enable custom_allreduce

python/sglang/srt/_custom_ops.py

@@ -19,14 +19,15 @@ logger = logging.getLogger(__name__)
 use_vllm_custom_allreduce = get_bool_env_var(
     "USE_VLLM_CUSTOM_ALLREDUCE", default="false"
 )
+use_dcu_custom_allreduce= get_bool_env_var(
+    "USE_DCU_CUSTOM_ALLREDUCE", default="false"
+)
 
 if not is_hpu():
     # ROCm does not use vllm custom allreduce
-    # if use_vllm_custom_allreduce and not is_hip():
-    if use_vllm_custom_allreduce:
+    if use_vllm_custom_allreduce and not is_hip():
         try:
             import vllm._C  # noqa: F401
-            print("[DEBUG] ✅ Using vLLM custom allreduce (vllm._C successfully imported)")
         except ImportError as e:
             logger.warning("Failed to import from vllm._C with %r", e)
     else:
@@ -35,12 +36,15 @@ if not is_hpu():
         except ImportError as e:
             logger.warning("Failed to import from custom_ar with %r", e)
 
+if use_dcu_custom_allreduce:
+    try:
+        import vllm._C
+    except ImportError as e:
+        logger.warning("Failed to import from vllm._C with %r", e)
 
-# if not is_hip() and not is_npu():
-if not is_npu():
+if not is_hip() and not is_npu():
     if use_vllm_custom_allreduce:
         custom_op = torch.ops._C_custom_ar
-        print("[DEBUG] ✅ custom_op = torch.ops._C_custom_ar (vLLM path active)")
     else:
         custom_op = sgl_kernel.allreduce
 
@@ -79,8 +83,79 @@ if not is_npu():
     ) -> None:
         custom_op.register_graph_buffers(fa, handles, offsets)
 
+elif is_hip and use_dcu_custom_allreduce:
+    # custom ar
+    def init_custom_ar(ipc_tensors: list[torch.Tensor], rank_data: torch.Tensor,
+                    rank: int, fully_connected: bool) -> int:
+        return torch.ops._C_custom_ar.init_custom_ar(ipc_tensors, rank_data, rank,
+                                                    fully_connected)
+
+
+    def all_reduce(fa: int, inp: torch.Tensor, out: torch.Tensor, reg_buffer: int,
+                reg_buffer_sz_bytes: int) -> None:
+        torch.ops._C_custom_ar.all_reduce(fa, inp, out, reg_buffer,
+                                        reg_buffer_sz_bytes)
+
+
+    def dispose(fa: int) -> None:
+        torch.ops._C_custom_ar.dispose(fa)
+
+
+    def meta_size() -> int:
+        return torch.ops._C_custom_ar.meta_size()
+
+
+    def register_buffer(fa: int, ipc_tensors: list[int]) -> None:
+        return torch.ops._C_custom_ar.register_buffer(fa, ipc_tensors)
+
+
+    def get_graph_buffer_ipc_meta(fa: int) -> tuple[list[int], list[int]]:
+        return torch.ops._C_custom_ar.get_graph_buffer_ipc_meta(fa)
+
+
+    def register_graph_buffers(fa: int, handles: list[list[int]],
+                            offsets: list[list[int]]) -> None:
+        torch.ops._C_custom_ar.register_graph_buffers(fa, handles, offsets)
+
+
+    def allocate_shared_buffer_and_handle(size: int) -> tuple[int, torch.Tensor]:
+        return torch.ops._C_custom_ar.allocate_shared_buffer_and_handle(size)
+
+
+    def open_mem_handle(mem_handle: torch.Tensor):
+        return torch.ops._C_custom_ar.open_mem_handle(mem_handle)
+
+
+    def free_shared_buffer(ptr: int) -> None:
+        torch.ops._C_custom_ar.free_shared_buffer(ptr)
+
+
+    def read_cache(
+            keys: torch.Tensor,
+            values: torch.Tensor,
+            key_caches: list[torch.Tensor],
+            value_caches: list[torch.Tensor],
+            slot_mapping: torch.Tensor,
+            kv_cache_dtype: str
+    ) -> None:
+        torch.ops._C_cache_ops.read_cache(keys, values, key_caches,
+                                        value_caches, slot_mapping,
+                                        kv_cache_dtype)
+
+    def write_cache_multi_layers(
+            keys: torch.Tensor,
+            values: torch.Tensor,
+            key_caches: list[torch.Tensor],
+            value_caches: list[torch.Tensor],
+            slot_mapping: torch.Tensor,
+            kv_cache_dtype: str
+    ) -> None:
+        torch.ops._C_cache_ops.write_cache_multi_layers(keys, values, key_caches,
+                                                        value_caches, slot_mapping,
+                                                        kv_cache_dtype)
+
 else:
-    # ROCM custom allreduce
+    # sgl_kernel ROCM custom allreduce
 
