juanrga (nospam.delete@this.juanrga.com) on August 6, 2014 11:55 am wrote:
> Alberto (git.delete@this.git.it) on August 6, 2014 3:51 am wrote:
> > Yuhong Bao (yuhongbao_386.delete@this.hotmail.com) on August 3, 2014 2:24 pm wrote:
> > > http://www.mondaynote.com/2014/08/03/macintel-the-end-is-nigh
> >
> > http://www.extremetech.com/computing/187513-why-apple-wont-dump-intel-x86-for-its-own-arm-chips-in-macbooks-and-the-mac-pro
> >
>
> I liked the part when they appeal to "independent research" and then mention the same crap paper
> that every Intel fanboy mentions. I still recall the first time that I did read the paper by
> Blem, Menon, and Sankaralingam. After my initial perplexity on how almost any decision they took
> (from hardware to compiler version) seemed orientated to favor x86 over ARM, I did search further
> info about the senior author and found that one of the coworkers of his research team is an Intel
> lab guy, that several students in his group are awarded Intel grants... LOL

Yes, the answer is not a "strong" one at all.

That paper was discussed here when it came out, and numerous issues were pointed out with it. Not to mention that it absolutely does *not* show that ISA does not make a difference. The most it really attempts to show is that when looking at devices ranging from A8 to i7, microarchitecture perf/power/cost target is the first order effect. Which it is. What it does not show is whether the ISA made, say, 10% difference when holding all else equal.

Then we have this

"Intel's then-mobile chief Mike Bell clearly stated that the concept of an 'x86 tax' simply isn't true."

Which is obviously something a marketing/executive person would say, but it's also completely false. The *concept* of an x86 tax is absolutely true. And not just the concept, but even in implementation, we can take a really simple example which is the instruction decoding complexity, and point to that.[*]

There have also been engineers in the past acknowledge some inefficiencies and estimate "x86 tax" for then-PC class designs. Whether those are still valid with x64 and ever more complex CPUs is up for debate, but certainly the *concept* of an x86 tax is there.

It's also not really disputed that at the very small scale, x86 designs can't compete with simple ARM based microarchitectures.

I have also heard from many people (it's possible this is just an uninformed 'echo chamber effect', but I think there is some merit to the idea) that x86 cores take significantly more design skill than an equivalent ARM core. Whether this is due to compatibility, or decoders, or necessity of more capable memory pipline and caches, I don't know, but it seems to also be an x86 tax.

So the author should have just left out the technical handwaving completely.

ISA debate aside, I think Apple probably has the talent and money to make a design of capable performance with ARM64 too, given several more years.

Software compatibility argument is relevant, however 1. Apple has done it before, and 2. iOS is on ARM and has a much bigger user base, so in some sense they have something to gain of compatibility if they do make the move.

I think they would find a way to make it happen, if the economics made sense. I think they would certainly be considering their options, and it's going to depend on how their mobile designs progress, design team capability, iOS and OSX markets, etc. My prediction is that anybody who says they certainly will or will not (without qualifying a short time frame) is wrong, because Apple probably have not ruled out either option at this point.