[Speculative Decoding 2/2 ] Integrate typical acceptance sampler into…

… Spec Decode Worker (vllm-project#5348)

tests/samplers/test_typical_acceptance_sampler.py

@@ -52,6 +52,19 @@ def get_draft_token_ids(batch_size: int, k: int, vocab_size: int,
     return draft_token_ids
 
 
+def get_acceptance_sampler(
+    posterior_threshold: float = 0.03,
+    posterior_alpha: float = 0.9,
+    disable_bonus_tokens: bool = False,
+    strict_mode: bool = False,
+) -> TypicalAcceptanceSampler:
+    """
+    Initializes and returns a TypicalAcceptanceSampler.
+    """
+    return TypicalAcceptanceSampler(posterior_threshold, posterior_alpha,
+                                    disable_bonus_tokens, strict_mode)
+
+
 @pytest.mark.parametrize("k", list(range(1, 6)))
 @pytest.mark.parametrize("vocab_size", [30_000, 50_000])
 @pytest.mark.parametrize("batch_size", list(range(1, 32)))
@@ -64,7 +77,7 @@ def test_no_crash_with_varying_dims(k: int, vocab_size: int, batch_size: int,
     different combinations of k, vocab_size, batch_size and num devices.
     """
     torch.set_default_device(device)
-    typical_acceptance_sampler = TypicalAcceptanceSampler()
+    typical_acceptance_sampler = get_acceptance_sampler()
     typical_acceptance_sampler.init_gpu_tensors(rank=0)
     target_probs = torch.rand(batch_size, k, vocab_size, dtype=torch.float32)
     bonus_token_ids = torch.randint(low=0,
@@ -76,7 +89,10 @@ def test_no_crash_with_varying_dims(k: int, vocab_size: int, batch_size: int,
                                     size=(batch_size, k),
                                     dtype=torch.int64)
     # Verify that sampling succeeds for all cases.
-    typical_acceptance_sampler(target_probs, bonus_token_ids, draft_token_ids)
+    typical_acceptance_sampler(target_probs,
+                               bonus_token_ids,
+                               draft_probs=None,
+                               draft_token_ids=draft_token_ids)
 
 
 @pytest.mark.parametrize("above_or_below_vocab_range", ["above", "below"])
@@ -94,7 +110,7 @@ def test_raises_when_vocab_oob(above_or_below_vocab_range: str,
     batch_size = 5
     vocab_size = 30_000
     torch.set_default_device(device)
-    typical_acceptance_sampler = TypicalAcceptanceSampler(strict_mode=True)
+    typical_acceptance_sampler = get_acceptance_sampler(strict_mode=True)
     typical_acceptance_sampler.init_gpu_tensors(rank=0)
     target_probs = torch.rand(batch_size, k, vocab_size, dtype=torch.float32)
     bonus_token_ids = torch.randint(low=0,
@@ -125,8 +141,10 @@ def test_raises_when_vocab_oob(above_or_below_vocab_range: str,
     oob_token_ids[0][0] = rogue_token_id
 
     with pytest.raises(AssertionError):
-        typical_acceptance_sampler(target_probs, bonus_token_ids,
-                                   draft_token_ids)
+        typical_acceptance_sampler(target_probs,
+                                   bonus_token_ids,
+                                   draft_probs=None,
+                                   draft_token_ids=draft_token_ids)
 
 
 @pytest.mark.parametrize("seed", list(range(10)))
@@ -151,7 +169,7 @@ def test_uniform_target_distribution_accepts_all_tokens(
     batch_size = 5
     vocab_size = 30_000
     torch.set_default_device(device)
-    typical_acceptance_sampler = TypicalAcceptanceSampler(
+    typical_acceptance_sampler = get_acceptance_sampler(
         strict_mode=True, disable_bonus_tokens=disable_bonus_tokens)
     typical_acceptance_sampler.init_gpu_tensors(rank=0)
     target_probs = torch.rand(batch_size, k, vocab_size, dtype=torch.float32)
@@ -163,9 +181,11 @@ def test_uniform_target_distribution_accepts_all_tokens(
                                     high=vocab_size,
                                     size=(batch_size, 1),
                                     dtype=torch.int64)
-    output_token_ids = typical_acceptance_sampler(target_probs,
-                                                  bonus_token_ids,
-                                                  draft_token_ids)
+    output_token_ids = typical_acceptance_sampler(
+        target_probs,
+        bonus_token_ids,
+        draft_probs=None,
+        draft_token_ids=draft_token_ids)
     # We are using a uniform target probability distribution.
     # For a uniform distribution the entropy is very high and it
     # should lead to all draft tokens being accepted. Verify that.
@@ -203,7 +223,7 @@ def test_temperature_zero_target_distribution(seed: int,
     vocab_size = 30_000
     torch.set_default_device(device)
 
