Test: added acceptance length tests (#32030)

Signed-off-by: rahul-tuli <rtuli@redhat.com>

tests/v1/spec_decode/__init__.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project

tests/v1/spec_decode/test_acceptance_length.py

+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+EAGLE3 Acceptance Length Regression Tests.
+
+These tests verify that acceptance lengths for EAGLE3 speculative decoding
+do not regress across vLLM commits. Each test runs inference on the MT-Bench
+dataset and asserts that the mean acceptance length is within tolerance of
+the expected baseline.
+"""
+
+from dataclasses import dataclass, field
+from types import SimpleNamespace
+
+import pytest
+import torch
+
+from tests.conftest import VllmRunner
+from tests.utils import large_gpu_mark
+from vllm import SamplingParams
+from vllm.benchmarks.datasets import get_samples
+from vllm.inputs import TokensPrompt
+from vllm.platforms import current_platform
+from vllm.v1.attention.backends.registry import AttentionBackendEnum
+from vllm.v1.attention.selector import AttentionSelectorConfig
+from vllm.v1.metrics.reader import Counter, Vector
+
+
+@dataclass
+class Eagle3ModelConfig:
+    verifier: str
+    drafter: str
+    expected_acceptance_length: float
+    expected_acceptance_lengths_per_pos: list[float] = field(default_factory=list)
+    id: str = ""
+    # Backends that are incompatible with this model (will be skipped)
+    excluded_backends: set[AttentionBackendEnum] = field(default_factory=set)
+
+
+# Model configurations for EAGLE3 acceptance length tests.
+# Expected acceptance lengths are determined by running baseline benchmarks
+# using examples/offline_inference/spec_decode.py with the MT-Bench dataset.
+EAGLE3_MODEL_CONFIGS = [
+    Eagle3ModelConfig(
+        verifier="meta-llama/Llama-3.1-8B-Instruct",
+        drafter="RedHatAI/Llama-3.1-8B-Instruct-speculator.eagle3",
+        expected_acceptance_length=2.60,
+        expected_acceptance_lengths_per_pos=[0.7296, 0.5208, 0.3545],
+        id="llama3-8b-eagle3",
+    ),
+    Eagle3ModelConfig(
+        verifier="Qwen/Qwen3-8B",
+        drafter="RedHatAI/Qwen3-8B-speculator.eagle3",
+        expected_acceptance_length=2.26,
+        expected_acceptance_lengths_per_pos=[0.6541, 0.3993, 0.2020],
+        id="qwen3-8b-eagle3",
+    ),
+    Eagle3ModelConfig(
+        verifier="openai/gpt-oss-20b",
+        drafter="RedHatAI/gpt-oss-20b-speculator.eagle3",
+        expected_acceptance_length=2.56,
+        expected_acceptance_lengths_per_pos=[0.7165, 0.5120, 0.3337],
+        id="gpt-oss-20b-eagle3",
+        # FLASHINFER incompatible: gpt-oss-20b uses sink attention which
+        # FLASHINFER does not support ("sink setting not supported")
+        excluded_backends={AttentionBackendEnum.FLASHINFER},
+    ),
+]
+
+# Default test parameters
+DEFAULT_NUM_SPEC_TOKENS = 3
+DEFAULT_NUM_PROMPTS = 80
+DEFAULT_OUTPUT_LEN = 256
+DEFAULT_MAX_MODEL_LEN = 16384
+DEFAULT_RTOL = 0.05
+
+# TP sizes to test
+TP_SIZES = [1, 2, 4]
+
+
+# Backends excluded from testing due to significantly different behavior
+EXCLUDED_BACKENDS = {AttentionBackendEnum.FLEX_ATTENTION}
+
+
+def get_available_attention_backends() -> list[str]:
+    if not hasattr(current_platform, "get_valid_backends"):
+        return ["FLASH_ATTN"]
+
+    device_capability = current_platform.get_device_capability()
+    if device_capability is None:
+        return ["FLASH_ATTN"]
+
+    attn_selector_config = AttentionSelectorConfig(
+        head_size=128,
+        dtype=torch.bfloat16,
+        kv_cache_dtype=None,
+        block_size=None,
