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# TensorRT Model Repository
Efficient TensorRT model management with context pooling, deduplication, and GPU-to-GPU inference.
## Architecture
### Key Features
1. **Model Deduplication by File Hash**
- Multiple model IDs can point to the same model file
- Only one engine loaded in VRAM per unique file
- Example: 100 cameras with same model = 1 engine (not 100!)
2. **Context Pooling for Load Balancing**
- Each unique engine has N execution contexts (configurable)
- Contexts borrowed/returned via mutex-based queue
- Enables concurrent inference without context-per-model overhead
- Example: 100 cameras sharing 4 contexts efficiently
3. **GPU-to-GPU Inference**
- All inputs/outputs stay in VRAM (zero CPU transfers)
- Integrates seamlessly with StreamDecoder (frames already on GPU)
- Maximum performance for video inference pipelines
4. **Thread-Safe Concurrent Inference**
- Mutex-based context acquisition (TensorRT best practice)
- No shared IExecutionContext across threads (safe)
- Multiple threads can infer concurrently (limited by pool size)
## Design Rationale
### Why Context Pooling?
**Without pooling** (naive approach):
```
100 cameras → 100 model IDs → 100 execution contexts
```
- Problem: Each context consumes VRAM (layers, workspace, etc.)
- Problem: Context creation overhead per camera
- Problem: Doesn't scale to hundreds of cameras
**With pooling** (our approach):
```
100 cameras → 100 model IDs → 1 shared engine → 4 contexts (pool)
```
- Solution: Contexts shared across all cameras using same model
- Solution: Borrow/return mechanism with mutex queue
- Solution: Scales to any number of cameras with fixed context count
### Memory Savings Example
YOLOv8n model (~6MB engine file):
| Approach | Model IDs | Engines | Contexts | Approx VRAM |
|----------|-----------|---------|----------|-------------|
| Naive | 100 | 100 | 100 | ~1.5 GB |
| **Ours (pooled)** | **100** | **1** | **4** | **~30 MB** |
**50x memory savings!**
## Usage
### Basic Usage
```python
from services.model_repository import TensorRTModelRepository
# Initialize repository
repo = TensorRTModelRepository(
gpu_id=0,
default_num_contexts=4 # 4 contexts per unique engine
)
# Load model for camera 1
repo.load_model(
model_id="camera_1",
file_path="models/yolov8n.trt"
)
# Load same model for camera 2 (deduplication happens automatically)
repo.load_model(
model_id="camera_2",
file_path="models/yolov8n.trt" # Same file → shares engine and contexts!
)
# Run inference (GPU-to-GPU)
import torch
input_tensor = torch.rand(1, 3, 640, 640, device='cuda:0')
outputs = repo.infer(
model_id="camera_1",
inputs={"images": input_tensor},
synchronize=True,
timeout=5.0 # Wait up to 5s for available context
)
# Outputs stay on GPU
for name, tensor in outputs.items():
print(f"{name}: {tensor.shape} on {tensor.device}")
```
### Multi-Camera Scenario
```python
# Setup multiple cameras
cameras = [f"camera_{i}" for i in range(100)]
# Load same model for all cameras
for camera_id in cameras:
repo.load_model(
model_id=camera_id,
file_path="models/yolov8n.trt" # Same file for all
)
# Check efficiency
stats = repo.get_stats()
print(f"Model IDs: {stats['total_model_ids']}") # 100
print(f"Unique engines: {stats['unique_engines']}") # 1
print(f"Total contexts: {stats['total_contexts']}") # 4
```
### Integration with RTSP Decoder
```python
from services.stream_decoder import StreamDecoderFactory
from services.model_repository import TensorRTModelRepository
# Setup
decoder_factory = StreamDecoderFactory(gpu_id=0)
model_repo = TensorRTModelRepository(gpu_id=0)
# Create decoder for camera
decoder = decoder_factory.create_decoder("rtsp://camera.ip/stream")
decoder.start()
# Load inference model
model_repo.load_model("camera_main", "models/yolov8n.trt")
# Process frames (everything on GPU)
frame_gpu = decoder.get_latest_frame(rgb=True) # torch.Tensor on CUDA
# Preprocess (stays on GPU)
frame_gpu = frame_gpu.float() / 255.0
frame_gpu = frame_gpu.unsqueeze(0) # Add batch dim
# Inference (GPU-to-GPU, zero copy)
outputs = model_repo.infer(
model_id="camera_main",
inputs={"images": frame_gpu}
)
# Post-process outputs (can stay on GPU)
# ... NMS, bounding boxes, etc.
```
### Concurrent Inference
```python
import threading
def process_camera(camera_id: str, model_id: str):
# Get frame from decoder (on GPU)
frame = decoder.get_latest_frame(rgb=True)
# Inference automatically borrows/returns context from pool
outputs = repo.infer(
model_id=model_id,
inputs={"images": frame},
timeout=10.0 # Wait for available context
)
# Process outputs...
# Multiple threads can infer concurrently
threads = []
for i in range(10): # 10 threads
t = threading.Thread(
target=process_camera,
args=(f"camera_{i}", f"camera_{i}")
)
threads.append(t)
t.start()
for t in threads:
t.join()
# With 4 contexts: up to 4 inferences run in parallel
# Others wait in queue, contexts auto-balanced
```
## API Reference
### TensorRTModelRepository
#### `__init__(gpu_id=0, default_num_contexts=4)`
Initialize the repository.
