Support custom mask for Triton attention (sgl-project#3317)

chongli-uw · Feb 15, 2025 · fa84ebe · fa84ebe
1 parent 31a00c4
commit fa84ebe
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Showing 3 changed files with 107 additions and 11 deletions.
diff --git a/python/sglang/srt/layers/attention/triton_backend.py b/python/sglang/srt/layers/attention/triton_backend.py
@@ -91,6 +91,7 @@ def init_forward_metadata(self, forward_batch: ForwardBatch):
 
             qo_indptr = None
             custom_mask = None
+            mask_offsets = None
         else:
             kv_indptr[1 : bs + 1] = torch.cumsum(
                 forward_batch.extend_prefix_lens, dim=0
@@ -115,6 +116,7 @@ def init_forward_metadata(self, forward_batch: ForwardBatch):
             qo_indptr[1 : bs + 1] = torch.cumsum(forward_batch.extend_seq_lens, dim=0)
             qo_indptr = qo_indptr[: bs + 1]
             custom_mask = None
+            mask_offsets = None
 
             attn_logits = None
             max_extend_len = torch.max(forward_batch.extend_seq_lens).item()
@@ -126,6 +128,7 @@ def init_forward_metadata(self, forward_batch: ForwardBatch):
             kv_indices,
             qo_indptr,
             custom_mask,
+            mask_offsets,
         )
 
     def init_cuda_graph_state(self, max_bs: int):
@@ -180,6 +183,7 @@ def init_forward_metadata_capture_cuda_graph(
             kv_indices,
             None,
             None,
+            None,
         )
 
     def init_forward_metadata_replay_cuda_graph(
@@ -233,9 +237,15 @@ def forward_extend(
                 layer, forward_batch.out_cache_loc, k, v
             )
 
-        _, max_extend_len, kv_indptr, kv_indices, qo_indptr, custom_mask = (
-            self.forward_metadata
-        )
+        (
+            _,
+            max_extend_len,
+            kv_indptr,
+            kv_indices,
+            qo_indptr,
+            custom_mask,
+            mask_offsets,
+        ) = self.forward_metadata
         self.extend_attention_fwd(
             q.view(-1, layer.tp_q_head_num, layer.qk_head_dim),
             k.contiguous(),
@@ -246,6 +256,8 @@ def forward_extend(
             qo_indptr,
             kv_indptr,
             kv_indices,
+            custom_mask,
+            mask_offsets,
             max_extend_len,
             layer.scaling,
             layer.logit_cap,
@@ -271,7 +283,7 @@ def forward_decode(
         else:
             o = torch.empty_like(q)
 
-        attn_logits, _, kv_indptr, kv_indices, _, _ = self.forward_metadata
+        attn_logits, _, kv_indptr, kv_indices, _, _, _ = self.forward_metadata
 
         if save_kv_cache:
             forward_batch.token_to_kv_pool.set_kv_buffer(

diff --git a/python/sglang/srt/layers/attention/triton_ops/extend_attention.py b/python/sglang/srt/layers/attention/triton_ops/extend_attention.py
@@ -49,6 +49,8 @@ def _fwd_kernel(
     qo_indptr,
     kv_indptr,
     kv_indices,
+    mask_ptr,
+    mask_offsets,
     sm_scale,
     kv_group_num,
     stride_qbs,
@@ -71,6 +73,7 @@ def _fwd_kernel(
     BLOCK_DV: tl.constexpr,
     BLOCK_M: tl.constexpr,
     BLOCK_N: tl.constexpr,
+    USE_CUSTOM_MASK: tl.constexpr,
 ):
     cur_seq = tl.program_id(0)
     cur_head = tl.program_id(1)
@@ -81,6 +84,10 @@ def _fwd_kernel(
     cur_seq_len_extend = tl.load(qo_indptr + cur_seq + 1) - cur_seq_extend_start_idx
     cur_seq_kv_start_idx = tl.load(kv_indptr + cur_seq)
     cur_seq_len_prefix = tl.load(kv_indptr + cur_seq + 1) - cur_seq_kv_start_idx
+    cur_seq_len = cur_seq_len_prefix + cur_seq_len_extend
+
+    if USE_CUSTOM_MASK:
+        cur_seq_mask_start_idx = tl.load(mask_offsets + cur_seq)
 
