First commit

vllm/distributed/utils.py

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+# Copyright 2023 The vLLM team.
+# Adapted from
+# https://github.com/NVIDIA/Megatron-LM/blob/main/megatron/core/tensor_parallel/utils.py
+# Copyright (c) 2022, NVIDIA CORPORATION. All rights reserved.
+from typing import Sequence, Tuple
+
+import torch
+
+import vllm.envs as envs
+from vllm.logger import init_logger
+
+logger = init_logger(__name__)
+
+
+def ensure_divisibility(numerator, denominator):
+    """Ensure that numerator is divisible by the denominator."""
+    assert numerator % denominator == 0, "{} is not divisible by {}".format(
+        numerator, denominator)
+
+
+def divide(numerator, denominator):
+    """Ensure that numerator is divisible by the denominator and return
+    the division value."""
+    ensure_divisibility(numerator, denominator)
+    return numerator // denominator
+
+
+def split_tensor_along_last_dim(
+    tensor: torch.Tensor,
+    num_partitions: int,
+    contiguous_split_chunks: bool = False,
+) -> Sequence[torch.Tensor]:
+    """ Split a tensor along its last dimension.
+
+        Arguments:
+            tensor: input tensor.
+            num_partitions: number of partitions to split the tensor
+            contiguous_split_chunks: If True, make each chunk contiguous
+                                     in memory.
+
+        Returns:
+            A list of Tensors
+    """
+    # Get the size and dimension.
+    last_dim = tensor.dim() - 1
+    last_dim_size = divide(tensor.size()[last_dim], num_partitions)
+    # Split.
+    tensor_list = torch.split(tensor, last_dim_size, dim=last_dim)
+    # NOTE: torch.split does not create contiguous tensors by default.
+    if contiguous_split_chunks:
+        return tuple(chunk.contiguous() for chunk in tensor_list)
+
+    return tensor_list
+
+
+def get_pp_indices(num_hidden_layers: int, pp_rank: int,
+                   pp_size: int) -> Tuple[int, int]:
+    """Try to evenly distribute layers across partitions.
+    If the number of layers is not divisible by the number of partitions,
+    the last partition will have the remaining layers.
+    """
+    partition_list_str = envs.VLLM_PP_LAYER_PARTITION
+    if partition_list_str is not None:
+        try:
+            partitions = [
+                int(layer) for layer in partition_list_str.split(",")
+            ]
+        except ValueError as err:
+            raise ValueError("Invalid partition string: {}".format(
+                partition_list_str)) from err
+        if len(partitions) != pp_size:
+            raise ValueError(f"{len(partitions)=} does not match {pp_size=}.")
+        if sum(partitions) != num_hidden_layers:
+            raise ValueError(
+                f"{sum(partitions)=} does not match {num_hidden_layers=}.")
+        start_layer = sum(partitions[:pp_rank])
+        end_layer = start_layer + partitions[pp_rank]
+    else:
+        layers_per_partition = num_hidden_layers // pp_size
+        start_layer = pp_rank * layers_per_partition
+        end_layer = start_layer + layers_per_partition
+
+        if pp_rank == pp_size - 1:
+            end_layer = num_hidden_layers
+
+    return (start_layer, end_layer)