[SpecDec] Remove Batch Expansion (2/3) (vllm-project#9298)

tests/spec_decode/test_scorer.py

@@ -1,3 +1,6 @@
+import random
+from typing import List
+
 import pytest
 import torch
 
@@ -10,31 +13,45 @@
 from .utils import create_batch, create_worker
 
 
-def create_proposal(batch_size: int, propose_len: int, vocab_size: int,
+def create_proposal(propose_lens: List[int], vocab_size: int,
                     device: str) -> SpeculativeProposals:
-    proposal_probs = torch.rand((batch_size, propose_len, vocab_size),
+    batch_size = len(propose_lens)
+    max_propose_len = max(propose_lens)
+    proposal_probs = torch.rand((batch_size, max_propose_len, vocab_size),
                                 device=device)
-    proposal_token_ids = torch.argmax(proposal_probs, dim=-1)
-    proposal_lens = torch.tensor([propose_len] * batch_size, device=device)
+
+    proposal_token_ids = torch.full((batch_size, max_propose_len),
+                                    fill_value=-1,
+                                    device=device)
+    for i in range(batch_size):
+        proposal_token_ids[i][:propose_lens[i]] = torch.argmax(
+            proposal_probs[i][:propose_lens[i]], dim=-1)
+
+    propose_lens = torch.tensor(propose_lens, device=device)
     return SpeculativeProposals(proposal_token_ids, proposal_probs,
-                                proposal_lens)
+                                propose_lens)
 
 
 def assert_score_equal(score1: SpeculativeScores,
                        score2: SpeculativeScores) -> None:
     assert torch.allclose(score1.probs, score2.probs)
     assert torch.allclose(score1.logprobs, score2.logprobs)
-    assert torch.equal(score1.token_ids, score2.token_ids)
+    assert torch.equal(
+        score1.token_ids,
+        score2.token_ids), f"{score1.token_ids}, {score2.token_ids}"
 
 
 @pytest.mark.parametrize('model_name', ['facebook/opt-125m'])
 @pytest.mark.parametrize('batch_size', [1, 2, 4, 8, 16])
-@pytest.mark.parametrize('propose_len', [1, 3, 5])
+@pytest.mark.parametrize('max_propose_len', [1, 3, 5])
+@pytest.mark.parametrize('mixed_propose_len', [True])
 @pytest.mark.parametrize('device', ['cuda'])
-def test_scoroer(model_name: str, batch_size: int, propose_len: int,
-                 device: str) -> None:
+def test_scorer(model_name: str, batch_size: int, max_propose_len: int,
+                mixed_propose_len: bool, device: str) -> None:
     """
-    Compare the batch expansion scorer and mqa scorer return the same score
+    Compare the batch expansion scorer and mqa scorer return the same score.
+    We test for both queries with the same propose length and different 
+    propose length.
     """
     seed = 0
     block_size = 32
@@ -46,13 +63,22 @@ def test_scoroer(model_name: str, batch_size: int, propose_len: int,
         should_modify_greedy_probs_inplace = True
 
     vocab_size = scorer_worker.vocab_size
-    proposals = create_proposal(batch_size, propose_len, vocab_size, device)
+
+    if not mixed_propose_len:
+        propose_lens = [max_propose_len] * batch_size
+    else:
+        non_zero_cnt = random.randint(0, batch_size)
+        propose_lens = [max_propose_len
+                        ] * non_zero_cnt + [0] * (batch_size - non_zero_cnt)
+        random.shuffle(propose_lens)
+
+    proposals = create_proposal(propose_lens, vocab_size, device)
     seq_group_metadatalist, _, _ = create_batch(batch_size,
-                                                propose_len,
+                                                max_propose_len,
                                                 block_size=block_size,
                                                 num_gpu_blocks=num_gpu_blocks)
     requests = ExecuteModelRequest(seq_group_metadatalist,
-                                   num_lookahead_slots=propose_len)
+                                   num_lookahead_slots=max_propose_len)
 
     batch_expansion_scorer = BatchExpansionTop1Scorer(scorer_worker, device,
                                                       vocab_size)

vllm/attention/backends/blocksparse_attn.py

@@ -186,11 +186,8 @@ class BlocksparseFlashAttentionMetadata(AttentionMetadata):
     # TODO(woosuk): Move `use_cuda_graph` out since it's unrelated to attention.
     use_cuda_graph: bool
 
