try:
+                latency = self.benchmark_allreduce_single(
+                    sequence_length,
+                    allreduce_fn,
+                    should_use_fn,
+                    context,
+                    num_warmup,
+                    num_trials,
+                )
+                if latency is not None:
+                    results[name] = latency
+            finally:
+                if destroy_fn is not None:
+                    destroy_fn()
+                # Restore environment variables to their original state
+                for key, original_value in saved_env.items():
+                    if original_value is None:
+                        os.environ.pop(key, None)
+                    else:
+                        os.environ[key] = original_value
 
         return results
 

benchmarks/kernels/benchmark_fused_collective.py

@@ -5,8 +5,11 @@
 Benchmark for FlashInfer fused collective operations vs standard operations.
 
 This benchmark compares:
-1. FlashInfer's allreduce_fusion (fused allreduce + rmsnorm + optional quant)
-2. Standard tensor_model_parallel_all_reduce + separate rmsnorm/quant operations
+1. FlashInfer's allreduce_fusion with trtllm backend
+   (fused allreduce + rmsnorm + optional FP8/FP4 quant)
+2. FlashInfer's allreduce_fusion with mnnvl backend
+   (fused allreduce + rmsnorm only, no quantization support)
+3. Standard tensor_model_parallel_all_reduce + separate rmsnorm/quant operations
 
 Usage with torchrun:
     torchrun --nproc_per_node=2 benchmark_fused_collective.py
@@ -48,8 +51,12 @@ SCALED_FP4_QUANT_OP = torch.ops._C.scaled_fp4_quant
 logger = init_logger(__name__)
 
 # Try to import FlashInfer
+TorchDistBackend = None
 try:
     import flashinfer.comm as flashinfer_comm  # type: ignore
+    from flashinfer.comm.mnnvl import (  # type: ignore
+        TorchDistBackend,
+    )
 
     if not (
         hasattr(flashinfer_comm, "allreduce_fusion")
@@ -74,11 +81,15 @@ _FI_MAX_SIZES = {
     8: 64 * MiB,  # 64MB
 }
 
-# Global workspace tensor for FlashInfer
-_FI_WORKSPACE = None
+# Global workspace tensors for FlashInfer (keyed by backend name)
+_FI_WORKSPACES: dict = {}
+
+# Backends to benchmark
+FLASHINFER_BACKENDS = ["trtllm", "mnnvl"]
 
 
 def setup_flashinfer_workspace(
+    backend: str,
     world_size: int,
     rank: int,
     hidden_dim: int,
@@ -86,41 +97,54 @@ def setup_flashinfer_workspace(
     dtype: torch.dtype,
 ):
     """Setup FlashInfer workspace for fused allreduce operations."""
-    global _FI_WORKSPACE
+    global FI_WORKSPACES
 
     if flashinfer_comm is None:
-        return None, None
+        return None
 
     if world_size not in _FI_MAX_SIZES:
         logger.warning("FlashInfer not supported for world size %s", world_size)
-        return None, None
+        return None
 
     try:
+        kwargs = {}
+        if TorchDistBackend is not None:
+            kwargs["comm_backend"] = TorchDistBackend(group=dist.group.WORLD)
+
         workspace = flashinfer_comm.create_allreduce_fusion_workspace(
-            backend="trtllm",
+            backend=backend,
             world_size=world_size,
             rank=rank,
             max_token_num=max_token_num,
             hidden_dim=hidden_dim,
             dtype=dtype,
+            **kwargs,
         )
 
-        _FI_WORKSPACE = workspace
+        _FI_WORKSPACES[backend] = workspace
         return workspace
     except Exception as e:
-        logger.error("Failed to setup FlashInfer workspace: %s", e)
+        logger.error(
+            "Failed to setup FlashInfer workspace (backend=%s): %s", backend, e
+        )
         return None
 
 
-def cleanup_flashinfer_workspace(workspace):
-    """Cleanup FlashInfer workspace."""
-    if flashinfer_comm is None or workspace is None:
+def cleanup_flashinfer_workspaces():
+    """Cleanup all FlashInfer workspaces."""
+    if flashinfer_comm is None:
         return
 
-    try:
-        workspace.destroy()
-    except Exception as e:
-        logger.error("Failed to cleanup FlashInfer workspace: %s", e)
+    for backend, workspace in _FI_WORKSPACES.items():
+        try:
+            workspace.destroy()
+        except Exception as e:
+            logger.error(
+                "Failed to cleanup FlashInfer workspace (backend=%s): %s",
+                backend,
+                e,
+            )
+    _FI_WORKSPACES.clear()
 
 
 class FlashInferFusedAllReduceParams:
@@ -134,7 +158,7 @@ class FlashInferFusedAllReduceParams:
         self.fp32_acc = True
         self.max_token_num = max_token_num
 
-    def get_trtllm_fused_allreduce_kwargs(self):
+    def get_flashinfer_fused_allreduce_kwargs(self):
         return {
             "launch_with_pdl": self.launch_with_pdl,
             "fp32_acc": self.fp32_acc,
@@ -147,11 +171,12 @@ def flashinfer_fused_allreduce_rmsnorm(
     rms_gamma: torch.Tensor,
     rms_eps: float,
     allreduce_params: "FlashInferFusedAllReduceParams",
+    workspace: object,
     use_oneshot: bool,
     norm_out: torch.Tensor | None = None,
 ):
     """FlashInfer fused allreduce + rmsnorm operation."""
-    if flashinfer_comm is None or _FI_WORKSPACE is None:
+    if flashinfer_comm is None or workspace is None:
         raise RuntimeError("FlashInfer not available or workspace not initialized")
 
     if norm_out is None:
@@ -160,9 +185,13 @@ def flashinfer_fused_allreduce_rmsnorm(
     else:
         residual_out = input_tensor
 