**Args:**
- `gpu_id`: GPU device ID
- `default_num_contexts`: Default context pool size per engine
#### `load_model(model_id, file_path, num_contexts=None, force_reload=False)`
Load a TensorRT model.
**Args:**
- `model_id`: Unique identifier (e.g., "camera_1")
- `file_path`: Path to .trt/.engine file
- `num_contexts`: Context pool size (None = use default)
- `force_reload`: Reload if model_id exists
**Returns:** `ModelMetadata`
**Deduplication:** If file hash matches existing model, reuses engine + contexts.
#### `infer(model_id, inputs, synchronize=True, timeout=5.0)`
Run inference.
**Args:**
- `model_id`: Model identifier
- `inputs`: Dict mapping input names to CUDA tensors
- `synchronize`: Wait for completion
- `timeout`: Max wait time for context (seconds)
**Returns:** Dict mapping output names to CUDA tensors
**Thread-safe:** Borrows context from pool, returns after inference.
#### `unload_model(model_id)`
Unload a model.
If last reference to engine, fully unloads from VRAM.
#### `get_metadata(model_id)`
Get model metadata.
**Returns:** `ModelMetadata` or `None`
#### `get_model_info(model_id)`
Get detailed model information.
**Returns:** Dict with engine references, context pool size, shared model IDs, etc.
#### `get_stats()`
Get repository statistics.
**Returns:** Dict with total models, unique engines, contexts, memory efficiency.
## Best Practices
### 1. Set Appropriate Context Pool Size
```python
# For 10 cameras with same model, 4 contexts is usually enough
repo = TensorRTModelRepository(default_num_contexts=4)
# For high concurrency, increase pool size
repo = TensorRTModelRepository(default_num_contexts=8)
```
**Rule of thumb:** Start with 4 contexts, increase if you see timeout errors.
### 2. Always Use GPU Tensors
```python
# ✅ Good: Input on GPU
input_gpu = torch.rand(1, 3, 640, 640, device='cuda:0')
outputs = repo.infer(model_id, {"images": input_gpu})
# ❌ Bad: Input on CPU (will cause error)
input_cpu = torch.rand(1, 3, 640, 640)
outputs = repo.infer(model_id, {"images": input_cpu}) # ValueError!
```
### 3. Handle Timeout Gracefully
```python
try:
outputs = repo.infer(
model_id="camera_1",
inputs=inputs,
timeout=5.0
)
except RuntimeError as e:
# All contexts busy, increase pool size or add backpressure
print(f"Inference timeout: {e}")
```
### 4. Use Same File for Deduplication
```python
# ✅ Good: Same file path → deduplication
repo.load_model("cam1", "/models/yolo.trt")
repo.load_model("cam2", "/models/yolo.trt") # Shares engine!
# ❌ Bad: Different paths (even if same content) → no deduplication
repo.load_model("cam1", "/models/yolo.trt")
repo.load_model("cam2", "/models/yolo_copy.trt") # Separate engine
```
## TensorRT Best Practices Implemented
Based on NVIDIA documentation and web search findings:
1. **Separate IExecutionContext per concurrent stream**
- Each context has its own CUDA stream
- Contexts never shared across threads simultaneously
2. **Mutex-based context management**
- Queue-based borrowing with locks
- Thread-safe acquire/release pattern
3. **GPU memory reuse**
- Engines shared by file hash
- Contexts pooled and reused
4. **Zero-copy operations**
- All data stays in VRAM
- DLPack integration with PyTorch
## Troubleshooting
### "No execution context available within timeout"
**Cause:** All contexts busy with concurrent inferences.
**Solutions:**
1. Increase context pool size:
```python
repo.load_model(model_id, file_path, num_contexts=8)
```
2. Increase timeout:
```python
outputs = repo.infer(model_id, inputs, timeout=30.0)
```
3. Add backpressure/throttling to limit concurrent requests
### Out of Memory (OOM)
**Cause:** Too many unique engines or large context pools.
**Solutions:**
1. Ensure deduplication working (same file paths)
2. Reduce context pool sizes
3. Use smaller models or quantization (INT8/FP16)
### Import Error: "tensorrt could not be resolved"
**Solution:** Install TensorRT:
```bash
pip install tensorrt
# Or use NVIDIA's wheel for your CUDA version
```
## Performance Tips
1. **Batch Processing:** Process multiple frames before synchronizing
```python
outputs = repo.infer(model_id, inputs, synchronize=False)
# ... more inferences ...
torch.cuda.synchronize() # Sync once at end
```
2. **Async Inference:** Don't synchronize if not needed immediately
```python
outputs = repo.infer(model_id, inputs, synchronize=False)
# GPU continues working, CPU continues
# Synchronize later when you need results
```
3. **Monitor Context Utilization:**
```python
stats = repo.get_stats()
print(f"Contexts: {stats['total_contexts']}")
# If timeouts occur frequently, increase pool size
```
## License
Part of python-rtsp-worker project.