[Model] Enable quantization support for transformers backend (#12960)

docs/source/models/supported_models.md

@@ -42,7 +42,7 @@ Alternatively, you can [open an issue on GitHub](https://github.com/vllm-project
 
 ### Transformers fallback
 
-After the merge of <gh-pr:11330>, `vllm` can fallback to models that are available in `transformers`. This does not work for all models for now, but most decoder language models are supported, and vision language model support is planned!
+`vllm` can fallback to models that are available in `transformers`. This does not work for all models for now, but most decoder language models are supported, and vision language model support is planned!
 
 To check if the backend is `transformers`, you can simply do this:
 
@@ -56,9 +56,13 @@ If it is `TransformersModel` then it means it's based on `transformers`!
 
 #### Supported features
 
-##### LORA and quantization
+##### Quantization
 
-Both are not supported yet! Make sure to open an issue and we'll work on this together with the `transformers` team!
+Transformers fallback has supported most of available quantization in vLLM (except GGUF). See [Quantization page](#quantization-index) for more information about supported quantization in vllm.
+
+##### LoRA
+
+LoRA hasn't supported on transformers fallback yet! Make sure to open an issue and we'll work on this together with the `transformers` team!
 
 Usually `transformers` model load weights via the `load_adapters` API, that depends on PEFT. We need to work a bit to either use this api (for now this would result in some weights not being marked as loaded) or replace modules accordingly.
 

tests/models/test_transformers.py

@@ -45,10 +45,14 @@ def check_implementation(
         ("meta-llama/Llama-3.2-1B-Instruct", "transformers"),
         ("openai-community/gpt2", "transformers"),
         ("ArthurZ/Ilama-3.2-1B", "auto"),  # CUSTOM CODE
-        ("meta-llama/Llama-3.2-1B-Instruct", "auto"),
     ])  # trust_remote_code=True by default
-def test_models(hf_runner, vllm_runner, example_prompts, model,
-                model_impl) -> None:
+def test_models(
+    hf_runner: Type[HfRunner],
+    vllm_runner: Type[VllmRunner],
+    example_prompts: list[str],
+    model: str,
+    model_impl: str,
+) -> None:
 
     maybe_raises = nullcontext()
     if model == "openai-community/gpt2" and model_impl == "transformers":
@@ -67,10 +71,50 @@ def test_models(hf_runner, vllm_runner, example_prompts, model,
 
 @multi_gpu_test(num_gpus=2)
 def test_distributed(
-    hf_runner,
-    vllm_runner,
+    hf_runner: Type[HfRunner],
+    vllm_runner: Type[VllmRunner],
     example_prompts,
 ):
     kwargs = {"model_impl": "transformers", "tensor_parallel_size": 2}
     check_implementation(hf_runner, vllm_runner, example_prompts,
                          "meta-llama/Llama-3.2-1B-Instruct", **kwargs)
+
+
+@pytest.mark.parametrize("model, quantization_kwargs", [
+    (
+        "meta-llama/Llama-3.2-1B-Instruct",
+        {
+            "quantization": "bitsandbytes",
+            "load_format": "bitsandbytes",
+        },
+    ),
+])
+@pytest.mark.parametrize("max_tokens", [32])
+@pytest.mark.parametrize("num_logprobs", [5])
+def test_quantization(
+    vllm_runner: Type[VllmRunner],
+    example_prompts: list[str],
+    model: str,
+    quantization_kwargs: dict[str, str],
+    max_tokens: int,
+    num_logprobs: int,
+) -> None:
+    with vllm_runner(
+            model, model_impl="auto", enforce_eager=True,
+            **quantization_kwargs) as vllm_model:  # type: ignore[arg-type]
+        vllm_outputs = vllm_model.generate_greedy_logprobs(
+            example_prompts, max_tokens=max_tokens, num_logprobs=num_logprobs)
+
+    with vllm_runner(
+            model,
+            model_impl="transformers",
+            enforce_eager=True,
+            **quantization_kwargs) as vllm_model:  # type: ignore[arg-type]
+        transformers_outputs = vllm_model.generate_greedy_logprobs(
+            example_prompts, max_tokens=max_tokens, num_logprobs=num_logprobs)
+    check_logprobs_close(
+        outputs_0_lst=transformers_outputs,
+        outputs_1_lst=vllm_outputs,
+        name_0="transformers",
+        name_1="vllm",
+    )

