[OMNIML-2244] enable fp8 and int8 ONNX export (#594)

## What does this PR do?

**Type of change:** 
Example update

**Overview:**
- Support ONNX export for fp8 and int8 precisions
- Added utility functions to check for fp8 and int8 quantization (will
be used in ONNXExporter)
- Fixed a bug in evaluation API for high batch sizes
- Added function to replace zeros from scales to smallest positive value
in fp16

## Usage
<!-- You can potentially add a usage example below. -->

```python
python torch_quant_to_onnx.py \
    --quantize_mode fp8/int8 \
    --onnx_save_path <onnx_path>  
```

## Testing
Validated the accuracy and latency of int8 and fp8 models:
| Metric | INT8 | FP8 |
|--------|------|-----|
| Top1 Accuracy | 84.584% | 85.062% |
| Top5 Accuracy | 97.3% | 97.534% |
| Inference Latency | 8.4825 ms | 8.15096 ms |

## Before your PR is "*Ready for review*"
<!-- If you haven't finished some of the above items you can still open
`Draft` PR. -->

- **Make sure you read and follow [Contributor
guidelines](https://github.com/NVIDIA/TensorRT-Model-Optimizer/blob/main/CONTRIBUTING.md)**
and your commits are signed.
- **Is this change backward compatible?**: Yes
- **Did you write any new necessary tests?**: No
- **Did you add or update any necessary documentation?**: Yes
- **Did you update
[Changelog](https://github.com/NVIDIA/TensorRT-Model-Optimizer/blob/main/CHANGELOG.rst)?**:
No

---------

Signed-off-by: ajrasane <131806219+ajrasane@users.noreply.github.com>

Author: ajrasane

examples/onnx_ptq/README.md

@@ -13,7 +13,7 @@ Model Optimizer enables highly performant quantization formats including NVFP4,
 | Pre-Requisites | Required & optional packages to use this technique | [Link](#pre-requisites) | |
 | Getting Started | Learn how to optimize your models using PTQ to reduce precision and improve inference efficiency | [Link](#getting-started) | [docs](https://nvidia.github.io/TensorRT-Model-Optimizer/guides/_onnx_quantization.html) |
 | Support Matrix | View the ONNX export supported LLM models | [Link](#onnx-export-supported-llm-models) | |
-| PyTorch to ONNX | Example scripts demonstrating how to quantize with PyTorch and then convert to ONNX | [Link](#torch-quantization-to-onnx-example-for-mxfp8-int4-or-nvfp4-precision) | |
+| PyTorch to ONNX | Example scripts demonstrating how to quantize with PyTorch and then convert to ONNX | [Link](#torch-quantization-to-onnx-export-example) | |
 | Advanced Features | Examples demonstrating use advanced ONNX quantization features | [Link](#advanced-features) | |
 | Pre-Quantized Checkpoints | Ready to deploy Hugging Face pre-quantized checkpoints | [Link](#pre-quantized-checkpoints) | |
 | Resources | Extra links to relevant resources | [Link](#resources) | |
@@ -80,7 +80,7 @@ python image_prep.py \
 
 The model can be quantized as an FP8, INT8 or INT4 model using either the CLI or Python API. For FP8 and INT8 quantization, you have a choice between `max` and `entropy` calibration algorithms. For INT4 quantization, [awq_clip](https://arxiv.org/abs/2306.00978) or [rtn_dq](https://ar5iv.labs.arxiv.org/html/2301.12017) algorithms can be chosen.
 
-> *For NVFP4 and MXFP8 ONNX, see the [PyTorch to ONNX section](#torch-quantization-to-onnx-example-for-mxfp8-int4-or-nvfp4-precision).*
+> *For NVFP4 and MXFP8 ONNX, see the [PyTorch to ONNX section](#torch-quantization-to-onnx-export-example).*
 
 > *Minimum opset requirements: int8 (13+), fp8 (21+), int4 (21+). ModelOpt will automatically upgrade lower opset versions to meet these requirements.*
 