-    typical_acceptance_sampler = TypicalAcceptanceSampler(
+    typical_acceptance_sampler = get_acceptance_sampler(
         strict_mode=True, disable_bonus_tokens=disable_bonus_tokens)
     typical_acceptance_sampler.init_gpu_tensors(rank=0)
     # Simulate temperature 0 probability distribution for target probabilities
@@ -224,9 +244,11 @@ def test_temperature_zero_target_distribution(seed: int,
     # 1.0 tokens in the target distribution we will reject all of them and
     # fallback to the greedy sampling for selecting 1 token for each sequence.
     # Verify the same.
-    output_token_ids = typical_acceptance_sampler(target_probs,
-                                                  bonus_token_ids,
-                                                  draft_token_ids)
+    output_token_ids = typical_acceptance_sampler(
+        target_probs,
+        bonus_token_ids,
+        draft_probs=None,
+        draft_token_ids=draft_token_ids)
     assert output_token_ids.shape[0] == batch_size
     assert output_token_ids.shape[1] == (k + 1)
     assert torch.all(output_token_ids[:, -1] == -1)
@@ -261,7 +283,7 @@ def test_mixed_target_distribution(seed: int, disable_bonus_tokens: bool,
     batch_size = 4
     vocab_size = 30_000
     torch.set_default_device(device)
-    typical_acceptance_sampler = TypicalAcceptanceSampler(
+    typical_acceptance_sampler = get_acceptance_sampler(
         strict_mode=True, disable_bonus_tokens=disable_bonus_tokens)
     typical_acceptance_sampler.init_gpu_tensors(rank=0)
     # For sequences 0 and 2 set the distribution to a temperature
@@ -277,9 +299,11 @@ def test_mixed_target_distribution(seed: int, disable_bonus_tokens: bool,
                                     high=vocab_size,
                                     size=(batch_size, 1),
                                     dtype=torch.int64)
-    output_token_ids = typical_acceptance_sampler(target_probs,
-                                                  bonus_token_ids,
-                                                  draft_token_ids)
+    output_token_ids = typical_acceptance_sampler(
+        target_probs,
+        bonus_token_ids,
+        draft_probs=None,
+        draft_token_ids=draft_token_ids)
     # verify the shape of output_token_ids
     assert output_token_ids.shape[0] == batch_size
     assert output_token_ids.shape[1] == (k + 1)
@@ -326,7 +350,7 @@ def test_accept_tokens_partially(seed: int, disable_bonus_tokens: bool,
     batch_size = 1
     vocab_size = 30_000
     torch.set_default_device(device)
-    typical_acceptance_sampler = TypicalAcceptanceSampler(
+    typical_acceptance_sampler = get_acceptance_sampler(
         strict_mode=True, disable_bonus_tokens=disable_bonus_tokens)
     typical_acceptance_sampler.init_gpu_tensors(rank=0)
     # Create a temperature zero target probability distribution and ensure
@@ -339,9 +363,11 @@ def test_accept_tokens_partially(seed: int, disable_bonus_tokens: bool,
                                     high=vocab_size,
                                     size=(batch_size, 1),
                                     dtype=torch.int64)
-    output_token_ids = typical_acceptance_sampler(target_probs,
-                                                  bonus_token_ids,
-                                                  draft_token_ids)
+    output_token_ids = typical_acceptance_sampler(
+        target_probs,
+        bonus_token_ids,
+        draft_probs=None,
+        draft_token_ids=draft_token_ids)