-    # Number of query tokens for each request in the batch.
-    # Currently, we require that all requests have the same number of query
-    # tokens during the decoding phase. When speculavie decoding is enabled,
-    # decode_query_len might be greater than 1. In all other cases, it is 1.
-    decode_query_len: Optional[int] = None
+    # Max number of query tokens for among request in the batch.
+    max_decode_query_len: Optional[int] = None
 
     _cached_prefill_metadata: Optional[
         "BlocksparseFlashAttentionMetadata"] = None

vllm/attention/backends/flash_attn.py

@@ -111,11 +111,8 @@ class FlashAttentionMetadata(AttentionMetadata):
     # Maximum query length in the batch.
     max_query_len: Optional[int]
 
-    # Number of query tokens for each request in the batch.
-    # Currently, we require that all requests have the same number of query
-    # tokens during the decoding phase. When speculavie decoding is enabled,
-    # decode_query_len might be greater than 1. In all other cases, it is 1.
-    decode_query_len: Optional[int]
+    # Max number of query tokens among request in the batch.
+    max_decode_query_len: Optional[int]
 
     # Maximum sequence length among prefill batch. 0 if there are decoding
     # requests only.
@@ -173,9 +170,9 @@ def prefill_metadata(self) -> Optional["FlashAttentionMetadata"]:
             slot_mapping=self.slot_mapping[:self.num_prefill_tokens],
             seq_lens=self.seq_lens[:self.num_prefills],
             seq_lens_tensor=self.seq_lens_tensor[:self.num_prefills],
-            decode_query_len=0,
             max_query_len=self.max_query_len,
             max_prefill_seq_len=self.max_prefill_seq_len,
+            max_decode_query_len=0,
             max_decode_seq_len=0,
             query_start_loc=self.query_start_loc[:self.num_prefills + 1],
             seq_start_loc=self.seq_start_loc[:self.num_prefills + 1],
@@ -202,12 +199,14 @@ def decode_metadata(self) -> Optional["FlashAttentionMetadata"]:
             slot_mapping=self.slot_mapping[self.num_prefill_tokens:],
             seq_lens=None,
             seq_lens_tensor=self.seq_lens_tensor[self.num_prefills:],
-            decode_query_len=self.decode_query_len,
+            max_decode_query_len=self.max_decode_query_len,
             max_query_len=self.max_query_len,
             max_prefill_seq_len=0,
             max_decode_seq_len=self.max_decode_seq_len,
-            query_start_loc=None,
-            seq_start_loc=None,
+            query_start_loc=self.query_start_loc[self.num_prefills:]
+            if self.query_start_loc is not None else None,
+            seq_start_loc=self.seq_start_loc[self.num_prefills:]
+            if self.seq_start_loc is not None else None,
             context_lens_tensor=None,
             block_tables=self.block_tables[self.num_prefills:],
             use_cuda_graph=self.use_cuda_graph,
@@ -413,9 +412,9 @@ def build(self, seq_lens: List[int], query_lens: List[int],
         max_query_len = max(query_lens)
         decode_query_lens = query_lens[self.num_prefills:]
         if len(decode_query_lens) > 0:
-            decode_query_len = max(decode_query_lens)
+            max_decode_query_len = max(decode_query_lens)
         else:
-            decode_query_len = 1
+            max_decode_query_len = 1
         max_prefill_seq_len = max(self.prefill_seq_lens, default=0)
         max_decode_seq_len = max(self.curr_seq_lens, default=0)
         num_decode_tokens = self.num_decode_tokens
@@ -468,7 +467,7 @@ def build(self, seq_lens: List[int], query_lens: List[int],
             seq_lens=seq_lens,
             seq_lens_tensor=seq_lens_tensor,
             max_query_len=max_query_len,
-            decode_query_len=decode_query_len,
+            max_decode_query_len=max_decode_query_len,
             max_prefill_seq_len=max_prefill_seq_len,
             max_decode_seq_len=max_decode_seq_len,
             query_start_loc=query_start_loc,
@@ -714,20 +713,37 @@ def unified_flash_attention(
 