     def init_custom_ar(
         meta: torch.Tensor,

python/sglang/srt/distributed/device_communicators/custom_all_reduce.py

@@ -27,10 +27,11 @@ _is_hip = is_hip()
 
 
 try:
-    # if ops.use_vllm_custom_allreduce and not _is_hip:
-    if ops.use_vllm_custom_allreduce:
+    if ops.use_vllm_custom_allreduce and not _is_hip:
         # Use vLLM custom allreduce
         ops.meta_size()
+    elif ops.use_dcu_custom_allreduce:
+        ops.meta_size()
     else:
         # Use custom allreduce from sgl kernel (ROCM and TRT-LLM)
         import sgl_kernel  # noqa: F401
@@ -420,3 +421,274 @@ class CustomAllreduce:
 
     def __del__(self):
         self.close()
+
+class DCUCustomAllreduce:
+
+    _SUPPORTED_WORLD_SIZES = [2, 4, 6, 8, 16]
+
+    # max_size: max supported allreduce size
+    def __init__(self,
+                 group: ProcessGroup,
+                 device: Union[int, str, torch.device],
+                 max_size=8192 * 512) -> None:
+        """
+        Args:
+            group: the process group to work on. If None, it will use the
+                default process group.
+            device: the device to bind the CustomAllreduce to. If None,
+                it will be bind to f"cuda:{local_rank}".
+        It is the caller's responsibility to make sure each communicator
+        is bind to a unique device, and all communicators in this group
+        are in the same node.
+        """
+        self._IS_CAPTURING = False
+        self.disabled = True
+
+        if not custom_ar:
+            # disable because of missing custom allreduce library
+            # e.g. in a non-GPU environment
+            logger.info("Custom allreduce is disabled because "
+                        "of missing custom allreduce library")
+            return
+
+        self.group = group
+
+        assert dist.get_backend(group) != dist.Backend.NCCL, (
+            "CustomAllreduce should be attached to a non-NCCL group.")
+
+        if not all(in_the_same_node_as(group, source_rank=0)):
+            # No need to initialize custom allreduce for multi-node case.
+            logger.warning(
+                "Custom allreduce is disabled because this process group"
+                " spans across nodes.")
+            return
+
+        rank = dist.get_rank(group=self.group)
+        self.rank = rank
+        world_size = dist.get_world_size(group=self.group)
+        
+        # if world_size > envs.VLLM_CUSTOM_ALLREDUCE_SUPPORTED_WORLDSIZE_MAX:
+        if world_size > 16:
+            return
+
+        if world_size == 1:
+            # No need to initialize custom allreduce for single GPU case.
+            return
+
+        if world_size not in CustomAllreduce._SUPPORTED_WORLD_SIZES:
+            logger.warning(
+                "Custom allreduce is disabled due to an unsupported world"
+                " size: %d. Supported world sizes: %s. To silence this "
+                "warning, specify disable_custom_all_reduce=True explicitly.",
+                world_size, str(CustomAllreduce._SUPPORTED_WORLD_SIZES))
+            return
+
+        if isinstance(device, int):
+            device = torch.device(f"cuda:{device}")
+        elif isinstance(device, str):
+            device = torch.device(device)
+        # now `device` is a `torch.device` object
+        assert isinstance(device, torch.device)
+        self.device = device
+
+        cuda_visible_devices = os.environ.get("CUDA_VISIBLE_DEVICES", None)
+        if cuda_visible_devices:
+            device_ids = list(map(int, cuda_visible_devices.split(",")))
+        else:
+            device_ids = list(range(torch.cuda.device_count()))
+
+        physical_device_id = device_ids[device.index]
+        tensor = torch.tensor([physical_device_id],
+                              dtype=torch.int,
+                              device="cpu")
+        gather_list = [
+            torch.tensor([0], dtype=torch.int, device="cpu")
+            for _ in range(world_size)
+        ]
+        dist.all_gather(gather_list, tensor, group=self.group)
+        physical_device_ids = [t.item() for t in gather_list]
+
+        # test nvlink first, this will filter out most of the cases
+        # where custom allreduce is not supported
+        # this checks hardware and driver support for NVLink
+        # assert current_platform.is_cuda_alike()
+        # fully_connected = current_platform.is_fully_connected(
+        #     physical_device_ids)
+        if _is_cuda or _is_hip:
+            fully_connected = is_full_nvlink(physical_device_ids, world_size)
+        
+        # if world_size > 2 and not fully_connected:
+        if not fully_connected:
+            max_size = 32 * 8192 * 2
+            # if not envs.VLLM_PCIE_USE_CUSTOM_ALLREDUCE:
+            #     logger.warning(
+            #         "Custom allreduce is disabled because it's not supported on"
+            #         " more than two PCIe-only GPUs. To silence this warning, "
+            #         "specify disable_custom_all_reduce=True explicitly.")
+            #     return
+            logger.warning(
+                "We are using PCIe's custom allreduce."
+                "If the performance is poor, we can add "
+                "--disable-custom-all-reduce in the instruction.")
+        # test P2P capability, this checks software/cudaruntime support
+        # this is expensive to compute at the first time
+        # then we cache the result
+        # On AMD GPU, p2p is always enabled between XGMI connected GPUs
+        if not _is_hip and not _can_p2p(rank, world_size):
+            logger.warning(
+                "Custom allreduce is disabled because your platform lacks "
+                "GPU P2P capability or P2P test failed. To silence this "
+                "warning, specify disable_custom_all_reduce=True explicitly.")
+            return
+
+        self.disabled = False
+        # Buffers memory are owned by this Python class and passed to C++.
+        # Meta data composes of two parts: meta data for synchronization and a
+        # temporary buffer for storing intermediate allreduce results.
+        self.meta_ptrs = self.create_shared_buffer(ops.meta_size() + max_size,
+                                                   group=group,
+                                                   uncached=True)
