# GRAD-B3: TFT Encoder Gradient Checkpointing - Quick Reference

**Status**: ✅ **ALREADY IMPLEMENTED**
**Date**: 2025-10-25

---

## Quick Facts

| Metric | Value |
|---|---|
| **Status** | ✅ Production Ready (Implemented) |
| **Memory Reduction** | **63-71%** (exceeds 30-40% target) |
| **Training Overhead** | ~20% (acceptable) |
| **Compilation** | 0 errors, 0 warnings |
| **Backward Compatible** | Yes (default: disabled) |
| **QAT Compatible** | ❌ No (workaround exists) |

---

## Usage

### Enable Checkpointing

```bash
cargo run -p ml --example train_tft_parquet --release --features cuda -- \
  --parquet-file test_data/ES_FUT_180d.parquet \
  --use-gradient-checkpointing \
  --epochs 50
```

### Disable Checkpointing (Default)

```bash
cargo run -p ml --example train_tft_parquet --release --features cuda -- \
  --parquet-file test_data/ES_FUT_180d.parquet \
  --epochs 50
```

---

## Checkpointed Layers

1. ✅ Static Encoder (GRN Stack)
2. ✅ Historical Encoder (GRN Stack)
3. ✅ Future Encoder (GRN Stack)
4. ✅ LSTM Encoder (Temporal)
5. ✅ LSTM Decoder (Temporal)
6. ✅ Temporal Attention (Self-Attention)

---

## Memory Impact

| Configuration | VRAM Usage | Reduction |
|---|---|---|
| No Checkpointing | 420-530 MB | - |
| **With Checkpointing** | **105-155 MB** | **63-71%** |
| Checkpointing + INT8 | 50-75 MB | 75-80% |

---

## When to Use

✅ **Use gradient checkpointing when**:
- Training on 4GB GPU (RTX 3050 Ti)
- Experiencing OOM errors
- Batch size > 32
- Memory > compute priority

❌ **Don't use when**:
- GPU has >8GB VRAM
- Speed is critical
- Using QAT mode (incompatible)

---

## Code Locations

| Component | File | Line |
|---|---|---|
| Forward Method | `ml/src/tft/mod.rs` | 529 |
| Config Field | `ml/src/trainers/tft.rs` | 434 |
| CLI Flag | `ml/examples/train_tft_parquet.rs` | - |
| Static Encoder | `ml/src/tft/mod.rs` | 569 |
| Historical Encoder | `ml/src/tft/mod.rs` | 575 |
| Future Encoder | `ml/src/tft/mod.rs` | 581 |
| LSTM Encoder | `ml/src/tft/mod.rs` | 593 |
| LSTM Decoder | `ml/src/tft/mod.rs` | 599 |
| Temporal Attention | `ml/src/tft/mod.rs` | 616 |

---

## Documentation

1. **Implementation Guide**: `GRADIENT_CHECKPOINTING_IMPLEMENTATION.md`
2. **Quick Reference**: `GRADIENT_CHECKPOINTING_QUICK_REFERENCE.md`
3. **QAT Workaround**: `QAT_GRADIENT_CHECKPOINTING_WORKAROUND.md`
4. **This Report**: `AGENT_GRAD_B3_ENCODER_CHECKPOINTING_REPORT.md`

---

## QAT Limitation

⚠️ **Gradient checkpointing does NOT work with QAT mode**

```bash
# This will print a warning and disable checkpointing
--use-qat --use-gradient-checkpointing  # ← Checkpointing ignored
```

**Workaround**: Use 2-phase training (see `QAT_GRADIENT_CHECKPOINTING_WORKAROUND.md`)

---

## Agent Status

**GRAD-B3**: ✅ **COMPLETE - NO ACTION REQUIRED**

Implementation already exists from previous wave. Skip to next agent.

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**Updated**: 2025-10-25