Add static quantization as an example for calibration flow (pytorch#487)

Summary:
So far quantization flow API that we provided (`quantize_`) does not require calibration (calibrate a model with sample data), this PR added a static quantization
example that serves as an example for calibration flow

* 1. first prepare the model for calibration
* 2. calibrate the prepared model with sample data
* 3. convert the calibrated model to quantized model

Test Plan:
python torchao/prototype/calibration_flow/static_quant.py

Reviewers:

Subscribers:

Tasks:

Tags:

test/dtypes/test_affine_quantized.py

@@ -14,10 +14,12 @@ class TestAffineQuantized(TestCase):
     @unittest.skipIf(not torch.cuda.is_available(), "Need CUDA available")
     @unittest.skipIf(TORCH_VERSION_AFTER_2_5, "int4 skipping 2.5+ for now")
     def test_tensor_core_layout_transpose(self):
-        t = torch.rand(128, 256, dtype=torch.bfloat16, device="cuda")
+        l = torch.nn.Linear(128, 256, dtype=torch.bfloat16, device="cuda")
+        t = l.weight
         shape = t.shape
         apply_int4_weight_only_quant = int4_weight_only(group_size=32)
-        aqt = apply_int4_weight_only_quant(t)
+        ql = apply_int4_weight_only_quant(l)
+        aqt = ql.weight
         aqt_shape = aqt.shape
         self.assertEqual(aqt_shape, shape)
 

torchao/dtypes/__init__.py

@@ -4,6 +4,7 @@
 from .affine_quantized_tensor import (
     AffineQuantizedTensor,
     to_affine_quantized,
+    to_affine_quantized_static,
     LayoutType,
     PlainLayoutType,
     TensorCoreTiledLayoutType,
@@ -15,6 +16,7 @@
     "UInt4Tensor"
     "AffineQuantizedTensor",
     "to_affine_quantized",
+    "to_affine_quantized_static",
     "LayoutType",
     "PlainLayoutType",
     "TensorCoreTiledLayoutType",

torchao/dtypes/affine_quantized_tensor.py

@@ -232,6 +232,7 @@ def from_float(
 
         scale, zero_point = choose_qparams_affine(input_float, mapping_type, block_size, target_dtype, quant_min, quant_max, eps, scale_dtype, zero_point_dtype, preserve_zero, zero_point_domain)
         int_data = quantize_affine(input_float, block_size, scale, zero_point, target_dtype, quant_min, quant_max, zero_point_domain)
+
         int_data = layout_type.post_process(int_data)
 
         layout_tensor_ctr = get_layout_tensor_constructor(type(layout_type))
@@ -246,8 +247,40 @@ def from_float(
             dtype=input_float.dtype
         )
 
+    @classmethod
+    def from_float_static(
+        cls,
+        input_float: torch.Tensor,
+        scale: torch.Tensor,
+        zero_point: torch.Tensor,
+        block_size: Tuple[int, ...],
+        target_dtype: torch.dtype,
+        quant_min: Optional[int] = None,
+        quant_max: Optional[int]  = None,
+        zero_point_domain: ZeroPointDomain = ZeroPointDomain.INT,
+        layout_type: LayoutType = PlainLayoutType(),
+    ):
+        original_shape = input_float.shape
+        input_float = layout_type.pre_process(input_float)
+
+        int_data = quantize_affine(input_float, block_size, scale, zero_point, target_dtype, quant_min, quant_max, zero_point_domain)
+
+        int_data = layout_type.post_process(int_data)
+
+        layout_tensor_ctr = get_layout_tensor_constructor(type(layout_type))
+        layout_tensor = layout_tensor_ctr(int_data, scale, zero_point, layout_type)
+        return cls(
+            layout_tensor,
+            block_size,
+            original_shape,
+            quant_min,
+            quant_max,
+            zero_point_domain,
+            dtype=input_float.dtype,
+        )
+
     @property
-    def layout_type(self) -> str:
+    def layout_type(self) -> LayoutType:
         return self.layout_tensor.layout_type
 