+    layout_code = None
+    if workspace.backend == "trtllm":
+        layout_code = flashinfer_comm.QuantizationSFLayout.SWIZZLED_128x4
+
     flashinfer_comm.allreduce_fusion(
         input=input_tensor,
-        workspace=_FI_WORKSPACE,
+        workspace=workspace,
         pattern=flashinfer_comm.AllReduceFusionPattern.kARResidualRMSNorm,
         residual_in=residual,
         residual_out=residual_out,
@@ -171,10 +200,10 @@ def flashinfer_fused_allreduce_rmsnorm(
         rms_eps=rms_eps,
         quant_out=None,
         scale_out=None,
-        layout_code=flashinfer_comm.QuantizationSFLayout.SWIZZLED_128x4,
+        layout_code=layout_code,
         scale_factor=None,
         use_oneshot=use_oneshot,
-        **allreduce_params.get_trtllm_fused_allreduce_kwargs(),
+        **allreduce_params.get_flashinfer_fused_allreduce_kwargs(),
     )
 
 
@@ -185,12 +214,16 @@ def flashinfer_fused_allreduce_rmsnorm_fp8_quant(
     rms_eps: float,
     scale_factor: torch.Tensor,
     allreduce_params: FlashInferFusedAllReduceParams,
+    workspace: object,
     use_oneshot: bool = True,
     norm_out: torch.Tensor | None = None,
     quant_out: torch.Tensor | None = None,
 ):
-    """FlashInfer fused allreduce + rmsnorm + FP8 quantization."""
-    if flashinfer_comm is None or _FI_WORKSPACE is None:
+    """FlashInfer fused allreduce + rmsnorm + FP8 quantization.
+
+    Note: Only supported by the trtllm backend.
+    """
+    if flashinfer_comm is None or workspace is None:
         raise RuntimeError("FlashInfer not available or workspace not initialized")
 
     if norm_out is None:
@@ -201,7 +234,7 @@ def flashinfer_fused_allreduce_rmsnorm_fp8_quant(
 
     flashinfer_comm.allreduce_fusion(
         input=input_tensor,
-        workspace=_FI_WORKSPACE,
+        workspace=workspace,
         pattern=flashinfer_comm.AllReduceFusionPattern.kARResidualRMSNormFP8Quant,
         residual_in=residual,
         residual_out=residual_out,
@@ -213,7 +246,7 @@ def flashinfer_fused_allreduce_rmsnorm_fp8_quant(
         layout_code=flashinfer_comm.QuantizationSFLayout.SWIZZLED_128x4,
         scale_factor=scale_factor,
         use_oneshot=use_oneshot,
-        **allreduce_params.get_trtllm_fused_allreduce_kwargs(),
+        **allreduce_params.get_flashinfer_fused_allreduce_kwargs(),
     )
 
 
@@ -224,13 +257,17 @@ def flashinfer_fused_allreduce_rmsnorm_fp4_quant(
     rms_eps: float,
     input_global_scale: torch.Tensor,
     allreduce_params: FlashInferFusedAllReduceParams,
+    workspace: object,
     quant_out: torch.Tensor,
     use_oneshot: bool,
     output_scale: torch.Tensor,
     norm_out: torch.Tensor | None = None,
 ):
-    """FlashInfer fused allreduce + rmsnorm + FP4 quantization."""
-    if flashinfer_comm is None or _FI_WORKSPACE is None:
+    """FlashInfer fused allreduce + rmsnorm + FP4 quantization.
+
+    Note: Only supported by the trtllm backend.
+    """
+    if flashinfer_comm is None or workspace is None:
         raise RuntimeError("FlashInfer not available or workspace not initialized")
 
     if norm_out is None:
@@ -241,7 +278,7 @@ def flashinfer_fused_allreduce_rmsnorm_fp4_quant(
 
     flashinfer_comm.allreduce_fusion(
         input=input_tensor,
-        workspace=_FI_WORKSPACE,
+        workspace=workspace,
         pattern=flashinfer_comm.AllReduceFusionPattern.kARResidualRMSNormFP4Quant,
         residual_in=residual,
         residual_out=residual_out,
@@ -253,7 +290,7 @@ def flashinfer_fused_allreduce_rmsnorm_fp4_quant(
         layout_code=flashinfer_comm.QuantizationSFLayout.SWIZZLED_128x4,
         scale_factor=input_global_scale,
         use_oneshot=use_oneshot,
-        **allreduce_params.get_trtllm_fused_allreduce_kwargs(),
+        **allreduce_params.get_flashinfer_fused_allreduce_kwargs(),
     )
 
 
@@ -386,13 +423,16 @@ def run_benchmarks(
     dtype: torch.dtype,
     use_residual: bool,
     allreduce_params: FlashInferFusedAllReduceParams | None,
+    workspaces: dict,
     quant_modes: set[str],
     no_oneshot: bool,
 ):
     """Run all benchmarks for given configuration.
 
     Args:
-        quant_mode: "none", "fp8_only", "fp4_only", or "all"
+        allreduce_params: Shared parameters for FlashInfer fused allreduce.
+        workspaces: Dict mapping backend name ("trtllm", "mnnvl") to workspace.
+        quant_modes: Set of quantization modes: "none", "fp8", "fp4".
     """
     (
         input_tensor,
@@ -454,10 +494,11 @@ def run_benchmarks(
                 logger.error("Standard AllReduce+RMSNorm Native Compiled failed: %s", e)
                 results["standard_allreduce_rmsnorm_native_compiled"] = float("inf")
 
