[CORE] Quantized lm-head Framework (#4442)

Co-authored-by: Robert Shaw <rshaw@neuralmagic.com>
Co-authored-by: ZX <zx@lbx.dev>

tests/quantization/test_lm_head.py

@@ -0,0 +1,45 @@
+"""Tests whether gptq models with quantized lm_head can be loaded.
+
+Run `pytest tests/quantization/test_quant_lm_head_true.py --forked`.
+"""
+from typing import Tuple
+
+import pytest
+import torch
+
+from vllm.model_executor.layers.linear import UnquantizedLinearMethod
+from vllm.model_executor.layers.quantization.gptq import GPTQLinearMethod
+from vllm.model_executor.layers.quantization.gptq_marlin import (
+    GPTQMarlinLinearMethod)
+from vllm.model_executor.layers.quantization.marlin import MarlinLinearMethod
+
+PROMPT = "On the surface of Mars, we found"
+
+MODELS_QUANT = [(
+    "LnL-AI/TinyLlama-1.1B-intermediate-step-1341k-3T-autoround-lm_head-symFalse",
+    True), ("TheBloke/TinyLlama-1.1B-Chat-v1.0-GPTQ", False),
+                ("neuralmagic/Meta-Llama-3-8B-Instruct-FP8", False)]
+
+
+@pytest.mark.parametrize("model_lm_head_quant", MODELS_QUANT)
+def test_lm_head(
+    vllm_runner,
+    model_lm_head_quant: Tuple[str, bool],
+) -> None:
+    model, lm_head_quantized = model_lm_head_quant
+    vllm_model = vllm_runner(model, dtype=torch.float16, max_model_len=2048)
+
+    lm_head_layer = (vllm_model.model.llm_engine.model_executor.driver_worker.
+                     model_runner.model.lm_head)
+
+    if lm_head_quantized:
+        assert isinstance(
+            lm_head_layer.linear_method,
+            (GPTQLinearMethod, GPTQMarlinLinearMethod, MarlinLinearMethod))
+    else:
+        assert isinstance(lm_head_layer.linear_method, UnquantizedLinearMethod)
+
+    print(
+        vllm_model.generate_greedy(prompts=["Hello my name is"],
+                                   max_tokens=10)[0][1])
+    del vllm_model