[reland] Move QAT out of prototype (#1152)

Move QAT out of prototype

Summary: Move QAT out of prototype so we can provide stronger
BC guarantees moving forward.

**(Future) BC-breaking notes**

Note: This commit itself doesn't break BC yet. A future PR
will do that. The following is just to save this BC breaking
note somewhere.

Before:
```
from torchao.quantization.prototype.qat import (
    disable_4w_fake_quant,
    disable_8da4w_fake_quant,
    enable_4w_fake_quant,
    enable_8da4w_fake_quant,
    ComposableQATQuantizer,
    Int4WeightOnlyQATQuantizer,
    Int4WeightOnlyEmbeddingQATQuantizer
    Int8DynActInt4WeightQATQuantizer,
    Int8DynActInt4WeightQATLinear,
)
from torchao.quantization.prototype.qat.api import (
    FakeQuantizeConfig,
)
from torchao.quantization.prototype.qat.fake_quantizer import (
    FakeQuantizer,
)
```

After:
```
from torchao.quantization.qat import (
    ComposableQATQuantizer,
    Int4WeightOnlyQATQuantizer,
    Int4WeightOnlyEmbeddingQATQuantizer
    Int8DynActInt4WeightQATQuantizer,
)
from torchao.quantization.qat.linear import (
    disable_4w_fake_quant,
    disable_8da4w_fake_quant,
    enable_4w_fake_quant,
    enable_8da4w_fake_quant,
    Int8DynActInt4WeightQATLinear,
)
from torchao.quantization.qat.api import (
    FakeQuantizeConfig,
)
from torchao.quantization.qat.fake_quantizer import (
    FakeQuantizer,
)
```

Test Plan:
python test/quantization/test_qat.py

ghstack-source-id: add9dcac61e45f3b4ddeed07c300cc78ee3fd23c
Pull Request resolved: #1091

