ColossalAI/tests/test_shardformer/test_layer/test_ring_attn.py

import torch
import torch.distributed as dist
import torch.nn.functional as F
from flash_attn import flash_attn_qkvpacked_func, flash_attn_varlen_qkvpacked_func
from torch.testing import assert_close

import colossalai
from colossalai.shardformer.layer import AttnMaskType
from colossalai.shardformer.layer.attn import AttnMaskType, RingAttention
from colossalai.shardformer.layer.utils import split_batch_zigzag, split_varlen_zigzag
from colossalai.testing import parameterize, rerun_if_address_is_in_use, spawn
from colossalai.utils import get_current_device


@parameterize("seq_len", [4096])
@parameterize("bs", [2])
@parameterize("nheads", [5])
@parameterize("d", [128])
@parameterize("dtype", [torch.bfloat16, torch.float16])
def check_ring_attn(seq_len, bs, nheads, d, dtype):
    torch.cuda.manual_seed(2)
    device = get_current_device()
    sp_group = dist.group.WORLD
    sp_size = dist.get_world_size()
    # Some outliers may seem large, but our errors are still lower than
    # than Megatron-LM context parallel's
    # (https://github.com/NVIDIA/TransformerEngine/blob/33a3d02f81c56e6f7b542c09bfa86657078d57fb/tests/pytorch/fused_attn/run_fused_attn_with_cp.py#L215)
    # and the original zigzag implementation's (https://github.com/zhuzilin/ring-flash-attention/tree/main)
    atol = rtol = 7e-3

    # Setup inputs
    qkv = torch.randn(bs, seq_len, 3, nheads, d, device=device, dtype=dtype, requires_grad=True)
    local_qkv = split_batch_zigzag(qkv, sp_group)
    q, k, v = local_qkv.unbind(dim=-3)
    q, k, v = [x.squeeze(2).detach().clone().transpose(1, 2) for x in (q, k, v)]  # (B, nHeads, Sq, D)
    q.requires_grad = k.requires_grad = v.requires_grad = True

    # Ring attention vs single GPU
    ring_out, ring_lse = RingAttention.attention(
        q,
        k,
        v,
        sp_group,
        AttnMaskType.CAUSAL,
        return_softmax=True,
        inner_ring_size=max(2, sp_size // 2),
        # inner_ring_size=4
    )
    ring_out = ring_out.transpose(1, 2)
    out, lse, _ = flash_attn_qkvpacked_func(
        qkv, dropout_p=0.0, causal=True, window_size=(-1, -1), alibi_slopes=None, return_attn_probs=True
    )

    # Checkout out and softmax denominator
    local_out = split_batch_zigzag(out, sp_group)
    local_lse = split_batch_zigzag(lse, sp_group, seq_dim=-1)
    local_lse = local_lse.transpose(1, 2).contiguous().view(-1, ring_lse.shape[-1])  # (B, nHeads, Sq) -> (T, nHeads)
    assert_close(ring_lse, local_lse, atol=atol, rtol=rtol)
    assert_close(ring_out, local_out, atol=atol, rtol=rtol)

    # Check grads
    ring_out.sum().backward()
    out.sum().backward()
    ring_dq, ring_dk, ring_dv = [x.transpose(1, 2) for x in (q.grad, k.grad, v.grad)]
    dqkv = qkv.grad
    local_dqkv = split_batch_zigzag(dqkv, sp_group)

    assert_close(ring_dq, local_dqkv[:, :, 0], atol=atol, rtol=rtol)
    assert_close(ring_dk, local_dqkv[:, :, 1], atol=atol, rtol=rtol)
    assert_close(ring_dv, local_dqkv[:, :, 2], atol=atol, rtol=rtol)
    if dist.get_rank() == 0:
        print(
            f"sp_size {dist.get_world_size()}, inner ring size {dist.get_world_size(RingAttention.INNER_RING_GROUP)} passed."
        )


