Add pyhccl (#503)

This is the first step to support trl vllm serve on Ascend NPU
https://github.com/vllm-project/vllm-ascend/issues/459.
This PR can work properly only when
https://github.com/vllm-project/vllm/pull/16464 is merged into vLLM.

---------

Signed-off-by: hzji210@gmail.com <hzji210@gmail.com>

tests/multicard/test_pyhccl_distributed.py

@@ -0,0 +1,111 @@
+#
+# Copyright (c) 2025 Huawei Technologies Co., Ltd. All Rights Reserved.
+# This file is a part of the vllm-ascend project.
+# Adapted from vllm/tests/basic_correctness/test_basic_correctness.py
+# Copyright 2023 The vLLM team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+import multiprocessing
+import os
+
+import torch
+import torch_npu  # noqa: F401
+from vllm.distributed.parallel_state import (get_world_group,
+                                             init_distributed_environment)
+from vllm.utils import update_environment_variables
+
+from vllm_ascend.distributed.device_communicators.pyhccl import \
+    PyHcclCommunicator
+
+
+def distributed_run(fn, world_size):
+    number_of_processes = world_size
+    processes: list[multiprocessing.Process] = []
+    for i in range(number_of_processes):
+        env: dict[str, str] = {}
+        env['RANK'] = str(i)
+        env['LOCAL_RANK'] = str(i)
+        env['WORLD_SIZE'] = str(number_of_processes)
+        env['LOCAL_WORLD_SIZE'] = str(number_of_processes)
+        env['MASTER_ADDR'] = 'localhost'
+        env['MASTER_PORT'] = '12345'
+        p = multiprocessing.Process(target=fn, args=(env, ))
+        processes.append(p)
+        p.start()
+
+    for p in processes:
+        p.join()
+
+    for p in processes:
+        assert p.exitcode == 0
+
+
+def worker_fn_wrapper(fn):
+    # `multiprocessing.Process` cannot accept environment variables directly
+    # so we need to pass the environment variables as arguments
+    # and update the environment variables in the function
+    def wrapped_fn(env):
+        update_environment_variables(env)
+        local_rank = os.environ['LOCAL_RANK']
+        device = torch.device(f"npu:{local_rank}")
+        torch.npu.set_device(device)
+        init_distributed_environment(backend="hccl")
+        fn()
+
+    return wrapped_fn
+
+
+@worker_fn_wrapper
+def worker_fn():
+    pynccl_comm = PyHcclCommunicator(get_world_group().cpu_group,
+                                     device=get_world_group().device)
+    tensor = torch.ones(16, 1024, 1024,
+                        dtype=torch.float32).npu(pynccl_comm.rank)
+    tensor = pynccl_comm.all_reduce(tensor)
+    torch.npu.synchronize()
+    assert torch.all(tensor == pynccl_comm.world_size).cpu().item()
+
+
+# def test_pyhccl():
+#     distributed_run(worker_fn, 2)
+
+
+@worker_fn_wrapper
+def broadcast_worker_fn():
+    # Test broadcast for every root rank.
+    # Essentially this is an all-gather operation.
+    pyhccl_comm = PyHcclCommunicator(get_world_group().cpu_group,
+                                     device=get_world_group().device)
+    recv_tensors = [
+        torch.empty(16,
+                    1024,
+                    1024,
+                    dtype=torch.float32,
+                    device=pyhccl_comm.device)
+        for i in range(pyhccl_comm.world_size)
+    ]
+    recv_tensors[pyhccl_comm.rank] = torch.ones(
+        16, 1024, 1024, dtype=torch.float32,
+        device=pyhccl_comm.device) * pyhccl_comm.rank
+
+    for i in range(pyhccl_comm.world_size):
+        pyhccl_comm.broadcast(recv_tensors[i], src=i)
+        # the broadcast op might be launched in a different stream
+        # need to synchronize to make sure the tensor is ready
+        torch.npu.synchronize()
+        assert torch.all(recv_tensors[i] == i).cpu().item()
+
+
+# def test_pyhccl_broadcast():
+#     distributed_run(broadcast_worker_fn, 4)

tests/singlecard/test_pyhccl.py

@@ -0,0 +1,30 @@
+#
+# Copyright (c) 2025 Huawei Technologies Co., Ltd. All Rights Reserved.
+# This file is a part of the vllm-ascend project.
+# Adapted from vllm/tests/basic_correctness/test_basic_correctness.py
+# Copyright 2023 The vLLM team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+import torch
+import torch_npu  # noqa: F401
+
+from vllm_ascend.distributed.device_communicators.pyhccl_wrapper import \
+    HCCLLibrary
+
+
+def test_hcclGetUniqueId():
+    torch.npu.set_device(0)
+    lib = HCCLLibrary()
+    unique_id = lib.hcclGetUniqueId()
+    assert unique_id is not None

