How to optimize GPU usage in an AI app: Windsurf

How to optimize GPU usage in an AI app: Windsurf

The Pragmatic Engineer • 2025-05-13 • 1:19 minutes • YouTube

🤖 AI-Generated Summary:

Optimizing Low-Latency Inference for High-Volume AI Systems

In the world of AI, serving models that process hundreds of billions of tokens daily with ultra-low latency is a formidable challenge. Unlike typical API providers where the time to first token can tolerate slight delays (e.g., 100 milliseconds), some systems aim to push this boundary much further—targeting sub-200-millisecond latency while also delivering hundreds of tokens per second. Achieving this level of performance requires sophisticated optimization strategies and a deep understanding of hardware capabilities.

The Latency vs. Throughput Trade-off

One of the core challenges in AI inference is balancing latency and throughput. GPUs, the workhorse of modern AI computation, offer tremendous compute power—often over 100 times that of CPUs. However, their memory bandwidth advantage is only about tenfold. This mismatch means that many operations can become memory-bound rather than compute-bound if not carefully managed.

To harness the full potential of GPUs, inference workloads must be highly parallelized. But increasing parallelism typically means batching many requests together, which can increase latency because the system waits to accumulate enough work. For latency-sensitive applications, this waiting is unacceptable. Thus, the key is to architect solutions that maximize GPU utilization without sacrificing the responsiveness users expect.

Smart Approaches to Inference Optimization

Several techniques can help navigate these trade-offs:

Speculative Decoding: This approach involves predicting possible next tokens ahead of time to reduce wait times during generation. By guessing multiple likely continuations and verifying them quickly, it can speed up inference without compromising accuracy.
Model Parallelism: Splitting the model across multiple GPUs or processors allows for handling larger models and distributing workload. However, this must be balanced carefully to avoid communication overhead and latency spikes.
Efficient Batching: While batching improves throughput by processing multiple requests simultaneously, it must be dynamically managed to keep latency within strict limits. Adaptive batching strategies can help by adjusting batch sizes based on current load and latency targets.

Understanding Hardware Constraints

A nuanced understanding of GPU architecture is essential. Since GPUs have significantly more compute capacity but relatively less memory bandwidth compared to CPUs, workloads that are not computation-intensive can quickly become memory bandwidth-limited. This insight drives the need for:

Optimizing memory access patterns to reduce bottlenecks.
Designing models and inference pipelines that maximize compute utilization.
Avoiding unnecessary memory transfers and synchronizations.

Conclusion

Building AI inference systems that serve hundreds of billions of tokens daily with sub-200-millisecond latency and high throughput is a complex engineering challenge. It requires balancing parallelism, latency, and hardware constraints through approaches like speculative decoding, model parallelism, and smart batching. Understanding the fundamental hardware trade-offs—between compute and memory bandwidth—guides these optimizations, enabling cutting-edge AI applications to run faster and more efficiently than ever before.

📝 Transcript (47 entries):

How do you deal with inference? You're serving the systems that serve hundreds of billions tokens per day as you just said with low latency. What smart approaches do you do to do this? What kind of optimizations have you looked into? Latency matters a ton in a way that's like very different than some of these API providers. Like I think for the API providers, time to first token is important, but it doesn't matter that time to first token is 100 milliseconds.

For us, that's the bar we are trying to look for. Can we get it to sub couple hundred milliseconds and then hundreds of tokens a second? So much faster than what all of the providers are providing in terms of throughput as well just because of how quickly we want this product to kind of run. And you can imagine there's a lot of things that we want to do, right? How do we run how do we do things like speculative decoding?

How do we do things like model parallels? How do we make sure we can actually batch requests properly to get the maximum utilization of the GPU all the while not hurting latency. GPUs are amazing. They have a lot of compute. If I were to draw an analogy to CPUs, GPUs have over sort of two orders of magnitude more compute than a CPU. It might have should be more on the more recent GPUs, but keep that in mind. But GPUs only have an order of magnitude more memory bandwidth in a CPU. So what that actually means is if you do things that are not compute intense, you will be memory bound. So that necessarily means to get the most out of the compute of your processor, you need to be doing a lot of things in parallel. But if you need to wait to do a lot of things in parallel, you're going to be hurting the latency. So there's all of these different trade-offs that we need to make.

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