Use torch.uint1 to torch.uint7 for Uintx tensor subclass

Summary:
Previously we are using bit_width for uintx quantization, but we can actually use `dtype` directly.

But there are still some workaround to convert from torch dtype to bit_width right now, if we want to remove
all the hacks, we'd need to support Uintx tensor subclass properly and have `torch.uintx` dispatch to the tensor subclass
this is probably not the highest priority for now since good perf is more important.

Test Plan:
python test/dtypes/test_affine_quantized.py
pytest test/dtypes/test_uintx.py

Reviewers:

Subscribers:

Tasks:

Tags:

test/dtypes/test_affine_quantized.py

@@ -9,13 +9,17 @@
     int8_dynamic_activation_int8_weight,
     int8_dynamic_activation_int8_semi_sparse_weight,
 )
+from torchao.dtypes import (
+    to_affine_quantized,
+)
 import torch
 import unittest
 import tempfile
 from torchao.utils import (
+    TORCH_VERSION_AFTER_2_3,
     TORCH_VERSION_AFTER_2_5,
 )
-
+from torchao.dtypes.uintx.Uintx import _DTYPE_TO_BIT_WIDTH
 
 class TestAffineQuantized(TestCase):
     @unittest.skipIf(not torch.cuda.is_available(), "Need CUDA available")
@@ -51,6 +55,45 @@ def test_weights_only(self):
                 else:
                     _ = torch.load(f, weights_only=False)
 
+    @unittest.skipIf(not torch.cuda.is_available(), "Need CUDA available")
+    @unittest.skipIf(not TORCH_VERSION_AFTER_2_3, "sub byte dtype requires torch 2.3+")
+    def test_uintx_target_dtype(self):
+        from torchao.quantization.quant_api import uintx_weight_only
+        for dtype in _DTYPE_TO_BIT_WIDTH.keys():
+            l = torch.nn.Linear(128, 256, dtype=torch.bfloat16, device="cuda")
+            # make sure it runs
+            uintx_weight_only(dtype)(l)
+            l = torch.compile(l)
+            l(torch.randn(1, 128, dtype=torch.bfloat16, device="cuda"))
+
+
+    @unittest.skipIf(not torch.cuda.is_available(), "Need CUDA available")
+    @unittest.skipIf(not TORCH_VERSION_AFTER_2_3, "sub byte dtype requires torch 2.3+")
+    def test_uintx_model_size(self):
+        from torchao.quantization.quant_api import uintx_weight_only
+        from torchao.utils import get_model_size_in_bytes
+        # scale size = 1/64 * 2 bytes = 1/32 bytes
+        # zero_point size = 1/64 * 4 bytes = 1/16 bytes
+        # dtype data size = 1 * bit_width/8 = bit_width/8 bytes
+        _dtype_to_ratio = {
+            torch.uint1: (1/8 + 1/16 + 1/32) / 2,
+            torch.uint2: (2/8 + 1/16 + 1/32) / 2,
+            torch.uint3: (3/8 + 1/16 + 1/32) / 2,
+            torch.uint4: (4/8 + 1/16 + 1/32) / 2,
+            torch.uint5: (5/8 + 1/16 + 1/32) / 2,
+            torch.uint6: (6/8 + 1/16 + 1/32) / 2,
+            torch.uint7: (7/8 + 1/16 + 1/32) / 2,
+        }
+        for dtype in _DTYPE_TO_BIT_WIDTH.keys():
+            l = torch.nn.Sequential(
+                torch.nn.Linear(128, 256, bias=False, dtype=torch.bfloat16, device="cuda")
+            )
+            bf16_size = get_model_size_in_bytes(l)
+            # make sure it runs
+            uintx_weight_only(dtype)(l[0])
+            quantized_size = get_model_size_in_bytes(l)
+            self.assertTrue(bf16_size * _dtype_to_ratio[dtype] == quantized_size)
 
 if __name__ == "__main__":
     run_tests()
+>

test/dtypes/test_uintx.py

@@ -6,7 +6,10 @@
 
 from torchao.dtypes.uintx.Uintx import to_uintx
 from torchao.quantization.quant_api import quantize_, uintx_weight_only
-from torchao.utils import TORCH_VERSION_AFTER_2_5
+from torchao.utils import (
+    TORCH_VERSION_AFTER_2_3,
+    TORCH_VERSION_AFTER_2_5,
+)
 
 from torchao.quantization.quant_primitives import (
     MappingType,
@@ -16,7 +19,12 @@
     dequantize_affine,
 )
 