     offs_d = tl.arange(0, BLOCK_DMODEL)
     offs_dv = tl.arange(0, BLOCK_DV)
@@ -152,7 +159,20 @@ def _fwd_kernel(
         if logit_cap > 0:
             qk = logit_cap * tanh(qk / logit_cap)
 
-        qk = tl.where(mask_m[:, None] & mask_n[None, :], qk, float("-inf"))
+        if USE_CUSTOM_MASK:
+            custom_mask = tl.load(
+                mask_ptr
+                + cur_seq_mask_start_idx
+                + (cur_block_m * BLOCK_M + offs_m[:, None]) * cur_seq_len
+                + start_n
+                + offs_n[None, :],
+                mask=(mask_m[:, None] & mask_n[None, :]),
+                other=0,
+            )
+            custom_mask &= mask_m[:, None] & mask_n[None, :]
+            qk = tl.where(custom_mask, qk, float("-inf"))
+        else:
+            qk = tl.where(mask_m[:, None] & mask_n[None, :], qk, float("-inf"))
 
         n_e_max = tl.maximum(tl.max(qk, 1), e_max)
         re_scale = tl.exp(e_max - n_e_max)
@@ -172,7 +192,7 @@ def _fwd_kernel(
 
         e_max = n_e_max
 
-    # stage 2: compute the trianlge part
+    # stage 2: compute the triangle part
 
     cur_block_m_end = tl.minimum(cur_seq_len_extend, (cur_block_m + 1) * BLOCK_M)
     for start_n in range(0, cur_block_m_end, BLOCK_N):
@@ -208,11 +228,25 @@ def _fwd_kernel(
         if logit_cap > 0:
             qk = logit_cap * tanh(qk / logit_cap)
 
-        mask_causual = (cur_block_m * BLOCK_M + offs_m[:, None]) >= (
-            start_n + offs_n[None, :]
-        )
-        mask_causual &= mask_m[:, None] & mask_n[None, :]
-        qk = tl.where(mask_causual, qk, float("-inf"))
+        if USE_CUSTOM_MASK:
+            custom_mask = tl.load(
+                mask_ptr
+                + cur_seq_mask_start_idx
+                + (cur_block_m * BLOCK_M + offs_m[:, None]) * cur_seq_len
+                + cur_seq_len_prefix
+                + start_n
+                + offs_n[None, :],
+                mask=(mask_m[:, None] & mask_n[None, :]),
+                other=0,
+            )
+            custom_mask &= mask_m[:, None] & mask_n[None, :]
+            qk = tl.where(custom_mask, qk, float("-inf"))
+        else:
+            mask_causual = (cur_block_m * BLOCK_M + offs_m[:, None]) >= (
+                start_n + offs_n[None, :]
+            )
+            mask_causual &= mask_m[:, None] & mask_n[None, :]
+            qk = tl.where(mask_causual, qk, float("-inf"))
 
         n_e_max = tl.maximum(tl.max(qk, 1), e_max)
         re_scale = tl.exp(e_max - n_e_max)
@@ -253,6 +287,8 @@ def extend_attention_fwd(
     qo_indptr,
     kv_indptr,
     kv_indices,
+    custom_mask,
+    mask_offsets,
     max_len_extend,
     sm_scale=None,
     logit_cap=0.0,
@@ -308,6 +344,8 @@ def extend_attention_fwd(
     batch_size, head_num = qo_indptr.shape[0] - 1, q_extend.shape[1]
     kv_group_num = q_extend.shape[1] // k_extend.shape[1]
 
