[tests] Added test_niah_standalone.py.

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Zijie Tian
2026-01-12 00:16:37 +08:00
parent 5895de0c97
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6 changed files with 686 additions and 9 deletions

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# RULER NIAH Standalone Test Plan
## Overview
This document describes how to independently test nano-vllm's CPU offload functionality using RULER benchmark's NIAH (Needle-In-A-Haystack) task data.
## Background
### Problem Being Investigated
When running 32K sequence length tests with CPU offload mode, the model outputs garbled text instead of finding the magic number. This issue was traced to:
- **Root Cause**: Ring buffer `max_seq_len` was set equal to `max_model_len` (32768)
- **Issue**: When prefill uses ~32K tokens, decode needs to store KV at position 32768+, but ring buffer only has indices 0-32767
- **Fix Applied**: In `nanovllm/kvcache/__init__.py`, changed `max_seq_len = max_model_len + 512`
### Test Objective
Verify that the fix works correctly by running a standalone test with actual RULER NIAH data.
## Step 1: Copy Test Data
### Source Location
```
/home/zijie/Code/x-attention/eval/RULER/scripts/benchmark_root/full_fuse_16_llama3.1-8b-chat/synthetic/32768/data/niah_single_1/validation.jsonl
```
### Data Format
Each line is a JSON object:
```json
{
"index": 0,
"input": "<|begin_of_text|><|start_header_id|>user<|end_header_id|>\n\nA special magic number is hidden within the following text...",
"outputs": ["8930103"],
"length": 32768
}
```
- `input`: Full prompt with Llama 3.1 chat template (~122K characters, ~30K tokens)
- `outputs`: Expected answer (the magic number to find)
- `length`: Target sequence length in tokens
### Copy Command
```bash
mkdir -p /home/zijie/Code/nano-vllm/tests/data/ruler_niah
cp /home/zijie/Code/x-attention/eval/RULER/scripts/benchmark_root/full_fuse_16_llama3.1-8b-chat/synthetic/32768/data/niah_single_1/validation.jsonl \
/home/zijie/Code/nano-vllm/tests/data/ruler_niah/niah_single_1_32k.jsonl
```
## Step 2: Create Test Script
Create `/home/zijie/Code/nano-vllm/tests/test_ruler_niah_32k.py`:
```python
"""
Standalone test for RULER NIAH task with 32K context length.
This test verifies that CPU offload mode correctly handles long sequences
where prefill tokens approach max_model_len.
Usage:
python tests/test_ruler_niah_32k.py
"""
import json
import torch
from pathlib import Path
from nanovllm import LLM
from nanovllm.config import SamplingParams
# Configuration
MODEL_PATH = "/data/models/Llama-3.1-8B-Instruct"
DATA_FILE = Path(__file__).parent / "data/ruler_niah/niah_single_1_32k.jsonl"
MAX_MODEL_LEN = 32768
MAX_NEW_TOKENS = 50
# CPU Offload Settings
ENABLE_CPU_OFFLOAD = True
NUM_GPU_BLOCKS = 4
BLOCK_SIZE = 1024
def load_test_sample(filepath: Path, index: int = 0) -> dict:
"""Load a single test sample from JSONL file."""
with open(filepath) as f:
for i, line in enumerate(f):
if i == index:
return json.loads(line)
raise ValueError(f"Sample index {index} not found")
def test_niah_single():
"""Test NIAH single needle task with 32K context."""
print("=" * 60)
print("RULER NIAH 32K Standalone Test")
print("=" * 60)
# Load test data
sample = load_test_sample(DATA_FILE, index=0)
prompt = sample["input"]
expected = sample["outputs"][0]
print(f"Prompt length: {len(prompt)} characters")
print(f"Expected answer: {expected}")
print()
# Initialize model with CPU offload
print("Initializing LLM with CPU offload...")
llm = LLM(
model=MODEL_PATH,
max_model_len=MAX_MODEL_LEN,
enable_cpu_offload=ENABLE_CPU_OFFLOAD,
num_gpu_blocks=NUM_GPU_BLOCKS,
kvcache_block_size=BLOCK_SIZE,
enforce_eager=True, # Disable CUDA graphs for debugging
)
# Generate
print("Generating response...")
sampling_params = SamplingParams(
temperature=0.0, # Greedy
max_tokens=MAX_NEW_TOKENS,
)
outputs = llm.generate([prompt], sampling_params)
generated_text = outputs[0].outputs[0].text
print()
print("=" * 60)
print("Results")
print("=" * 60)
print(f"Expected: {expected}")
print(f"Generated: {generated_text[:200]}...")
