Said another way, I highly doubt we will see a non-Apple ARM CPU outclass the x86 competition in such a way anytime soon, so saying "never x86 again" might not be very wise. ARM is not a magic bullet.
A lot of people asking for ARM based machines do not really realize that the reason is not because of ARM, but they just want faster/more efficient machines. I think to make a analogy for HN frontend sw devs, imagine a non-technical marketing person going to a developer and saying "I want this website in AMP, because AMP is fast.". And sure, a lot of sites with AMP framework are fast... but that doesn't mean that you have to build a site in AMP to make it fast. You could build a simple site with similar principles and get it fast too. Similarly, not all ARM laptops are fast. Even if the laptops hw is fast, you want something that can efficiently run x86 code as well for compatibility purposes for many years.
Some examples:
- x86 guarantees strong memory ordering on multi-processor systems, which adds completely unnecessary overhead to every memory access. arm64 uses a weak memory model instead, providing atomic instructions with relaxed or acquire/release semantics (see https://youtu.be/KeLBd2EJLOU?t=28m19s for a more detailed discussion). This significantly improves performance all around the board, but especially with reference counting operations (which are extremely common and often a bottleneck in code written in ObjC/Swift): https://twitter.com/Catfish_Man/status/1326238434235568128
> fun fact: retaining and releasing an NSObject takes ~30 nanoseconds on current gen Intel, and ~6.5 nanoseconds on an M1
- x86 instruction decode is pretty awful, a significant bottleneck, and not parallelizable due to the haphazardly-designed variable-length CISC instruction set. arm64’s instruction set is highly regular and easy to decode, so Apple can decode up to 8 instructions per clock (as opposed to 4 for x86 chips). Most sources agree this is why the M1 can have such a big out-of-order-execution window and achieve such high instruction-level parallelism compared to Intel/AMD.
- x86_64 has only 16 architectural registers, compared to 32 for arm64. This means the compiler has a much harder time generating efficient, parallelizable code and must resort to spilling registers much more often.
Apple has a much bigger issue, though. ARM doesn't scale: it's a fundamental conceit of the architecture, one that a lot of people are probably willing to take on a laptop that will mostly be used for Twitter and YouTube. This presents issues for the rest of the market though, and it will be fascinating to see how Apple retains their pro userbase while missing out on the high-performance hardware sector entirely.
I think x86 is pretty terrible too, if it's any consolation, but really it's the only option you've got as a programmer in the 21st century. I hopped on the Raspberry Pi bandwagon when I was still in middle school, I grew up rooting for the little guy here. Looking out on the future landscape of computer hardware though, I really only see RISC-V. ARM is an improvement on x86, but I don't think it's profound enough to make people care. RISC-V, on the other hand, blows both of them out of the water. On consumer hardware, it's able to accelerate pretty much any workload while sipping a few mW. On professional hardware, you can strap a few hundred of those cores together and they'll work together to create highly complex pipelines for data processing. On server hardware, it will probably move like gangbusters. Even assuming that cloud providers pocket half the improvements, a 5x price/performance increase will have the business sector racing to support it.
So yeah, it is a pretty complex situation. Apple did a cool thing with the M1, but they have a long ways to go if they want to dethrone x86 in it's entirety.
> ARM is really old now.
Well aarch64 was announced in 2011 so not really that old.
> Apple’s implementation of ARM is decidedly CISC.
CISC is a description of the instruction set not the implementation.
> ARM doesn’t scale.
No idea what this means but you can get 128 core Arm CPUs and address huge amounts of memory but perhaps you have another definition of scaling.
And so on.
Stuff like hardware primitives for AES/SHA, or the FJCVTZS “JavaScript instruction” don’t make a processor CISC just because they’re specialized. They all encode trivial, single-cycle hardware operations that would otherwise be difficult to express in software (even though they may be a bit more specialized than something like “add”, they’re not any more complex). x86 is CISC because the instruction encoding is more complicated, specifying many hardware operations with one software instruction.
I’m not exactly sure whar all the “cruft” is in ARM that you’re referring to. The M1 only implements AArch64, which is less than 10 years old and is a completely new architecture that is not backwards-compatible with 32-bit ARM (it has been described as being closer to MIPS than to arm32). NEON doesn’t strike me as a good example of cruft because SIMD provides substantial performance gains for math-heavy programs, and in any case 10 years of cruft is much better than 45.
I’m curious as to why RISC-V is different or better? I don’t know much about RISC-V — but looking at the Wikipedia article, it just looks like a generic RISC similar to MIPS or AArch64 (and it’s a couple years older than AArch64 as well). Is there some sort of drastic design difference I’m missing?
Of course the flexibility of the RISC-V model allows approaches such as that being pursued by Esperanto [1] with lots and lots of simpler cores.
[1] https://www.esperanto.ai/wp-content/uploads/2021/08/HC2021.E...
I find it hard to believe that they didn't drop Thumb from AArch64 without a lot of analysis of the impact on performance.
Remember that M1 is just a mobile SoC that work for iPad/MacBook Air. It's exceptionally great so people tend to confuse M1 is targeted higher end. 16GB max is fine for a mobile SoC in 2021. I can't wait M1X.
If we were to go back in time to before apple introduced it’s own SoC and before it had acquired chip design start ups, even before than ARM was on the table as that is what the iPhone ran.
RISC-V wasn’t a thing back then. So the alternatives were MIPS, Power or maybe a home grown instruction set.
So we just have to go with what the reality is now. The apple silicon has been well optimised for performance per watt. And it runs on an ARM instruction set that apple itself helped in the design of.
Also non Apple Arm CPUs do outclass x86 in a huge segment of the cpu marketplace - on smartphones and tablets.
I’d don’t think that anyone previously has thrown the amount of cash at laptop / desktop / server Arm designs that Intel spends on x86 designs - we are now seeing a number of firms having a serious go (AWS / Ampere / Qualcomm / Nvidia possibly) so with Intel fighting back on its process issues it will be an interesting few years!
Since almost (all?) mobile phones use ARM I can see a similar process of adapting other ARM processors to the PC market.
But of course Apple is so far ahead that we really don't know wether and when there will be a competitive alternative, so it may as well be a streamlined x64, or a new ISA, sure.
It seems to all depend on some very experienced CPU design teams and it seems that actually Apple lost some of them in the last year, I would track these news to get a better model of predicting the future than the ARM/x64 divide.