vllm_ascend/distributed/communicator.py

@@ -30,5 +30,6 @@ class NPUCommunicator(DeviceCommunicatorBase):
                  device_group: Optional[ProcessGroup] = None,
                  unique_name: str = ""):
         super().__init__(cpu_group, device, device_group, unique_name)
+        # TODO(hz): Refer to CudaCommunicator's implementation to integrate PyHcclCommunicator
         # init device according to rank
         self.device = torch.npu.current_device()

vllm_ascend/distributed/device_communicators/pyhccl.py

@@ -0,0 +1,166 @@
+#
+# Copyright (c) 2025 Huawei Technologies Co., Ltd. All Rights Reserved.
+# This file is a part of the vllm-ascend project.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+from typing import Optional, Union
+
+import torch
+import torch.distributed as dist
+import torch_npu  # noqa: F401
+from torch.distributed import ProcessGroup, ReduceOp
+from vllm.distributed.utils import StatelessProcessGroup
+from vllm.logger import logger
+
+from vllm_ascend.distributed.device_communicators.pyhccl_wrapper import (
+    HCCLLibrary, aclrtStream_t, buffer_type, hcclComm_t, hcclDataTypeEnum,
+    hcclRedOpTypeEnum, hcclUniqueId)
+from vllm_ascend.utils import current_stream
+
+
+class PyHcclCommunicator:
+
+    def __init__(
+        self,
+        group: Union[ProcessGroup, StatelessProcessGroup],
+        device: Union[int, str, torch.device],
+        library_path: Optional[str] = None,
+    ):
+        """
+        Args:
+            group: the process group to work on. If None, it will use the
+                default process group.
+            device: the device to bind the PyHcclCommunicator to. If None,
+                it will be bind to f"npu:{local_rank}".
+            library_path: the path to the HCCL library. If None, it will
+                use the default library path.
+        It is the caller's responsibility to make sure each communicator
+        is bind to a unique device.
+        """
+
+        if not isinstance(group, StatelessProcessGroup):
+            assert dist.is_initialized()
+            assert dist.get_backend(group) != dist.Backend.HCCL, (
+                "PyHcclCommunicator should be attached to a non-HCCL group.")
+            # note: this rank is the rank in the group
+            self.rank = dist.get_rank(group)
+            self.world_size = dist.get_world_size(group)
+        else:
+            self.rank = group.rank
+            self.world_size = group.world_size
+
+        self.group = group
+
+        # if world_size == 1, no need to create communicator
+        if self.world_size == 1:
+            self.available = False
+            self.disabled = True
+            return
+
+        try:
+            self.hccl = HCCLLibrary(library_path)
+        except Exception:
+            # disable because of missing HCCL library
+            # e.g. in a non-NPU environment
+            self.available = False
+            self.disabled = True
+            return
+
+        self.available = True
+        self.disabled = False
+
+        logger.info("vLLM is using pyhccl")
+
+        if isinstance(device, int):
+            device = torch.device(f"npu:{device}")
+        elif isinstance(device, str):
+            device = torch.device(device)
+        # now `device` is a `torch.device` object
+        assert isinstance(device, torch.device)
+        self.device = device
+
+        if self.rank == 0:
+            # get the unique id from HCCL
+            with torch.npu.device(device):
+                self.unique_id = self.hccl.hcclGetUniqueId()
+        else:
+            # construct an empty unique id
+            self.unique_id = hcclUniqueId()
+
+        if not isinstance(group, StatelessProcessGroup):
+            tensor = torch.ByteTensor(list(self.unique_id.internal))
+            ranks = dist.get_process_group_ranks(group)
+            # arg `src` in `broadcast` is the global rank
+            dist.broadcast(tensor, src=ranks[0], group=group)
+            byte_list = tensor.tolist()
+            for i, byte in enumerate(byte_list):
+                self.unique_id.internal[i] = byte
+        else:
+            self.unique_id = group.broadcast_obj(self.unique_id, src=0)
+
+        # hccl communicator and stream will use this device
+        # `torch.npu.device` is a context manager that changes the
+        # current npu device to the specified one
+        with torch.npu.device(device):
+            self.comm: hcclComm_t = self.hccl.hcclCommInitRank(
+                self.world_size, self.unique_id, self.rank)
+
+            stream = current_stream()
+            # A small all_reduce for warmup.
+            data = torch.zeros(1, device=device)
+            self.all_reduce(data)
+            stream.synchronize()
+            del data
+
+    def all_reduce(self,
+                   in_tensor: torch.Tensor,
+                   op: ReduceOp = ReduceOp.SUM,
+                   stream=None) -> torch.Tensor:
+        if self.disabled:
+            return None
+        # hccl communicator created on a specific device
+        # will only work on tensors on the same device
+        # otherwise it will cause "illegal memory access"
+        assert in_tensor.device == self.device, (
+            f"this hccl communicator is created to work on {self.device}, "
+            f"but the input tensor is on {in_tensor.device}")
+
+        out_tensor = torch.empty_like(in_tensor)
+
+        if stream is None:
+            stream = current_stream()
+        self.hccl.hcclAllReduce(buffer_type(in_tensor.data_ptr()),
+                                buffer_type(out_tensor.data_ptr()),
+                                in_tensor.numel(),
+                                hcclDataTypeEnum.from_torch(in_tensor.dtype),
+                                hcclRedOpTypeEnum.from_torch(op), self.comm,
+                                aclrtStream_t(stream.npu_stream))
+        return out_tensor
+
+    def broadcast(self, tensor: torch.Tensor, src: int, stream=None):
+        if self.disabled:
+            return
+        assert tensor.device == self.device, (
+            f"this hccl communicator is created to work on {self.device}, "
+            f"but the input tensor is on {tensor.device}")
+        if stream is None:
+            stream = current_stream()
+        if src == self.rank:
+            buffer = buffer_type(tensor.data_ptr())
+        else:
+            buffer = buffer_type(tensor.data_ptr())
+        self.hccl.hcclBroadcast(buffer, tensor.numel(),
+                                hcclDataTypeEnum.from_torch(tensor.dtype), src,
+                                self.comm, aclrtStream_t(stream.npu_stream))