README.md

@@ -59,7 +59,7 @@ In practice these features alongside int4 weight only quantization allow us to *
 Post-training quantization can result in a fast and compact model, but may also lead to accuracy degradation. We recommend exploring Quantization Aware Training (QAT) to overcome this limitation. In collaboration with Torchtune, we've developed a QAT recipe that demonstrates significant accuracy improvements over traditional PTQ, recovering **96% of the accuracy degradation on hellaswag and 68% of the perplexity degradation on wikitext** for Llama3 compared to post-training quantization (PTQ). And we've provided a full recipe [here](https://pytorch.org/blog/quantization-aware-training/)
 
 ```python
-from torchao.quantization.prototype.qat import Int8DynActInt4WeightQATQuantizer
+from torchao.quantization.qat import Int8DynActInt4WeightQATQuantizer
 
 qat_quantizer = Int8DynActInt4WeightQATQuantizer()
 

test/quantization/test_qat.py

@@ -22,22 +22,22 @@
     PerRow,
     PerToken,
 )
-from torchao.quantization.prototype.qat.api import (
+from torchao.quantization.qat.api import (
     ComposableQATQuantizer,
     FakeQuantizeConfig,
 )
-from torchao.quantization.prototype.qat.fake_quantizer import (
+from torchao.quantization.qat.fake_quantizer import (
     FakeQuantizer,
 )
-from torchao.quantization.prototype.qat.embedding import (
+from torchao.quantization.qat.embedding import (
     FakeQuantizedEmbedding,
 )
-from torchao.quantization.prototype.qat.linear import (
+from torchao.quantization.qat.linear import (
     FakeQuantizedLinear,
     Int8DynActInt4WeightQATLinear,
     Int4WeightOnlyQATLinear
 )
-from torchao.quantization.prototype.qat.utils import (
+from torchao.quantization.qat.utils import (
     _choose_qparams_per_token_asymmetric,
     _fake_quantize_per_channel_group,
     _fake_quantize_per_token,
@@ -181,7 +181,7 @@ def _set_ptq_weight(
             Int8DynActInt4WeightLinear,
             WeightOnlyInt4Linear,
         )
-        from torchao.quantization.prototype.qat.linear import (
+        from torchao.quantization.qat.linear import (
             Int8DynActInt4WeightQATLinear,
             Int4WeightOnlyQATLinear,
         )
@@ -213,7 +213,7 @@ def _set_ptq_weight(
 
     @unittest.skipIf(not TORCH_VERSION_AT_LEAST_2_4, "skipping when torch version is 2.4 or lower")
     def test_qat_8da4w_linear(self):
-        from torchao.quantization.prototype.qat.linear import Int8DynActInt4WeightQATLinear
+        from torchao.quantization.qat.linear import Int8DynActInt4WeightQATLinear
         from torchao.quantization.GPTQ import Int8DynActInt4WeightLinear
 
         group_size = 128
@@ -238,7 +238,7 @@ def test_qat_8da4w_linear(self):
 
     @unittest.skipIf(not TORCH_VERSION_AT_LEAST_2_4, "skipping when torch version is 2.4 or lower")
     def test_qat_8da4w_quantizer(self):
-        from torchao.quantization.prototype.qat import Int8DynActInt4WeightQATQuantizer
+        from torchao.quantization.qat import Int8DynActInt4WeightQATQuantizer
         from torchao.quantization.GPTQ import Int8DynActInt4WeightQuantizer
 
         group_size = 16
@@ -272,7 +272,7 @@ def test_qat_8da4w_quantizer(self):
 
     @unittest.skipIf(not TORCH_VERSION_AT_LEAST_2_4, "skipping when torch version is 2.4 or lower")
     def test_qat_8da4w_quantizer_meta_weights(self):
-        from torchao.quantization.prototype.qat import Int8DynActInt4WeightQATQuantizer
+        from torchao.quantization.qat import Int8DynActInt4WeightQATQuantizer
 
         with torch.device("meta"):
             m = M()
@@ -287,7 +287,7 @@ def test_qat_8da4w_quantizer_disable_fake_quant(self):
         """
         Test that 8da4w QAT with disabled fake quant matches nn.Linear in forward.
         """
-        from torchao.quantization.prototype.qat import (
+        from torchao.quantization.qat.linear import (
             Int8DynActInt4WeightQATQuantizer,
             disable_8da4w_fake_quant,
             enable_8da4w_fake_quant,
@@ -346,7 +346,7 @@ def test_qat_8da4w_quantizer_disable_fake_quant_backward(self):
         """