-bit_widths = (1, 2, 3, 4, 5, 6, 7)
+# torch.uintx dtypes are introduced in 2.3
+if TORCH_VERSION_AFTER_2_3:
+    dtypes = (torch.uint1, torch.uint2, torch.uint3, torch.uint4, torch.uint5, torch.uint6, torch.uint7)
+else:
+    dtypes = ()
+
 group_sizes = [32, 64, 128]
 devices = ["cpu", "cuda"]
 @pytest.fixture(autouse=True)
@@ -36,57 +44,51 @@ def __init__(self, scale, device):
     def forward(self, x):
         return self.net(x)
 
-@pytest.mark.parametrize("bit_width", bit_widths)
+@pytest.mark.parametrize("dtype", dtypes)
 @pytest.mark.parametrize("group_size", group_sizes)
 @pytest.mark.parametrize("device", devices)
 @pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA not available")
 @pytest.mark.skipif(not TORCH_VERSION_AFTER_2_5, reason="only works with fix in the nightly build")
-def test_uintx_weight_only_model_quant(bit_width, group_size, device):
+def test_uintx_weight_only_model_quant(dtype, group_size, device):
     scale = 512
     fp16 = Linear16(scale, device)
-    quantize_(fp16, uintx_weight_only(bit_width, group_size=group_size))
+    quantize_(fp16, uintx_weight_only(dtype, group_size=group_size))
     uintx = torch.compile(fp16, fullgraph=True)
     test_input = torch.randn(scale*2, dtype=torch.float16, device=device)
     output = uintx.forward(test_input)
     assert output != None, "model quantization failed"
 
-@pytest.mark.parametrize("bit_width", bit_widths)
+@pytest.mark.parametrize("dtype", dtypes)
 @pytest.mark.parametrize("group_size", group_sizes)
 @pytest.mark.parametrize("device", devices)
 @pytest.mark.skipif(not torch.cuda.is_available(), reason="CUDA not available")
 @pytest.mark.skipif(not TORCH_VERSION_AFTER_2_5, reason="only works with fix in the nightly build")
-def test_uintx_weight_only_quant(bit_width, group_size, device):
+def test_uintx_weight_only_quant(dtype, group_size, device):
     input_float = torch.randn((1, 256), dtype=torch.float16, device = device)
     mapping_type = MappingType.SYMMETRIC
-    quant_min = 0
-    quant_max = 2 ** bit_width - 1
     eps = torch.finfo(torch.float32).eps
     zero_point_dtype = torch.int32
     zero_point_domain = ZeroPointDomain.INT
-    target_dtype = torch.uint8
     block_size = (1, group_size)
 
     scale, zero_point = choose_qparams_affine(
         input_float, mapping_type, block_size,
-        target_dtype, quant_min, quant_max, eps, torch.float32,
-        zero_point_dtype, True, zero_point_domain
+        dtype, eps=eps, scale_dtype=torch.float32,
+        zero_point_dtype=zero_point_dtype, preserve_zero=True, zero_point_domain=zero_point_domain
     )
 
     aqt = quantize_affine(
         input_float, block_size, scale,
-        zero_point, target_dtype,
-        quant_min = quant_min,
-        quant_max = quant_max,
-        zero_point_domain = zero_point_domain
+        zero_point, dtype,
+        zero_point_domain=zero_point_domain
     )
+    # Note: output will be uint8 tensor for sub byte tensors for now
 
-    q =  to_uintx(aqt, bit_width, -1)
+    q =  to_uintx(aqt, dtype, -1)
     assert q != None, "quantization failed"
     deqaunt = dequantize_affine(
         q, block_size, scale,
-        zero_point, target_dtype,
-        quant_min = quant_min,
-        quant_max = quant_max,
-        zero_point_domain = zero_point_domain
+        zero_point, dtype,
+        zero_point_domain=zero_point_domain
     )
     assert deqaunt != None, "deqauntization failed"

torchao/dtypes/affine_quantized_tensor.py

@@ -30,6 +30,7 @@
 
 aten = torch.ops.aten
 
+
 ###############################
 # Base Layout Tensor Subclass #
 ###############################
@@ -200,6 +201,7 @@ 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)
+        # Note: output will be uint8 tensor for sub byte tensors for now
         int_data = layout_type.post_process(int_data)
 
