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vllm-project--vllm/tests/models/quantization/test_fp8_per_channel.py
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Python

# SPDX-License-Identifier: Apache-2.0
# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
"""E2E tests for online FP8 per-channel quantization.
Loads a BF16 model with ``--quantization fp8_per_channel`` (online
quantization) and compares log-probabilities against the same model served in
BF16 without quantization. This exercises the full pipeline: config parsing,
``Fp8PtpcOnlineLinearMethod``, ``Fp8PtpcOnlineMoEMethod``, weight
loading, online quantization / shuffling, and inference.
``example_prompts`` is a pytest fixture (from conftest.py) that loads 8
diverse prompts from ``tests/prompts/example.txt``.
"""
import pytest
from tests.quantization.utils import is_quant_method_supported
from ..utils import check_logprobs_close
# Small MoE model that fits on a single GPU and exercises both linear + MoE.
MOE_MODEL = "allenai/OLMoE-1B-7B-0125-Instruct"
# Small dense model (no MoE) to validate the linear-only path.
DENSE_MODEL = "Qwen/Qwen3-0.6B"
MAX_MODEL_LEN = 1024
MAX_TOKENS = 4
NUM_LOG_PROBS = 8
@pytest.mark.skipif(
not is_quant_method_supported("fp8"),
reason="fp8 is not supported on this GPU type.",
)
@pytest.mark.quant_model
@pytest.mark.parametrize("model", [DENSE_MODEL, MOE_MODEL], ids=["dense", "moe"])
def test_fp8_per_channel_logprobs(
vllm_runner,
example_prompts,
model: str,
monkeypatch: pytest.MonkeyPatch,
) -> None:
"""Compare BF16 baseline logprobs against online per-channel-quantized
model.
Runs the same model twice -- once in BF16 (baseline) and once with online
FP8 per-channel quantization -- then checks that the top log-probabilities
are close. Only 4 tokens are generated to keep the test fast while still
catching numerical divergence beyond expected per-channel error.
"""
with monkeypatch.context() as m:
m.setenv("TOKENIZERS_PARALLELISM", "true")
with vllm_runner(
model,
max_model_len=MAX_MODEL_LEN,
enforce_eager=True,
) as vllm_model:
baseline_outputs = vllm_model.generate_greedy_logprobs(
example_prompts, MAX_TOKENS, NUM_LOG_PROBS
)
with vllm_runner(
model,
max_model_len=MAX_MODEL_LEN,
enforce_eager=True,
quantization="fp8_per_channel",
) as vllm_model:
test_outputs = vllm_model.generate_greedy_logprobs(
example_prompts, MAX_TOKENS, NUM_LOG_PROBS
)
check_logprobs_close(
outputs_0_lst=baseline_outputs,
outputs_1_lst=test_outputs,
name_0="bf16",
name_1="fp8_per_channel",
)