     assert output_token_ids.shape[0] == batch_size
     assert output_token_ids.shape[1] == (k + 1)
     assert torch.all(output_token_ids[:, 0:-1] == draft_token_ids)
@@ -357,9 +383,11 @@ def test_accept_tokens_partially(seed: int, disable_bonus_tokens: bool,
         batch_size, k, vocab_size, zero_temperature_token_ids)
     draft_token_ids = torch.cat(
         (draft_token_ids[:, :2], draft_token_ids_to_replace[:, -3:]), dim=1)
-    output_token_ids = typical_acceptance_sampler(target_probs,
-                                                  bonus_token_ids,
-                                                  draft_token_ids)
+    output_token_ids = typical_acceptance_sampler(
+        target_probs,
+        bonus_token_ids,
+        draft_probs=None,
+        draft_token_ids=draft_token_ids)
     assert output_token_ids.shape[0] == batch_size
     assert output_token_ids.shape[1] == (k + 1)
     assert torch.all(output_token_ids[:, :2] == draft_token_ids[:, :2])
@@ -384,7 +412,7 @@ def test_accept_tokens_set_non_default_posteriors(seed: int,
     batch_size = 1
     vocab_size = 30_000
     torch.set_default_device(device)
-    typical_acceptance_sampler = TypicalAcceptanceSampler(
+    typical_acceptance_sampler = get_acceptance_sampler(
         strict_mode=True, disable_bonus_tokens=disable_bonus_tokens)
     typical_acceptance_sampler.init_gpu_tensors(rank=0)
     # Simulate temperature 0 probability distribution for target
@@ -402,9 +430,11 @@ def test_accept_tokens_set_non_default_posteriors(seed: int,
                                     high=vocab_size,
                                     size=(batch_size, 1),
                                     dtype=torch.int64)
-    output_token_ids = typical_acceptance_sampler(target_probs,
-                                                  bonus_token_ids,
-                                                  draft_token_ids)
+    output_token_ids = typical_acceptance_sampler(
+        target_probs,
+        bonus_token_ids,
+        draft_probs=None,
+        draft_token_ids=draft_token_ids)
     assert output_token_ids.shape[0] == batch_size
     assert output_token_ids.shape[1] == (k + 1)
     assert torch.all(output_token_ids[:, 1:-1] == -1)
@@ -418,9 +448,11 @@ def test_accept_tokens_set_non_default_posteriors(seed: int,
         posterior_threshold=0.0,
         posterior_alpha=0.0)
     typical_acceptance_sampler.init_gpu_tensors(rank=0)
-    output_token_ids = typical_acceptance_sampler(target_probs,
-                                                  bonus_token_ids,
-                                                  draft_token_ids)
+    output_token_ids = typical_acceptance_sampler(
+        target_probs,
+        bonus_token_ids,
+        draft_probs=None,
+        draft_token_ids=draft_token_ids)
     assert output_token_ids.shape[0] == batch_size
     assert output_token_ids.shape[1] == (k + 1)
     assert torch.all(output_token_ids[:, 0:-1] == draft_token_ids)
@@ -451,7 +483,7 @@ def test_replacement_token_ids(seed: int, disable_bonus_tokens: bool,
     batch_size = 5
     vocab_size = 30_000
     torch.set_default_device(device)
-    typical_acceptance_sampler = TypicalAcceptanceSampler(
+    typical_acceptance_sampler = get_acceptance_sampler(
         strict_mode=True, disable_bonus_tokens=disable_bonus_tokens)
     typical_acceptance_sampler.init_gpu_tensors(rank=0)
     target_probs = torch.rand(batch_size, k, vocab_size, dtype=torch.float32)

