ARM or x86? ISA Doesn't Matter (2021)

The ongoing debate between ARM and x86 instruction set architectures (ISAs) has been a focal point in discussions about CPU performance. However, recent insights suggest that the differences in ISAs are less significant than previously thought. Notably, Jim Keller, a prominent CPU designer, argues that the historical distinctions between CISC (x86) and RISC (ARM) have largely converged, with modern performance being dictated more by microarchitectural design than by the ISA itself. Research indicates that both ARM and x86 CPUs have been optimized for different use cases, leading to variations in power consumption and performance, but not due to inherent advantages of one ISA over the other. Studies have shown that the complexity of decoding instructions, often cited as a disadvantage for x86, does not significantly impact performance in high-end CPUs. Both architectures have adopted similar techniques, such as micro-op caches, to mitigate decoding costs. Furthermore, ARM instructions can also decode into multiple micro-operations, challenging the notion of ARM's efficiency. Ultimately, the conclusion is that the implementation of the CPU design is far more critical than the ISA, and competition in the high-performance CPU market is driven by design choices rather than instruction set differences.

- The differences between ARM and x86 ISAs are becoming less relevant in terms of performance.

- Modern CPU performance is more influenced by microarchitectural design than by the ISA itself.

- Both ARM and x86 have adopted similar techniques to improve efficiency, such as micro-op caches.

- ARM instructions can decode into multiple micro-operations, challenging the efficiency narrative.

- Implementation choices are more critical than ISA differences in the high-performance CPU market.