-        # FlashInfer Fused AllReduce + RMSNorm Oneshot/Twoshot
-        if flashinfer_comm is not None and allreduce_params is not None:
+        # FlashInfer Fused AllReduce + RMSNorm (all backends)
+        for backend, workspace in workspaces.items():
             for use_oneshot in use_oneshot_options:
                 suffix = "_oneshot" if use_oneshot else "_twoshot"
+                key = f"flashinfer_{backend}_fused_allreduce_rmsnorm{suffix}"
                 try:
                     time_ms = benchmark_operation(
                         flashinfer_fused_allreduce_rmsnorm,
@@ -467,14 +508,17 @@ def run_benchmarks(
                         rms_gamma=rms_gamma,
                         rms_eps=rms_eps,
                         allreduce_params=allreduce_params,
+                        workspace=workspace,
                         use_oneshot=use_oneshot,
                     )
-                    results[f"flashinfer_fused_allreduce_rmsnorm{suffix}"] = time_ms
+                    results[key] = time_ms
                 except Exception as e:
-                    logger.error("FlashInfer Fused AllReduce+RMSNorm failed: %s", e)
-                    results[f"flashinfer_fused_allreduce_rmsnorm{suffix}"] = float(
-                        "inf"
+                    logger.error(
+                        "FlashInfer (%s) Fused AllReduce+RMSNorm failed: %s",
+                        backend,
+                        e,
                     )
+                    results[key] = float("inf")
 
     if "fp8" in quant_modes:
         # Standard AllReduce + RMSNorm + FP8 Quant
@@ -540,10 +584,12 @@ def run_benchmarks(
                     "inf"
                 )
 
-        # FlashInfer Fused AllReduce + RMSNorm + FP8 Quant Oneshot
-        if flashinfer_comm is not None and allreduce_params is not None:
+        # FlashInfer Fused AllReduce + RMSNorm + FP8 Quant (trtllm only)
+        if "trtllm" in workspaces:
+            trtllm_ws = workspaces["trtllm"]
             for use_oneshot in use_oneshot_options:
                 suffix = "_oneshot" if use_oneshot else "_twoshot"
+                key = f"flashinfer_trtllm_fused_allreduce_rmsnorm_fp8_quant{suffix}"
                 try:
                     time_ms = benchmark_operation(
                         flashinfer_fused_allreduce_rmsnorm_fp8_quant,
@@ -555,19 +601,16 @@ def run_benchmarks(
                         scale_factor=scale_fp8,
                         quant_out=quant_out_fp8,
                         allreduce_params=allreduce_params,
+                        workspace=trtllm_ws,
                         use_oneshot=use_oneshot,
                     )
-                    results[f"flashinfer_fused_allreduce_rmsnorm_fp8_quant{suffix}"] = (
-                        time_ms
-                    )
+                    results[key] = time_ms
                 except Exception as e:
                     logger.error(
-                        "FlashInfer Fused AllReduce+RMSNorm+FP8 Oneshot failed: %s",
+                        "FlashInfer (trtllm) Fused AllReduce+RMSNorm+FP8 failed: %s",
                         e,
                     )
-                    results[f"flashinfer_fused_allreduce_rmsnorm_fp8_quant{suffix}"] = (
-                        float("inf")
-                    )
+                    results[key] = float("inf")
 
     if "fp4" in quant_modes and current_platform.has_device_capability(100):
         # Standard AllReduce + RMSNorm + FP4 Quant
@@ -627,10 +670,12 @@ def run_benchmarks(
                     "inf"
                 )
 
-        # FlashInfer Fused AllReduce + RMSNorm + FP4 Quant Oneshot
-        if flashinfer_comm is not None and allreduce_params is not None:
+        # FlashInfer Fused AllReduce + RMSNorm + FP4 Quant (trtllm only)
+        if "trtllm" in workspaces:
+            trtllm_ws = workspaces["trtllm"]
             for use_oneshot in use_oneshot_options:
                 suffix = "_oneshot" if use_oneshot else "_twoshot"
+                key = f"flashinfer_trtllm_fused_allreduce_rmsnorm_fp4_quant{suffix}"
                 try:
                     time_ms = benchmark_operation(
                         flashinfer_fused_allreduce_rmsnorm_fp4_quant,
@@ -641,49 +686,18 @@ def run_benchmarks(
                         rms_eps=rms_eps,
                         input_global_scale=scale_fp4,
                         allreduce_params=allreduce_params,
+                        workspace=trtllm_ws,
                         quant_out=fp4_quant_out,
                         output_scale=fp4_output_scale,
                         use_oneshot=use_oneshot,
                     )
-                    results[f"flashinfer_fused_allreduce_rmsnorm_fp4_quant{suffix}"] = (
-                        time_ms
-                    )
+                    results[key] = time_ms
                 except Exception as e:
                     logger.error(
-                        "FlashInfer Fused AllReduce+RMSNorm+FP4 Oneshot failed: %s",
+                        "FlashInfer (trtllm) Fused AllReduce+RMSNorm+FP4 failed: %s",
                         e,
                     )
-                    results[f"flashinfer_fused_allreduce_rmsnorm_fp4_quant{suffix}"] = (
-                        float("inf")
-                    )
-
-        # FlashInfer Fused AllReduce + RMSNorm + FP4 Quant Two-shot
-        if flashinfer_comm is not None and allreduce_params is not None:
-            try:
-                time_ms = benchmark_operation(
-                    flashinfer_fused_allreduce_rmsnorm_fp4_quant,
-                    input_tensor,
-                    residual=residual,
-                    norm_out=norm_out,
-                    rms_gamma=rms_gamma,
-                    rms_eps=rms_eps,
-                    input_global_scale=scale_fp4,
-                    allreduce_params=allreduce_params,
-                    quant_out=fp4_quant_out,
-                    output_scale=fp4_output_scale,
-                    use_oneshot=False,
-                )
-                results["flashinfer_fused_allreduce_rmsnorm_fp4_quant_twoshot"] = (
-                    time_ms
-                )
-            except Exception as e:
-                logger.error(
-                    "FlashInfer Fused AllReduce+RMSNorm+FP4 Two-shot failed: %s",
-                    e,
-                )
-                results["flashinfer_fused_allreduce_rmsnorm_fp4_quant_twoshot"] = float(
-                    "inf"
-                )
+                    results[key] = float("inf")
 
     return results
 
@@ -1021,8 +1035,7 @@ def main():
 
     configs = list(itertools.product(args.num_tokens, dtypes, residual_options))
 
