Prefix Cache Aware Scheduling [1/n] (vllm-project#10128)

Signed-off-by: rickyx <[email protected]>
Signed-off-by: Maxime Fournioux <[email protected]>

tests/core/block/test_prefix_caching_block.py

@@ -5,9 +5,14 @@
 
 import pytest
 
+from tests.core.utils import create_dummy_sequence
+from vllm.core.block.cpu_gpu_block_allocator import CpuGpuBlockAllocator
 from vllm.core.block.interfaces import Block, BlockAllocator
-from vllm.core.block.prefix_caching_block import (PrefixCachingBlock,
+from vllm.core.block.prefix_caching_block import (ComputedBlocksTracker,
+                                                  PrefixCachingBlock,
                                                   PrefixCachingBlockAllocator)
+from vllm.sequence import Logprob
+from vllm.utils import Device
 
 
 class TestPrefixCachingBlock:
@@ -726,18 +731,71 @@ def test_touch_block():
                 token_ids=common_token_ids,
                 allocator=allocator,
             )
-            block_ids = [block.block_id for block in blocks]
+            block_hashes = [block.content_hash for block in blocks]
             # The allocated blocks should  be marked as touched
             # but not computed.
-            computed_block_ids = allocator.get_computed_block_ids(
-                [], block_ids, skip_last_block_id=False)
+            computed_block_ids = allocator.find_cached_blocks_prefix(
+                block_hashes)
             assert len(computed_block_ids) == 0
 
         allocator.mark_blocks_as_computed([])
-        computed_block_ids = allocator.get_computed_block_ids(
-            [], block_ids, skip_last_block_id=False)
+        computed_block_ids = allocator.find_cached_blocks_prefix(
+            block_hashes=block_hashes)
         assert len(computed_block_ids) == common_blocks
 
+    @staticmethod
+    def test_find_cached_blocks_prefix():
+        """
+        This test verifies the behavior of find_cached_blocks_prefix.
+        """
+        block_size = 4
+        num_blocks = 8
+        total_test_blocks = 12
+        allocator = PrefixCachingBlockAllocator(num_blocks=num_blocks,
+                                                block_size=block_size)
+
+        token_ids = list(range(total_test_blocks * block_size))
+        block_tokens_seq1 = token_ids[:num_blocks * block_size]
+        blocks_seq1 = TestPrefixCachingBlockAllocator.create_immutable_chain(
+            block_size=block_size,
+            token_ids=block_tokens_seq1,
+            allocator=allocator,
+        )
+        block_hashes_seq1 = [block.content_hash for block in blocks_seq1]
+        allocator.mark_blocks_as_computed([])
+
+        # All blocks should be cached.
+        cached_blocks_seq1 = allocator.find_cached_blocks_prefix(
+            block_hashes=block_hashes_seq1)
+        assert len(cached_blocks_seq1) == num_blocks
+
+        # Free the first sequence.
+        for block in blocks_seq1:
+            allocator.free(block)
+
+        # All blocks should be still be cached if not required to be allocated.
+        cached_blocks = allocator.find_cached_blocks_prefix(
+            block_hashes=block_hashes_seq1)
+        assert len(cached_blocks) == num_blocks
+
+        block_tokens_seq2 = token_ids[num_blocks * block_size:]
+        blocks_seq2 = TestPrefixCachingBlockAllocator.create_immutable_chain(
+            block_size=block_size,
+            token_ids=block_tokens_seq2,
+            allocator=allocator,
+        )
+        block_hashes_seq2 = [block.content_hash for block in blocks_seq2]
+        allocator.mark_blocks_as_computed([])
+        cached_blocks = allocator.find_cached_blocks_prefix(
+            block_hashes=block_hashes_seq2)
+        assert len(cached_blocks) == len(blocks_seq2)
+
+        # Half of the blocks from seq1 should still be cached.
+        num_evicted_blocks = len(blocks_seq2)
+        cached_blocks = allocator.find_cached_blocks_prefix(
+            block_hashes=block_hashes_seq1)
+        assert len(cached_blocks) == len(blocks_seq1) - num_evicted_blocks
+
     @staticmethod
     def create_immutable_chain(
         block_size: int,
@@ -762,3 +820,114 @@ def create_immutable_chain(
             blocks.append(prev_block)
 
