Assembly Hall of Shame
The 'Assembly Hall of Shame' project takes an adversarial approach to CPU performance, meticulously crafting single x86 instructions to run as slowly as possible, rather than optimizing for speed. It documents ingenious strategies to exploit obscure microarchitectural behaviors and system bottlenecks, pushing instructions to execute for seconds or even minutes. This deep dive into hardware idiosyncrasies captivates HN's low-level enthusiasts who appreciate the perverse artistry of maximum inefficiency.
The Lowdown
The 'Assembly Hall of Shame' is a unique research project that inverts the typical goal of performance optimization. Instead of making code faster, it seeks to identify and engineer single x86 instructions to execute with the longest possible latency. This involves a deep and creative understanding of CPU microarchitecture and system interactions to turn otherwise fast operations into excruciatingly slow ones.
- The project maintains an x86 leaderboard, detailing instructions ranked by their maximum achievable execution time.
- Each entry includes a specific "strategy" explaining the precise method used to induce extreme latency.
- The current champion,
fxrstor64, achieves a staggering 62-second execution time by loading a large FPU/MMX/XMM state from a high-latency MMIO region while other CPU cores simultaneously pound different MMIO registers, saturating the PCIe fabric. - Other high-ranking instructions exploit behaviors such as unaligned memory accesses across MMIO regions, split locks forcing external bus locks, denormal floating-point calculations triggering microcode assists, and interactions with specific high-latency Model Specific Registers (MSRs) or I/O ports.
- Strict rules govern the competition, ensuring only a single instruction is scored, traps are excluded, and hardware remains in factory configuration.
- The project plans to expand with leaderboards for ARM and RISC-V architectures.
This collection serves as a fascinating, if counter-intuitive, exploration of CPU internals, showcasing the complex interplay between instructions, memory, and system buses that can be manipulated for extreme performance degradation.