-    # Setup FlashInfer workspace if available
-    workspace = None
+    # Setup FlashInfer workspaces for all backends
     allreduce_params = None
 
     if flashinfer_comm is not None:
@@ -1037,15 +1050,17 @@ def main():
             args.hidden_dim * max_element_size
         )
 
-        workspace = setup_flashinfer_workspace(
-            world_size,
-            rank,
-            args.hidden_dim,
-            max_num_token,
-            dtype=workspace_dtype,
-        )
+        for backend in FLASHINFER_BACKENDS:
+            setup_flashinfer_workspace(
+                backend=backend,
+                world_size=world_size,
+                rank=rank,
+                hidden_dim=args.hidden_dim,
+                max_token_num=max_num_token,
+                dtype=workspace_dtype,
+            )
 
-        if workspace is not None:
+        if _FI_WORKSPACES:
             allreduce_params = FlashInferFusedAllReduceParams(
                 max_token_num=max_num_token,
             )
@@ -1071,6 +1086,7 @@ def main():
                 dtype,
                 use_residual,
                 allreduce_params,
+                workspaces=_FI_WORKSPACES,
                 quant_modes=quant_modes,
                 no_oneshot=args.no_oneshot,
             )
@@ -1109,11 +1125,13 @@ def main():
 
     finally:
         # Cleanup
-        if workspace is not None:
-            cleanup_flashinfer_workspace(workspace)
+        cleanup_flashinfer_workspaces()
 
         dist.barrier()
 
 
 if __name__ == "__main__":
-    main()
+    from vllm.config import VllmConfig, set_current_vllm_config
+
+    with set_current_vllm_config(VllmConfig()):
+        main()

tests/compile/passes/distributed/test_fusion_all_reduce.py

@@ -142,7 +142,6 @@ class TestAllReduceFusedAddRMSNormStaticQuantFP4Model(torch.nn.Module):
             *(scaled_fp4_quant(w, wg) for w, wg in zip(self.w, wgscale))
         )
         self.wq, self.wscale = list(wq_gen), list(wscale_gen)
-        print(f"{self.wq=}, {self.wscale=}")
 
     def forward(self, hidden_states):
         # avoid having graph input be an arg to a pattern directly
@@ -199,6 +198,7 @@ class TestAllReduceFusedAddRMSNormStaticQuantFP4Model(torch.nn.Module):
 @pytest.mark.parametrize("hidden_size", [64])
 @pytest.mark.parametrize("dtype", [torch.bfloat16])
 @pytest.mark.parametrize("enable_rms_norm_custom_op", [True, False])
+@pytest.mark.parametrize("flashinfer_allreduce_backend", ["trtllm", "mnnvl"])
 @pytest.mark.skipif(envs.VLLM_TARGET_DEVICE not in ["cuda"], reason="Only test on CUDA")
 @pytest.mark.skipif(
     not find_spec("flashinfer")
@@ -215,6 +215,7 @@ def test_all_reduce_fusion_pass_replace(
     dtype: torch.dtype,
     enable_rms_norm_custom_op,
     enable_quant_fp8_custom_op,
+    flashinfer_allreduce_backend,
 ):
     num_processes = 2
     if (
@@ -238,6 +239,7 @@ def test_all_reduce_fusion_pass_replace(
                 dtype,
                 enable_rms_norm_custom_op,
                 enable_quant_fp8_custom_op,
+                flashinfer_allreduce_backend,
             ),
             nprocs=nprocs,
         )
@@ -255,6 +257,7 @@ def all_reduce_fusion_pass_on_test_model(
     dtype: torch.dtype,
     enable_rms_norm_custom_op,
     enable_quant_fp8_custom_op,
+    flashinfer_allreduce_backend,
 ):
     set_random_seed(0)
 
@@ -270,6 +273,7 @@ def all_reduce_fusion_pass_on_test_model(
             "WORLD_SIZE": str(world_size),
             "MASTER_ADDR": "localhost",
             "MASTER_PORT": "12345",
+            "VLLM_FLASHINFER_ALLREDUCE_BACKEND": flashinfer_allreduce_backend,
         }
     )
 
@@ -317,6 +321,10 @@ def all_reduce_fusion_pass_on_test_model(
         compiled_model = torch.compile(model, backend=backend)
         compiled_model(hidden_states)
 
+        results_unfused = model(hidden_states)
+        results_fused = compiled_model(hidden_states)
+        torch.testing.assert_close(results_unfused, results_fused, atol=1e-2, rtol=1e-2)
+
         assert all_reduce_fusion_pass.matched_count == 4, (
             f"{all_reduce_fusion_pass.matched_count=}"
         )

vllm/compilation/passes/fusion/allreduce_rms_fusion.py

@@ -22,7 +22,9 @@ from vllm.model_executor.layers.quantization.utils.quant_utils import (
     kFp8StaticTensorSym,
 )
 from vllm.platforms import current_platform
-from vllm.utils.torch_utils import direct_register_custom_op
+from vllm.utils.torch_utils import (
+    direct_register_custom_op,
+)
 
 from ..inductor_pass import enable_fake_mode
 from ..vllm_inductor_pass import VllmInductorPass, VllmPatternMatcherPass
@@ -44,8 +46,6 @@ if find_spec("flashinfer"):
     except ImportError:
         pass
 