vllm_ascend/distributed/device_communicators/pyhccl_wrapper.py

@@ -0,0 +1,253 @@
+#
+# Copyright (c) 2025 Huawei Technologies Co., Ltd. All Rights Reserved.
+# This file is a part of the vllm-ascend project.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import ctypes
+import platform
+from dataclasses import dataclass
+from typing import Any, Dict, List, Optional
+
+import torch
+from torch.distributed import ReduceOp
+from vllm.logger import logger
+
+from vllm_ascend.utils import find_hccl_library
+
+# export types and functions from hccl to Python ===
+# for the original hccl definition, please check
+# https://github.com/EternalLied/cann-hccl-new/blob/64ec6ce2923319caa5df8c3c531e06bdc148ce9c/inc/hccl/hccl.h#L90
+# https://github.com/EternalLied/cann-hccl-new/blob/64ec6ce2923319caa5df8c3c531e06bdc148ce9c/inc/hccl/hccl_types.h#L48
+
+hcclResult_t = ctypes.c_int
+hcclComm_t = ctypes.c_void_p
+
+
+class hcclUniqueId(ctypes.Structure):
+    _fields_ = [("internal", ctypes.c_byte * 4108)]
+
+
+aclrtStream_t = ctypes.c_void_p
+buffer_type = ctypes.c_void_p
+
+hcclDataType_t = ctypes.c_int
+
+
+class hcclDataTypeEnum:
+    hcclInt8 = 0
+    hcclInt16 = 1
+    hcclInt32 = 2
+    hcclFloat16 = 3
+    hcclFloat32 = 4
+    hcclInt64 = 5
+    hcclUint64 = 6
+    hcclUint8 = 7
+    hcclUint16 = 8
+    hcclUint32 = 9
+    hcclFloat64 = 10
+    hcclBfloat16 = 11
+    hcclInt128 = 12
+
+    @classmethod
+    def from_torch(cls, dtype: torch.dtype) -> int:
+        if dtype == torch.int8:
+            return cls.hcclInt8
+        if dtype == torch.uint8:
+            return cls.hcclUint8
+        if dtype == torch.int32:
+            return cls.hcclInt32
+        if dtype == torch.int64:
+            return cls.hcclInt64
+        if dtype == torch.float16:
+            return cls.hcclFloat16
+        if dtype == torch.float32:
+            return cls.hcclFloat32
+        if dtype == torch.float64:
+            return cls.hcclFloat64
+        if dtype == torch.bfloat16:
+            return cls.hcclBfloat16
+        raise ValueError(f"Unsupported dtype: {dtype}")
+
+
+hcclRedOp_t = ctypes.c_int
+
+
+class hcclRedOpTypeEnum:
+    hcclSum = 0
+    hcclProd = 1
+    hcclMax = 2
+    hcclMin = 3
+
+    @classmethod
+    def from_torch(cls, op: ReduceOp) -> int:
+        if op == ReduceOp.SUM:
+            return cls.hcclSum
+        if op == ReduceOp.PRODUCT:
+            return cls.hcclProd
+        if op == ReduceOp.MAX:
+            return cls.hcclMax
+        if op == ReduceOp.MIN:
+            return cls.hcclMin
+        raise ValueError(f"Unsupported op: {op}")
+
+
+@dataclass
+class Function:
+    name: str
+    restype: Any
+    argtypes: List[Any]
+
+
+class HCCLLibrary:
+    exported_functions = [
+        # const char* HcclGetErrorString(HcclResult code);
+        Function("HcclGetErrorString", ctypes.c_char_p, [hcclResult_t]),
+
+        # HcclResult HcclGetRootInfo(HcclRootInfo *rootInfo);
+        Function("HcclGetRootInfo", hcclResult_t,
+                 [ctypes.POINTER(hcclUniqueId)]),
+
+        # HcclResult HcclCommInitRootInfo(
+        #   uint32_t nRanks, const HcclRootInfo *rootInfo, uint32_t rank, HcclComm *comm);
+        # note that HcclComm is a pointer type, so the last argument is a pointer to a pointer
+        Function("HcclCommInitRootInfo", hcclResult_t, [
+            ctypes.c_int,
+            ctypes.POINTER(hcclUniqueId),
+            ctypes.c_int,
+            ctypes.POINTER(hcclComm_t),
+        ]),
+
+        # HcclResult HcclAllReduce(
+        #   void *sendBuf, void *recvBuf, uint64_t count,
+        #   HcclDataType dataType, HcclReduceOp op, HcclComm comm,
+        #   aclrtStream stream);
+        Function("HcclAllReduce", hcclResult_t, [
+            buffer_type,
+            buffer_type,
+            ctypes.c_size_t,
+            hcclDataType_t,
+            hcclRedOp_t,
+            hcclComm_t,
+            aclrtStream_t,
+        ]),
+
+        # HcclResult HcclBroadcast(
+        #   void *buf, uint64_t count,
+        #   HcclDataType dataType, uint32_t root,
+        #   HcclComm comm, aclrtStream stream);
+        Function("HcclBroadcast", hcclResult_t, [
+            buffer_type,
+            ctypes.c_size_t,