         Test that 8da4w QAT with disabled fake quant matches nn.Linear in backward.
         """
-        from torchao.quantization.prototype.qat import (
+        from torchao.quantization.qat.linear import (
             Int8DynActInt4WeightQATQuantizer,
             disable_8da4w_fake_quant,
         )
@@ -428,7 +428,7 @@ def _test_qat_quantized_gradients(self, quantizer):
 
     @unittest.skipIf(not TORCH_VERSION_AT_LEAST_2_4, "skipping when torch version is 2.4 or lower")
     def test_qat_8da4w_quantizer_gradients(self):
-        from torchao.quantization.prototype.qat import Int8DynActInt4WeightQATQuantizer
+        from torchao.quantization.qat import Int8DynActInt4WeightQATQuantizer
         quantizer = Int8DynActInt4WeightQATQuantizer(groupsize=16)
         self._test_qat_quantized_gradients(quantizer)
 
@@ -518,7 +518,7 @@ def test_qat_4w_primitives(self):
     @unittest.skipIf(not TORCH_VERSION_AT_LEAST_2_4, "skipping when torch version is 2.4 or lower")
     @unittest.skipIf(not _CUDA_IS_AVAILABLE, "skipping when cuda is not available")
     def test_qat_4w_linear(self):
-        from torchao.quantization.prototype.qat.linear import Int4WeightOnlyQATLinear
+        from torchao.quantization.qat.linear import Int4WeightOnlyQATLinear
         from torchao.quantization.GPTQ import WeightOnlyInt4Linear
 
         group_size = 128
@@ -545,14 +545,14 @@ def test_qat_4w_linear(self):
 
     @unittest.skipIf(not TORCH_VERSION_AT_LEAST_2_4, "skipping when torch version is 2.4 or lower")
     def test_qat_4w_quantizer_gradients(self):
-        from torchao.quantization.prototype.qat import Int4WeightOnlyQATQuantizer
+        from torchao.quantization.qat import Int4WeightOnlyQATQuantizer
         quantizer = Int4WeightOnlyQATQuantizer(groupsize=32, inner_k_tiles=8)
         self._test_qat_quantized_gradients(quantizer)
 
     @unittest.skipIf(not TORCH_VERSION_AT_LEAST_2_4, "skipping when torch version is 2.4 or lower")
     @unittest.skipIf(not _CUDA_IS_AVAILABLE, "skipping when cuda is not available")
     def test_qat_4w_quantizer(self):
-        from torchao.quantization.prototype.qat import Int4WeightOnlyQATQuantizer
+        from torchao.quantization.qat import Int4WeightOnlyQATQuantizer
         from torchao.quantization.GPTQ import Int4WeightOnlyQuantizer
 
         group_size = 32
@@ -630,7 +630,7 @@ def test_composable_qat_quantizer(self):
 
     @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
+        from torchao.quantization.qat import Int4WeightOnlyEmbeddingQATQuantizer
         model = M2()
         x = model.example_inputs()
         out = model(*x)
@@ -937,6 +937,59 @@ def embedding_forward_4w(x: torch.Tensor, weight: torch.Tensor) -> torch.Tensor:
         baseline_out = embedding_forward_4w(x2, fq_embedding.weight)
         torch.testing.assert_close(baseline_out, fq_out, atol=0, rtol=0)
 
+    @unittest.skipIf(not TORCH_VERSION_AT_LEAST_2_4, "skipping when torch version is 2.4 or lower")
+    def test_qat_prototype_bc(self):
+        """
+        Just to make sure we can import all the old prototype paths.
+        We will remove this test in the near future when we actually break BC.
+        """
+        from torchao.quantization.prototype.qat import (
+            disable_4w_fake_quant,
+            disable_8da4w_fake_quant,
+            enable_4w_fake_quant,
+            enable_8da4w_fake_quant,
+            ComposableQATQuantizer,
+            Int8DynActInt4WeightQATLinear,
+            Int4WeightOnlyEmbeddingQATQuantizer,
+            Int4WeightOnlyQATQuantizer,
+            Int8DynActInt4WeightQATQuantizer,
+        )
+        from torchao.quantization.prototype.qat._module_swap_api import (
+            disable_4w_fake_quant_module_swap,
+            enable_4w_fake_quant_module_swap,
+            disable_8da4w_fake_quant_module_swap,
+            enable_8da4w_fake_quant_module_swap,
+            Int4WeightOnlyQATQuantizerModuleSwap,
+            Int8DynActInt4WeightQATQuantizerModuleSwap,
+        )
+        from torchao.quantization.prototype.qat.affine_fake_quantized_tensor import (
+            AffineFakeQuantizedTensor,
+            to_affine_fake_quantized,