-logger = init_logger(__name__)
-
 if hasattr(torch.ops._C, "scaled_fp4_quant"):
     STATIC_FP4_QUANT_OP = torch.ops._C.scaled_fp4_quant.default
 
@@ -82,7 +82,16 @@ _FI_ALLREDUCE_ONE_SHOT_MAX_SIZES_MB: dict[int, dict[int, float]] = {
 
 
 if flashinfer_comm is not None:
-    _FI_WORKSPACE = None
+    from vllm.distributed.device_communicators.flashinfer_all_reduce import (
+        destroy_fi_ar_workspace,
+        get_fi_ar_quant_workspace,
+        get_fi_ar_workspace,
+        initialize_fi_ar_quant_workspace,
+        initialize_fi_ar_workspace,
+    )
+
+    ar_fusion_patterns = flashinfer_comm.AllReduceFusionPattern
+
     MiB = 1024 * 1024
 
     def call_trtllm_fused_allreduce_norm(
@@ -122,9 +131,19 @@ if flashinfer_comm is not None:
             max_one_shot_size is None or current_tensor_size <= max_one_shot_size * MiB
         )
 
-        assert _FI_WORKSPACE is not None, (
-            "Flashinfer must be enabled when using flashinfer"
+        # Select workspace based on pattern: quant patterns use the
+        # trtllm quant workspace, non-quant patterns use the primary workspace.
+        if pattern_code in (
+            ar_fusion_patterns.kARResidualRMSNormFP8Quant,
+            ar_fusion_patterns.kARResidualRMSNormFP4Quant,
+        ):
+            workspace = get_fi_ar_quant_workspace()
+        else:
+            workspace = get_fi_ar_workspace()
+        assert workspace is not None, (
+            "Flashinfer workspace must be initialized when using flashinfer"
         )
+        assert flashinfer_comm is not None
         if norm_out is None:
             norm_out = allreduce_in
             residual_out = residual
@@ -133,25 +152,30 @@ if flashinfer_comm is not None:
             # as flashinfer does not support rms_norm
             # and allreduce_out together
             residual_out = allreduce_in
-        # For the sizes that are smaller than the max size,
-        # we only use flashinfer one shot allreduce
+
+        layout_code = None
+        # layout_code only supported by trtllm backend
+        if workspace.backend == "trtllm":
+            # in vllm we only support swizzled layout
+            layout_code = flashinfer_comm.QuantizationSFLayout.SWIZZLED_128x4
+
         flashinfer_comm.allreduce_fusion(
             input=allreduce_in,
-            workspace=_FI_WORKSPACE,
+            workspace=workspace,
             pattern=pattern_code,
-            residual_in=residual,
+            launch_with_pdl=launch_with_pdl,
+            output=None,
             residual_out=residual_out,
             norm_out=norm_out,
-            rms_gamma=rms_gamma,
-            rms_eps=rms_eps,
-            launch_with_pdl=launch_with_pdl,
-            use_oneshot=use_oneshot,
-            fp32_acc=fp32_acc,
             quant_out=quant_out,
             scale_out=scale_out,
-            # in vllm we only support swizzled layout
-            layout_code=flashinfer_comm.QuantizationSFLayout.SWIZZLED_128x4,
+            residual_in=residual,
+            rms_gamma=rms_gamma,
+            rms_eps=rms_eps,
             scale_factor=scale_factor,
+            layout_code=layout_code,
+            use_oneshot=use_oneshot,
+            fp32_acc=fp32_acc,
         )
 
     def call_trtllm_fused_allreduce_norm_fake(
@@ -729,29 +753,36 @@ class AllReduceFusionPass(VllmPatternMatcherPass):
             scope="global",
         )
 
-        try:
-            self.workspace = flashinfer_comm.create_allreduce_fusion_workspace(
-                backend="trtllm",
-                world_size=self.tp_size,
-                rank=rank,
-                max_token_num=self.max_token_num,
-                hidden_dim=self.hidden_dim,
-                dtype=self.model_dtype,
-            )
-        except RuntimeError as e:
-            if "multicast" not in str(e).lower():
-                raise
-            logger.warning_once(
-                "AllReduce fusion pass is disabled: flashinfer workspace "
-                "creation failed: %s. This is expected on GPUs without "
-                "NVSwitch (e.g., NVLink bridge-only or PCIe topologies). "
-                "Falling back to non-fused allreduce.",
-                str(e),
-            )
-            return
+        for workspace_init_fn in [
+            initialize_fi_ar_workspace,
+            initialize_fi_ar_quant_workspace,
+        ]:
+            try:
+                workspace_init_fn(
+                    world_size=self.tp_size,
+                    rank=rank,
+                    max_token_num=self.max_token_num,
+                    hidden_dim=self.hidden_dim,
+                    dtype=self.model_dtype,
+                    group=self.group,
+                )
+            except Exception as e:
+                if "multicast" in str(e).lower():
+                    logger.warning(
+                        "AllReduce fusion pass is disabled: flashinfer workspace "
+                        "creation failed: %s. This is expected on GPUs without "
+                        "NVSwitch (e.g., NVLink bridge-only or PCIe topologies). "
+                        "Falling back to non-fused allreduce.",
+                        str(e),
+                    )
+                else:
+                    logger.warning(
+                        "Failed to initialize FlashInfer All Reduce workspace: %s. "
+                        "AllReduce fusion pass will be disabled.",
+                        e,
+                    )
+                return
 
-        global _FI_WORKSPACE
-        _FI_WORKSPACE = self.workspace
         self.allreduce_params = FlashInferFusedAllReduceParams(
             world_size=self.tp_size,
             max_token_num=self.max_token_num,
@@ -762,32 +793,34 @@ class AllReduceFusionPass(VllmPatternMatcherPass):
 