     if decode_meta := attn_metadata.decode_metadata:
         # Decoding run.
-        _, num_head, head_dim = decode_query.shape
-        decode_query = decode_query.reshape(-1, decode_meta.decode_query_len,
-                                            num_head, head_dim)
-        decode_output = flash_attn_with_kvcache(
-            q=decode_query,
-            k_cache=key_cache,
-            v_cache=value_cache,
-            block_table=decode_meta.block_tables,
-            cache_seqlens=decode_meta.seq_lens_tensor,
-            softmax_scale=softmax_scale,
-            causal=True,
-            alibi_slopes=alibi_slopes,
-            softcap=logits_soft_cap,
-        ).squeeze(1)
+        # Use flash_attn_varlen_func kernel for speculative decoding
+        # because different queries might have different lengths.
+        assert decode_meta.max_decode_query_len is not None
+        if decode_meta.max_decode_query_len > 1:
+            decode_output = flash_attn_varlen_func(
+                q=decode_query,
+                k=key_cache,
+                v=value_cache,
+                cu_seqlens_q=decode_meta.query_start_loc,
+                max_seqlen_q=decode_meta.max_decode_query_len,
+                cu_seqlens_k=decode_meta.seq_start_loc,
+                max_seqlen_k=decode_meta.max_decode_seq_len,
+                softmax_scale=softmax_scale,
+                causal=True,
+                alibi_slopes=alibi_slopes,
+                softcap=logits_soft_cap,
+                block_table=decode_meta.block_tables,
+            )
+        else:
+            # Use flash_attn_with_kvcache for normal decoding.
+            decode_output = flash_attn_with_kvcache(
+                q=decode_query.unsqueeze(1),
+                k_cache=key_cache,
+                v_cache=value_cache,
+                block_table=decode_meta.block_tables,
+                cache_seqlens=decode_meta.seq_lens_tensor,
+                softmax_scale=softmax_scale,
+                causal=True,
+                alibi_slopes=alibi_slopes,
+                softcap=logits_soft_cap,
+            ).squeeze(1)
 
     if prefill_output is None:
         assert decode_output is not None
@@ -739,7 +755,6 @@ def unified_flash_attention(
     # Chunked prefill does not work with speculative decoding.
     # Therefore, the query length for decode should be 1 in chunked prefill.
     assert decode_meta is not None
-    assert decode_meta.decode_query_len == 1
     decode_output = decode_output.squeeze(1)
     output = torch.cat([prefill_output, decode_output], dim=0)
     return output.view(num_tokens, hidden_size)

vllm/attention/backends/rocm_flash_attn.py

@@ -121,11 +121,8 @@ class ROCmFlashAttentionMetadata(AttentionMetadata, PagedAttentionMetadata):
     # so far).
     context_lens_tensor: Optional[torch.Tensor]
 
-    # Number of query tokens for each request in the batch.
-    # Currently, we require that all requests have the same number of query
-    # tokens during the decoding phase. When speculavie decoding is enabled,
-    # decode_query_len might be greater than 1. In all other cases, it is 1.
-    decode_query_len: Optional[int] = None
+    # Max number of query tokens among request in the batch.
+    max_decode_query_len: Optional[int] = None
 
     _cached_prefill_metadata: Optional["ROCmFlashAttentionMetadata"] = None
     _cached_decode_metadata: Optional["ROCmFlashAttentionMetadata"] = None

vllm/attention/backends/utils.py

@@ -313,7 +313,7 @@ def graph_capture_get_metadata_for_batch(
             seq_lens=None,
             seq_lens_tensor=self._graph_seq_lens[:batch_size],
             max_query_len=1,
-            decode_query_len=1,
+            max_decode_query_len=1,
             max_prefill_seq_len=0,
             max_decode_seq_len=self.runner.max_seq_len_to_capture,
             query_start_loc=None,

vllm/attention/backends/xformers.py

@@ -118,11 +118,8 @@ class XFormersMetadata(AttentionMetadata, PagedAttentionMetadata):
     # Maximum query length in the batch. None for decoding.
     max_query_len: Optional[int] = None
 
-    # Number of query tokens for each request in the batch.
-    # Currently, we require that all requests have the same number of query
-    # tokens during the decoding phase. When speculavie decoding is enabled,
-    # decode_query_len might be greater than 1. In all other cases, it is 1.
-    decode_query_len: Optional[int] = None
+    # Max number of query tokens among request in the batch.
+    max_decode_query_len: Optional[int] = None
 