+        )
+        from torchao.quantization.prototype.qat.api import (
+            ComposableQATQuantizer,
+            FakeQuantizeConfig,
+        )
+        from torchao.quantization.prototype.qat.embedding import (
+            FakeQuantizedEmbedding,
+            Int4WeightOnlyEmbeddingQATQuantizer,
+            Int4WeightOnlyEmbedding,
+            Int4WeightOnlyQATEmbedding,
+        )
+        from torchao.quantization.prototype.qat.fake_quantizer import (
+            FakeQuantizer,
+        )
+        from torchao.quantization.prototype.qat.linear import (
+            disable_4w_fake_quant,
+            disable_8da4w_fake_quant,
+            enable_4w_fake_quant,
+            enable_8da4w_fake_quant,
+            FakeQuantizedLinear,
+            Int4WeightOnlyQATLinear,
+            Int4WeightOnlyQATQuantizer,
+            Int8DynActInt4WeightQATLinear,
+            Int8DynActInt4WeightQATQuantizer,
+        )
 
 if __name__ == "__main__":
-    unittest.main()
+    unittest.main()

torchao/quantization/prototype/qat/README.md

@@ -1,125 +1,3 @@
-# Quantization-Aware Training (QAT)
-
-Quantization-Aware Training (QAT) refers to applying fake quantization during the
-training or fine-tuning process, such that the final quantized model will exhibit
-higher accuracies and perplexities. Fake quantization refers to rounding the float
-values to quantized values without actually casting them to dtypes with lower
-bit-widths, in contrast to post-training quantization (PTQ), which does cast the
-quantized values to lower bit-width dtypes, e.g.:
-
-```
-# PTQ: x_q is quantized and cast to int8
-# scale and zero point (zp) refer to parameters used to quantize x_float
-# qmin and qmax refer to the range of quantized values
-x_q = (x_float / scale + zp).round().clamp(qmin, qmax).cast(int8)
-
-# QAT: x_fq is still in float
-# Fake quantize simulates the numerics of quantize + dequantize
-x_fq = (x_float / scale + zp).round().clamp(qmin, qmax)
-x_fq = (x_fq - zp) * scale
-```
-
-## API
-
-torchao currently supports two QAT schemes for linear layers:
-- int8 per token dynamic activations + int4 per group weights
-- int4 per group weights (using the efficient [int4 tinygemm kernel](https://github.com/pytorch/pytorch/blob/a672f6c84e318bbf455f13dfdd3fd7c68a388bf5/aten/src/ATen/native/cuda/int4mm.cu#L1097) after training)
-
-QAT typically involves applying a transformation to your model before and after training.
-In torchao, these are represented as the prepare and convert steps: (1) prepare inserts
-fake quantize operations into linear layers, and (2) convert transforms the fake quantize
-operations to actual quantize and dequantize operations after training, thereby producing
-a quantized model (dequantize operations are typically fused with linear after lowering).
-Between these two steps, training can proceed exactly as before.
-
-![qat](images/qat_diagram.png)
-
-To use QAT in torchao, apply the prepare step using the appropriate Quantizer before
-training, then apply the convert step after training for inference or generation.
-For example, on a single GPU:
-
-```python
-import torch
-from torchtune.models.llama3 import llama3
-from torchao.quantization.prototype.qat import Int8DynActInt4WeightQATQuantizer
-
-# Smaller version of llama3 to fit in a single GPU
-model = llama3(
-    vocab_size=4096,
-    num_layers=16,
-    num_heads=16,
-    num_kv_heads=4,
-    embed_dim=2048,
-    max_seq_len=2048,
-).cuda()
-
-# Quantizer for int8 dynamic per token activations +
-# int4 grouped per channel weights, only for linear layers
-qat_quantizer = Int8DynActInt4WeightQATQuantizer()
-
-# Insert "fake quantize" operations into linear layers.
-# These operations simulate quantization numerics during
-# training without performing any dtype casting
-model = qat_quantizer.prepare(model)
-
-# Standard training loop
-optimizer = torch.optim.SGD(model.parameters(), lr=0.001, momentum=0.9, weight_decay=1e-5)
-loss_fn = torch.nn.CrossEntropyLoss()
-for i in range(10):
-    example = torch.randint(0, 4096, (2, 16)).cuda()
-    target = torch.randn((2, 16, 4096)).cuda()
