Model FLOPs Utilization (MFU)

MFU is a ratio intended to describe how much of a system's theoretical compute capability is being used for the model's useful work. A common conceptual formula is estimated model FLOPs executed per second divided by the hardware's theoretical peak FLOPs per second for the same arithmetic precision. For a language model, estimated work per token can be combined with observed token throughput to form the numerator. Both terms require clear definitions. The model-FLOP estimate depends on architecture. Dense layers, attention, sequence length, parameter sharing, mixture-of-experts routing, and training versus inference affect how much work a token requires. The denominator depends on GPU generation, precision mode, and whether the peak assumes specialized units. Using an incompatible peak or counting FLOPs differently can make comparisons misleading. MFU is not GPU utilization from a system monitor. A device may report busy while spending time on memory movement, communication, kernels with low arithmetic intensity, or work not counted in the model-FLOP estimate. Conversely, a high MFU says nothing by itself about model quality, energy efficiency, or whether the training run is cost-effective. Pair it with throughput, latency, memory use, scaling efficiency, power, and evaluation metrics. Published large-scale training reports give context but not a universal goal. Some Megatron-LM results report roughly 30 percent of peak in one setup, while other large-scale reports describe per-GPU or MFU values in the low-to-mid 50 percent range under different models and systems. These figures use particular hardware, parallelism, and accounting choices. They are examples, not an expected range for every model. Use consistent conventions when comparing configurations. Record precision, theoretical peak source, model-FLOP formula, tokens processed, warmup, communication inclusion, and whether results are averaged across devices. Investigate low MFU with profiling rather than assuming the GPU needs replacement.