         layout_tensor_ctr = get_layout_tensor_constructor(type(layout_type))

torchao/dtypes/uintx/Uintx.py

@@ -11,10 +11,30 @@
     _dispatch__torch_dispatch__,
 )
 from torchao.dtypes.affine_quantized_tensor import PlainAQTLayout, register_layout_cls
-
+from torchao.utils import TORCH_VERSION_AFTER_2_3
 
 aten = torch.ops.aten
 
+# Note: Uintx does not work for torch 2.3 and below
+_DTYPE_TO_BIT_WIDTH = {}
+_BIT_WIDTH_TO_DTYPE = {}
+
+if TORCH_VERSION_AFTER_2_3:
+    _DTYPE_TO_BIT_WIDTH = {
+        torch.uint1: 1,
+        torch.uint2: 2,
+        torch.uint3: 3,
+        torch.uint4: 4,
+        torch.uint5: 5,
+        torch.uint6: 6,
+        torch.uint7: 7,
+    }
+
+    _BIT_WIDTH_TO_DTYPE = {v: k for k, v in _DTYPE_TO_BIT_WIDTH.items()}
+else:
+    print("uintx feature need torch 2.3+, please upgrade pytorch")
+
+
 class UintxTensor(torch.Tensor):
     """
     Splits int data into packed shards based on bit size
@@ -90,15 +110,18 @@ def get_plain(self):
     def apply_transformation(self, fn):
         og = self.get_plain()
         new = fn(og)
-        return self.from_uint8(new, self.bit_width, self.pack_dim)
+        dtype = _BIT_WIDTH_TO_DTYPE[self.bit_width]
+        return self.from_uint8(new, dtype, self.pack_dim)
 
     # temporary until kernels on packed tensors are created
     def apply_fn_to_shards(self, fn):
         new_shards = [fn(shard) for shard in self.get_shards()]
         return self.__class__(new_shards, self.packed_shape, self.bit_width, self.pack_dim)
 
     @classmethod
-    def from_uint8(cls, int_data: torch.Tensor, bit_width, pack_dim: int = -1):
+    def from_uint8(cls, int_data: torch.Tensor, dtype: torch.dtype, pack_dim: int = -1):
+        assert dtype in _DTYPE_TO_BIT_WIDTH.keys(), "Expected dtype to be one of {_DTYPE_TO_BITWIDTH.keys()}"
+        bit_width = _DTYPE_TO_BIT_WIDTH[dtype]
         shards = pack(int_data, bit_width, dim=pack_dim)
         shape = list(int_data.shape)
         shape[pack_dim] = shape[pack_dim] * bit_width // 8
@@ -107,7 +130,6 @@ def from_uint8(cls, int_data: torch.Tensor, bit_width, pack_dim: int = -1):
 
 implements = UintxTensor.implements
 
-
 @implements(aten.detach.default)
 def _(func, types, args, kwargs):
     return return_and_correct_aliasing(
@@ -137,16 +159,17 @@ def _(func, types, args, kwargs):
     return return_and_correct_aliasing(
         func, args, kwargs, args[0].apply_transformation(lambda x: (x * args[1]).to(torch.uint8))
     )
+
 # quantization api integrations
 to_uintx = UintxTensor.from_uint8
 
 @dataclass(frozen=True)
 class UintxLayoutType(LayoutType):
-    bit_width: int
+    dtype: torch.dtype
     pack_dim: int = -1
 
     def post_process(self, input: torch.Tensor) -> torch.Tensor:
-        return to_uintx(input, self.bit_width, self.pack_dim)
+        return to_uintx(input, self.dtype, self.pack_dim)
 
 @register_layout_cls(UintxLayoutType)
 class UintxAQTLayout(PlainAQTLayout):

torchao/quantization/quant_api.py

@@ -483,36 +483,36 @@ def int8_dynamic_activation_int8_semi_sparse_weight():
     return int8_dynamic_activation_int8_weight(layout_type=SemiSparseLayoutType())
 
