aphrodite-engine/aphrodite/distributed/device_communicators/custom_all_reduce.py

from contextlib import contextmanager
from typing import Any, List, Optional, Union

import torch
import torch.distributed as dist
from loguru import logger
from torch.distributed import ProcessGroup

import aphrodite.common.envs as envs
from aphrodite import _custom_ops as ops
from aphrodite.common.utils import cuda_device_count_stateless
from aphrodite.distributed.device_communicators.custom_all_reduce_utils import (
    gpu_p2p_access_check)
from aphrodite.distributed.parallel_state import in_the_same_node_as
from aphrodite.platforms import current_platform

try:
    ops.meta_size()

    custom_ar = True
except Exception:
    # For AMD GPUs and CPUs
    custom_ar = False


def _can_p2p(rank: int, world_size: int) -> bool:
    for i in range(world_size):
        if i == rank:
            continue
        if not gpu_p2p_access_check(rank, i):
            return False
    return True


def is_weak_contiguous(inp: torch.Tensor):
    return inp.is_contiguous() or (inp.storage().nbytes() -
                                   inp.storage_offset() * inp.element_size()
                                   == inp.numel() * inp.element_size())


class CustomAllreduce:

    _SUPPORTED_WORLD_SIZES = [2, 4, 6, 8]

    # max_size: max supported allreduce size
    def __init__(self,
                 group: ProcessGroup,
                 device: Union[int, str, torch.device],
                 max_size=8192 * 1024) -> 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-cuda environment
            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)
        world_size = dist.get_world_size(group=self.group)
        if world_size == 1:
            # No need to initialize custom allreduce for single GPU case.
            return

        if world_size not in CustomAllreduce._SUPPORTED_WORLD_SIZES:
            if rank == 0:
                logger.warning(
                    "Custom allreduce is disabled due to an unsupported world"
                    f" size: {world_size}. Supported world sizes:"
                    f"{str(CustomAllreduce._SUPPORTED_WORLD_SIZES)}. To "
                    "silence this warning, specify disable_custom_all_reduce="
                    "True explicitly.")
            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 = envs.CUDA_VISIBLE_DEVICES
        if cuda_visible_devices:
            device_ids = list(map(int, cuda_visible_devices.split(",")))
        else:
            device_ids = list(range(cuda_device_count_stateless()))

        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()
        from aphrodite.platforms.cuda import CudaPlatform
        cuda_platform: CudaPlatform = current_platform
        full_nvlink = cuda_platform.is_full_nvlink(physical_device_ids)
        if world_size > 2 and not full_nvlink:
            if rank == 0:
                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
        # test P2P capability, this checks software/cudaruntime support
        # this is expensive to compute at the first time
        # then we cache the result
        if not _can_p2p(rank, world_size):
            if rank == 0:
                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
        # (256 bytes) and a temporary buffer for storing intermediate
        # allreduce results.
        self.meta = torch.zeros(ops.meta_size() + max_size,
                                dtype=torch.uint8,
                                device=self.device)
        # This is a pre-registered IPC buffer. In eager mode, input tensors
        # are first copied into this buffer before allreduce is performed
        self.buffer = torch.empty(max_size,
                                  dtype=torch.uint8,
                                  device=self.device)
        # 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
        handles, offsets = self._get_ipc_meta(self.meta)
        self.full_nvlink = full_nvlink
        self._ptr = ops.init_custom_ar(self.meta, self.rank_data, handles,
                                       offsets, rank, self.full_nvlink)
        self.register_buffer(self.buffer)

    @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 _get_ipc_meta(self, inp: torch.Tensor):
        data = inp.untyped_storage()._share_cuda_()
        shard_data = (
            data[1],  # ipc handle to base ptr
            data[3],  # offset of base ptr
        )
        return self._gather_ipc_meta(shard_data)

    def _gather_ipc_meta(self, shard_data):
        # Note: don't use `[[None]] * self.world_size` here
        # because it will create a list of the same reference
        all_data: List[Optional[Any]] = [[None]
                                         for i in range(self.world_size)]
        all_data[self.rank][0] = shard_data

        ranks = dist.get_process_group_ranks(group=self.group)
        ranks.sort()
        for i, rank in enumerate(ranks):
            dist.broadcast_object_list(all_data[i],
                                       src=rank,
                                       group=self.group,
                                       device="cpu")

        # 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.

        handles = []
        offsets = []
        for i in range(len(all_data)):
            handles.append(all_data[i][0][0])  # type: ignore
            offsets.append(all_data[i][0][1])  # type: ignore
        return handles, offsets

    def register_buffer(self, inp: torch.Tensor):
        handles, offsets = self._get_ipc_meta(inp)
        ops.register_buffer(self._ptr, inp, handles, offsets)

    def register_graph_buffers(self):
        handle, offset = ops.get_graph_buffer_ipc_meta(self._ptr)
        handles, offsets = self._gather_ipc_meta((bytes(handle), offset))
        if self.rank == 0:
            logger.info(f"Registering {len(offset)} cuda graph addresses")
        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.
        if self.world_size == 2 or self.full_nvlink:
            return inp_size < self.max_size
        return False

    # all reduce, assuming inp tensor is IPC registered with register_buffer,
    # or, in the context of cuda graphs, register_graph_buffers
    def all_reduce_reg(self, inp: torch.Tensor, out: torch.Tensor = None):
        if out is None:
            out = torch.empty_like(inp)
        ops.all_reduce_reg(self._ptr, inp, out)
        return out

    # all reduce, assuming inp tensor is NOT IPC registered
    def all_reduce_unreg(self, inp: torch.Tensor, out: torch.Tensor = None):
        if out is None:
            out = torch.empty_like(inp)
        ops.all_reduce_unreg(self._ptr, inp, self.buffer, out)
        return out

    def custom_all_reduce(self, input: torch.Tensor) -> Optional[torch.Tensor]:
        # when custom allreduce is disabled, this will be None
        if self.disabled:
            return None
        if self._IS_CAPTURING:
            if torch.cuda.is_current_stream_capturing():
                if self.should_custom_ar(input):
                    return self.all_reduce_reg(input)
            else:
                if self.should_custom_ar(input):
                    # 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
            # gains of using custom kernels
            if self.should_custom_ar(input):
                return self.all_reduce_unreg(input)

        return None

    def close(self):
        if not self.disabled and self._ptr:
            ops.dispose(self._ptr)
            self._ptr = 0

    def __del__(self):
        self.close()