+            hcclDataType_t,
+            ctypes.c_int,
+            hcclComm_t,
+            aclrtStream_t,
+        ]),
+
+        # HcclResult HcclCommDestroy(HcclComm comm);
+        Function("HcclCommDestroy", hcclResult_t, [hcclComm_t]),
+    ]
+
+    # class attribute to store the mapping from the path to the library
+    # to avoid loading the same library multiple times
+    path_to_library_cache: Dict[str, Any] = {}
+
+    # class attribute to store the mapping from library path
+    # to the correspongding directory
+    path_to_dict_mapping: Dict[str, Dict[str, Any]] = {}
+
+    def __init__(self, so_file: Optional[str] = None):
+
+        so_file = so_file or find_hccl_library()
+
+        try:
+            if so_file not in HCCLLibrary.path_to_dict_mapping:
+                lib = ctypes.CDLL(so_file)
+                HCCLLibrary.path_to_library_cache[so_file] = lib
+            self.lib = HCCLLibrary.path_to_library_cache[so_file]
+        except Exception as e:
+            logger.error(
+                "Failed to load HCCL library from %s. "
+                "It is expected if you are not running on Ascend NPUs."
+                "Otherwise, the hccl library might not exist, be corrupted "
+                "or it does not support the current platform %s. "
+                "If you already have the library, please set the "
+                "environment variable HCCL_SO_PATH"
+                " to point to the correct hccl library path.", so_file,
+                platform.platform())
+            raise e
+
+        if so_file not in HCCLLibrary.path_to_dict_mapping:
+            _funcs: Dict[str, Any] = {}
+            for func in HCCLLibrary.exported_functions:
+                f = getattr(self.lib, func.name)
+                f.restype = func.restype
+                f.argtypes = func.argtypes
+                _funcs[func.name] = f
+            HCCLLibrary.path_to_dict_mapping[so_file] = _funcs
+        self._funcs = HCCLLibrary.path_to_dict_mapping[so_file]
+
+    def hcclGetErrorString(self, result: hcclResult_t) -> str:
+        return self._funcs["HcclGetErrorString"](result).decode("utf-8")
+
+    def HCCL_CHECK(self, result: hcclResult_t) -> None:
+        if result != 0:
+            error_str = self.hcclGetErrorString(result)
+            raise RuntimeError(f"HCCL error: {error_str}")
+
+    def hcclGetUniqueId(self) -> hcclUniqueId:
+        unique_id = hcclUniqueId()
+        self.HCCL_CHECK(self._funcs["HcclGetRootInfo"](
+            ctypes.byref(unique_id)))
+        return unique_id
+
+    def hcclCommInitRank(self, world_size: int, unique_id: hcclUniqueId,
+                         rank: int) -> hcclComm_t:
+        comm = hcclComm_t()
+        self.HCCL_CHECK(self._funcs["HcclCommInitRootInfo"](
+            world_size, ctypes.byref(unique_id), rank, ctypes.byref(comm)))
+        return comm
+
+    def hcclAllReduce(self, sendbuff: buffer_type, recvbuff: buffer_type,
+                      count: int, datatype: int, op: int, comm: hcclComm_t,
+                      stream: aclrtStream_t) -> None:
+        # `datatype` actually should be `hcclDataType_t`
+        # and `op` should be `hcclRedOp_t`
+        # both are aliases of `ctypes.c_int`
+        # when we pass int to a function, it will be converted to `ctypes.c_int`
+        # by ctypes automatically
+        self.HCCL_CHECK(self._funcs["HcclAllReduce"](sendbuff, recvbuff, count,
+                                                     datatype, op, comm,
+                                                     stream))
+
+    def hcclBroadcast(self, buf: buffer_type, count: int, datatype: int,
+                      root: int, comm: hcclComm_t,
+                      stream: aclrtStream_t) -> None:
+        self.HCCL_CHECK(self._funcs["HcclBroadcast"](buf, count, datatype,
+                                                     root, comm, stream))
+
+    def hcclCommDestroy(self, comm: hcclComm_t) -> None:
+        self.HCCL_CHECK(self._funcs["HcclCommDestroy"](comm))
+
+
+__all__ = [
+    "HCCLLibrary",
+    "hcclDataTypeEnum",
+    "hcclRedOpTypeEnum",
+    "hcclUniqueId",
+    "hcclComm_t",
+    "aclrtStream_t",
+    "buffer_type",
+]