@parameterize("seqlen", [4096])
@parameterize("bs", [2])
@parameterize("nheads", [5])
@parameterize("d", [128])
@parameterize("dtype", [torch.bfloat16, torch.float16])
def check_packed_seq(seqlen, bs, nheads, d, dtype):
    device = get_current_device()
    sp_group = dist.group.WORLD
    sp_size = dist.get_world_size()
    atol = rtol = 7e-3
    torch.cuda.manual_seed(2)
    # Prepare varlen attention mask
    padding_mask = torch.ones((bs, seqlen), dtype=torch.int, device=device)
    padding_mask[: bs // 2, (seqlen // 4) * 3 :] = 0
    padding_mask[:, seqlen // 2 :] = 0

    input_embeds = torch.randn(bs, seqlen, nheads, d, device=device, dtype=dtype, requires_grad=True)

    # Forward
    # out = ColoAttention.attention(q, k, v, **mask_info)
    flat_input = input_embeds.view(-1, nheads, d)[padding_mask.flatten().nonzero().squeeze()]
    qkv = torch.stack([flat_input] * 3, dim=1)
    qkv.retain_grad()

    input_embeds, mask_info, _ = RingAttention.prepare_varlen_batch(padding_mask, sp_group, input_embeds)
    out, lse, _ = flash_attn_varlen_qkvpacked_func(
        qkv,
        mask_info["cu_seqlens"] * sp_size,
        mask_info["max_seqlen"] * sp_size,
        return_attn_probs=True,
        causal=True,
        # deterministic=True
    )
    # Test the splitting function
    local_input = split_varlen_zigzag(
        flat_input, mask_info["cu_seqlens"] * sp_size, sp_group, mask_info["max_seqlen"] * sp_size
    )
    assert (local_input == input_embeds.view(-1, nheads, d)[mask_info["valid_indices"]]).all()
    del local_input, flat_input

    q_ring, k_ring, v_ring = [input_embeds.clone().transpose(1, 2) for _ in range(3)]
    q_ring.retain_grad()
    k_ring.retain_grad()
    v_ring.retain_grad()

    ring_out, ring_lse = RingAttention.attention(
        q_ring,
        k_ring,
        v_ring,
        sp_group,
        **mask_info,
        pad_output=False,
        return_softmax=True,
        # deterministic=True
    )
    ring_out = ring_out.transpose(1, 2).reshape(-1, nheads, d)
    # Check output
    lse = lse.transpose(0, 1)
    out, lse = split_varlen_zigzag(
        [out, lse], mask_info["cu_seqlens"] * sp_size, sp_group, mask_info["max_seqlen"] * sp_size
    )
    assert_close(lse, ring_lse, atol=atol, rtol=rtol)
    assert_close(out, ring_out, atol=atol, rtol=rtol)

    # Check grads
    labels = torch.ones(out.shape[0], dtype=dtype, device=device)
    F.mse_loss(out.sum((-2, -1)), labels).backward()
    F.mse_loss(ring_out.sum((-2, -1)), labels[: ring_out.shape[0]]).backward()
    dq, dk, dv = [
        split_varlen_zigzag(
            qkv.grad[:, i], mask_info["cu_seqlens"] * sp_size, sp_group, mask_info["max_seqlen"] * sp_size
        )
        for i in range(3)
    ]
    dq_ring, dk_ring, dv_ring = [
        x.transpose(1, 2).reshape(-1, nheads, d)[mask_info["valid_indices"]]
        for x in (q_ring.grad, k_ring.grad, v_ring.grad)
    ]

    assert_close(dq, dq_ring, atol=atol, rtol=rtol)
    assert_close(dk, dk_ring, atol=atol, rtol=rtol)
    assert_close(dv, dv_ring, atol=atol, rtol=rtol)


def launch_single_ring(rank, world_size, port):
    colossalai.launch(rank, world_size, "localhost", port)
    check_packed_seq()
    check_ring_attn()


def launch_double_ring(rank, world_size, port):
    colossalai.launch(rank, world_size, "localhost", port)
    check_ring_attn()


@rerun_if_address_is_in_use()
@parameterize("world_size", [2])
def test_ring_attn(world_size):
    spawn(launch_single_ring, nprocs=world_size)


@rerun_if_address_is_in_use()
@parameterize("world_size", [4])
def test_double_ring(world_size):
    spawn(launch_double_ring, nprocs=world_size)


if __name__ == "__main__":
    test_ring_attn()
    test_double_ring()