Quantization-Aware Training (QAT)

This chapter describes how to compile a model with Quantization-Aware Training (QAT) using DX-COM. QAT fine-tunes the model while simulating quantization, which can recover accuracy that is otherwise lost by post-training quantization (PTQ) alone.

QAT reuses the same JSON configuration as a normal (PTQ) compile. When the configuration file contains a qmaster block, dx_com.compile() automatically switches to QAT mode and runs the training pipeline using the same dataset and preprocessing settings as PTQ calibration.

Version Support

QAT (the qmaster block) is supported in DX-COM v2.4.0 and later.

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How QAT Is Triggered

QAT is enabled by adding a qmaster block to the JSON configuration. No separate command-line flag is required.

• If the config contains a qmaster block → DX-COM runs QAT (Calibration → Training → Compilation).
• If the config has no qmaster block → DX-COM runs the normal PTQ compile.

{
  "inputs": { "input.1": [1, 3, 224, 224] },
  "calibration_num": 100,
  "calibration_method": "ema",
  "default_loader": { "dataset_path": "/datasets/ILSVRC2012/train", "file_extensions": ["jpeg","jpg","png","JPEG"], "preprocessings": [ "..." ] },
  "qmaster": { "epochs": 30, "lr": 1e-5, "use_kd": true }
}

Reuses Your Existing Config

inputs, calibration_*, and default_loader work exactly as described in JSON File Configuration. The image preprocessing pipeline (default_loader.preprocessings) is the single source of truth for both calibration and QAT training data — you do not redefine it inside qmaster.

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Compilation Stages

A QAT compile runs three stages automatically:

1. Calibration — estimates initial quantization parameters (shared with PTQ).
2. Training (Stage 1) — runs the QAT fine-tuning loop. The best checkpoint (lowest validation loss) is saved to qat_checkpoint/qat_checkpoint.qxnn.
3. Compilation (Stage 2) — converts the trained weights into the NPU binary (*.dxnn).

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The qmaster Block

The qmaster block holds training hyperparameters only. Every key is optional; omitted keys fall back to the defaults below.

Parameter Quick Reference

Parameter	Default	Description
batch_size	1	Training batch size. Also selects the internal compile path (see note below). Default 1 uses the single-shot path; set to > 1 (e.g. 16) to use the staged path recommended for most models.
num_workers	4	Number of DataLoader workers.
train_limit / val_limit	500 / 50	Number of training / validation samples (subset).
device	"cuda:0"	Training device.
epochs	30	Maximum number of training epochs.
lr	1e-5	Learning rate.
optimizer	"adamw"	Optimizer: "adamw" or "sgd".
criterion	mse	Task loss: mse or cross_entropy. Applied when use_kd = false, or when use_kd = true and kd_alpha < 1.0 (task loss weight = 1 - kd_alpha). With the default use_kd = true and kd_alpha = 1.0, task loss is disabled and this value has no effect.
scheduler	null	LR scheduler: null, "cosine", or "step".
scheduler_step_size	max(1, (epochs - warmup_epochs) // 3)	Step interval (in epochs) for the "step" scheduler. Only used when scheduler = "step".
weight_decay	1e-4	Optimizer weight decay.
max_grad_norm	1.0	Gradient-clipping max norm.
use_amp	true	Mixed-precision (AMP) training.
warmup_epochs	0	Scheduler warmup epochs.
gradient_accumulation_steps	1	Effective batch = batch_size × this value.
early_stopping_patience	5	Stop early after N epochs with no improvement.
early_stopping_delta	1e-3	Minimum improvement counted as progress.
save_best_model	true	Save the best (lowest val-loss) checkpoint.
use_kd	true	Enable Knowledge Distillation (FP teacher → quantized student).
kd_loss	"mse"	KD loss type.
kd_alpha	1.0	KD loss weight. The task loss is weighted by 1 - kd_alpha, so the default 1.0 trains with KD only (task loss disabled).
kd_temperature	4.0	KD softening temperature.
encoder_mode	false	Track accuracy as cosine similarity instead of classification accuracy (for embedding/encoder-style models). Does not by itself disable the task loss — combine with kd_alpha = 1.0 for pure KD training.
freeze_bn_after	null	Freeze BatchNorm from the given epoch. See warning below.
train_cpu_fp	false	Keep the FP teacher on CPU to save GPU memory (slightly slower).
fast_run	false	Quick smoke test: 1 epoch × 1 batch. Result is not accuracy-meaningful.

Batch Size and the Internal Compile Path

batch_size > 1 runs the staged path (recommended for most models); batch_size = 1 runs the single-shot path. If a batched run is not possible for a given model, DX-COM automatically falls back to single-shot at batch size 1.

