add interface for pure extend and decode

Author: sunjiweiswift

python/sgl_kernel/flash_attn.py

@@ -26,6 +26,74 @@ def is_fa3_supported(device=None) -> bool:
 
 def maybe_contiguous(x):
     return x.contiguous() if x is not None and x.stride(-1) != 1 else x
+def flash_attn_extended( q,
+    k_cache,
+    v_cache,
+    k=None,
+    v=None,
+    qv=None,
+    rotary_cos=None,
+    rotary_sin=None,
+    cache_seqlens: Optional[Union[(int, torch.Tensor)]] = None,
+    cache_batch_idx: Optional[torch.Tensor] = None,
+    cache_leftpad: Optional[torch.Tensor] = None,
+    page_table: Optional[torch.Tensor] = None,
+    cu_seqlens_q: Optional[torch.Tensor] = None,
+    cu_seqlens_k_new: Optional[torch.Tensor] = None,
+    max_seqlen_q: Optional[int] = None,
+    rotary_seqlens: Optional[torch.Tensor] = None,
+    q_descale: Optional[torch.Tensor] = None,
+    k_descale: Optional[torch.Tensor] = None,
+    v_descale: Optional[torch.Tensor] = None,
+    softmax_scale=None,
+    softmax_sink=None,
+    causal=False,
+    window_size=(-1, -1),  # -1 means infinite context window
+    softcap=0.0,  # 0.0 means deactivated
+    rotary_interleaved=True,
+    scheduler_metadata=None,
+    num_splits=0,  # Can be tuned for speed
+    pack_gqa=None,  # Can be tuned for speed
+    sm_margin=0,  # Can be tuned if some SMs are used for communication
+    return_softmax_lse=False,
+):
+    assert k_cache.stride(-1) == 1, "k_cache must have contiguous last dimension"
+    assert v_cache.stride(-1) == 1, "v_cache must have contiguous last dimension"
+
+def flash_attn_decode( q,
+    k_cache,
+    v_cache,
+    k=None,
+    v=None,
+    qv=None,
+    rotary_cos=None,
+    rotary_sin=None,
+    cache_seqlens: Optional[Union[(int, torch.Tensor)]] = None,
+    cache_batch_idx: Optional[torch.Tensor] = None,
+    cache_leftpad: Optional[torch.Tensor] = None,
+    page_table: Optional[torch.Tensor] = None,
+    cu_seqlens_q: Optional[torch.Tensor] = None,
+    cu_seqlens_k_new: Optional[torch.Tensor] = None,
+    max_seqlen_q: Optional[int] = None,
+    rotary_seqlens: Optional[torch.Tensor] = None,
+    q_descale: Optional[torch.Tensor] = None,
+    k_descale: Optional[torch.Tensor] = None,
+    v_descale: Optional[torch.Tensor] = None,
+    softmax_scale=None,
+    softmax_sink=None,
+    causal=False,
+    window_size=(-1, -1),  # -1 means infinite context window
+    softcap=0.0,  # 0.0 means deactivated
+    rotary_interleaved=True,
+    scheduler_metadata=None,
+    num_splits=0,  # Can be tuned for speed
+    pack_gqa=None,  # Can be tuned for speed
+    sm_margin=0,  # Can be tuned if some SMs are used for communication
+    return_softmax_lse=False,
+):
+    assert k_cache.stride(-1) == 1, "k_cache must have contiguous last dimension"
+    assert v_cache.stride(-1) == 1, "v_cache must have contiguous last dimension"
+
 
 
 def flash_attn_with_kvcache(