test_eplb_algo.py

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

import pytest
import torch

from vllm.distributed.eplb.rebalance_algo import rebalance_experts


def test_basic_rebalance():
    """Test basic rebalancing functionality"""
    # Example from https://github.com/deepseek-ai/eplb
    weight = torch.tensor([
        [90, 132, 40, 61, 104, 165, 39, 4, 73, 56, 183, 86],
        [20, 107, 104, 64, 19, 197, 187, 157, 172, 86, 16, 27],
    ])

    num_layers = weight.shape[0]
    num_replicas = 16
    num_groups = 4
    num_nodes = 2
    num_gpus = 8

    phy2log, log2phy, logcnt = rebalance_experts(weight, num_replicas,
                                                 num_groups, num_nodes,
                                                 num_gpus)

    # Verify output shapes
    assert phy2log.shape == (
        2,
        16,
    ), f"Expected `phy2log` shape (2, 16), got {phy2log.shape}"
    assert (log2phy.shape[0] == 2
            ), f"Expected `log2phy` first dimension 2, got {log2phy.shape[0]}"
    assert (
        log2phy.shape[1] == 12
    ), f"Expected `log2phy` second dimension 12, got {log2phy.shape[1]}"
    assert logcnt.shape == (
        2,
        12,
    ), f"Expected `logcnt` shape (2, 12), got {logcnt.shape}"

    # Verify physical to logical expert mapping range is correct
    assert torch.all(phy2log >= 0) and torch.all(
        phy2log < 12), "Physical to logical mapping should be in range [0, 12)"

    # Verify expert count reasonableness
    assert torch.all(
        logcnt >= 1), "Each logical expert should have at least 1 replica"
    assert (
        torch.sum(logcnt, dim=1).sum() == num_replicas *
        num_layers), f"Total replicas should be {num_replicas * num_layers}"

    # Verify expected output
    expected_phy2log = torch.tensor([
        [5, 6, 5, 7, 8, 4, 3, 4, 10, 9, 10, 2, 0, 1, 11, 1],
        [7, 10, 6, 8, 6, 11, 8, 9, 2, 4, 5, 1, 5, 0, 3, 1],
    ])
    assert torch.all(phy2log == expected_phy2log)

    expected_logcnt = torch.tensor([[1, 2, 1, 1, 2, 2, 1, 1, 1, 1, 2, 1],
                                    [1, 2, 1, 1, 1, 2, 2, 1, 2, 1, 1, 1]])
    assert torch.all(logcnt == expected_logcnt)


def test_single_gpu_case():
    """Test single GPU case"""
    weight = torch.tensor([[10, 20, 30, 40]])
    num_replicas = 4
    num_groups = 1
    num_nodes = 1
    num_gpus = 1

    phy2log, log2phy, logcnt = rebalance_experts(weight, num_replicas,
                                                 num_groups, num_nodes,
                                                 num_gpus)

    # Verify shapes
    assert phy2log.shape == (1, 4)
    assert log2phy.shape[0] == 1
    assert log2phy.shape[1] == 4
    assert logcnt.shape == (1, 4)

    # Verify all logical experts are mapped
    assert set(phy2log[0].tolist()) == {0, 1, 2, 3}


def test_equal_weights():
    """Test case with equal weights"""
    weight = torch.tensor([[50, 50, 50, 50, 50, 50, 50, 50]])
    num_replicas = 8
    num_groups = 2
    num_nodes = 2
    num_gpus = 4

    phy2log, log2phy, logcnt = rebalance_experts(weight, num_replicas,
                                                 num_groups, num_nodes,
                                                 num_gpus)

    # Verify shapes
    assert phy2log.shape == (1, 8)
    assert logcnt.shape == (1, 8)

    # With equal weights, each expert should have exactly one replica
    assert torch.all(
        logcnt == 1
    ), "With equal weights and no replication, " \
       "each expert should have exactly 1 replica"


def test_extreme_weight_imbalance():
    """Test extreme weight imbalance case"""
    weight = torch.tensor([[1000, 1, 1, 1, 1, 1, 1, 1]])
    num_replicas = 12
    num_groups = 2
    num_nodes = 2
    num_gpus = 4

    phy2log, log2phy, logcnt = rebalance_experts(weight, num_replicas,
                                                 num_groups, num_nodes,
                                                 num_gpus)

    # Verify shapes
    assert phy2log.shape == (1, 12)
    assert logcnt.shape == (1, 8)

    # Expert with highest weight (index 0) should have more replicas
    assert (
        logcnt[0, 0]
        > logcnt[0, 1]), "Expert with highest weight should have more replicas"


def test_multiple_layers():
    """Test multiple layers case"""
    weight = torch.tensor([
        [10, 20, 30, 40, 50, 60],  # First layer
        [60, 50, 40, 30, 20, 10],  # Second layer (opposite weight pattern)
        [25, 25, 25, 25, 25, 25],  # Third layer (equal weights)
    ])
    num_replicas = 8
    num_groups = 2
    num_nodes = 2
    num_gpus = 4

    phy2log, log2phy, logcnt = rebalance_experts(weight, num_replicas,
                                                 num_groups, num_nodes,
                                                 num_gpus)

