Peter Lewis (peter.delete@this.notyahoo.com) on June 1, 2022 3:55 pm wrote:
> >> I think x86 will eventually be killed by variable length instruction decode, Moore’s law slowing
> >> down, availability of software binary translation from x86 to something else and most low-performance
> >> software running on top of JavaScript. The x86 instruction sets will eventually have the same market
> >> significance as the IBM 360 instruction set. I own Intel stock and I’m not selling because I think
> >> it will take more than 20 years for x86 to be displaced from the dominant position it has today.
> >
> > Why? What are the market forces that you believe will displace
> > x86? What do you think will replace it, RISC-V?
>
> My guess is the higher complexity and higher power consumption of x86 will eventually allow ARM implementations
> to outperform x86 implementations. Apple’s M1 P-cores currently decode 8 instructions per clock, while Intel’s
> Golden Cove cores in Alder Lake and Sapphire Rapids decode 6 instructions per clock. When ARM implementations
> are decoding 32 instructions per clock, it will be very difficult for x86 implementations to keep up.
>


People have been predicting this ever since the first superscalar RISCs appeared over 30 years ago, and it still hasn't happened. A couple years ago people were saying 3/4 wide was the best x86 could manage, now they've beat it. Are you saying where they are now is the limit, or will the goalposts shift again in 5 years when they take the next step wider?

There are obvious diminishing returns with decoding more instructions per clock, we will never see anything remotely approaching 32 wide (and if we did it would be stupid and pointless) Even 8 per clock is only useful a minority of the time. Anyway decode isn't a very large percentage of the power budget. Yes, it is a pain in the ass with x86's variable length instructions, but they've made it work.

Apple's M1 cores have lower power consumption because they are designed with power consumption having primacy over performance because phones are Apple's most profitable product. Thus they target frequencies 40% lower than Intel and AMD cores that are designed for PCs since there is effectively no x86 mobile device market. While laptops are growing in importance in the PC market they still take a back seat to CPUs operating in desktops and servers, so laptops get underclocked/undervolted/undercored versions of Intel and AMD cores optimized for devices running on wall power.