vllm_ascend/envs.py

@@ -46,6 +46,8 @@ env_variables: Dict[str, Callable[[], Any]] = {
     # Used for disaggregated prefilling
     "HCCN_PATH":
     lambda: os.getenv("HCCN_PATH", "/usr/local/Ascend/driver/tools/hccn_tool"),
+    "HCCL_SO_PATH":
+    lambda: os.environ.get("HCCL_SO_PATH", None),
     "PROMPT_DEVICE_ID":
     lambda: os.getenv("PROMPT_DEVICE_ID", None),
     "DECODE_DEVICE_ID":
@@ -53,7 +55,7 @@ env_variables: Dict[str, Callable[[], Any]] = {
     "LLMDATADIST_COMM_PORT":
     lambda: os.getenv("LLMDATADIST_COMM_PORT", "26000"),
     "LLMDATADIST_SYNC_CACHE_WAIT_TIME":
-    lambda: os.getenv("LLMDATADIST_SYNC_CACHE_WAIT_TIME", "5000")
+    lambda: os.getenv("LLMDATADIST_SYNC_CACHE_WAIT_TIME", "5000"),
 }
 
 # end-env-vars-definition

vllm_ascend/utils.py

@@ -17,8 +17,11 @@
 # limitations under the License.
 #
 import torch
+import torch_npu  # noqa: F401
 from vllm.logger import logger
 
+import vllm_ascend.envs as envs
+
 
 def try_register_lib(lib_name: str, lib_info: str = ""):
     import importlib
@@ -33,6 +36,28 @@ def try_register_lib(lib_name: str, lib_info: str = ""):
         pass
 
 
+def find_hccl_library() -> str:
+    """
+    We either use the library file specified by the `HCCL_SO_PATH`
+    environment variable, or we find the library file brought by PyTorch.
+    After importing `torch`, `libhccl.so` can be
+    found by `ctypes` automatically.
+    """
+    so_file = envs.HCCL_SO_PATH
+
+    # manually load the hccl library
+    if so_file:
+        logger.info("Found hccl from environment variable HCCL_SO_PATH=%s",
+                    so_file)
+    else:
+        if torch.version.cann is not None:
+            so_file = "libhccl.so"
+        else:
+            raise ValueError("HCCL only supports Ascend NPU backends.")
+        logger.info("Found hccl from library %s", so_file)
+    return so_file
+
+
 _current_stream = None