     @enable_fake_mode
     def register_patterns(self) -> None:
+        supports_quantization = get_fi_ar_quant_workspace() is not None
         for epsilon in [1e-5, 1e-6]:
-            AllReduceFusedRMSNormStaticQuantFP8Pattern(
-                epsilon,
-                self.model_dtype,
-                self.device,
-                self.allreduce_params,
-            ).register(self.patterns)
-            AllReduceFusedAddRMSNormStaticQuantFP8Pattern(
-                epsilon,
-                self.model_dtype,
-                self.device,
-                self.allreduce_params,
-            ).register(self.patterns)
-            if current_platform.has_device_capability(100):
-                AllReduceFusedRMSNormStaticQuantNVFP4Pattern(
+            if supports_quantization:
+                AllReduceFusedRMSNormStaticQuantFP8Pattern(
                     epsilon,
                     self.model_dtype,
                     self.device,
                     self.allreduce_params,
                 ).register(self.patterns)
-                AllReduceFusedAddRMSNormStaticQuantNVFP4Pattern(
+                AllReduceFusedAddRMSNormStaticQuantFP8Pattern(
                     epsilon,
                     self.model_dtype,
                     self.device,
                     self.allreduce_params,
                 ).register(self.patterns)
+                if current_platform.has_device_capability(100):
+                    AllReduceFusedRMSNormStaticQuantNVFP4Pattern(
+                        epsilon,
+                        self.model_dtype,
+                        self.device,
+                        self.allreduce_params,
+                    ).register(self.patterns)
+                    AllReduceFusedAddRMSNormStaticQuantNVFP4Pattern(
+                        epsilon,
+                        self.model_dtype,
+                        self.device,
+                        self.allreduce_params,
+                    ).register(self.patterns)
             AllReduceRMSNormPattern(
                 epsilon,
                 self.model_dtype,
@@ -825,6 +858,5 @@ class AllReduceFusionPass(VllmPatternMatcherPass):
     def __del__(self) -> None:
         if getattr(self, "disabled", True):
             return
-        if getattr(self, "workspace", None) is not None:
-            with contextlib.suppress(Exception):
-                self.workspace.destroy()
+        with contextlib.suppress(Exception):
+            destroy_fi_ar_workspace()

vllm/distributed/device_communicators/cuda_communicator.py

@@ -34,19 +34,25 @@ class CudaCommunicator(DeviceCommunicatorBase):
             # custom allreduce or torch symm mem can be used only by tp
             use_custom_allreduce = False
             use_torch_symm_mem = False
+            use_flashinfer_allreduce = False
         else:
             from vllm.distributed.parallel_state import _ENABLE_CUSTOM_ALL_REDUCE
 
             use_custom_allreduce = _ENABLE_CUSTOM_ALL_REDUCE
             use_torch_symm_mem = envs.VLLM_ALLREDUCE_USE_SYMM_MEM
+            use_flashinfer_allreduce = envs.VLLM_ALLREDUCE_USE_FLASHINFER
 
         self.use_custom_allreduce = use_custom_allreduce
         self.use_torch_symm_mem = use_torch_symm_mem
+        self.use_flashinfer_allreduce = use_flashinfer_allreduce
 
         # lazy import to avoid documentation build error
         from vllm.distributed.device_communicators.custom_all_reduce import (
             CustomAllreduce,
         )
+        from vllm.distributed.device_communicators.flashinfer_all_reduce import (
+            FlashInferAllReduce,
+        )
         from vllm.distributed.device_communicators.pynccl import PyNcclCommunicator
         from vllm.distributed.device_communicators.quick_all_reduce import (
             QuickAllReduce,
@@ -65,12 +71,20 @@ class CudaCommunicator(DeviceCommunicatorBase):
         self.ca_comm: CustomAllreduce | None = None
         self.qr_comm: QuickAllReduce | None = None
         self.symm_mem_comm: SymmMemCommunicator | None = None
+        self.fi_ar_comm: FlashInferAllReduce | None = None
+
         if use_torch_symm_mem and current_platform.is_cuda():
             self.symm_mem_comm = SymmMemCommunicator(
                 group=self.cpu_group,
                 device=self.device,
             )
 
+        if self.use_flashinfer_allreduce and self.world_size > 1:
+            self.fi_ar_comm = FlashInferAllReduce(
+                group=self.cpu_group,
+                device=self.device,
+            )
+
         if use_custom_allreduce and self.world_size > 1:
             # Initialize a custom fast all-reduce implementation.
             self.ca_comm = CustomAllreduce(
@@ -136,7 +150,7 @@ class CudaCommunicator(DeviceCommunicatorBase):
             out = torch.ops.vllm.all_reduce_symmetric_with_copy(input_)
             if out is not None:
                 return out
-        # always try quick reduce first, then custom allreduce,
+        # always try quick reduce first, then flashinfer, then custom allreduce,
         # and then pynccl. (quick reduce just for ROCM MI3*)
         qr_comm = self.qr_comm
         if (
@@ -147,6 +161,15 @@ class CudaCommunicator(DeviceCommunicatorBase):
             out = qr_comm.quick_all_reduce(input_)
             assert out is not None
             return out
+        fi_ar_comm = self.fi_ar_comm
+        if (
+            fi_ar_comm is not None
+            and not fi_ar_comm.disabled
+            and fi_ar_comm.should_use_fi_ar(input_)
+        ):
+            out = fi_ar_comm.all_reduce(input_)
+            assert out is not None
+            return out
         ca_comm = self.ca_comm
         if (
             ca_comm is not None
@@ -270,6 +293,9 @@ class CudaCommunicator(DeviceCommunicatorBase):
             self.pynccl_comm = None
         if self.ca_comm is not None:
             self.ca_comm = None
+        if self.fi_ar_comm is not None:
+            self.fi_ar_comm.destroy()
+            self.fi_ar_comm = None
         if self.all2all_manager is not None:
             self.all2all_manager.destroy()
             self.all2all_manager = None