+        # This is a pre-registered IPC buffer. In eager mode, input tensors
+        # are first copied into this buffer before allreduce is performed
+        self.buffer_ptrs = self.create_shared_buffer(max_size, group=group)
+        # This is a buffer for storing the tuples of pointers pointing to
+        # IPC buffers from all ranks. Each registered tuple has size of
+        # 8*world_size bytes where world_size is at most 8. Allocating 8MB
+        # is enough for 131072 such tuples. The largest model I've seen only
+        # needs less than 10000 of registered tuples.
+        self.rank_data = torch.empty(8 * 1024 * 1024,
+                                     dtype=torch.uint8,
+                                     device=self.device)
+        self.max_size = max_size
+        self.rank = rank
+        self.world_size = world_size
+        self.fully_connected = fully_connected
+        self._ptr = ops.init_custom_ar(self.meta_ptrs, self.rank_data, rank,
+                                       self.fully_connected)
+        ops.register_buffer(self._ptr, self.buffer_ptrs)
+
+    @contextmanager
+    def capture(self):
+        """
+        The main responsibility of this context manager is the 
+        `register_graph_buffers` call at the end of the context.
+        It records all the buffer addresses used in the CUDA graph.
+        """
+        try:
+            self._IS_CAPTURING = True
+            yield
+        finally:
+            self._IS_CAPTURING = False
+            if not self.disabled:
+                self.register_graph_buffers()
+
+    def register_graph_buffers(self):
+        handle, offset = ops.get_graph_buffer_ipc_meta(self._ptr)
+        logger.info("Registering %d cuda graph addresses", len(offset))
+        # We cannot directly use `dist.all_gather_object` here
+        # because it is incompatible with `gloo` backend under inference mode.
+        # see https://github.com/pytorch/pytorch/issues/126032 for details.
+        all_data = [[None, None]
+                    for _ in range(dist.get_world_size(group=self.group))]
+        all_data[self.rank] = [handle, offset]
+        ranks = sorted(dist.get_process_group_ranks(group=self.group))
+        for i, rank in enumerate(ranks):
+            dist.broadcast_object_list(all_data[i],
+                                       src=rank,
+                                       group=self.group,
+                                       device="cpu")
+        # Unpack list of tuples to tuple of lists.
+        handles = [d[0] for d in all_data]  # type: ignore
+        offsets = [d[1] for d in all_data]  # type: ignore
+        ops.register_graph_buffers(self._ptr, handles, offsets)
+
+    def should_custom_ar(self, inp: torch.Tensor):
+        if self.disabled:
+            return False
+        inp_size = inp.numel() * inp.element_size()
+        # custom allreduce requires input byte size to be multiples of 16
+        if inp_size % 16 != 0:
+            return False
+        if not is_weak_contiguous(inp):
+            return False
+        # for 4 or more non NVLink-capable GPUs, custom allreduce provides
+        # little performance improvement over NCCL.
+        return inp_size <= self.max_size
+
+    def all_reduce(self,
+                   inp: torch.Tensor,
+                   *,
+                   out: torch.Tensor = None,
+                   registered: bool = False):
+        """Performs an out-of-place all reduce.
+        
+        If registered is True, this assumes inp's pointer is already
+        IPC-registered. Otherwise, inp is first copied into a pre-registered
+        buffer.
+        """
+        if out is None:
+            out = torch.empty_like(inp)
+        if registered:
+            ops.all_reduce(self._ptr, inp, out, 0, 0)
+        else:
+            ops.all_reduce(self._ptr, inp, out, self.buffer_ptrs[self.rank],
+                           self.max_size)
+        return out
+
+    def custom_all_reduce(self, input: torch.Tensor) -> Optional[torch.Tensor]:
+        """The main allreduce API that provides support for cuda graph."""
+        # When custom allreduce is disabled, this will be None.
+        if self.disabled or not self.should_custom_ar(input):
+            return None
+        if self._IS_CAPTURING:
+            if torch.cuda.is_current_stream_capturing():
+                return self.all_reduce(input, registered=False)
+            else:
+                # If warm up, mimic the allocation pattern since custom
+                # allreduce is out-of-place.
+                return torch.empty_like(input)
+        else:
+            # Note: outside of cuda graph context, custom allreduce incurs a
+            # cost of cudaMemcpy, which should be small (<=1% of overall
+            # latency) compared to the performance gain of using custom kernels
+            return self.all_reduce(input, registered=False)
+
+    def close(self):
+        if not self.disabled and self._ptr:
+            if ops is not None:
+                ops.dispose(self._ptr)
+            self._ptr = 0
+            self.free_shared_buffer(self.meta_ptrs, rank=self.rank)
+            self.free_shared_buffer(self.buffer_ptrs, rank=self.rank)
+
+    def __del__(self):
+        self.close()
+
+
+    @staticmethod
+    def create_shared_buffer(size_in_bytes: int,
+                             group: Optional[ProcessGroup] = None,
+                             uncached: Optional[bool] = False) -> list[int]:
+        pointer, handle = ops.allocate_shared_buffer_and_handle(size_in_bytes)
+
+        world_size = dist.get_world_size(group=group)
+        rank = dist.get_rank(group=group)
+        handles = [None] * world_size
+        dist.all_gather_object(handles, handle, group=group)
+
+        pointers: list[int] = []
+        for i, h in enumerate(handles):
+            if i == rank:
+                pointers.append(pointer)  # type: ignore
+            else:
+                pointers.append(ops.open_mem_handle(h))
+        return pointers
+
+    @staticmethod
+    def free_shared_buffer(pointers: list[int],
+                           group: Optional[ProcessGroup] = None,
+                           rank: Optional[int] = 0) -> None:
+        if rank is None:
+            rank = dist.get_rank(group=group)
+        if ops is not None:
+            ops.free_shared_buffer(pointers[rank])

