# Change: Add GPU Acceleration Support for OCR Processing

## Why
PaddleOCR supports CUDA GPU acceleration which can significantly improve OCR processing speed for batch operations. Currently, the system always uses CPU processing, which is slower and less efficient for large document batches. By adding GPU detection and automatic CUDA support, the system will:
- Automatically utilize available GPU hardware when present
- Fall back gracefully to CPU processing when GPU is unavailable
- Reduce processing time for large batches by leveraging parallel GPU computation
- Improve overall system throughput and user experience

## What Changes
- Add GPU detection logic to environment setup script (`setup_dev_env.sh`)
- Automatically install CUDA-enabled PaddlePaddle when compatible GPU is detected
- Install CPU-only PaddlePaddle when no compatible GPU is found
- Add GPU availability detection in OCR processing code
- Automatically enable GPU acceleration in PaddleOCR when GPU is available
- Add configuration option to force CPU mode (for testing or troubleshooting)
- Add GPU status reporting in API health check endpoint
- Update documentation with GPU requirements and setup instructions

## Impact
- **Affected capabilities**:
  - `ocr-processing`: Add GPU acceleration support with automatic detection
  - `environment-setup`: Add GPU detection and CUDA installation logic

- **Affected code**:
  - `setup_dev_env.sh`: GPU detection and conditional CUDA package installation
  - `backend/app/services/ocr_service.py`: GPU availability detection and configuration
  - `backend/app/api/v1/endpoints/health.py`: GPU status reporting
  - `backend/app/core/config.py`: GPU configuration settings
  - `.env.local`: GPU-related environment variables

- **Dependencies**:
  - When GPU available: `paddlepaddle-gpu` (with matching CUDA version)
  - When GPU unavailable: `paddlepaddle` (CPU-only, current default)
  - Detection tools: `nvidia-smi` (NVIDIA GPUs), `lspci` (hardware detection)

- **Configuration**:
  - New env var: `FORCE_CPU_MODE` (default: false) - Override GPU detection
  - New env var: `CUDA_VERSION` (auto-detected or manual override)
  - GPU memory allocation settings for PaddleOCR
  - Batch size adjustment based on GPU memory availability

- **Performance Impact**:
  - Expected 3-10x speedup for OCR processing on GPU-enabled systems
  - No performance degradation on CPU-only systems (same as current behavior)
  - Automatic memory management to prevent GPU OOM errors

- **Backward Compatibility**:
  - Fully backward compatible - existing CPU-only installations continue to work
  - No breaking changes to API or configuration
  - Existing installations can opt-in by re-running setup script on GPU-enabled hardware

## Known Issues and Limitations

### Chart Recognition Feature Disabled (PaddlePaddle 3.0.0 API Limitation)

**Issue**: Chart recognition feature in PP-StructureV3 is currently disabled due to API incompatibility.

**Root Cause**:
- PaddleOCR-VL chart recognition model requires `paddle.incubate.nn.functional.fused_rms_norm_ext` API
- PaddlePaddle 3.0.0 stable only provides `fused_rms_norm` (base version)
- The extended version `fused_rms_norm_ext` is not yet available in stable release

**Impact**:
- ✅ **Still Works**: Layout analysis can detect and extract chart/figure regions as images
- ✅ **Still Works**: Tables, formulas, and text recognition all function normally
- ❌ **Disabled**: Deep chart understanding (chart type detection, data extraction, axis/legend parsing)
- ❌ **Disabled**: Converting chart content to structured data (JSON, tables)

**Workaround**:
- Set `use_chart_recognition=False` in PP-StructureV3 initialization
- Charts are saved as image files but content is not analyzed

**Future Resolution**:
- Wait for PaddlePaddle 3.0.x/3.1.x update that adds `fused_rms_norm_ext` API
- Or use PaddlePaddle develop version (unstable, not recommended for production)

**Code Location**: [backend/app/services/ocr_service.py:216](../../backend/app/services/ocr_service.py#L216)

**Status**: Documented limitation, pending PaddlePaddle framework update