utils.py

from typing import Any, Optional, Tuple

import torch
import torch.distributed as dist

from .deep_ep_cpp import EventHandle


class EventOverlap:
    """
    A wrapper class to manage CUDA events, also for better overlapping convenience.

    Attributes:
        event: the CUDA event captured.
        extra_tensors: an easier way to simulate PyTorch tensor `record_stream`, may be useful with CUDA graph.
    """

    def __init__(
        self, event: Optional[EventHandle] = None, extra_tensors: Optional[Tuple[torch.Tensor]] = None
    ) -> None:
        """
        Initialize the class.

        Arguments:
            event: the CUDA event captured.
            extra_tensors: an easier way to simulate PyTorch tensor `record_stream`, may be useful with CUDA graph.
        """
        self.event = event

        # NOTES: we use extra tensors to achieve stream recording, otherwise,
        # stream recording will be incompatible with CUDA graph.
        self.extra_tensors = extra_tensors

    def current_stream_wait(self) -> None:
        """
        The current stream `torch.cuda.current_stream()` waits for the event to be finished.
        """
        assert self.event is not None
        self.event.current_stream_wait()

    def __enter__(self) -> Any:
        """
        Utility for overlapping and Python `with` syntax.

        You can overlap the kernels on the current stream with the following example:
        ```python
        event_overlap = event_after_all_to_all_kernels()
        with event_overlap():
            do_something_on_current_stream()
        # After exiting the `with` scope, the current stream with wait the event to be finished.
        ```
        """
        return self

    def __exit__(self, exc_type: Any, exc_val: Any, exc_tb: Any) -> None:
        """
        Utility for overlapping and Python `with` syntax.

        Please follow the example in the `__enter__` function.
        """
        if self.event is not None:
            self.event.current_stream_wait()


def check_nvlink_connections(group: dist.ProcessGroup):
    """
    Check NVLink connection between every pair of GPUs.

    Arguments:
        group: the communication group.
    """
    # TODO