Data and Device

"qmaster": {
  "batch_size": 16,
  "num_workers": 4,
  "train_limit": 500,
  "val_limit": 50,
  "device": "cuda:0"
}

Training Loop

"qmaster": {
  "epochs": 30,
  "lr": 1e-5,
  "optimizer": "adamw",
  "criterion": "mse",
  "scheduler": "cosine",
  "warmup_epochs": 1,
  "weight_decay": 1e-4,
  "max_grad_norm": 1.0,
  "use_amp": true,
  "early_stopping_patience": 5
}

Knowledge Distillation (KD)

KD uses the original floating-point model as a teacher to guide the quantized student. It is enabled by default and generally improves accuracy.

"qmaster": {
  "use_kd": true,
  "kd_loss": "mse",
  "kd_alpha": 1.0,
  "kd_temperature": 4.0
}

KD Loss Weighting

kd_alpha weights the KD term; the task loss is weighted by 1 - kd_alpha. With the default kd_alpha = 1.0 the model trains with KD only. Lower it (e.g. 0.7) to blend KD with the task loss.

Encoder Mode

For embedding/encoder-style models (e.g. CLIP image encoders), set "encoder_mode": true. This switches the tracked metric to cosine similarity (instead of classification accuracy). It does not disable the task loss on its own; keep kd_alpha = 1.0 (the default) for pure KD training.

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Control Parameters (Python API)

The following parameters control training vs. compilation behavior. They are available through the Python API (dx_com.compile()); the dxcom CLI runs the full QAT pipeline directly from the qmaster block.

Parameter	Type	Default	Description
quantization_mode	str	"ptq"	Keep as "ptq" (default) to let QAT be auto-selected when a qmaster block is present. Set to "qat" only when supplying qat_config directly in Python — doing so bypasses qmaster auto-detection. (When set to "qat", you must provide either qat_config for training or qat_skip_training=True for compile-only/resume)
qat_config	Optional[Dict]	None	QAT training hyperparameters. (Normally supplied via the qmaster block in the config JSON; this argument is an alternative for callers that build the config in code)
qat_skip_training	bool	False	Skip the training loop and run compilation only. (Stage 2, use with qat_resume_from_checkpoint)
qat_resume_from_checkpoint	Optional[str]	None	Path to a qat_checkpoint.qxnn. (Loads trained weights, then compiles or continues)

Re-running Compilation Only

Training can take a long time. After a successful run you can regenerate the .dxnn without re-training by passing the saved checkpoint: qat_skip_training=True together with qat_resume_from_checkpoint="<path>.qxnn".

fast_run Is a Config Key

To run a quick smoke test, set "fast_run": true inside the qmaster block of the JSON config (it is not a compile() argument).

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Usage

CLI (dxcom)

Add a qmaster block to your config and compile as usual — QAT runs automatically.

dxcom -m model.onnx -c config_with_qmaster.json -o output/

Python API

import dx_com

# Basic QAT (training + compilation). qmaster block in config triggers QAT automatically.
dx_com.compile(
    model="model.onnx",
    config="config_with_qmaster.json",
    output_dir="output/",
)

# Compilation only, reusing a previously trained checkpoint.
dx_com.compile(
    model="model.onnx",
    config="config_with_qmaster.json",
    output_dir="output/",
    quantization_mode="qat",
    qat_skip_training=True,
    qat_resume_from_checkpoint="output/qat_checkpoint/qat_checkpoint.qxnn",
)

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Output Files

File	Description
<output_dir>/*.dxnn	Compiled NPU binary (the deliverable).
<output_dir>/qat_checkpoint/qat_checkpoint.qxnn	Best training checkpoint, for qat_resume_from_checkpoint.

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Notes and Recommendations

BatchNorm Freezing

freeze_bn_after = 0 freezes BatchNorm from the very first epoch, which can cause the loss to diverge (nan). Leave it as null unless you specifically need BN freezing, and in that case start from a later epoch.

Dataset Path

If default_loader.dataset_path is missing or invalid, DX-COM falls back to a default ImageNet location instead of failing. Verify the dataset path in the log to make sure training used the data you intended.

Reducing GPU Memory

If you hit out-of-memory errors, lower batch_size and/or raise gradient_accumulation_steps to keep the effective batch size constant. Setting "train_cpu_fp": true moves the FP teacher to CPU to save GPU memory (slightly slower).

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Related Pages

• JSON File Configuration — base config (inputs, calibration_*, default_loader).
• Execution of DX-COM — CLI and Python API reference.
• Change Log — QAT was added in v2.4.0.