test_prefix_caching.py

# SPDX-License-Identifier: Apache-2.0
"""Compare the with and without prefix caching.

Run `pytest tests/prefix_caching/test_prefix_caching.py`.
"""

import pytest

from tests.conftest import VllmRunner
from tests.core.utils import SchedulerProxy, create_dummy_prompt
from tests.kernels.utils import override_backend_env_variable
from vllm import SamplingParams, TokensPrompt
from vllm.core.scheduler import Scheduler
from vllm.engine.llm_engine import LLMEngine

from ..models.utils import check_outputs_equal

MODELS = [
    "facebook/opt-125m",
]

UNSTABLE_PROMPT_SEQUENCE = [
    ([0] * 588) + ([1] * 1332) + ([2] * 30) + ([3] * 1),
    ([0] * 588) + ([1] * 1332) + ([4] * 3) + ([5] * 50),
    ([0] * 588) + ([1] * 1332) + ([2] * 30) + ([6] * 95),
    ([0] * 588) + ([1] * 1332) + ([4] * 3) + ([7] * 174),
    ([0] * 588) + ([8] * 1539),
]


@pytest.mark.parametrize("model", MODELS)
@pytest.mark.parametrize("backend", ["FLASH_ATTN", "FLASHINFER", "XFORMERS"])
@pytest.mark.parametrize("dtype", ["half"])
@pytest.mark.parametrize("max_tokens", [5])
@pytest.mark.parametrize("cached_position", [0, 1])
@pytest.mark.parametrize("enable_chunked_prefill", [True, False])
@pytest.mark.parametrize("block_size", [16])
def test_mixed_requests(
    hf_runner,
    vllm_runner,
    example_prompts,
    model: str,
    backend: str,
    dtype: str,
    max_tokens: int,
    cached_position: int,
    enable_chunked_prefill: bool,
    block_size: int,
    monkeypatch,
) -> None:
    """
    Test the case when some sequences have the prefix cache hit
    and the others don't. The cached position determines where
    the sequence is at among the batch of prefills.
    """
    override_backend_env_variable(monkeypatch, backend)

    with hf_runner(model, dtype=dtype) as hf_model:
        hf_outputs = hf_model.generate_greedy(example_prompts, max_tokens)

    cached_prompt = example_prompts[cached_position]
    with vllm_runner(
            model,
            dtype=dtype,
            enable_prefix_caching=True,
            enable_chunked_prefill=enable_chunked_prefill,
            block_size=block_size,
    ) as vllm_model:
        # Run the first prompt so the cache is populated
        vllm_outputs = vllm_model.generate_greedy([cached_prompt], max_tokens)

        # Run all the promopts
        greedy_params = SamplingParams(temperature=0.0, max_tokens=max_tokens)
        req_outputs = vllm_model.model.generate(example_prompts, greedy_params)

        # Verify number of cached tokens
        for i in range(len(req_outputs)):
            if i == cached_position:
                expected_num_cached_tokens = (
                    len(req_outputs[i].prompt_token_ids) //
                    block_size) * block_size
            else:
                expected_num_cached_tokens = 0
            assert (
                req_outputs[i].num_cached_tokens == expected_num_cached_tokens)

        vllm_outputs = [(
            output.prompt_token_ids + list(output.outputs[0].token_ids),
            output.prompt + output.outputs[0].text,
        ) for output in req_outputs]

    check_outputs_equal(
        outputs_0_lst=hf_outputs,
        outputs_1_lst=vllm_outputs,
        name_0="hf",
        name_1="vllm",
    )


@pytest.mark.parametrize("backend", ["FLASH_ATTN", "FLASHINFER", "XFORMERS"])
def test_unstable_prompt_sequence(
    vllm_runner,
    backend: str,
    monkeypatch,
) -> None:
    override_backend_env_variable(monkeypatch, backend)

    with vllm_runner(
            "Qwen/Qwen2.5-0.5B-Instruct",
            enable_chunked_prefill=True,
            enable_prefix_caching=True,
            max_model_len=4096,
    ) as vllm_model:
        for prompt in UNSTABLE_PROMPT_SEQUENCE:
            vllm_model.generate(TokensPrompt(prompt_token_ids=prompt),
                                SamplingParams(max_tokens=1))


@pytest.mark.parametrize("model", MODELS)
def test_fully_cached_prefill_needs_uncached_token(model):
    block_size = 16
    max_num_batched_tokens = 16
    num_output_tokens = 5
    # Make a vllm engine
    runner = VllmRunner(
        model_name=model,
        gpu_memory_utilization=0.7,
        enable_chunked_prefill=True,
        enforce_eager=True,
        enable_prefix_caching=True,
        block_size=block_size,
        max_num_batched_tokens=max_num_batched_tokens,
        max_num_seqs=max_num_batched_tokens,
    )
    engine: LLMEngine = runner.model.llm_engine

    scheduler: Scheduler = SchedulerProxy(engine.scheduler[0])  # type: ignore
    engine.scheduler[0] = scheduler

    # SeqA
    seqA_tokens = list(range(2 * block_size))
    seqA, seq_groupA = create_dummy_prompt(
        request_id="0",
        prompt_tokens=seqA_tokens,
        max_tokens=num_output_tokens,
        block_size=block_size,
    )

    scheduler.add_seq_group(seq_groupA)

    assert seqA.data.get_num_computed_tokens() == 0

    # Prefill seqA
    while not seqA.is_finished():
        engine.step()

    # seqB
    seqB_tokens = [t + 1 for t in seqA_tokens]  # shift by 1
    seqB, seq_groupB = create_dummy_prompt(
        request_id="1",
        prompt_tokens=seqB_tokens,
        max_tokens=num_output_tokens,
        block_size=block_size,
    )

    # seqC is the same as seqA
    seqC, seq_groupC = create_dummy_prompt(
        request_id="2",
        prompt_tokens=seqA_tokens,
        max_tokens=num_output_tokens,
        block_size=block_size,
    )

    scheduler.add_seq_group(seq_groupB)
    scheduler.add_seq_group(seq_groupC)

    # Even seqC is fully cached, it should not be prefilled since we
    # require at least 1 uncached token.
    engine.step()

    sched_metas, sched_out, _ = scheduler.last_schedule_ret()
    assert len(sched_out.scheduled_seq_groups) == 1
    assert (sched_out.scheduled_seq_groups[0].seq_group.request_id ==
            seq_groupB.request_id)
    assert (sched_out.scheduled_seq_groups[0].token_chunk_size ==
            max_num_batched_tokens)

    # When seqB is finished, seqC could be prefilled.
    while not seqB.is_finished():
        engine.step()
        sched_metas, sched_out, _ = scheduler.last_schedule_ret()
        assert len(sched_out.scheduled_seq_groups) == 1
        assert (sched_out.scheduled_seq_groups[0].seq_group.request_id ==
                seq_groupB.request_id)

    engine.step()
    sched_metas, sched_out, _ = scheduler.last_schedule_ret()
    assert len(sched_out.scheduled_seq_groups) == 1
    assert (sched_out.scheduled_seq_groups[0].seq_group.request_id ==
            seq_groupC.request_id)
    assert sched_out.scheduled_seq_groups[0].token_chunk_size == len(
        seqA_tokens)