    # Verify shapes
    assert phy2log.shape == (3, 8)
    assert logcnt.shape == (3, 6)

    # Verify expert allocation is reasonable for each layer
    for layer in range(3):
        assert torch.all(phy2log[layer] >= 0) and torch.all(
            phy2log[layer] < 6
        ), f"Layer {layer} physical to logical mapping" \
            "should be in range [0, 6)"
        assert (torch.sum(logcnt[layer]) == num_replicas
                ), f"Layer {layer} total replicas should be {num_replicas}"


def test_parameter_validation():
    """Test parameter validation"""
    weight = torch.tensor([[10, 20, 30, 40]])

    # Test non-divisible case - this should handle normally without throwing
    # errors because the function will fall back to global load balancing
    # strategy
    phy2log, log2phy, logcnt = rebalance_experts(weight, 8, 3, 2, 4)
    assert phy2log.shape == (1, 8)
    assert logcnt.shape == (1, 4)

    # Test cases that will actually cause errors:
    # num_physical_experts not divisible by num_gpus
    with pytest.raises(AssertionError):
        rebalance_experts(weight, 7, 2, 2, 4)  # 7 not divisible by 4


def test_small_scale_hierarchical():
    """Test small-scale hierarchical load balancing"""
    weight = torch.tensor([
        [100, 50, 200, 75, 150, 25, 300, 80],  # 8 experts
    ])
    num_replicas = 12
    num_groups = 4  # 4 groups, 2 experts each
    num_nodes = 2  # 2 nodes
    num_gpus = 4  # 4 GPUs

    phy2log, log2phy, logcnt = rebalance_experts(weight, num_replicas,
                                                 num_groups, num_nodes,
                                                 num_gpus)

    # Verify basic constraints
    assert phy2log.shape == (1, 12)
    assert logcnt.shape == (1, 8)
    assert torch.sum(logcnt) == num_replicas
    assert torch.all(logcnt >= 1)

    # Expert with highest weight should have more replicas
    max_weight_expert = torch.argmax(weight[0])
    assert (logcnt[0, max_weight_expert]
            >= 2), "Highest weight expert should have multiple replicas"


def test_global_load_balance_fallback():
    """Test global load balancing fallback case"""
    # When num_groups % num_nodes != 0, should fall back to global load
    # balancing
    weight = torch.tensor([[10, 20, 30, 40, 50, 60]])
    num_replicas = 8
    num_groups = 3  # Cannot be divided evenly by num_nodes=2
    num_nodes = 2
    num_gpus = 4

    phy2log, log2phy, logcnt = rebalance_experts(weight, num_replicas,
                                                 num_groups, num_nodes,
                                                 num_gpus)

    # Should work normally, just using global load balancing strategy
    assert phy2log.shape == (1, 8)
    assert logcnt.shape == (1, 6)
    assert torch.sum(logcnt) == num_replicas


@pytest.mark.parametrize("device", ["cpu", "cuda"])
def test_device_compatibility(device):
    """Test device compatibility"""
    if device == "cuda" and not torch.cuda.is_available():
        pytest.skip("CUDA not available")

    weight = torch.tensor([[10, 20, 30, 40]], device=device)
    num_replicas = 6
    num_groups = 2
    num_nodes = 1
    num_gpus = 2

    phy2log, log2phy, logcnt = rebalance_experts(weight, num_replicas,
                                                 num_groups, num_nodes,
                                                 num_gpus)

    # Function will convert to CPU internally, but should handle different
    # device inputs normally
    assert phy2log.shape == (1, 6)
    assert logcnt.shape == (1, 4)


def test_additional_cases():
    """Test more edge cases and different parameter combinations"""

    # Test case 1: Large-scale distributed setup
    weight1 = torch.tensor(
        [[50, 100, 75, 120, 90, 60, 80, 110, 40, 70, 95, 85, 65, 55, 45, 35]])
    phy2log1, log2phy1, logcnt1 = rebalance_experts(weight1, 24, 8, 4, 8)

    assert phy2log1.shape == (1, 24)
    assert logcnt1.shape == (1, 16)
    assert torch.sum(logcnt1) == 24

    # Test case 2: Different weight distributions
    weight2 = torch.tensor([
        [200, 150, 100, 50, 25, 12],  # Decreasing weights
        [12, 25, 50, 100, 150, 200],  # Increasing weights
    ])
    phy2log2, log2phy2, logcnt2 = rebalance_experts(weight2, 10, 3, 1, 2)

    assert phy2log2.shape == (2, 10)
    assert logcnt2.shape == (2, 6)

    # Verify high-weight experts have more replicas
    for layer in range(2):
        max_weight_idx = torch.argmax(weight2[layer])
        assert logcnt2[layer, max_weight_idx] >= 2


if __name__ == "__main__":
    weight = torch.tensor([
        [90, 132, 40, 61, 104, 165, 39, 4, 73, 56, 183, 86],
        [20, 107, 104, 64, 19, 197, 187, 157, 172, 86, 16, 27],
    ])

    num_replicas = 16
    num_groups = 4
    num_nodes = 2
    num_gpus = 8

    phy2log, log2phy, logcnt = rebalance_experts(weight, num_replicas,
                                                 num_groups, num_nodes,
                                                 num_gpus)
    print(phy2log)

    test_basic_rebalance()