Posts by Menghsuan Yang
Debugging NaN Results in CK Tile GEMM: A rocgdb Detective Story
- 30 January 2026
When developing high-performance GPU kernels, subtle bugs can lead to catastrophic failures like NaN (Not-a-Number) outputs. This post chronicles our journey of debugging a tricky NaN issue in AMD’s Composable Kernel (CK) Tile GEMM implementation using rocgdb. What started as mysterious NaN outputs ended with discovering a single-character typo that corrupted the data distribution.
Avoiding LDS Bank Conflicts on AMD GPUs Using CK-Tile Framework
- 25 July 2025
LDS bank conflict is a common performance bottleneck in GPU kernel development. Composable Kernel (CK-Tile), a kernel development framework for AMD GPUs, provides a framework-level solution for LDS bank conflicts. Composable Kernel for ROCm is used to build portable high-performance kernels for accelerating computing, e.g. HPC, DL and LLMs for training and inference workloads. In this blog, we show you how to analyze, detect, and eliminate LDS bank conflicts using CK-Tile, AMD’s composable GPU kernel framework. A GEMM kernel serves as a classic example for analyzing how threads interact with LDS during both reads and writes. Starting with a naïve memory layout, we evaluate bank conflict behavior, explore mitigation techniques such as padding, and ultimately demonstrate how an XOR-based swizzle transformation achieves a bank conflict-free design.