         return blocks
+
+
+class TestComputedBlocksTracker:
+
+    @staticmethod
+    def _get_mock_allocator():
+        return MagicMock(spec=PrefixCachingBlockAllocator)
+
+    @staticmethod
+    def test_get_num_cached_tokens():
+        """
+        Test it correctly computes the number of cached tokens for a given
+        sequence:
+
+        - The cache token count is derived from the number of cached blocks.
+        - The cache token count is updated when the allocator is updated.
+        - When a sequence is removed, the cache token count should be updated
+        accordingly.
+
+        # TODO(rickyx): This behaviour for prefill sequence is a hack until
+        we fix the computed blocks tracking.
+        - The cache token count for prefill sequence doesn't change while
+        the sequence is in continuous prefill (chunked prefill).
+        """
+        block_size = 4
+        mock_allocator = TestComputedBlocksTracker._get_mock_allocator()
+        tracker = ComputedBlocksTracker(
+            allocator=mock_allocator,
+            block_size=block_size,
+            enable_caching=True,
+        )
+
+        # Not yet allocated.
+        tokens = [0, 1, 2, 3, 4, 5]
+        seq1 = create_dummy_sequence(request_id=0,
+                                     token_ids=tokens,
+                                     block_size=block_size)
+        mock_allocator.find_cached_blocks_prefix.return_value = []
+        assert tracker.get_num_cached_tokens(seq1) == 0
+
+        mock_allocator.find_cached_blocks_prefix.return_value = [
+            None
+        ]  # 1 block cached.
+        # Result is cached for prefill sequence.
+        assert tracker.get_num_cached_tokens(seq1) == 0
+
+        # Mark the sequence as non-prefill.
+        seq1.data.update_num_computed_tokens(len(tokens))  # 6 tokens computed.
+        assert not seq1.is_prefill()
+
+        # Recomputes for decoding sequence.
+        assert tracker.get_num_cached_tokens(seq1) == 4
+
+        # Append new tokens to the sequence.
+        num_new_tokens = 3
+        for i in range(num_new_tokens):
+            seq1.append_token_id(i, {i: Logprob(logprob=0.0)})
+
+        assert tracker.get_num_cached_tokens(seq1) == 4
+
+        # Update the allocator.
+        mock_allocator.find_cached_blocks_prefix.return_value = [
+            None
+        ] * 2  # 2 blocks cached.
+        assert tracker.get_num_cached_tokens(seq1) == 8
+
+        # Remove the sequence.
+        tracker.remove_seq(seq1.seq_id)
+
+        # Re-create the sequence with the same request id to simulate recompute.
+        seq1 = create_dummy_sequence(request_id=0,
+                                     token_ids=tokens,
+                                     block_size=block_size)
+        mock_allocator.find_cached_blocks_prefix.return_value = [
+        ]  # no cached block
+        assert tracker.get_num_cached_tokens(seq1) == 0
+
+    @staticmethod
+    def test_correct_block_hash():
+        """
+        Test that the block hash is correctly computed for a sequence (should
+        match the underlying block allocator's block hash). So the number of
+        cached tokens is correctly retrieved.
+        """
+        block_size = 4
+        allocator = CpuGpuBlockAllocator.create(
+            allocator_type="prefix_caching",
+            num_gpu_blocks=16,
+            num_cpu_blocks=16,
+            block_size=block_size,
+        )
+        gpu_allocator = allocator._allocators[Device.GPU]
+
+        tracker = ComputedBlocksTracker(
+            allocator=allocator,
+            block_size=block_size,
+            enable_caching=True,
+        )
+
+        tokens = list(range(block_size * 4))  # 4 blocks.
+        seq = create_dummy_sequence(request_id=0,
+                                    token_ids=tokens,
+                                    block_size=block_size)
+        _ = TestPrefixCachingBlockAllocator.create_immutable_chain(
+            block_size=block_size,
+            token_ids=tokens,
+            allocator=gpu_allocator,
+        )
+        allocator.mark_blocks_as_computed([])
+
+        assert tracker.get_num_cached_tokens(seq) == len(tokens)