-    output = model(example)
-    loss = loss_fn(output, target)
-    loss.backward()
-    optimizer.step()
-    optimizer.zero_grad()
-
-# Convert fake quantize to actual quantize operations
-# The quantized model has the exact same structure as the
-# quantized model produced in the corresponding PTQ flow
-# through `Int8DynActInt4WeightQuantizer`
-model = qat_quantizer.convert(model)
-
-# inference or generate
-```
-
-Users can also leverage our integration with [torchtune](https://github.com/pytorch/torchtune)
-and apply quantized-aware fine-tuning as follows:
-
-```
-tune run --nproc_per_node 8 qat_distributed --config llama3/8B_qat_full
-```
-
-For more detail, please refer to [this QAT tutorial](https://pytorch.org/torchtune/main/tutorials/qat_finetune.html).
-
-
-## Evaluation Results
-
-Evaluation was performed on 6-8 A100 GPUs (80GB each) using the torchtune QAT
-integration described above. We fine-tune [Llama3-8B](https://huggingface.co/meta-llama/Meta-Llama-3-8B-Instruct)
-on the [C4 dataset](https://huggingface.co/datasets/allenai/c4) (en subset)
-for 5000 steps using a group size of 256 for the weights. Note that extensive
-hyperparameter tuning may further improve these results.
-
-Results for int8 per token dynamic activations + int4 per group weights, using a learning rate of 2e-5:
-
-|                  | hellaswag<br>(acc) | hellaswag<br>(acc_norm) | wikitext<br>(word_perplexity) | wikitext<br>(byte_perplexity) | wikitext<br>(bits_per_byte) |
-| ---------------- | ------ | ------ | ------ | ------ | ------ |
-| No quantization  | 57.86% | 76.60% | 8.905  | 1.505  | 0.590  |
-| PTQ              | 51.74% | 70.66% | 11.878 | 1.588  | 0.668  |
-| QAT (quantized)  | 57.25% | 76.51% | 9.859  | 1.534  | 0.617  |
-| PTQ degradation  | -6.11% | -5.94% | +2.973 | +0.083 | +0.078 |
-| QAT degradation  | -0.61% | -0.21% | +0.947 | +0.029 | +0.027 |
-
-Results for int4 per group weights, using a learning rate of 2e-6. For this quantization scheme, the
-quantized path uses the more efficient [int4 tinygemm kernel](https://github.com/pytorch/pytorch/blob/a672f6c84e318bbf455f13dfdd3fd7c68a388bf5/aten/src/ATen/native/cuda/int4mm.cu#L1097).
-
-|                  | hellaswag<br>(acc) | hellaswag<br>(acc_norm) | wikitext<br>(word_perplexity) | wikitext<br>(byte_perplexity) | wikitext<br>(bits_per_byte) |
-| ---------------- | -------- | ------- | ------ | ------ | ------ |
-| No quantization  | 57.16%  | 77.02% | 8.858  | 1.504  | 0.589  |
-| PTQ              | 55.06%  | 74.24% | 10.311 | 1.547  | 0.630  |
-| QAT (quantized)  | 55.86%  | 75.06% | 10.134 | 1.542  | 0.625  |
-| PTQ degradation  | -2.10%  | -2.78% | +1.453 | +0.043 | +0.041 |
-| QAT degradation  | -1.30%  | -1.96% | +1.276 | +0.038 | +0.036 |
-
-For more details, please refer to [this blog post](https://pytorch.org/blog/quantization-aware-training).
+Note: QAT has been moved to torchao/quantization/qat.
+This is a legacy folder only for backward compatibility
+and will be removed in the near future.

torchao/quantization/prototype/qat/__init__.py

@@ -1,17 +1,15 @@
-from .api import (
+from torchao.quantization.qat import (
     ComposableQATQuantizer,
+    Int4WeightOnlyEmbeddingQATQuantizer,
+    Int4WeightOnlyQATQuantizer,
+    Int8DynActInt4WeightQATQuantizer,
 )
-from .linear import (
+from torchao.quantization.qat.linear import (
     disable_4w_fake_quant,
     disable_8da4w_fake_quant,
     enable_4w_fake_quant,
     enable_8da4w_fake_quant,
-    Int4WeightOnlyQATQuantizer,
     Int8DynActInt4WeightQATLinear,
-    Int8DynActInt4WeightQATQuantizer,
-)
-from .embedding import (
-    Int4WeightOnlyEmbeddingQATQuantizer,
 )
 
 __all__ = [

torchao/quantization/prototype/qat/_module_swap_api.py

@@ -1,7 +1,7 @@
 # For backward compatibility only
 # These will be removed in the future
 
-from .linear import (
+from torchao.quantization.qat.linear import (
     Int8DynActInt4WeightQATQuantizer as Int8DynActInt4WeightQATQuantizerModuleSwap,
     Int4WeightOnlyQATQuantizer as Int4WeightOnlyQATQuantizerModuleSwap,
     enable_8da4w_fake_quant as enable_8da4w_fake_quant_module_swap,