[BugFix] llama4 fa3 fix - RuntimeError: scheduler_metadata must have shape (metadata_size) (#16998)

Signed-off-by: Lucas Wilkinson <lwilkinson@neuralmagic.com>

vllm/v1/attention/backends/flash_attn.py

@@ -105,6 +105,7 @@ class FlashAttentionMetadata:
         local_block_table: torch.Tensor
         local_max_query_len: int
         local_max_seq_len: int
+        local_scheduler_metadata: Optional[torch.Tensor]
 
     local_attn_metadata: Optional[LocalAttentionMetadata] = None
 
@@ -282,7 +283,9 @@ class FlashAttentionMetadataBuilder:
 
         self.runner = runner
         self.aot_schedule = (get_flash_attn_version() == 3)
-        self.num_heads = model_config.get_num_attention_heads(
+        self.num_heads_q = model_config.get_num_attention_heads(
+            runner.parallel_config)
+        self.num_heads_kv = model_config.get_num_kv_heads(
             runner.parallel_config)
         self.headdim = model_config.get_head_size()
         self.page_size = self.runner.block_size
@@ -304,6 +307,23 @@ class FlashAttentionMetadataBuilder:
         slot_mapping = self.runner.slot_mapping_cpu[:num_actual_tokens].to(
             self.runner.device, non_blocking=True).long()
 
+        def schedule(batch_size, cu_query_lens, max_query_len, seqlens,
+                     max_seq_len, causal):
+            if self.aot_schedule:
+                return get_scheduler_metadata(
+                    batch_size=batch_size,
+                    max_seqlen_q=max_query_len,
+                    max_seqlen_k=max_seq_len,
+                    cache_seqlens=seqlens,
+                    num_heads_q=self.num_heads_q,
+                    num_heads_kv=self.num_heads_kv,
+                    headdim=self.headdim,
+                    page_size=self.page_size,
+                    cu_seqlens_q=cu_query_lens,
+                    causal=causal,
+                )
+            return None
+
         # for local attention
         local_attn_metadata = None
         if self.runner.attention_chunk_size is not None:
@@ -315,36 +335,31 @@ class FlashAttentionMetadataBuilder:
                     block_table,
                     self.runner.block_size,
                 )
+            local_query_start_loc = torch.from_numpy(virt_q_cu_seqlens_np).to(
+                self.runner.device, non_blocking=True)
+            local_seqused_k = torch.from_numpy(virt_k_seqlens_np).to(
+                self.runner.device, non_blocking=True)
+            local_max_query_len = seqlens_q_local_np.max()
+            local_max_seq_len = virt_k_seqlens_np.max()
+            local_scheduler_metadata = schedule(
+                batch_size=local_query_start_loc.shape[0] - 1,
+                cu_query_lens=local_query_start_loc,
+                max_query_len=local_max_query_len,
+                seqlens=local_seqused_k,
+                max_seq_len=local_max_seq_len,
+                causal=True)
+
             local_attn_metadata = FlashAttentionMetadata.LocalAttentionMetadata(
-                local_query_start_loc=torch.from_numpy(
+                local_query_start_loc=local_query_start_loc,
-                    virt_q_cu_seqlens_np).to(self.runner.device,
+                local_seqused_k=local_seqused_k,
-                                             non_blocking=True),
-                local_seqused_k=torch.from_numpy(virt_k_seqlens_np).to(
-                    self.runner.device, non_blocking=True),
                 local_block_table=virt_block_table,
-                local_max_query_len=seqlens_q_local_np.max(),
+                local_max_query_len=local_max_query_len,
-                local_max_seq_len=virt_k_seqlens_np.max(),
+                local_max_seq_len=local_max_seq_len,
+                local_scheduler_metadata=local_scheduler_metadata,
             )
 
         use_cascade = common_prefix_len > 0
 
-        def schedule(cu_query_lens, max_query_len, seqlens, max_seq_len,
-                     causal):
-            if self.aot_schedule:
-                return get_scheduler_metadata(
-                    batch_size=num_reqs,
-                    max_seqlen_q=max_query_len,
-                    max_seqlen_k=max_seq_len,
-                    cache_seqlens=seqlens,
-                    num_heads_q=self.num_heads,
-                    num_heads_kv=self.num_heads,
-                    headdim=self.headdim,
-                    page_size=self.page_size,
-                    cu_seqlens_q=cu_query_lens,
-                    causal=causal,
-                )
-            return None
-
         if use_cascade:
             cu_prefix_query_lens = torch.tensor([0, num_actual_tokens],
                                                 dtype=torch.int32,
@@ -357,12 +372,14 @@ class FlashAttentionMetadataBuilder:
             suffix_kv_lens = torch.from_numpy(suffix_kv_lens).to(
                 self.runner.device)
             prefix_scheduler_metadata = schedule(
+                batch_size=num_reqs,
                 cu_query_lens=cu_prefix_query_lens,
                 max_query_len=num_actual_tokens,
                 seqlens=prefix_kv_lens,
                 max_seq_len=common_prefix_len,
                 causal=False)
-            scheduler_metadata = schedule(cu_query_lens=query_start_loc,
+            scheduler_metadata = schedule(batch_size=num_reqs,
+                                          cu_query_lens=query_start_loc,
                                           max_query_len=max_query_len,
                                           seqlens=suffix_kv_lens,
                                           max_seq_len=max_seq_len -
@@ -373,7 +390,8 @@ class FlashAttentionMetadataBuilder:
             prefix_kv_lens = None
             suffix_kv_lens = None
             prefix_scheduler_metadata = None
-            scheduler_metadata = schedule(cu_query_lens=query_start_loc,
+            scheduler_metadata = schedule(batch_size=num_reqs,
+                                          cu_query_lens=query_start_loc,
                                           max_query_len=max_query_len,
                                           seqlens=seq_lens,
                                           max_seq_len=max_seq_len,
@@ -540,12 +558,14 @@ class FlashAttentionImpl(AttentionImpl):
                 max_seqlen_q = local_metadata.local_max_query_len
                 max_seqlen_k = local_metadata.local_max_seq_len
                 block_table = local_metadata.local_block_table
+                scheduler_metadata = local_metadata.local_scheduler_metadata
             else:
                 cu_seqlens_q = attn_metadata.query_start_loc
                 seqused_k = attn_metadata.seq_lens
                 max_seqlen_q = attn_metadata.max_query_len
                 max_seqlen_k = attn_metadata.max_seq_len
                 block_table = attn_metadata.block_table
+                scheduler_metadata = attn_metadata.scheduler_metadata
 
             descale_shape = (cu_seqlens_q.shape[0] - 1, key.shape[1])
 
@@ -564,7 +584,7 @@ class FlashAttentionImpl(AttentionImpl):
                 window_size=self.sliding_window,
                 block_table=block_table,
                 softcap=self.logits_soft_cap,
-                scheduler_metadata=attn_metadata.scheduler_metadata,
+                scheduler_metadata=scheduler_metadata,
                 fa_version=self.vllm_flash_attn_version,
                 q_descale=layer._q_scale.expand(descale_shape),
                 k_descale=layer._k_scale.expand(descale_shape),