+    USE_CUSTOM_MASK = custom_mask is not None
+
     grid = (batch_size, head_num, triton.cdiv(max_len_extend, BLOCK_M))
     num_stages = 1
 
@@ -325,6 +363,8 @@ def extend_attention_fwd(
         qo_indptr,
         kv_indptr,
         kv_indices,
+        custom_mask,
+        mask_offsets,
         sm_scale,
         kv_group_num,
         q_extend.stride(0),
@@ -347,6 +387,7 @@ def extend_attention_fwd(
         BLOCK_N=BLOCK_N,
         Lq=Lq,
         Lv=Lv,
+        USE_CUSTOM_MASK=USE_CUSTOM_MASK,
         num_warps=num_warps,
         num_stages=num_stages,
         **extra_kargs,

diff --git a/test/srt/test_triton_attention_kernels.py b/test/srt/test_triton_attention_kernels.py
@@ -89,6 +89,9 @@ def _test_extend_attention_once(self, B, N_CTX, H_Q, H_KV, D):
             ).normal_(mean=0.1, std=0.2)
 
         o_extend = torch.empty((extend_token_num, H_Q, D), dtype=dtype, device="cuda")
+        o_extend_mask = torch.empty(
+            (extend_token_num, H_Q, D), dtype=dtype, device="cuda"
+        )
         o_redundant = torch.empty(
             (extend_token_num, H_Q, D), dtype=dtype, device="cuda"
         )
@@ -98,6 +101,9 @@ def _test_extend_attention_once(self, B, N_CTX, H_Q, H_KV, D):
         qo_indptr = torch.zeros((B + 1,), dtype=torch.int32, device="cuda")
         qo_indptr[1 : B + 1] = torch.cumsum(b_seq_len_extend[:B], dim=0)
 
+        custom_mask = None
+        mask_offsets = None
+
         extend_attention_fwd(
             q_extend,
             k_extend,
@@ -108,6 +114,42 @@ def _test_extend_attention_once(self, B, N_CTX, H_Q, H_KV, D):
             qo_indptr,
             kv_indptr,
             kv_indices,
+            custom_mask,
+            mask_offsets,
+            max_len_extend,
+        )
+
+        b_seq_mask_len = b_seq_len_extend * b_seq_len
+        custom_mask = torch.ones(
+            (b_seq_mask_len.sum().item(),), dtype=torch.bool, device="cuda"
+        )
+        mask_offsets = torch.zeros((B + 1,), dtype=torch.int64, device="cuda")
+        mask_offsets[1 : B + 1] = torch.cumsum(b_seq_mask_len[:B], dim=0)
+        for i in range(B):
+            causal_mask = (
+                torch.tril(
+                    torch.ones(b_seq_len_extend[i], b_seq_len_extend[i]), diagonal=0
+                )
+                == 1
+            )
+            prefix_mask = torch.ones(
+                b_seq_len_extend[i], b_seq_len_prefix[i], dtype=torch.bool
+            )
+            mask_flatten = torch.cat([prefix_mask, causal_mask], dim=1).flatten()
+            custom_mask[mask_offsets[i] : mask_offsets[i + 1]] = mask_flatten
+
+        extend_attention_fwd(
+            q_extend,
+            k_extend,
+            v_extend,
+            o_extend_mask,
+            k_buffer,
+            v_buffer,
+            qo_indptr,
+            kv_indptr,
+            kv_indices,
+            custom_mask,
+            mask_offsets,
             max_len_extend,
         )
 
@@ -124,6 +166,7 @@ def _test_extend_attention_once(self, B, N_CTX, H_Q, H_KV, D):
         )
 
         self.assertTrue(torch.allclose(o_extend, o_redundant, rtol=1e-2))
+        self.assertTrue(torch.allclose(o_extend_mask, o_redundant, rtol=1e-2))
 
     def test_extend_attention(self):