     @classmethod
@@ -809,3 +842,4 @@ def t(func, *args, **kwargs):
     return return_and_correct_aliasing(func, args, kwargs, new)
 
 to_affine_quantized = AffineQuantizedTensor.from_float
+to_affine_quantized_static = AffineQuantizedTensor.from_float_static

torchao/prototype/quant_llm/quant_llm.py

@@ -7,6 +7,7 @@
 from torchao.prototype.custom_fp_utils import _f32_to_fpx_unpacked, _fpx_unpacked_to_f32, _n_ones
 from torchao.ops import quant_llm_linear
 from torchao.dtypes.utils import _implements, _ATEN_OP_OR_TORCH_FN_TABLE
+from torchao.quantization.quant_api import _get_linear_subclass_inserter
 
 
 _ONES_TABLE = [_n_ones(i) for i in range(8)]
@@ -456,8 +457,8 @@ def apply_quant_llm(weight: Tensor) -> Tensor:
         if (in_dim % 64 != 0) or (out_dim % 256 != 0):
             return weight
         return QuantLlmLinearWeight.from_float(weight, ebits, mbits)
-    return apply_quant_llm
+    return _get_linear_subclass_inserter(apply_quant_llm)
 
 
 def fp6_llm_weight_only():
-    return quant_llm_fpx_weight_only(3, 2)
+    return _get_linear_subclass_inserter(quant_llm_fpx_weight_only(3, 2))

torchao/quantization/quant_api.py

@@ -259,12 +259,12 @@ def insert_subclass(lin):
 
     return insert_subclass
 
-def quantize_(model: torch.nn.Module, apply_tensor_subclass: Callable[[torch.Tensor], torch.Tensor], filter_fn: Optional[Callable[[torch.nn.Module, str], bool]]=None, set_inductor_config: bool=True):
+def quantize_(model: torch.nn.Module, apply_tensor_subclass: Callable[[torch.nn.Module], torch.nn.Module], filter_fn: Optional[Callable[[torch.nn.Module, str], bool]]=None, set_inductor_config: bool=True):
     """Convert the weight of linear modules in the model with `apply_tensor_subclass`, model is modified inplace
 
     Args:
         model (torch.nn.Module): input model
-        apply_tensor_subclass (Callable[[torch.Tensor], torch.Tensor]): function that convert a floating point Tensor to a (quantized) tensor subclass instance (e.g. affine quantized tensor instance)
+        apply_tensor_subclass (Callable[[torch.nn.Module], torch.nn.Module]): function that applies tensor subclass conversion to the weight of a module and return the module (e.g. convert the weight tensor of linear to affine quantized tensor)
         filter_fn (Optional[Callable[[torch.nn.Module, str], bool]]): function that takes a nn.Module instance and fully qualified name of the module, returns True if we want to run `apply_tensor_subclass` on
         the weight of the module
         set_inductor_config (bool, optional): Whether to automatically use recommended inductor config settings (defaults to True)
@@ -300,19 +300,24 @@ def quantize_(model: torch.nn.Module, apply_tensor_subclass: Callable[[torch.Ten
           x, "asymmetric", (1, groupsize), torch.int32, 0, 15, 1e-6,
           zero_point_dtype=torch.bfloat16, preserve_zero=False, zero_point_domain="float")
 
+        def apply_weight_quant_to_linear(linear):
+            linear.weight = torch.nn.Parameter(apply_weight_quant(linear.weight), requires_grad=False)
+            return linear
+
         # apply to modules under block0 submodule
         def filter_fn(module: nn.Module, fqn: str) -> bool:
             return isinstance(module, nn.Linear)
 
         m = nn.Sequential(nn.Linear(32, 1024), nn.Linear(1024, 32))
-        quantize_(m, apply_weight_quant, filter_fn)
+        quantize_(m, apply_weight_quant_to_linear, filter_fn)
 
     """
     if set_inductor_config:
         torchao.quantization.utils.recommended_inductor_config_setter()
+
     _replace_with_custom_fn_if_matches_filter(
         model,
-        _get_linear_subclass_inserter(apply_tensor_subclass),
+        apply_tensor_subclass,
         _is_linear if filter_fn is None else filter_fn,
     )
 
@@ -356,7 +361,7 @@ def get_per_token_block_size(x):
         weight = to_linear_act_quantized(weight, input_quant_func)
         return weight
 