 
-def uintx_weight_only(bit_width, group_size=64, pack_dim=-1):
+def uintx_weight_only(dtype, group_size=64, pack_dim=-1):
     """
     Applies uintx weight-only asymmetric per-group quantization to linear layers, using uintx quantization where
-    x is the number of bits specified by the `bit_width` argument
+    x is the number of bits specified by `dtype`
+
+    Args:
+        `dtype`: torch.uint1 to torch.uint7 sub byte dtypes
+        `group_size`: parameter for quantization, controls the granularity of quantization, smaller
+         size is more fine grained, defaults to 64
+        `pack_dim`: the dimension we use for packing, defaults to -1
     """
     from torchao.quantization.quant_primitives import (
         MappingType,
         ZeroPointDomain,
-        choose_qparams_affine,
-        quantize_affine,
-        dequantize_affine,
     )
     from torchao.dtypes.uintx.Uintx import UintxLayoutType
     from torchao.dtypes import to_affine_quantized
     from torchao.quantization.quant_api import _get_linear_subclass_inserter
-    def apply_uintx_weight_only_quant(weight):
 
-        layout_type = UintxLayoutType(bit_width=bit_width, pack_dim=pack_dim)
+    def apply_uintx_weight_only_quant(weight):
+        layout_type = UintxLayoutType(dtype=dtype, pack_dim=pack_dim)
         mapping_type = MappingType.ASYMMETRIC
         block_size = (1, group_size)
-        quant_min = 0
-        quant_max = 2**bit_width - 1
         eps = torch.finfo(torch.float32).eps
         zero_point_dtype = torch.int32
         zero_point_domain = ZeroPointDomain.INT
 
         return to_affine_quantized(
-            weight, mapping_type, block_size, torch.uint8,
-            quant_min = quant_min, quant_max = quant_max,
-            eps = eps, zero_point_dtype=zero_point_dtype,
+            weight, mapping_type, block_size, dtype,
+            eps=eps, zero_point_dtype=zero_point_dtype,
             zero_point_domain=zero_point_domain,
             layout_type=layout_type,
         )

torchao/quantization/quant_primitives.py

@@ -65,17 +65,21 @@ class ZeroPointDomain(Enum):
     torch.int16: (-(2**15), 2**15 - 1),
     torch.int32: (-(2**31), 2**31 - 1),
 }
+_SUB_BYTE_DTYPE_BOUNDS: Dict[torch.dtype, Tuple[int, int]] = {}
 
 if TORCH_VERSION_AFTER_2_3:
-    _DTYPE_TO_QVALUE_BOUNDS.update({
+    _SUB_BYTE_DTYPE_BOUNDS = {
         torch.uint1: (0, 2**1-1),
         torch.uint2: (0, 2**2-1),
         torch.uint3: (0, 2**3-1),
         torch.uint4: (0, 2**4-1),
         torch.uint5: (0, 2**5-1),
         torch.uint6: (0, 2**6-1),
         torch.uint7: (0, 2**7-1),
-    })
+    }
+    _DTYPE_TO_QVALUE_BOUNDS.update(
+        _SUB_BYTE_DTYPE_BOUNDS
+    )
 
 
 quant_lib = torch.library.Library("quant", "FRAGMENT")
@@ -213,6 +217,10 @@ def _quantize_affine(
     """op definition that has compatible signatures with custom op library
     """
     quant_min, quant_max = _get_and_check_qmin_qmax(output_dtype, quant_min, quant_max)
+    # workaround for uintx dtypes, since we don't have native Uintx dtype connected with
+    # torch.uintx dtypes yet
+    if output_dtype in _SUB_BYTE_DTYPE_BOUNDS:
+        output_dtype = torch.uint8
     return _quantize_affine_no_dtype_cast(
         input,
         block_size,
@@ -325,10 +333,9 @@ def _dequantize_affine(
 ) -> torch.Tensor:
     """op definition that has compatible signatures with custom op library
     """
-
-    # TODO: validations
     # TODO: validate scale/zero_point dimensions are compatible with block_size
-    assert input.dtype == input_dtype, f"Expected: {input_dtype}, got: {input.dtype}"
+    if input_dtype not in _SUB_BYTE_DTYPE_BOUNDS:
+        assert input.dtype == input_dtype, f"Expected: {input_dtype}, got: {input.dtype}"
     assert output_dtype in [torch.float32, torch.float16, torch.bfloat16], f"Unsupported output dtype: {output_dtype}"
     quant_min, quant_max = _get_and_check_qmin_qmax(input_dtype, quant_min, quant_max)
     return _dequantize_affine_no_dtype_check(