+        use_mla=False,
+        has_sink=False,
+        use_sparse=False,
+        use_mm_prefix=False,
+    )
+
+    valid_backends, _ = current_platform.get_valid_backends(
+        device_capability=device_capability,
+        attn_selector_config=attn_selector_config,
+    )
+
+    return [
+        backend.name
+        for backend, _ in valid_backends
+        if backend not in EXCLUDED_BACKENDS
+    ]
+
+
+def get_attention_backend_params() -> list[str]:
+    return get_available_attention_backends()
+
+
+def get_tp_size_params() -> list[pytest.param]:
+    num_gpus = torch.cuda.device_count() if torch.cuda.is_available() else 1
+    return [pytest.param(tp, id=f"tp{tp}") for tp in TP_SIZES if tp <= num_gpus]
+
+
+def get_mt_bench_prompts(
+    tokenizer, num_prompts: int = DEFAULT_NUM_PROMPTS
+) -> list[list[int]]:
+    args = SimpleNamespace(
+        dataset_name="hf",
+        dataset_path="philschmid/mt-bench",
+        num_prompts=num_prompts,
+        seed=42,
+        no_oversample=False,
+        endpoint_type="openai-chat",
+        input_len=None,
+        output_len=DEFAULT_OUTPUT_LEN,
+        sharegpt_output_len=DEFAULT_OUTPUT_LEN,
+        hf_name=None,
+        hf_split="train",
+        hf_subset=None,
+        hf_output_len=DEFAULT_OUTPUT_LEN,
+        no_stream=True,
+        disable_shuffle=False,
+        skip_chat_template=False,
+    )
+    samples = get_samples(args, tokenizer)
+    prompt_ids = [
+        tokenizer.encode(sample.prompt, add_special_tokens=False) for sample in samples
+    ]
+    return prompt_ids
+
+
+def extract_acceptance_metrics(metrics, num_spec_tokens: int) -> dict:
+    num_drafts = 0
+    num_accepted_tokens = 0
+    acceptance_counts = [0] * num_spec_tokens
+
+    for metric in metrics:
+        if metric.name == "vllm:spec_decode_num_drafts":
+            assert isinstance(metric, Counter)
+            num_drafts += metric.value
+        elif metric.name == "vllm:spec_decode_num_accepted_tokens":
+            assert isinstance(metric, Counter)
+            num_accepted_tokens += metric.value
+        elif metric.name == "vllm:spec_decode_num_accepted_tokens_per_pos":
+            assert isinstance(metric, Vector)
+            for pos in range(min(len(metric.values), num_spec_tokens)):
+                acceptance_counts[pos] += metric.values[pos]
+
+    # Calculate mean acceptance length
+    # Formula: 1 + (accepted_tokens / num_drafts)
+    acceptance_length = 1 + (num_accepted_tokens / num_drafts) if num_drafts > 0 else 1
+
+    # Calculate per-position acceptance lengths (contribution to total)
+    # Each position contributes: accepted_at_pos / num_drafts
+    acceptance_lengths_per_pos = [
+        count / num_drafts if num_drafts > 0 else 0.0 for count in acceptance_counts
+    ]
+
+    return {
+        "acceptance_length": acceptance_length,
+        "acceptance_lengths_per_pos": acceptance_lengths_per_pos,
+        "num_drafts": num_drafts,
+        "num_accepted_tokens": num_accepted_tokens,
+    }
+
+
+@large_gpu_mark(min_gb=40)
+@pytest.mark.parametrize(
+    "model_config",
+    [pytest.param(config, id=config.id) for config in EAGLE3_MODEL_CONFIGS],
+)
+@pytest.mark.parametrize("num_spec_tokens", [DEFAULT_NUM_SPEC_TOKENS])
+@pytest.mark.parametrize("tp_size", get_tp_size_params())
+@pytest.mark.parametrize("attention_backend", get_attention_backend_params())
+def test_eagle3_acceptance_length(
+    model_config: Eagle3ModelConfig,
+    num_spec_tokens: int,
+    tp_size: int,
+    attention_backend: str,
+    monkeypatch: pytest.MonkeyPatch,