python/sglang/srt/distributed/parallel_state.py

@@ -53,6 +53,7 @@ from sglang.srt.utils import (
     is_xpu,
     supports_custom_op,
 )
+from sglang.srt import _custom_ops as ops
 
 _is_npu = is_npu()
 _is_cpu = is_cpu()
@@ -303,7 +304,7 @@ class GroupCoordinator:
 
         # Lazy import to avoid documentation build error
         from sglang.srt.distributed.device_communicators.custom_all_reduce import (
-            CustomAllreduce,
+            CustomAllreduce, DCUCustomAllreduce
         )
         from sglang.srt.distributed.device_communicators.pymscclpp import (
             PyMscclppCommunicator,
@@ -347,11 +348,17 @@ class GroupCoordinator:
             else:
                 ca_max_size = 8 * 1024 * 1024
             try:
-                self.ca_comm = CustomAllreduce(
-                    group=self.cpu_group,
-                    device=self.device,
-                    max_size=ca_max_size,
-                )
+                if is_hip() and ops.use_dcu_custom_allreduce:
+                    self.ca_comm = DCUCustomAllreduce(
+                        group=self.cpu_group,
+                        device=self.device,
+                    )
+                else:
+                    self.ca_comm = CustomAllreduce(
+                        group=self.cpu_group,
+                        device=self.device,
+                        max_size=ca_max_size,
+                    )
             except Exception as e:
                 logger.warning(
                     f"Setup Custom allreduce failed with {e}. To silence this "