[Feat] Add sparse attn to sgl-kernel (#5327)

sgl-kernel/python/sgl_kernel/sparse_flash_attn.py

@@ -0,0 +1,175 @@
+from typing import List, Optional, Tuple, Union
+
+import torch
+import torch.nn as nn
+
+
+def maybe_contiguous(x):
+    return x.contiguous() if x is not None and x.stride(-1) != 1 else x
+
+
+def sparse_attn_func(
+    q,
+    k,
+    v,
+    block_count,
+    block_offset,
+    column_count,
+    column_index,
+    dropout_p=0.0,
+    softmax_scale=None,
+    causal=False,
+    softcap=0.0,  # 0.0 means deactivated
+    alibi_slopes=None,
+    deterministic=False,
+    return_attn_probs=False,
+    *,
+    return_softmax_lse=False,
+    out=None,
+):
+    """Compute attention with vertical and slash sparsity patterns.
+    Most Arguments are the same with the flash_attn_func interface, except for 4 extra args:
+    block_count and block_offset for slash sparsity patterns, and
+    column_count and column_index for vertical sparsity patterns.
+    For more details please refer to Appendix C.4.2 of paper https://arxiv.org/abs/2407.02490.
+
+    Arguments:
+        q: (batch_size, seqlen, nheads, headdim)
+        k: (batch_size, seqlen, nheads_k, headdim)
+        v: (batch_size, seqlen, nheads_k, headdim)
+        block_count: (batch_size, nheads, cdiv(seqlen, BLOCK_M))
+        block_offset: (batch_size, nheads, cdiv(seqlen, BLOCK_M), NNZ_S)
+        column_count: (batch_size, nheads, cdiv(seqlen, BLOCK_M))
+        column_index: (batch_size, nheads, cdiv(seqlen, BLOCK_M), NNZ_V)
+        dropout_p: float. Dropout probability.
+        softmax_scale: float. The scaling of QK^T before applying softmax.
+            Default to 1 / sqrt(headdim).
+        causal: bool. Whether to apply causal attention mask (e.g., for auto-regressive modeling).
+        alibi_slopes: (nheads,) or (batch_size, nheads), fp32. A bias of
+            (-alibi_slope * |i + seqlen_k - seqlen_q - j|)
+            is added to the attention score of query i and key j.
+        deterministic: bool. Whether to use the deterministic implementation of the backward pass,
+            which is slightly slower and uses more memory. The forward pass is always deterministic.
+        return_attn_probs: bool. Whether to return the attention probabilities. This option is for
+           testing only. The returned probabilities are not guaranteed to be correct
+           (they might not have the right scaling).
+    Return:
+        out: (batch_size, seqlen, nheads, headdim).
+        softmax_lse [optional, if return_softmax_lse=True]: (batch_size, nheads, seqlen). The
+            logsumexp of each row of the matrix QK^T * scaling (e.g., log of the softmax
+            normalization factor).
+    """
+    if softmax_scale is None:
+        softmax_scale = q.shape[-1] ** (-0.5)
+
+    q, k, v = [maybe_contiguous(x) for x in (q, k, v)]
+    out, softmax_lse = torch.ops.sgl_kernel.fwd_sparse.default(
+        q,
+        k,
+        v,
+        block_count,
+        block_offset,
+        column_count,
+        column_index,
+        out,
+        alibi_slopes,
+        dropout_p,
+        softmax_scale,
+        causal,
+        softcap,
+        return_attn_probs and dropout_p > 0,
+        None,
+    )
+    return (out, softmax_lse) if return_softmax_lse else out
+
+
+def sparse_attn_varlen_func(
+    q,
+    k,
+    v,
+    block_count,
+    block_offset,
+    column_count,
+    column_index,
+    cu_seqlens_q,
+    cu_seqlens_k,
+    max_seqlen_q,
+    max_seqlen_k,
+    dropout_p=0.0,
+    softmax_scale=None,
+    causal=False,
+    softcap=0.0,  # 0.0 means deactivated
+    alibi_slopes=None,
+    deterministic=False,
+    return_attn_probs=False,
+    *,
+    return_softmax_lse=False,
+    out=None,
+):
+    """Compute attention with vertical and slash sparsity patterns.
+    Most Arguments are the same with the flash_attn_varlen_func interface, except for 4 extra args:
+    block_count and block_offset for slash sparsity patterns, and
+    column_count and column_index for vertical sparsity patterns.
+    For more details please refer to Appendix C.4.2 of paper https://arxiv.org/abs/2407.02490.
+
+    Arguments:
+        q: (total_q, nheads, headdim), where total_q = total number of query tokens in the batch.
+        k: (total_k, nheads_k, headdim), where total_k = total number of key tokens in the batch.
+        v: (total_k, nheads_k, headdim), where total_k = total number of key tokens in the batch.
+        block_count: (batch_size, nheads, cdiv(seqlen, BLOCK_M))
+        block_offset: (batch_size, nheads, cdiv(seqlen, BLOCK_M), NNZ_S)
+        column_count: (batch_size, nheads, cdiv(seqlen, BLOCK_M))
+        column_index: (batch_size, nheads, cdiv(seqlen, BLOCK_M), NNZ_V)
+        cu_seqlens_q: (batch_size + 1,), dtype torch.int32. The cumulative sequence lengths
+           of the sequences in the batch, used to index into q.
+        cu_seqlens_k: (batch_size + 1,), dtype torch.int32. The cumulative sequence lengths
+           of the sequences in the batch, used to index into kv.
+        max_seqlen_q: int. Maximum query sequence length in the batch.
+        max_seqlen_k: int. Maximum key sequence length in the batch.
+        dropout_p: float. Dropout probability.
+        softmax_scale: float. The scaling of QK^T before applying softmax.
+            Default to 1 / sqrt(headdim).
+        causal: bool. Whether to apply causal attention mask (e.g., for auto-regressive modeling).
+        softcap: float. Anything > 0 activates softcapping attention.
+        alibi_slopes: (nheads,) or (batch_size, nheads), fp32. A bias of
+            (-alibi_slope * |i + seqlen_k - seqlen_q - j|)
+            is added to the attention score of query i and key j.
+        deterministic: bool. Whether to use the deterministic implementation of the backward pass,
+            which is slightly slower and uses more memory. The forward pass is always deterministic.
+        return_attn_probs: bool. Whether to return the attention probabilities. This option is for
+           testing only. The returned probabilities are not guaranteed to be correct
+           (they might not have the right scaling).
+    Return:
+        out: (total, nheads, headdim).
+        softmax_lse [optional, if return_softmax_lse=True]: (nheads, total_q_seqlen). The
+            logsumexp of each row of the matrix QK^T * scaling (e.g., log of the softmax
+            normalization factor).
+    """
+    if softmax_scale is None:
+        softmax_scale = q.shape[-1] ** (-0.5)
+
+    q, k, v = [maybe_contiguous(x) for x in (q, k, v)]
+    out, softmax_lse = torch.ops.sgl_kernel.varlen_fwd_sparse.default(
+        q,
+        k,
+        v,
+        block_count,
+        block_offset,
+        column_count,
+        column_index,
+        out,
+        cu_seqlens_q,
+        cu_seqlens_k,
+        None,
+        alibi_slopes,
+        max_seqlen_q,
+        max_seqlen_k,
+        dropout_p,
+        softmax_scale,
+        False,
+        causal,
+        softcap,
+        return_attn_probs and dropout_p > 0,
+        None,
+    )
+    return (out, softmax_lse) if return_softmax_lse else out