vllm/distributed/device_communicators/flashinfer_all_reduce.py

@@ -0,0 +1,252 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+
+import torch
+import torch.distributed as dist
+from torch.distributed import ProcessGroup
+
+import vllm.envs as envs
+from vllm.config.compilation import PassConfig
+from vllm.logger import init_logger
+from vllm.platforms import current_platform
+
+logger = init_logger(__name__)
+
+fi_ar_available = False
+try:
+    import flashinfer.comm as flashinfer_comm  # type: ignore[no-redef]
+    from flashinfer.comm.mnnvl import (
+        TorchDistBackend,  # type: ignore[import-not-found, no-redef]
+    )
+
+    fi_ar_available = hasattr(flashinfer_comm, "allreduce_fusion")
+except ImportError:
+    pass
+
+# Global workspace for standalone allreduce and non-quant ar+rms fusion
+_fi_ar_workspace = None
+# Extra workspace for quant fusion patterns (only supported by trtllm backend)
+# Only created if primary workspace is not already trtllm
+_fi_ar_quant_workspace = None
+
+
+def get_fi_ar_workspace():
+    return _fi_ar_workspace
+
+
+def get_fi_ar_quant_workspace():
+    return _fi_ar_quant_workspace
+
+
+def initialize_fi_ar_workspace(
+    world_size: int,
+    rank: int,
+    max_token_num: int,
+    hidden_dim: int,
+    dtype: torch.dtype,
+    group: ProcessGroup,
+) -> None:
+    """
+    Initialize the workspace if not already initialized.
+
+    Currently, this function is called by either the AllReduceFusionPass
+    or the FlashInferAllReduce backend for standalone allreduce.
+    If the fusion pass is enabled via
+    --compilation-config.pass_config.fuse_allreduce_rms=true,
+    it will create the workspace first, and the standalone backend
+    will reuse the workspace. Otherwise, the standalone backend will
+    create the workspace.
+    """
+    global _fi_ar_workspace
+    if _fi_ar_workspace is not None:
+        return
+
+    backend = envs.VLLM_FLASHINFER_ALLREDUCE_BACKEND
+    comm_backend = TorchDistBackend(group=group)
+    _fi_ar_workspace = flashinfer_comm.create_allreduce_fusion_workspace(
+        backend=backend,
+        world_size=world_size,
+        rank=rank,
+        max_token_num=max_token_num,
+        hidden_dim=hidden_dim,
+        dtype=dtype,
+        comm_backend=comm_backend,
+    )
+    assert _fi_ar_workspace is not None
+    logger.debug(
+        "Initialized FlashInfer All Reduce workspace: backend=%s, "
+        "world_size=%d, rank=%d, max_token_num=%d, hidden_dim=%d, dtype=%s",
+        backend,
+        world_size,
+        rank,
+        max_token_num,
+        hidden_dim,
+        dtype,
+    )
+
+
+def initialize_fi_ar_quant_workspace(
+    world_size: int,
+    rank: int,
+    max_token_num: int,
+    hidden_dim: int,
+    dtype: torch.dtype,
+    group: ProcessGroup,
+) -> None:
+    """
+    Initialize the workspace used by quantization fusion patterns.
+
+    Currently this always creates a workspace for trtllm backend as only it
+    supports quantization fusion (FP8/FP4). If the primary workspace
+    is already trtllm, the quant workspace aliases to it.
+    """
+    global _fi_ar_quant_workspace
+    if _fi_ar_quant_workspace is not None:
+        return
+
+    # If primary workspace is already trtllm, reuse it
+    if _fi_ar_workspace is not None and _fi_ar_workspace.backend == "trtllm":
+        _fi_ar_quant_workspace = _fi_ar_workspace
+        return
+
+    comm_backend = TorchDistBackend(group=group)
+    _fi_ar_quant_workspace = flashinfer_comm.create_allreduce_fusion_workspace(
+        backend="trtllm",
+        world_size=world_size,
+        rank=rank,
+        max_token_num=max_token_num,
+        hidden_dim=hidden_dim,
+        dtype=dtype,
+        comm_backend=comm_backend,
+    )
+    assert _fi_ar_quant_workspace is not None
+    logger.debug(
+        "Initialized FlashInfer All Reduce workspace: backend=trtllm, "
+        "world_size=%d, rank=%d, max_token_num=%d, hidden_dim=%d, dtype=%s",
+        world_size,
+        rank,
+        max_token_num,
+        hidden_dim,
+        dtype,
+    )
+
+
+def destroy_fi_ar_workspace():
+    global _fi_ar_workspace
+    global _fi_ar_quant_workspace
+    if (
+        _fi_ar_quant_workspace is not None
+        and _fi_ar_quant_workspace is not _fi_ar_workspace
+    ):
+        _fi_ar_quant_workspace.destroy()
+    _fi_ar_quant_workspace = None
+    if _fi_ar_workspace is not None:
+        _fi_ar_workspace.destroy()
+        _fi_ar_workspace = None
+
+
+class FlashInferAllReduce:
+    def __init__(
+        self,
+        group: ProcessGroup,
+        device: int | str | torch.device,
+    ):
+        self.disabled = True
+
+        if not fi_ar_available:
+            logger.info(
+                "FlashInfer All Reduce is disabled because flashinfer is not available"
+            )
+            return
+
+        if not current_platform.is_cuda():
+            logger.info(
+                "FlashInfer All Reduce is disabled because it requires CUDA platform"
+            )
+            return
+
+        self.group = group
+        self.world_size = dist.get_world_size(self.group)
+        self.rank = dist.get_rank(self.group)
+        self.device = device
+        if self.world_size == 1:
+            return
+
+        # Use the same threshold as the allreduce-rms fusion pass
+        # TODO: tune the threshold
+        MiB = 1024 * 1024
+        max_workspace_size = PassConfig.default_fi_allreduce_fusion_max_size_mb().get(
+            self.world_size, None
+        )
+        if not max_workspace_size:
+            logger.warning(
+                "FlashInfer All Reduce is disabled because it "
+                "is not supported for world_size=%d.",
+                self.world_size,
+            )
+            return
+        self.max_workspace_size = max_workspace_size * MiB
+        self.max_num_tokens = 0
+        self.disabled = False
+
+    def _ensure_workspace(self, hidden_dim: int, dtype: torch.dtype) -> bool:
+        """Ensure the all reduce workspace is initialized."""
+        if get_fi_ar_workspace() is not None:
+            return True
+        if self.max_num_tokens == 0:
+            element_size = torch.tensor([], dtype=dtype, device="cpu").element_size()
+            self.max_num_tokens = self.max_workspace_size // (hidden_dim * element_size)
+        try:
+            initialize_fi_ar_workspace(
+                world_size=self.world_size,
+                rank=self.rank,
+                max_token_num=self.max_num_tokens,
+                hidden_dim=hidden_dim,
+                dtype=dtype,
+                group=self.group,
+            )
+            return True
+        except Exception as e:
+            logger.warning(
+                "Failed to initialize FlashInfer All Reduce workspace: %s. "
+                "FlashInfer All Reduce will be disabled.",
+                e,
+            )
+            self.disabled = True
+            return False
+
+    def should_use_fi_ar(self, input_tensor: torch.Tensor) -> bool:
+        if self.disabled:
+            return False
+
+        if not input_tensor.is_cuda:
+            return False
+
+        if not input_tensor.is_contiguous():
+            return False
+
+        if len(input_tensor.shape) != 2:
+            return False
+
+        num_tokens, hidden_dim = input_tensor.shape
+        if not self.max_num_tokens:
+            element_size = torch.tensor([], dtype=input_tensor.dtype).element_size()
+            self.max_num_tokens = self.max_workspace_size // (hidden_dim * element_size)
+
+        if num_tokens > self.max_num_tokens:
+            return False
+
+        return self._ensure_workspace(hidden_dim, input_tensor.dtype)
+
+    def all_reduce(self, input_tensor: torch.Tensor) -> torch.Tensor:
+        workspace = get_fi_ar_workspace()
+        return flashinfer_comm.allreduce_fusion(
+            input=input_tensor,
+            workspace=workspace,
+            pattern=flashinfer_comm.AllReduceFusionPattern.kAllReduce,
+        )
+
+    def destroy(self):
+        if not self.disabled:
+            destroy_fi_ar_workspace()

