Comment on Linus Torvalds says RISC-V will make the same mistakes as Arm and x86
Traister101@lemmy.today 2 months agoCounterintuitive but more instructions are usually better. It enables you (but let’s be honest the compiler) to be much more specific which usually have positive performance implications for minimal if any binary size. Take for example SIMD which is hyper specific math operations on large chunks of data. These instructions are extremely specific but when properly utilized have huge performance improvements.
JayDee@lemmy.ml 2 months ago
I understand some instruction expansions today are used to good effect in x86, but that there are also a sizeable number of instructions that are rarely utilized by compilers and are mostly only continuing to exist for backwards compatibility. That does not really make me think “more instructions are usually better”. It makes me think “CISC ISAs are usually bloated with unused instructions”.
My whole understanding is that while more specific instruction options do provide benefits, the use-cases of these instructions make up a small amount of code and often sacrifice single-cycle completion. The most commonly cited benefit for RISC is that RISC can complete more work (measured in ‘clockcycles per program’ over ‘clockrate’) in a shorter cyclecount, and it’s often argued that it does so at a lower energy cost.
I imagine that RISC-V will introduce other standards in the future (hopefully after it’s finalized the ones already waiting), hopefully with thoroughly thought out instructions that will actually find regular use.
I do see RISC-V proponents running simulated benchmarks showing RISC-V is more effective. I have not seen anything similar from x86 proponents, who usually either make general arguments, or worse , just point at the modern x86 chips that have decades of research, funding, and design behind them.
Overall, I see alot of doubt that ISAs even matter to performance in any significant fashion, and I believe it for performance at the GHz/s level of speed.