     # (batch_size + 1,). The cumulative subquery lengths of the sequences in
     # the batch, used to index into subquery. E.g., if the subquery length

vllm/spec_decode/mqa_scorer.py

@@ -18,6 +18,7 @@ def score_proposals(
         target_seq_id_start = max(
             get_all_seq_ids(execute_model_req.seq_group_metadata_list)) + 1
         all_proposal_tokens = proposals.proposal_token_ids.tolist()
+        all_proposal_lengths = proposals.proposal_lens.tolist()
         for i, seq_group_metadata in enumerate(
                 execute_model_req.seq_group_metadata_list):
             seq_data_dict = seq_group_metadata.seq_data
@@ -27,7 +28,8 @@ def score_proposals(
             seq_data: SequenceData = seq_data_dict[seq_id]
             prompt_token_ids = seq_data.get_prompt_token_ids()
             output_token_ids = seq_data.get_output_token_ids()
-            proposal_token_ids = all_proposal_tokens[i]
+            proposal_token_ids = all_proposal_tokens[
+                i][:all_proposal_lengths[i]]
             new_output_token_ids = [*output_token_ids, *proposal_token_ids]
 
             target_seq_id = target_seq_id_start + i
@@ -62,18 +64,42 @@ def score_proposals(
 
         target_sampler_output = target_sampler_output[0]
 
-        bs, k = proposals.proposal_token_ids.shape
-        all_tokens = target_sampler_output.sampled_token_ids.reshape(bs, k + 1)
-
-        all_probs = target_sampler_output.sampled_token_probs.reshape(
-            bs, k + 1, self._vocab_size)
-        all_logprobs = target_sampler_output.logprobs.reshape(
-            bs, k + 1, self._vocab_size)
+        k = execute_model_req.num_lookahead_slots
+        bs = len(execute_model_req.seq_group_metadata_list)
+        target_token_ids = target_sampler_output.sampled_token_ids
+        target_probs = target_sampler_output.sampled_token_probs
+        target_logprobs = target_sampler_output.logprobs
+        # If all requests have the same number of query tokens, we can avoid
+        # the for loop to build output for better performance.
+        if min(all_proposal_lengths) == k:
+            bs, _ = proposals.proposal_token_ids.shape
+            all_tokens = target_token_ids.reshape(bs, k + 1)
+            all_probs = target_probs.reshape(bs, k + 1, self._vocab_size)
+            all_logprobs = target_logprobs.reshape(bs, k + 1, self._vocab_size)
+        else:
+            all_tokens = target_token_ids.new_full(size=(bs, k + 1),
+                                                   fill_value=-1)
+            all_probs = target_probs.new_zeros(*all_tokens.shape,
+                                               self._vocab_size)
+            all_logprobs = target_logprobs.new_full(size=all_probs.shape,
+                                                    fill_value=-float("inf"))
+            target_token_ids = target_token_ids.flatten()
+            start_loc = 0
+            for i, proposed_len in enumerate(all_proposal_lengths):
+                output_len = proposed_len + 1
+                end_loc = start_loc + output_len
+                all_tokens[
+                    i, :output_len] = target_token_ids[start_loc:end_loc]
+                all_probs[i, :output_len] = target_probs[start_loc:end_loc]
+                all_logprobs[
+                    i, :output_len] = target_logprobs[start_loc:end_loc]
+                start_loc = end_loc
 
         hidden_states = None
         if target_sampler_output.hidden_states is not None:
             hidden_states = target_sampler_output.hidden_states.reshape(
                 bs, (k + 1), -1)
+
         return SpeculativeScores(probs=all_probs,
                                  token_ids=all_tokens,
                                  logprobs=all_logprobs,

vllm/spec_decode/spec_decode_worker.py

@@ -190,12 +190,6 @@ def create_worker(
                     "[Speculative Decoding] Disabling MQA scorer as the "
                     "MQA is only available with flash attn backend.")
 
-            if ngram_prompt_lookup_max > 0:
-                disable_mqa_scorer = True
-                logger.info(
-                    "[Speculative Decoding] Disabling MQA scorer as the "
-                    "NGramWorker does not support MQA scorer.")
-
             if "model_config" in draft_worker_kwargs and \
                 draft_worker_kwargs["model_config"].max_model_len < \
                     scorer_worker.model_config.max_model_len: