Task Failed Successfully: Saturating NIC and Disk Bandwidth
4 days ago
- #Performance Optimization
- #AI Debugging
- #System Analysis
- AI agent successfully optimized system performance but provided incorrect explanations, leading to a deeper analysis.
- Initial demo showed bottleneck at half NIC bandwidth due to CPU cost from per-I/O buffer handling with Direct I/O.
- Using io_uring registered buffers (READ_FIXED) eliminated per-I/O page-table walks and pinning, allowing NIC saturation.
- Scaling to a larger deployment revealed new bottleneck, with throughput only half of theoretical maximum.
- Ruled out iou-wrk overhead, fget costs, and CRC computation as primary bottlenecks through experiments.
- Identified TLB misses as the real bottleneck due to 4 KiB page translations during data scanning.
- Using hugepages reduced dTLB misses and resolved the bottleneck, enabling near-NIC saturation.