Add int4 weight-only embedding QAT (pytorch#947)

Based on changes in pytorch#886 by @TiRune

test/quantization/test_qat.py

@@ -81,6 +81,17 @@ def forward(self, x):
         x = self.linear2(x)
         return x
 
+class M2(torch.nn.Module):
+    def __init__(self):
+        super().__init__()
+        self.embedding = torch.nn.Embedding(10, 512)
+
+    def example_inputs(self):
+        return (torch.randint(1, 10, (1, 512)),)
+
+    def forward(self, x):
+        return self.embedding(x)
+
 
 class TestQAT(unittest.TestCase):
     SEED = 123
@@ -669,5 +680,17 @@ def test_composable_qat_quantizer(self):
         values_list = getattr(model.linear1, self._MyQATQuantizer.ATTR_NAME)
         self.assertEqual(values_list, ["quantizer1", "quantizer2", "quantizer1", "quantizer2"])
 
+    @unittest.skipIf(not TORCH_VERSION_AT_LEAST_2_4, "skipping when torch version is 2.4 or lower")
+    def test_qat_4w_embedding(self):
+        from torchao.quantization.prototype.qat import Int4WeightOnlyEmbeddingQATQuantizer
+        model = M2()
+        x = model.example_inputs()
+        out = model(*x)
+        quantizer = Int4WeightOnlyEmbeddingQATQuantizer()
+        prepared = quantizer.prepare(model)
+        prepared_out = prepared(*x)
+        converted = quantizer.convert(model)
+        converted_out = converted(*x)
+
 if __name__ == "__main__":
     unittest.main()

torchao/quantization/prototype/qat/__init__.py

@@ -13,6 +13,9 @@
 from ._module_swap_api import (
     Int8DynActInt4WeightQATLinear,
 )
+from .embedding import (
+    Int4WeightOnlyEmbeddingQATQuantizer,
+)
 
 __all__ = [
     "disable_4w_fake_quant",
@@ -23,6 +26,7 @@
     "int8_dynamic_activation_int4_weight_fake_quantize",
     "ComposableQATQuantizer",
     "Int4WeightOnlyQATQuantizer",
+    "Int4WeightOnlyEmbeddingQATQuantizer"
     "Int8DynActInt4WeightQATQuantizer",
     "Int8DynActInt4WeightQATLinear",
 ]

torchao/quantization/prototype/qat/_module_swap_api.py

@@ -28,23 +28,23 @@
     _choose_qparams_per_token_asymmetric,
     _fake_quantize_per_channel_group,
     _fake_quantize_per_token,
+    _get_qmin_qmax,
 )
 
 
-# TODO: deprecate this flow in favor of the tensor subclass flow under qat/api.py
-# This is currently needed for DDP and FSDP1, which are not compatible with the
-# subclass flow.
+# TODO: make module swap the main flow again, and remove the quantize_ flow
+# TODO: rename this file to linear.py
+
+# =========================================================
+# |   Linear int8 dynamic activations + int4 weight QAT   |
+# =========================================================
 
 
 class Int8DynActInt4WeightQATQuantizerModuleSwap(Int8DynActInt4WeightQATQuantizer):
     """
     Quantizer for performing QAT on a model, where linear layers have int8
     dynamic per token fake quantized activations and int4 fake quantized
     grouped per channel weights.
-
-    Note: This quantizer is implemented using module swaps and may be
-    deprecated in the future. Please use `Int8DynActInt4WeightQATQuantizer`
-    instead if possible.
     """
 
     def prepare(
@@ -92,7 +92,7 @@ def _convert_qat_linear_8da4w(module: torch.nn.Module):
 
             # Load weights and qparams into quantized linear
             n_bit = 4
-            (qmin, qmax) = child._get_qmin_qmax(n_bit)
+            (qmin, qmax) = _get_qmin_qmax(n_bit)
             (s, zp) = get_group_qparams_symmetric(child.weight, n_bit, child.groupsize)
             from torchao._executorch_ops import _quantized_decomposed_quantize_per_channel_group_wrapper
             q_weight = _quantized_decomposed_quantize_per_channel_group_wrapper(
@@ -156,7 +156,7 @@ def forward(self, x: torch.Tensor) -> torch.Tensor:
             (act_scales, act_zp) = _choose_qparams_per_token_asymmetric(
                 x, self.scales_precision, self.zero_points_precision,
             )
-            (act_qmin, act_qmax) = self._get_qmin_qmax(8)
+            (act_qmin, act_qmax) = _get_qmin_qmax(8)
             x_fq = _fake_quantize_per_token(
                 x, act_scales, act_zp, act_qmin, act_qmax,
             )
@@ -170,7 +170,7 @@ def forward(self, x: torch.Tensor) -> torch.Tensor:
             )
             # TODO: pass zp dtype to `get_group_qparams_symmetric` instead
             weight_zp = weight_zp.to(self.zero_points_precision)
-            (weight_qmin, weight_qmax) = self._get_qmin_qmax(4)
+            (weight_qmin, weight_qmax) = _get_qmin_qmax(4)
             w_fq = _fake_quantize_per_channel_group(
                 self.weight,
                 weight_scales,
@@ -183,12 +183,6 @@ def forward(self, x: torch.Tensor) -> torch.Tensor:
             w_fq = self.weight
         return F.linear(x_fq, w_fq)
 
-    # TODO: move this to common util
-    def _get_qmin_qmax(self, n_bit: int):
-        qmin = -(2 ** (n_bit - 1))
-        qmax = 2 ** (n_bit - 1) - 1
-        return (qmin, qmax)
-
 
 def enable_8da4w_fake_quant_module_swap(mod: torch.nn.Module):
     """
@@ -206,19 +200,15 @@ def disable_8da4w_fake_quant_module_swap(mod: torch.nn.Module):
         mod.disable_fake_quant()
 
 
-# ==================
-# |   int4wo QAT   |
-# ==================
+# ===================================
+# |   Linear int4 weight-only QAT   |
+# ===================================
 
 
 class Int4WeightOnlyQATQuantizerModuleSwap(Int4WeightOnlyQATQuantizer):
     """
     Quantizer for performing QAT on a model, where linear layers have
     int4 fake quantized grouped per channel weights.
-
-    Note: This quantizer is implemented using module swaps and may be
-    deprecated in the future. Please use `Int4WeightOnlyQATQuantizer`
-    instead if possible.
     """
 
     def prepare(