print()
# Check if expected number is in output
if expected in generated_text:
print("SUCCESS: Magic number found in output!")
return True
else:
print("FAILED: Magic number NOT found in output")
print(f"Full output: {generated_text}")
return False
def test_multiple_samples(num_samples: int = 5):
"""Test multiple NIAH samples."""
print("=" * 60)
print(f"Testing {num_samples} NIAH samples with 32K context")
print("=" * 60)
# Initialize model once
llm = LLM(
model=MODEL_PATH,
max_model_len=MAX_MODEL_LEN,
enable_cpu_offload=ENABLE_CPU_OFFLOAD,
num_gpu_blocks=NUM_GPU_BLOCKS,
kvcache_block_size=BLOCK_SIZE,
enforce_eager=True,
)
sampling_params = SamplingParams(
temperature=0.0,
max_tokens=MAX_NEW_TOKENS,
)
correct = 0
for i in range(num_samples):
sample = load_test_sample(DATA_FILE, index=i)
prompt = sample["input"]
expected = sample["outputs"][0]
outputs = llm.generate([prompt], sampling_params)
generated_text = outputs[0].outputs[0].text
if expected in generated_text:
print(f"Sample {i}: PASS (found {expected})")
correct += 1
else:
print(f"Sample {i}: FAIL (expected {expected}, got: {generated_text[:50]}...)")
print()
print(f"Accuracy: {correct}/{num_samples} ({100*correct/num_samples:.1f}%)")
return correct == num_samples
if __name__ == "__main__":
import sys
if len(sys.argv) > 1 and sys.argv[1] == "--all":
success = test_multiple_samples(5)
else:
success = test_niah_single()
sys.exit(0 if success else 1)
```
## Step 3: Run Test
### Single Sample Test
```bash
cd /home/zijie/Code/nano-vllm
CUDA_VISIBLE_DEVICES=2,3,4,5 python tests/test_ruler_niah_32k.py
```
### All 5 Samples
```bash
cd /home/zijie/Code/nano-vllm
CUDA_VISIBLE_DEVICES=2,3,4,5 python tests/test_ruler_niah_32k.py --all
```
## Step 4: Expected Results
### Before Fix (Bug)
- Output: Garbled text like "not only has been replaced by thesiums..."
- Score: 0% (magic number not found)
- Time: ~80 seconds per sample
### After Fix (Expected)
- Output: The magic number (e.g., "8930103")
- Score: ~100% (magic number found)
- Time: ~80 seconds per sample (same, as the compute is unchanged)
## Debugging Tips
### Enable Verbose Logging
```python
import logging
logging.basicConfig(level=logging.DEBUG)
```
### Check Ring Buffer Size
In the logs, verify:
```
OffloadEngine initializing: num_layers=32, num_kv_buffers=4, max_seq_len=33280
```
The `max_seq_len` should be `32768 + 512 = 33280` (not 32768).
### Monitor GPU Memory
```bash
watch -n 1 nvidia-smi
```
With CPU offload, GPU memory for KV cache should be ~640MB (ring buffer only).
## Related Files
| File | Description |
|------|-------------|
| `nanovllm/kvcache/__init__.py` | Fix location: `max_seq_len = max_model_len + 512` |
| `nanovllm/kvcache/offload_engine.py` | Ring buffer allocation |
| `nanovllm/engine/model_runner.py` | Layer-wise offload prefill/decode |
| `nanovllm/kvcache/hybrid_manager.py` | CPU block management |
## Test Data Details
### NIAH Task Description
The NIAH (Needle-In-A-Haystack) task tests the model's ability to retrieve a specific piece of information (the "needle") from a large context (the "haystack").
- **Needle**: A magic number associated with a keyword (e.g., "worried-purse")
- **Haystack**: ~30K tokens of distractor text
- **Task**: Extract the magic number when asked
### Sample Prompt Structure
```
<|begin_of_text|><|start_header_id|>user<|end_header_id|>
A special magic number is hidden within the following text. Make sure to memorize it. I will quiz you about the number afterwards.
[... ~30K tokens of haystack text ...]
The special magic number for worried-purse is 8930103.
[... more haystack text ...]
What is the special magic number for worried-purse mentioned in the provided text?
<|eot_id|><|start_header_id|>assistant<|end_header_id|>
The special magic number for worried-purse mentioned in the provided text is
```
The model should complete with: `8930103`