tests/spec_decode/e2e/test_multistep_correctness.py

@@ -11,9 +11,15 @@
 numerics, see https://arxiv.org/pdf/2302.01318.pdf), we can expect greedy
 equality. This gives us good coverage of temp=0.
 
+At temp=0, the TypicalAcceptanceSampler ensures that only the tokens with the
+highest probability in the target distribution are accepted. Therefore, we can 
+expect greedy equality for the TypicalAcceptanceSampler at temp=0.
+
 For temp>0, we rely on unit tests on the rejection sampler to verify that the
 output distribution is the same with spec decode vs. no spec decode (this would
-be prohibitively expensive to run with a real model).
+be prohibitively expensive to run with a real model). Similarly, for the
+TypicalAcceptance sampler also, we rely on unit tests to validate temp>0
+test cases.
 
 NOTE: Speculative decoding's distribution equality requires that the measured
 distributions of the target model and proposal model be deterministic given the
@@ -611,3 +617,49 @@ def test_many_k(baseline_llm_generator, test_llm_generator, batch_size: int,
                                          batch_size,
                                          max_output_len=output_len,
                                          force_output_len=True)
+
+
+@pytest.mark.parametrize(
+    "common_llm_kwargs",
+    [{
+        "model": "JackFram/llama-160m",
+
+        # Skip cuda graph recording for fast test.
+        "enforce_eager": True,
+
+        # Required for spec decode.
+        "use_v2_block_manager": True
+    }])
+@pytest.mark.parametrize("per_test_common_llm_kwargs", [{}])
+@pytest.mark.parametrize("baseline_llm_kwargs", [{}])
+@pytest.mark.parametrize(
+    "test_llm_kwargs",
+    [
+        {
+            "speculative_model": "JackFram/llama-68m",
+            "num_speculative_tokens": k,
+            "spec_decoding_acceptance_method": "typical_acceptance_sampler"
+        }
+        # Try a range of common k.
+        for k in [1, 2, 3]
+    ])
+@pytest.mark.parametrize("batch_size", [1, 32])
+@pytest.mark.parametrize(
+    "output_len",
+    [
+        # Use smaller output len for fast test.
+        32,
+    ])
+@pytest.mark.parametrize("seed", [1])
+def test_typical_acceptance_sampling(baseline_llm_generator,
+                                     test_llm_generator, batch_size: int,
+                                     output_len: int):
+    """Verify that speculative decoding produces exact equality to without spec
+    decode with TypicalAcceptanceSampler as the draft token acceptance
+    sampling method.
+    """
+    run_greedy_equality_correctness_test(baseline_llm_generator,
+                                         test_llm_generator,
+                                         batch_size,
+                                         max_output_len=output_len,
+                                         force_output_len=True)

tests/spec_decode/test_dynamic_spec_decode.py

@@ -3,33 +3,35 @@
 import pytest
 import torch
 
-from vllm.model_executor.layers.rejection_sampler import RejectionSampler
 from vllm.sequence import ExecuteModelRequest
 from vllm.spec_decode.metrics import AsyncMetricsCollector
 from vllm.spec_decode.multi_step_worker import MultiStepWorker
 from vllm.spec_decode.spec_decode_worker import SpecDecodeWorker
 from vllm.spec_decode.top1_proposer import Top1Proposer
 
+from .test_utils import mock_spec_decode_sampler
 from .utils import create_batch, mock_worker
 
 
 @pytest.mark.parametrize('queue_size', [4])
 @pytest.mark.parametrize('batch_size', [1])
 @pytest.mark.parametrize('k', [1])
+@pytest.mark.parametrize("acceptance_sampler_method",
+                         ["rejection_sampler", "typical_acceptance_sampler"])
 @torch.inference_mode()
-def test_disable_spec_tokens(queue_size: int, batch_size: int, k: int):
+def test_disable_spec_tokens(queue_size: int, batch_size: int, k: int,
+                             acceptance_sampler_method: str):
     """Verify that speculative tokens are disabled when the batch size
     exceeds the threshold.
     """
     disable_by_batch_size = 3
-
     draft_worker = mock_worker(cls=MultiStepWorker)
     target_worker = mock_worker()
-    rejection_sampler = MagicMock(spec=RejectionSampler)
     metrics_collector = MagicMock(spec=AsyncMetricsCollector)
     worker = SpecDecodeWorker(proposer_worker=draft_worker,
                               scorer_worker=target_worker,
-                              rejection_sampler=rejection_sampler,
+                              spec_decode_sampler=mock_spec_decode_sampler(
+                                  acceptance_sampler_method),
                               metrics_collector=metrics_collector,
                               disable_by_batch_size=disable_by_batch_size)