+):
+    # Skip if this backend is incompatible with the model
+    backend_enum = AttentionBackendEnum[attention_backend]
+    if backend_enum in model_config.excluded_backends:
+        pytest.skip(f"{attention_backend} is incompatible with {model_config.id}")
+
+    with monkeypatch.context() as m:
+        m.setenv("VLLM_ALLOW_INSECURE_SERIALIZATION", "1")
+        m.setenv("VLLM_ATTENTION_BACKEND", attention_backend)
+
+        with VllmRunner(
+            model_name=model_config.verifier,
+            speculative_config={
+                "method": "eagle3",
+                "model": model_config.drafter,
+                "num_speculative_tokens": num_spec_tokens,
+            },
+            tensor_parallel_size=tp_size,
+            gpu_memory_utilization=0.7,
+            disable_log_stats=False,
+            max_model_len=DEFAULT_MAX_MODEL_LEN,
+        ) as vllm_runner:
+            tokenizer = vllm_runner.llm.get_tokenizer()
+            prompt_ids = get_mt_bench_prompts(tokenizer, DEFAULT_NUM_PROMPTS)
+
+            sampling_params = SamplingParams(
+                temperature=0,
+                max_tokens=DEFAULT_OUTPUT_LEN,
+            )
+            vllm_runner.llm.generate(
+                [TokensPrompt(prompt_token_ids=ids) for ids in prompt_ids],
+                sampling_params=sampling_params,
+            )
+
+            metrics = vllm_runner.llm.get_metrics()
+            results = extract_acceptance_metrics(metrics, num_spec_tokens)
+
+            actual_acceptance_length = results["acceptance_length"]
+            expected = model_config.expected_acceptance_length
+            actual_per_pos = results["acceptance_lengths_per_pos"]
+            expected_per_pos = model_config.expected_acceptance_lengths_per_pos
+
+            rel_error = abs(actual_acceptance_length - expected) / expected
+
+            assert rel_error <= DEFAULT_RTOL, (
+                f"Acceptance length regression detected for {model_config.id}!\n"
+                f"  Expected: {expected:.3f}\n"
+                f"  Actual:   {actual_acceptance_length:.3f}\n"
+                f"  Relative error: {rel_error:.2%} (tolerance: {DEFAULT_RTOL:.2%})\n"
+                f"  Drafts: {results['num_drafts']}, "
+                f"Accepted tokens: {results['num_accepted_tokens']}"
+            )
+
+            if expected_per_pos and len(expected_per_pos) == len(actual_per_pos):
+                for pos, (actual, exp) in enumerate(
+                    zip(actual_per_pos, expected_per_pos)
+                ):
+                    if exp > 0:
+                        pos_rel_error = abs(actual - exp) / exp
+                        assert pos_rel_error <= DEFAULT_RTOL, (
+                            f"Per-position acceptance length regression at pos {pos} "
+                            f"for {model_config.id}!\n"
+                            f"  Expected: {exp:.3f}\n"
+                            f"  Actual:   {actual:.3f}\n"
+                            f"  Relative error: {pos_rel_error:.2%} "
+                            f"(tolerance: {DEFAULT_RTOL:.2%})"
+                        )
+
+            print(
+                f"\n{model_config.id} [tp={tp_size}, backend={attention_backend}]: "
+                f"acceptance_length={actual_acceptance_length:.3f}"
+                f" (expected={expected:.3f}, rel_error={rel_error:.2%})"
+            )
+            print(f"  Per-position: {[f'{v:.3f}' for v in actual_per_pos]}")
+            if expected_per_pos:
+                print(f"  Expected:     {[f'{v:.3f}' for v in expected_per_pos]}")