@@ -129,9 +129,9 @@ The top5 accuracy of the model is <accuracy score between 0-100%>
 Inference latency of the model is <X> ms
 ```
 
-## Torch quantization to ONNX example for MXFP8, INT4 or NVFP4 precision
+## Torch quantization to ONNX export example
 
-This example demonstrates how to quantize a [timm](https://github.com/huggingface/pytorch-image-models) vision model using MXFP8, INT4 or NVFP4 precision formats, and then export it to ONNX. The script leverages the ModelOpt toolkit for both quantization and ONNX export.
+This example demonstrates how to quantize a [timm](https://github.com/huggingface/pytorch-image-models) vision model for various precision formats followed by export to ONNX. The script leverages the ModelOpt toolkit for both quantization and ONNX export.
 
 > *Opset 20 is used to export the torch models to ONNX.*
 
@@ -148,7 +148,7 @@ This example demonstrates how to quantize a [timm](https://github.com/huggingfac
 ```bash
 python torch_quant_to_onnx.py \
     --timm_model_name=vit_base_patch16_224 \
-    --quantize_mode=<mxfp8|nvfp4|int4_awq> \
+    --quantize_mode=<fp8|mxfp8|int8|nvfp4|int4_awq> \
     --onnx_save_path=<path to save the exported ONNX model>
 ```
 

examples/onnx_ptq/evaluation.py

@@ -152,8 +152,9 @@ def evaluate_accuracy(
 
         # Calculate accuracy
         outputs = outputs[0] if isinstance(outputs, list) else outputs.data
-
         labels_size = labels.size(0)
+        outputs = outputs[:labels_size]
+
         total += labels_size
 
         labels = labels.to(outputs.device)

examples/onnx_ptq/torch_quant_to_onnx.py

@@ -323,7 +323,7 @@ def main():
         )
         print(f"Quantized Model - Top-1 Accuracy: {top1:.2f}%, Top-5 Accuracy: {top5:.2f}%")
 
-    if args.quantize_mode in ["fp8", "int8", "auto"]:
+    if args.quantize_mode in ["auto"]:
         print(
             f"The selected quantization mode {args.quantize_mode} is not supported for ONNX export yet."
         )

modelopt/onnx/quantization/qdq_utils.py

@@ -1037,6 +1037,21 @@ def remove_graph_input_q(onnx_model: onnx.ModelProto) -> onnx.ModelProto:
     return onnx_model
 
 
+def replace_zero_scale_with_smallest_nonzero(onnx_model: onnx.ModelProto) -> onnx.ModelProto:
+    """Replace zero scale values with smallest nonzero fp16 value in the ONNX model."""
+    graph = onnx_model.graph
+    fp16_smallest_nonzero = np.float16(6e-08)
+    scale_nodes = [node.input[1] for node in graph.node if node.op_type == "QuantizeLinear"]
+    for node in graph.node:
+        if node.op_type == "Constant" and node.output[0] in scale_nodes:
+            for attr in node.attribute:
+                if attr.name == "value":
+                    tensor = numpy_helper.to_array(attr.t)
+                    new_tensor = np.where(tensor == 0, fp16_smallest_nonzero, tensor)
+                    attr.t.CopyFrom(numpy_helper.from_array(new_tensor, attr.t.name))
+    return onnx_model
+
+
 def _cast_initializer_to_dtype(
     node: onnx.NodeProto, dtype: str, initializer_map: dict[str, onnx.TensorProto]
 ):

modelopt/torch/_deploy/utils/torch_onnx.py

@@ -37,6 +37,7 @@
     qdq_to_dq,
     quantize_weights_to_int4,
     quantize_weights_to_mxfp8,
+    replace_zero_scale_with_smallest_nonzero,
 )
 from modelopt.onnx.utils import (
     get_input_names,
@@ -336,6 +337,32 @@ def is_mxfp8_quantized(model: nn.Module) -> bool:
     return False
 
 
+def is_int8_quantized(model: nn.Module) -> bool:
+    """Check if the model is quantized in INT8 mode."""
+    for _, module in model.named_modules():
+        if (
+            hasattr(module, "weight_quantizer")
+            and hasattr(module, "input_quantizer")
+            and module.weight_quantizer._num_bits == 8
+            and module.input_quantizer._num_bits == 8
+        ):
+            return True
+    return False
+
+
+def is_fp8_quantized(model: nn.Module) -> bool:
+    """Check if the model is quantized in FP8 mode."""
+    for _, module in model.named_modules():
+        if (
+            hasattr(module, "weight_quantizer")
+            and hasattr(module, "input_quantizer")
+            and module.weight_quantizer._num_bits == (4, 3)
+            and module.input_quantizer._num_bits == (4, 3)
+        ):
+            return True
+    return False
+
+
 def get_onnx_bytes_and_metadata(
     model: nn.Module,
     dummy_input: Any | tuple,
@@ -510,6 +537,9 @@ def get_onnx_bytes_and_metadata(
                 onnx_opt_graph, low_precision_type=weights_dtype, keep_io_types=False
             )
 
+        # TensorRT expects all scales to be postive
+        onnx_opt_graph = replace_zero_scale_with_smallest_nonzero(onnx_opt_graph)
+
     # If the onnx model contains external data store the external tensors in one file and save the onnx model
     if has_external_data(onnx_save_path):
         tensor_paths = get_external_tensor_paths(onnx_path)