Actually many inference systems instead batch all requests within a time period and submit them as a single shot. It increases the average latency but handles more requests per unit time. (at least, this is my understanding how production serving of expensive models that support batching work)
I've done a bunch of optimization for GPU code (in CUDA) and there are typically a few bottle necks that really matter:
- memory bandwidth
- interconnect bandwidth between the CPU and GPU
- interconnect bandwidth between GPUs
- thermals and power if you're doing a good job of optimizing the rest
I don't see how a batching mechanism would improve on any of those, superficially it looks as though that would make matters worse rather than better. Can you explain where the advantage comes from?
It's a latency vs. throughput tradeoff. I was surprised as well. But most GPUs can do 32 inferences in the same time as they can do 1 inference. They have all the parallel units required and there are significant setup costs that can be amortized since all the inferences share the same model, weights, etc.
Very interesting, thank you. I will point one of my colleagues that is busy with this stuff to these and I thank you on his behalf as well, it is exactly the kind of thing they are engaged in.
I think in the case of LLM inference the main bottleneck is streaming the weights from VRAM to CU/SM/EU (whatever naming your GPU vendor of choice uses).
If you're doing inference on multiple prompts at the same time by doing batching, you don't take more time in streaming. But each streamed weights gets used for, say, 32 calculations instead of 1, making better use of the GPU's compute resources.
