[Quantization] Support more than one quant-compressor

src/compressed_tensors/compressors/model_compressors/model_compressor.py

@@ -169,7 +169,7 @@ def from_pretrained_model(
         cls,
         model: Module,
         sparsity_config: Union[SparsityCompressionConfig, str, None] = None,
-        quantization_format: Optional[str] = None,
+        quantization_format: Optional[Union[str, List[str]]] = None,
     ) -> Optional["ModelCompressor"]:
         """
         Given a pytorch model and optional sparsity and/or quantization configs,
@@ -182,7 +182,6 @@ def from_pretrained_model(
             algorithm
         :return: compressor for the configs, or None if model is not compressed
         """
-        # reconstruct config from schemes attached to modules
         quantization_config = QuantizationConfig.from_pretrained(
             model, format=quantization_format
         )
@@ -203,6 +202,9 @@ def from_pretrained_model(
             sparsity_config=sparsity_config,
             quantization_config=quantization_config,
             transform_config=transform_config,
+            compression_formats=[quantization_format]
+            if isinstance(quantization_format, str)
+            else quantization_format,
         )
 
     @staticmethod
@@ -263,30 +265,61 @@ def parse_quantization_config(
 
         return quantization_config
 
+    def _fetch_unique_quantization_formats(self) -> List[str]:
+        """
+        Get all unique compression formats present in a model.
+        :return: list of quantization formats
+        """
+        quantization_formats = []
+        for _, scheme in self.quantization_config.config_groups.items():
+            if scheme.format is not None and scheme.format not in quantization_formats:
+                quantization_formats.append(scheme.format)
+
+        if (
+            len(quantization_formats) == 0
+            and self.quantization_config.format
+            != CompressionFormat.mixed_precision.value
+        ):
+            quantization_formats.append(self.quantization_config.format)
+        return quantization_formats
+
     def __init__(
         self,
         sparsity_config: Optional[SparsityCompressionConfig] = None,
         quantization_config: Optional[QuantizationConfig] = None,
         transform_config: Optional[TransformConfig] = None,
+        compression_formats: Optional[List[str]] = None,
     ):
         self.sparsity_config = sparsity_config
         self.quantization_config = quantization_config
         self.transform_config = transform_config
+        self.compression_formats = compression_formats
 
         self.sparsity_compressor = None
         self.quantization_compressor: Optional[
-            Union[BaseQuantizationCompressor, DenseCompressor]
+            Dict[str, Union[BaseQuantizationCompressor, DenseCompressor]]
         ] = None
         # no transform compressor is required
 
         if sparsity_config is not None:
             self.sparsity_compressor = BaseCompressor.load_from_registry(
                 sparsity_config.format, config=sparsity_config
             )
+
         if quantization_config is not None:
-            self.quantization_compressor = BaseCompressor.load_from_registry(
-                quantization_config.format, config=quantization_config
-            )
+            # If a list of compression_format is not provided, we resolve the
+            # relevant quantization formats using the config groups from the config
+            # and if those are not defined, we fall-back to the global quantization format
+            if not self.compression_formats:
+                self.compression_formats = self._fetch_unique_quantization_formats()
+
+            self.quantization_compressor = {}
+            for format in self.compression_formats:
+                self.quantization_compressor[
+                    format
+                ] = BaseCompressor.load_from_registry(
+                    format, config=quantization_config
+                )
 
     # ----- used by hf quantizer ----- #
 
@@ -381,12 +414,13 @@ def get_unexpected_file_keys(self, model: Module) -> List[str]:
                     targets=scheme.targets,
                     ignore=self.quantization_config.ignore,
                 )
-                unexpected_keys.update(
-                    merge_names(target, param)
-                    for target in quant_targets
-                    for param in self.quantization_compressor.compression_param_names
-                    if param != "weight"
-                )
+                for quant_compressor in self.quantization_compressor.values():
+                    unexpected_keys.update(
+                        merge_names(target, param)
+                        for target in quant_targets
+                        for param in quant_compressor.compression_param_names
+                        if param != "weight"
+                    )
 
         return list(unexpected_keys)
 
@@ -424,7 +458,21 @@ def compress_model(self, model: Module):
 
                 # quantization first
                 if prefix in module_to_scheme:
-                    state_dict = self.quantization_compressor.compress(
+                    if (
+                        not hasattr(module.quantization_scheme, "format")
+                        or module.quantization_scheme.format is None
+                    ):
+                        if len(self.compression_formats) > 1:
+                            raise ValueError(
+                                "Applying multiple compressors without defining "
+                                "per module formats is not supported "
+                            )
+                        format = self.compression_formats[0]
+                    else:
+                        format = module.quantization_scheme.format
+
+                    quant_compressor = self.quantization_compressor.get(format)
+                    state_dict = quant_compressor.compress(
                         state_dict,
                         names_to_scheme=module_to_scheme,
                         show_progress=False,
@@ -495,12 +543,24 @@ def decompress_model(self, model: Module):
 
