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Profiling with Nsight

Nsight Systems answers where wall-clock time goes across CPU, kernels and copies; Nsight Compute answers why one kernel is slow, from hardware counters. The skill interviewers test is the order: timeline first, then the Speed of Light section, then the two or three metrics that name the bottleneck, so that a memory-bound kernel is recognized from its profile in under a minute and the fix is bytes, not occupancy.

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RELATED CONCEPTS

Memory Coalescing Occupancy and Register Pressure Kernel Fusion Roofline Model torch.compile and CUDA Graphs Stragglers and Hangs

PRACTICE THIS IN REAL QUESTIONS

GPU & Accelerator ArchitectureAn Nsight summary reads DRAM 90%, SM 30%, occupancy 45%, L2 hit rate 20%. What is the bottleneck?→CUDA, Triton & Kernel EngineeringA training step runs at 20 percent model FLOPs utilization. Profile it and find where the missing time goes.→CUDA, Triton & Kernel EngineeringHere is an Nsight Compute report for a slow kernel. Read it, name the bottleneck, and tell me what you would change.→LLM Inference & Servingnvidia-smi shows 30 percent utilization on our serving fleet. Is that a problem, and what would you look at instead?→CUDA, Triton & Kernel EngineeringExplain FlashAttention. Why is it called IO-aware, and what does it actually save?→Napkin Math, Cost & CapacityA kernel does 4 TFLOP and moves 40 GB in one call. On an H100, is it memory-bound or compute-bound?→