-    return apply_int8_dynamic_activation_int4_weight_quant
+    return _get_linear_subclass_inserter(apply_int8_dynamic_activation_int4_weight_quant)
 
 
 def int4_weight_only(group_size=128, inner_k_tiles=8):
@@ -394,7 +399,7 @@ def apply_int4_weight_only_quant(weight):
         layout_type = TensorCoreTiledLayoutType(inner_k_tiles=inner_k_tiles)
         return to_affine_quantized(weight, mapping_type, block_size, target_dtype, quant_min, quant_max, eps, zero_point_dtype=zero_point_dtype, preserve_zero=preserve_zero, zero_point_domain=zero_point_domain, layout_type=layout_type)
 
-    return apply_int4_weight_only_quant
+    return _get_linear_subclass_inserter(apply_int4_weight_only_quant)
 
 
 def int8_weight_only():
@@ -412,7 +417,7 @@ def apply_int8wo_quant(weight):
         block_size = (1, weight.shape[1])
         return to_affine_quantized(weight, mapping_type, block_size, target_dtype, eps=eps, zero_point_dtype=zero_point_dtype)
 
-    return apply_int8wo_quant
+    return _get_linear_subclass_inserter(apply_int8wo_quant)
 
 def int8_dynamic_activation_int8_weight():
     """
@@ -454,4 +459,4 @@ def get_per_token_block_size(x):
         weight = to_linear_act_quantized(weight, input_quant_func)
         return weight
 
-    return apply_int8_dynamic_activation_int8_weight_quant
+    return _get_linear_subclass_inserter(apply_int8_dynamic_activation_int8_weight_quant)