                 # quantization second
                 if prefix in module_to_scheme:
-                    state_dict = (
-                        self.quantization_compressor.decompress_module_from_state_dict(
-                            prefix,
-                            state_dict,
-                            scheme=module_to_scheme[prefix],
-                        )
+
+                    if (
+                        not hasattr(module.quantization_scheme, "format")
+                        or module.quantization_scheme.format is None
+                    ):
+                        if len(self.compression_formats) > 1:
+                            raise ValueError(
+                                "Applying multiple compressors without defining "
+                                "per module formats is not supported "
+                            )
+                        format = self.compression_formats[0]
+                    else:
+                        format = module.quantization_scheme.format
+                    quant_compressor = self.quantization_compressor.get(format)
+                    state_dict = quant_compressor.decompress_module_from_state_dict(
+                        prefix,
+                        state_dict,
+                        scheme=module_to_scheme[prefix],
                     )
 
                 # remove any existing parameters
@@ -539,7 +599,9 @@ def compress(
 
         if self.quantization_compressor is not None:
             module_to_scheme = map_module_to_scheme(model)
-            state_dict = self.quantization_compressor.compress(
+            # Note - compress only supports one compression format atm
+            quant_compressor = next(iter(self.quantization_compressor.values()))
+            state_dict = quant_compressor.compress(
                 state_dict,
                 names_to_scheme=module_to_scheme,
                 show_progress=show_progress,
@@ -588,14 +650,20 @@ def decompress(self, model_path: str, model: Module):
         """
         model_path = get_safetensors_folder(model_path)
         sparse_decompressed = False
+        quant_compressor = (
+            next(iter(self.quantization_compressor.values()))
+            if self.quantization_compressor is not None
+            else None
+        )
 
         if (
             self.sparsity_compressor is not None
             and self.sparsity_config.format != CompressionFormat.dense.value
         ):
+            # note - decompress only supports one compressor atm
             params_to_ignore = None
-            if self.quantization_compressor is not None:
-                params_to_ignore = self.quantization_compressor.compression_param_names
+            if quant_compressor is not None:
+                params_to_ignore = quant_compressor.compression_param_names
             # Sparse decompression is applied on the model_path
             # The compressor will try and load any quantization parameters as well
             # params_to_skip_load will skip over quantization params from being loaded
@@ -606,7 +674,7 @@ def decompress(self, model_path: str, model: Module):
             setattr(model, SPARSITY_CONFIG_NAME, self.sparsity_compressor.config)
             sparse_decompressed = True
 
-        if self.quantization_compressor is not None:
+        if quant_compressor is not None:
             # Temporarily set quantization status to FROZEN to prevent
             # quantization during apply_quantization_config. This ensures
             # that the dtypes of the weights are not unintentionally updated.
@@ -629,15 +697,15 @@ def decompress(self, model_path: str, model: Module):
                     # including initialization
                     load_weight_quantization=(
                         sparse_decompressed
-                        or isinstance(self.quantization_compressor, DenseCompressor)
+                        or isinstance(quant_compressor, DenseCompressor)
                     ),
                 )
 
             model_path_or_state_dict = (
                 model.state_dict() if sparse_decompressed else model_path
             )
 
-            dense_gen = self.quantization_compressor.decompress(
+            dense_gen = quant_compressor.decompress(
                 model_path_or_state_dict, names_to_scheme=names_to_scheme
             )
             # TODO: all weight quantization params will be moved to the compressor

src/compressed_tensors/config/base.py

@@ -32,6 +32,7 @@ class CompressionFormat(Enum):
     naive_quantized = "naive-quantized"
     pack_quantized = "pack-quantized"
     marlin_24 = "marlin-24"
+    mixed_precision = "mixed-precision"
     nvfp4_pack_quantized = "nvfp4-pack-quantized"
 
 

src/compressed_tensors/quantization/quant_config.py

@@ -234,6 +234,12 @@ def from_pretrained(
                 format = CompressionFormat.int_quantized.value
             else:
                 format = CompressionFormat.dense.value
+        elif isinstance(format, list):
+            format = (
+                CompressionFormat.mixed_precision.value
+                if len(format) > 1
+                else format[0]
+            )
 
         return QuantizationConfig(
             config_groups=config_groups,

src/compressed_tensors/quantization/quant_scheme.py

@@ -16,6 +16,7 @@
 from copy import deepcopy
 from typing import List, Optional
 
+from compressed_tensors.config import CompressionFormat
 from compressed_tensors.quantization.quant_args import (
     DynamicType,
     QuantizationArgs,
@@ -42,12 +43,14 @@ class QuantizationScheme(BaseModel):
     :param weights: quantization config for layer weights
     :param input_activations: quantization config for layer inputs
     :param output_activations: quantization config for layer outputs
+    :param format: CompressionFormat for the layer
     """
 
     targets: List[str]
     weights: Optional[QuantizationArgs] = None
     input_activations: Optional[QuantizationArgs] = None
     output_activations: Optional[QuantizationArgs] = None
+    format: Optional[str] = None
 