vllm/model_executor/models/transformers.py

@@ -28,6 +28,7 @@ from vllm.distributed import get_tensor_model_parallel_world_size
 from vllm.distributed.utils import divide
 from vllm.logger import init_logger
 from vllm.model_executor.layers.linear import (ColumnParallelLinear,
+                                               ReplicatedLinear,
                                                RowParallelLinear)
 from vllm.model_executor.layers.logits_processor import LogitsProcessor
 from vllm.model_executor.layers.sampler import SamplerOutput, get_sampler
@@ -37,6 +38,7 @@ from vllm.model_executor.model_loader.weight_utils import default_weight_loader
 from vllm.model_executor.sampling_metadata import SamplingMetadata
 from vllm.sequence import IntermediateTensors
 
+from .interfaces import SupportsQuant
 from .utils import maybe_prefix
 
 logger = init_logger(__name__)
@@ -50,10 +52,10 @@ def vllm_flash_attention_forward(
         value: torch.Tensor,
         attention_mask: torch.Tensor,
         # Transformers kwargs
-        scaling: float = None,
+        scaling: Optional[float] = None,
         # vLLM kwargs
-        attn_metadata: AttentionMetadata = None,
-        attention_instances: list[Attention] = None,
+        attn_metadata: Optional[AttentionMetadata] = None,
+        attention_instances: Optional[list[Attention]] = None,
         **kwargs):
     self_attn = attention_instances[module.layer_idx]
     if scaling is not None:
@@ -99,13 +101,7 @@ def replace_linear_class(
     vllm_linear_cls = {
         "colwise": ColumnParallelLinear,
         "rowwise": RowParallelLinear,
-    }.get(style)
-
-    if vllm_linear_cls is None:
-        logger.warning(
-            "Unsupported parallel style value: %s. "
-            "This layer will not be tensor parallelized.", style)
-        return linear
+    }.get(style, ReplicatedLinear)
 
     class HFCompatibleLinear(vllm_linear_cls):
         """
@@ -119,10 +115,11 @@ def replace_linear_class(
         input_size=linear.in_features,
         output_size=linear.out_features,
         bias=linear.bias is not None,
+        quant_config=quant_config,
     )
 
 
-class TransformersModel(nn.Module):
+class TransformersModel(nn.Module, SupportsQuant):
     embedding_padding_modules = ["lm_head"]
     embedding_modules = ["embed_tokens"
                          ]  # TODO transformers will have a util to get it
@@ -133,10 +130,8 @@ class TransformersModel(nn.Module):
 
         config = vllm_config.model_config.hf_config
         cache_config = vllm_config.cache_config
-        quant_config = vllm_config.quant_config
 
         self.config = config
-        self.quant_config = quant_config
         self.vocab_size = config.vocab_size
         self.unpadded_vocab_size = config.vocab_size
 
@@ -162,7 +157,7 @@ class TransformersModel(nn.Module):
                 scale=config.head_dim**-0.5,
                 num_kv_heads=divide(config.num_key_value_heads, tp_size),
                 cache_config=cache_config,
-                quant_config=None,
+                quant_config=self.quant_config,
                 prefix=f"{i}.attn") for i in range(config.num_hidden_layers)
         ]
 
@@ -172,7 +167,7 @@ class TransformersModel(nn.Module):
         # ForCausalLM modifications
         self.lm_head = ParallelLMHead(config.vocab_size,
                                       config.hidden_size,
-                                      quant_config=None,
+                                      quant_config=self.quant_config,
                                       prefix=maybe_prefix(prefix, "lm_head"))
         if config.tie_word_embeddings:
             self.lm_head.weight = self.model.get_input_embeddings().weight