tutorials/calibration_flow/static_quant.py

@@ -0,0 +1,145 @@
+"""
+Demo for static quantization flow
+"""
+import torch
+import copy
+
+# TODO: use the generalized observer for affine qunatization in the future
+from torch.ao.quantization.observer import MinMaxObserver, PerChannelMinMaxObserver
+import torch.nn.functional as F
+from torch import Tensor
+from torchao.dtypes import to_affine_quantized_static
+from torchao.quantization.utils import compute_error
+from torchao.quantization import quantize_
+from torchao.quantization.subclass import to_linear_act_quantized
+from torchao.quantization.quant_api import _replace_with_custom_fn_if_matches_filter
+
+
+
+class ObservedLinear(torch.nn.Linear):
+    def __init__(self, in_features: int, out_features: int, act_obs: torch.nn.Module, weight_obs: torch.nn.Module, bias: bool = True, device=None, dtype=None):
+        super().__init__(in_features, out_features, bias, device, dtype)
+        self.act_obs = act_obs
+        self.weight_obs = weight_obs
+
+    def forward(self, input: Tensor):
+        observed_input = self.act_obs(input)
+        observed_weight = self.weight_obs(self.weight)
+        return F.linear(observed_input, observed_weight, self.bias)
+
+    @classmethod
+    def from_float(cls, float_linear, act_obs, weight_obs):
+        observed_linear = cls(float_linear.in_features, float_linear.out_features, act_obs, weight_obs, False, device=float_linear.weight.device, dtype=float_linear.weight.dtype)
+        observed_linear.weight = float_linear.weight
+        observed_linear.bias = float_linear.bias
+        return observed_linear
+
+def insert_observers_(model, act_obs, weight_obs):
+    _is_linear = lambda m, fqn: isinstance(m, torch.nn.Linear)
+    replacement_fn = lambda m: ObservedLinear.from_float(m, act_obs, weight_obs)
+    act_obs = copy.deepcopy(act_obs)
+    weight_obs = copy.deepcopy(weight_obs)
+    _replace_with_custom_fn_if_matches_filter(model, replacement_fn, _is_linear)
+
+# converting observed linear module to linear module with quantzied weights (and quantized activations)
+# with tensor subclasses
+def apply_static_quant(observed_linear):
+    target_dtype = torch.uint8
+
+    # weight quantization
+    weight_scale, weight_zero_point = observed_linear.weight_obs.calculate_qparams()
+    def weight_quant_func(weight):
+        block_size = (1, weight.shape[1])
+        return to_affine_quantized_static(weight, weight_scale, weight_zero_point, block_size, target_dtype)
+    linear = torch.nn.Linear(observed_linear.in_features, observed_linear.out_features, False, device=observed_linear.weight.device, dtype=observed_linear.weight.dtype)
+    linear.weight = observed_linear.weight
+    linear.bias = observed_linear.bias
+
+    linear.weight = torch.nn.Parameter(weight_quant_func(linear.weight), requires_grad=False)
+
+    # activation quantization
+    act_scale, act_zero_point = observed_linear.act_obs.calculate_qparams()
+    input_quant_func = lambda x: to_affine_quantized_static(x, act_scale, act_zero_point, x.shape, target_dtype)
+    linear.weight = torch.nn.Parameter(to_linear_act_quantized(linear.weight, input_quant_func), requires_grad=False)
+
+    return linear
+
+
+# alternative for converting observed linear module to quantized linear module
+class QuantizedLinear(torch.nn.Module):
+    def __init__(self, in_features: int, out_features: int, act_obs: torch.nn.Module, weight_obs: torch.nn.Module, weight: torch.Tensor, bias: torch.Tensor):
+        super().__init__()
+        self.act_scale, self.act_zero_point = act_obs.calculate_qparams()
+        weight_scale, weight_zero_point = weight_obs.calculate_qparams()
+        assert weight.dim() == 2
+        block_size = (1, weight.shape[1])
+        target_dtype = torch.uint8
+        self.qweight = to_affine_quantized_static(weight, weight_scale, weight_zero_point, block_size, target_dtype)
+        self.bias = bias
+
+    def forward(self, input: Tensor):
+        block_size = input.shape
+        target_dtype = torch.uint8
+        qinput = to_affine_quantized_static(input, self.act_scale, self.act_zero_point, block_size, target_dtype)
+        return F.linear(qinput, self.qweight, self.bias)
+
+    @classmethod
+    def from_observed(cls, observed_linear):
+        quantized_linear = cls(observed_linear.in_features, observed_linear.out_features, observed_linear.act_obs, observed_linear.weight_obs, observed_linear.weight, observed_linear.bias)
+        return quantized_linear
+
+def apply_static_quant2(observed_linear):
+    return QuantizedLinear.from_observed(observed_linear)
+
+class ToyLinearModel(torch.nn.Module):
+    def __init__(self, m=64, n=32, k=64):
+        super().__init__()
+        self.linear1 = torch.nn.Linear(m, n, bias=False)
+        self.linear2 = torch.nn.Linear(n, k, bias=False)
+
+    def example_inputs(self, batch_size=1, dtype=torch.float32, device="cpu"):
+        return (torch.randn(batch_size, self.linear1.in_features, dtype=dtype, device=device),)
+
+    def forward(self, x):
+        x = self.linear1(x)
+        x = self.linear2(x)
+        return x
+
+dtype = torch.bfloat16
+m = ToyLinearModel(1024, 1024, 1024).eval().to(dtype).to("cuda")
+m_bf16 = copy.deepcopy(m)
+example_inputs = m.example_inputs(dtype=dtype, device="cuda")
+
+m_bf16 = torch.compile(m_bf16, mode='max-autotune')
+
+# TODO: use the generalized observer for affine qunatization in the future
+act_obs = MinMaxObserver(dtype=torch.uint8, qscheme=torch.per_tensor_affine).to("cuda")
+weight_obs = PerChannelMinMaxObserver(dtype=torch.uint8, qscheme=torch.per_channel_affine).to("cuda")
+
+before_quant = m(*example_inputs)
+
+insert_observers_(m, act_obs, weight_obs)
+# calibrating / training
+for _ in range(10):
+    m(*example_inputs)
+
+after_obs = m(*example_inputs)
+
+m2 = copy.deepcopy(m)
+
+is_observed_linear = lambda m, fqn: isinstance(m, ObservedLinear)
+
+# quantized linear represented as an nn.Linear with modified tensor subclass weights
+# for both activation and weight quantization
+quantize_(m, apply_static_quant, is_observed_linear)
+print("quantized model (applying tensor subclass to weight):", m)
+after_quant = m(*example_inputs)
+assert compute_error(before_quant, after_quant) > 30
+print("test passed")
+
+# quantized linear as a standalone module
+quantize_(m2, apply_static_quant2, is_observed_linear)
+print("quantized model (quantized module):", m2)
+after_quant = m2(*example_inputs)
+assert compute_error(before_quant, after_quant) > 30
+print("test passed")