     @model_validator(mode="after")
     def validate_model_after(model: "QuantizationScheme") -> "QuantizationScheme":

tests/test_compressors/model_compressors/test_model_compressor.py

@@ -20,8 +20,12 @@
 import torch
 import torch.nn as nn
 from compressed_tensors.compressors import ModelCompressor
-from compressed_tensors.config import SparsityCompressionConfig
-from compressed_tensors.quantization import QuantizationConfig
+from compressed_tensors.config import CompressionFormat, SparsityCompressionConfig
+from compressed_tensors.quantization import (
+    QuantizationArgs,
+    QuantizationConfig,
+    QuantizationScheme,
+)
 from safetensors.torch import save_file
 from tests.testing_utils import induce_sparsity, requires_hf_quantizer
 from transformers import AutoModelForCausalLM
@@ -395,7 +399,7 @@ def _get_combined_config(s_config, q_config):
 )
 def test_compress_model(model_stub, q_format, s_config, tmpdir):
     model = AutoModelForCausalLM.from_pretrained(model_stub, torch_dtype=torch.float32)
-    compressor = ModelCompressor.from_pretrained_model(model, s_config, q_format)
+    compressor = ModelCompressor.from_pretrained_model(model, s_config, [q_format])
 
     # compress model by eagerly compressing state dict
     true_compressed = dict(compressor.compress(model))
@@ -443,7 +447,7 @@ def test_compress_model_meta(model_stub, q_format, s_config):
         model_stub, torch_dtype=torch.float32
     )
     reference_compressor = ModelCompressor.from_pretrained_model(
-        cpu_model, s_config, q_format
+        cpu_model, s_config, [q_format]
     )
     # Only stores dtype because meta model does not store values
     expected = {k: v.dtype for k, v in reference_compressor.compress(cpu_model).items()}
@@ -459,7 +463,7 @@ def test_compress_model_meta(model_stub, q_format, s_config):
             module.to_empty(device="meta")
 
     # Compress in-place on meta model
-    compressor = ModelCompressor.from_pretrained_model(meta_model, s_config, q_format)
+    compressor = ModelCompressor.from_pretrained_model(meta_model, s_config, [q_format])
     compressor.compress_model(meta_model)
 
     # Compare keys and dtypes
@@ -469,6 +473,43 @@ def test_compress_model_meta(model_stub, q_format, s_config):
         assert compressed[key].dtype == dtype, f"{key} has incorrect dtype"
 
 
+def test_multiple_quant_compressors():
+    model = torch.nn.Sequential(torch.nn.Linear(1, 2), torch.nn.Linear(2, 3))
+    input_activations = QuantizationArgs(num_bits=8, type="float")
+    weights = QuantizationArgs(num_bits=8, type="float")
+
+    scheme_fp8 = QuantizationScheme(
+        targets=["Linear"],
+        weights=weights,
+        input_activations=input_activations,
+        format=CompressionFormat.float_quantized.value,
+    )
+
+    input_activations = QuantizationArgs(num_bits=4, type="float")
+    weights = QuantizationArgs(num_bits=4, type="float")
+
+    scheme_nvfp4 = QuantizationScheme(
+        targets=["Linear"],
+        weights=weights,
+        input_activations=input_activations,
+        format=CompressionFormat.nvfp4_pack_quantized.value,
+    )
+
+    model[0].quantization_scheme = scheme_fp8
+    model[0].quantization_status = "frozen"
+    model[1].quantization_scheme = scheme_nvfp4
+    model[1].quantization_status = "frozen"
+
+    formats = [scheme_fp8.format, scheme_nvfp4.format]
+
+    compressor = ModelCompressor.from_pretrained_model(model, None, formats)
+    assert isinstance(compressor.quantization_compressor, dict)
+    assert (
+        compressor.quantization_config.format == CompressionFormat.mixed_precision.value
+    )
+    assert all(format in compressor.quantization_compressor for format in formats)
+
+
 @pytest.mark.parametrize(
     "model_stub,comp_stub",
     [

tests/test_quantization/test_quant_scheme.py

@@ -26,24 +26,27 @@ def test_basic_scheme():
     assert scheme.weights == weights
     assert scheme.input_activations is None
     assert scheme.output_activations is None
+    assert scheme.format is None
 
 
 def test_full_scheme():
     targets = ["Linear"]
     weights = QuantizationArgs()
-    input_activations = QuantizationArgs(num_bits=4)
+    input_activations = QuantizationArgs(num_bits=8)
     output_activations = QuantizationArgs(num_bits=8, type="float", symmetric=False)
 
     scheme = QuantizationScheme(
         targets=targets,
         weights=weights,
         input_activations=input_activations,
         output_activations=output_activations,
+        format="float-quantized",
     )
     assert scheme.targets == targets
     assert scheme.weights == weights
     assert scheme.input_activations == input_activations
     assert scheme.output_activations == output_activations
+    assert scheme.format is "float-quantized"
 
 
 def test_needs_targets():
@@ -57,3 +60,4 @@ def test_defaults():
     assert output.weights is None
     assert output.input_activations is None
     assert output.output_activations is None
+    assert output.format is None