vllm/envs.py

@@ -168,6 +168,7 @@ if TYPE_CHECKING:
     VLLM_FLASHINFER_MOE_BACKEND: Literal["throughput", "latency", "masked_gemm"] = (
         "latency"
     )
+    VLLM_FLASHINFER_ALLREDUCE_BACKEND: Literal["auto", "trtllm", "mnnvl"] = "auto"
     VLLM_FLASHINFER_WORKSPACE_BUFFER_SIZE: int = 394 * 1024 * 1024
     VLLM_XGRAMMAR_CACHE_MB: int = 0
     VLLM_MSGPACK_ZERO_COPY_THRESHOLD: int = 256
@@ -206,6 +207,7 @@ if TYPE_CHECKING:
     VLLM_ROCM_FP8_MFMA_PAGE_ATTN: bool = False
     VLLM_USE_FLASHINFER_MOE_MXFP4_MXFP8_CUTLASS: bool = False
     VLLM_ALLREDUCE_USE_SYMM_MEM: bool = True
+    VLLM_ALLREDUCE_USE_FLASHINFER: bool = False
     VLLM_TUNED_CONFIG_FOLDER: str | None = None
     VLLM_GPT_OSS_SYSTEM_TOOL_MCP_LABELS: set[str] = set()
     VLLM_USE_EXPERIMENTAL_PARSER_CONTEXT: bool = False
@@ -1290,6 +1292,14 @@ environment_variables: dict[str, Callable[[], Any]] = {
         "latency",
         ["throughput", "latency", "masked_gemm"],
     ),
+    # Flashinfer fused allreduce backend.
+    # "auto" will default to "mnnvl", which performs mostly same/better than "trtllm".
+    # But "mnnvl" backend does not support fuse with quantization.
+    "VLLM_FLASHINFER_ALLREDUCE_BACKEND": env_with_choices(
+        "VLLM_FLASHINFER_ALLREDUCE_BACKEND",
+        "auto",
+        ["auto", "trtllm", "mnnvl"],
+    ),
     # Control the workspace buffer size for the FlashInfer backend.
     "VLLM_FLASHINFER_WORKSPACE_BUFFER_SIZE": lambda: int(
         os.getenv("VLLM_FLASHINFER_WORKSPACE_BUFFER_SIZE", str(394 * 1024 * 1024))
@@ -1448,6 +1458,10 @@ environment_variables: dict[str, Callable[[], Any]] = {
     "VLLM_ALLREDUCE_USE_SYMM_MEM": lambda: bool(
         int(os.getenv("VLLM_ALLREDUCE_USE_SYMM_MEM", "1"))
     ),
+    # Whether to use FlashInfer allreduce
+    "VLLM_ALLREDUCE_USE_FLASHINFER": lambda: bool(
+        int(os.getenv("VLLM_ALLREDUCE_USE_FLASHINFER", "0"))
+    ),
     # Experimental: use this to enable MCP tool calling for non harmony models
     "VLLM_USE_EXPERIMENTAL_PARSER_CONTEXT": lambda: bool(
         int(os.getenv("VLLM_USE_EXPERIMENTAL_PARSER_CONTEXT", "0"))