---
id: wiki-2026-0508-real-time-operation
title: Real-time Operation
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Real-time Systems, RTOS, Real-time Inference]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [real-time, latency, rtos, streaming, inference]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: python
  framework: vllm
---

# Real-time Operation

## 매 한 줄
> **"매 deadline 의 miss 의 failure"**. Real-time 의 fast 와 X — predictable latency budget 의 within. Hard RT (RTOS, avionics) 의 missed deadline 의 catastrophic; soft RT (video, LLM streaming) 의 degraded UX.

## 매 핵심

### 매 분류
- **Hard RT**: 매 deadline 의 absolute (pacemaker, ABS brake). RTOS — VxWorks, QNX, Zephyr.
- **Firm RT**: 매 occasional miss 의 OK but useless after deadline (live video frame).
- **Soft RT**: 매 best-effort, degraded quality on miss (LLM token stream, web UI).

### 매 Latency budgets
- **HFT**: <10μs.
- **Game frame (60fps)**: 16.6ms.
- **VR frame (90fps)**: 11ms (motion-to-photon <20ms).
- **Web TTI**: <200ms perceived instant.
- **LLM TTFT**: <500ms (Claude Opus 4.7 streaming).
- **LLM inter-token**: <50ms (20 tok/s minimum readable).

### 매 Web real-time
- **SSE**: 매 server-push, HTTP/1.1 + 2, simple. LLM streaming default.
- **WebSocket**: bidirectional, binary OK. Chat, multiplayer.
- **WebRTC**: 매 P2P, sub-100ms voice/video.
- **HTTP/3 + WebTransport**: 매 2026 emerging — UDP-based, multiplexed.

### 매 AI Real-time inference
- **vLLM**: PagedAttention — 매 24x throughput vs naive.
- **MLX (Apple Silicon)**: M3/M4 의 unified memory — Llama 3.x 70B 의 local realtime.
- **Speculative decoding**: small draft model 의 2-3x speedup.
- **KV cache**: 매 prefix sharing — system prompt 의 cache.
- **Prompt caching (Anthropic)**: 매 90% cost cut, lower TTFT.

### 매 응용
1. LLM chat 의 streaming token-by-token.
2. Video conferencing (WebRTC).
3. Trading systems (kdb+, FPGA).
4. Robotics control loop (ROS 2 + Zephyr).
5. Live captioning (Whisper streaming).

## 💻 패턴

### LLM streaming with prompt cache
```python
from anthropic import Anthropic

client = Anthropic()

with client.messages.stream(
    model="claude-opus-4-7",
    max_tokens=2048,
    system=[{
        "type": "text",
        "text": LARGE_SYSTEM_PROMPT,  # 10k+ tokens
        "cache_control": {"type": "ephemeral"},
    }],
    messages=[{"role": "user", "content": "..."}],
) as stream:
    for text in stream.text_stream:
        print(text, end="", flush=True)
```

### SSE in FastAPI
```python
from fastapi import FastAPI
from fastapi.responses import StreamingResponse
import asyncio

app = FastAPI()

async def event_stream():
    for i in range(100):
        yield f"data: token {i}\n\n"
        await asyncio.sleep(0.05)

@app.get("/stream")
async def stream():
    return StreamingResponse(event_stream(), media_type="text/event-stream")
```

### vLLM batched inference server
```python
from vllm import LLM, SamplingParams

llm = LLM(model="meta-llama/Llama-3.3-70B", tensor_parallel_size=4,
          enable_prefix_caching=True)
params = SamplingParams(max_tokens=512, temperature=0.7)

# Continuous batching — 매 새 request 의 mid-batch 의 join.
outputs = llm.generate(prompts, params)
```

### Game loop (fixed timestep)
```rust
const DT: f32 = 1.0 / 60.0;
let mut acc = 0.0;
let mut last = Instant::now();

loop {
    let now = Instant::now();
    acc += (now - last).as_secs_f32();
    last = now;
    while acc >= DT {
        physics_step(DT);
        acc -= DT;
    }
    render(acc / DT); // interpolate
}
```

### RTOS task (Zephyr)
```c
K_THREAD_DEFINE(ctrl_tid, 1024, control_loop, NULL, NULL, NULL,
                K_PRIO_PREEMPT(2), 0, 0);

void control_loop(void *p1, void *p2, void *p3) {
    while (1) {
        read_sensors();
        compute_pid();
        actuate();
        k_sleep(K_MSEC(10));  // 100Hz hard deadline
    }
}
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Safety-critical (medical, auto) | Hard RT — RTOS, formal verification |
| LLM chat | SSE streaming + prompt cache |
| Multiplayer game | UDP + WebRTC / custom protocol |
| Voice/video call | WebRTC |
| HFT | Kernel bypass (DPDK), FPGA |
| Robotics | ROS 2 + Zephyr/PREEMPT_RT Linux |

**기본값**: SSE + Anthropic streaming for LLM, WebSocket for bidirectional chat.

## 🔗 Graph
- 부모: [[Distributed-Systems]]
- 변형: [[Streaming]]
- 응용: [[WebRTC]] · [[Game-Loop]]
- Adjacent: [[Latency-Optimization]] · [[LLM_Optimization_and_Deployment_Strategies|vLLM]]

## 🤖 LLM 활용
**언제**: 매 user-facing chat (TTFT < 500ms), 매 long-output (token streaming UX), tool-use loops.
**언제 X**: batch processing (use Batch API — 50% cheaper), embeddings (single-shot), latency-insensitive analytics.

## ❌ 안티패턴
- **Block on full response**: 매 user 의 spinner 의 30s — 매 stream 의 use.
- **Soft RT 의 hard guarantees claim**: Linux + GC 의 hard RT X.
- **No timeout**: hung connection 의 leak — `httpx.Timeout(30.0, connect=5.0)`.
- **No backpressure**: producer 의 consumer 의 outpace → OOM.
- **Synchronous in event loop**: `time.sleep` 의 asyncio 의 block.

## 🧪 검증 / 중복
- Verified (vLLM docs, Anthropic streaming API, WebRTC RFC, Zephyr docs).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — RT systems + web streaming + LLM inference unified |