Intel Dismisses 'x86 Tax', Sees No Future For ARM

MrSeb writes "In an interview with ExtremeTech, Mike Bell — Intel's new mobile chief, previously of Apple and Palm — has completely dismissed the decades-old theory that x86 is less power efficient than ARM. 'There is nothing in the instruction set that is more or less energy efficient than any other instruction set,' Bell says. 'I see no data that supports the claims that ARM is more efficient.' The interview also covers Intel's inherent tech advantage over ARM and the foundries ('There are very few companies on Earth who have the capabilities we've talked about, and going forward I don't think anyone will be able to match us' Bell says), the age-old argument that Intel can't compete on price, and whether Apple will eventually move its iOS products from ARM to x86, just like it moved its Macs from Power to x86 in 2005."

Comments

Speed versus complexity

[girlintraining]

You know, we had the same argument with RISC versus CISC architecture. And we know who lost that one. Badly. And the reason for that is because the bandwidth outside the processor, the I/O, is so damnably slow compared to what's possible on the die itself. That's why the data transfers to and from the CPU are only about 1/30th or less the speed at which the CPU runs internally. The only logical course of action is to do as much as you can on each byte of data coming off the bus as you can. Besides, look at Nvidia's GPU cores: They throw hundreds of cores onto the die, but it eats hundreds of watts as well. Massively parallel and simple instruction sets don't appear to translate into energy savings.

Re:Speed versus complexity

[phantomfive]

Intel won the CPU wars because of manufacturing, not because of a superior instruction set. They are always able to get a smaller manufacturing process.

For example, taking your point about data bandwidth, because the x86 has so few registers, it has to do data IO a lot more compared to something like the PowerPC or SPARC.

To make up for that, Intel built a lot of logic in microcode and pipe-lining. It was a lot of work, but they did it well, so the x86 gets acceptable performance. All that extra logic takes power though. So Intel has a tradeoff between power consumption and performance that they can make. This guy seems to be saying they will switch to reduce power consumption, and then make up for it by having the best manufacturing process once again.

And they do. For probably as long as chips continue to get smaller, Intel will have the advantage.

Re:Speed versus complexity

[Chas]

Intel won the CPU wars because of manufacturing, not because of a superior instruction set.

There's nothing inherently "superior" about ARM or PPC instruction sets.

Each has its strengths and weaknesses and prescribed methods of capitalizing on the former while working around the latter.

Is x86, possibly, more inelegant than ARM or PPC? Maybe. Then again, what exactly is so elegant about a "catch all" platform where the basic processor architecture can change wildly between manufacturers, leading one to require many "flavors" of code simply to cover multiple vendor platforms?

x86 may be ugly and hackish. But it's probably THE best documented platform in history and has very VERY few platform segregation points.

Re:Speed versus complexity

[danlip]

And we know who lost that one. Badly.

We do? The world's fastest supercomputer (K computer) is RISC based, and ARM is RISC, so it seems very much alive. Also CISC now has pipelining which was the thing that originally made RISC awesome, and RISC has gotten more complex, so they have evolved to be closer to each other. I am sure there are other factors that are more important for energy efficiency (mainly transistor size) and I don't have an opinion on that, but I don't understand where you are coming from.

Re:Speed versus complexity

[Anonymous Coward]

The processor architecture is not wildly different between manufacturers. The System On Chip designs in which the CPU is just one element is what makes them different. Should Intel produce custom x86 SoC you can expect the same.

Re:Speed versus complexity

[10101001 10101001]

There's nothing inherently "superior" about ARM or PPC instruction sets.

The GP didn't say anything of the sort. He was pointing out that to say "CISC won" is only true if you consider that x86 is CISC and Intel spend gobs of money to be at the forefront of CPU manufacturing technology, both in shrinking die size/increasing clock speed and shoehorning all the negative characteristics of the x86 design into a form that was more RISC like so it could allow for super-scalar and deep pipeline designs. Intel deserves a lot of credit in proving just how far CISC design can go. But it certainly wasn't that CISC won because it had greater strengths.

Is x86, possibly, more inelegant than ARM or PPC? Maybe. Then again, what exactly is so elegant about a "catch all" platform where the basic processor architecture can change wildly between manufacturers, leading one to require many "flavors" of code simply to cover multiple vendor platforms?

Sounds like Linux on the x86, actually. Seriously, though, RISC design tends to have a few very strong design elements: it tends to have a good many registers which absolves a lot of cache/stack work, it tends to have a fixed opcode size and requires aligned memory which usually improves throughput and allows for a much more streamlined instruction decoding engine, and precisely because there's a lot less need to support legacy platforms there's a lot more leeway to segment memory for power considerations.

x86 may be ugly and hackish. But it's probably THE best documented platform in history and has very VERY few platform segregation points.

Well, you can think MS's monopolistic actions for that. Seriously, "ugly and hackish"* might well describe near everything MS and Intel can be known for, in their question to maintain backwards compatibility. And if Intel had started out with an 8-bit RISC design, I'm certain there'd be the same problems, so it's not really an x86/CISC thing. Never the less, it's precisely the fact that Intel is unlikely to allow platform segregation points that x86 will probably never be low power.

*And please realize, I say this with a great deal of respect towards both Intel and MS in maintaining performance giving how many hacks they've put in over the years to compensate for not only their own bugs but the bugs of other developers. So, as pretty and clever as a lot of the hacks may be, it's still ugly overall to have the hacks in the first place and to have so many over so many places and to be so incapable of removing any without the risk of significant backlash or simply to lose their customer base. Ie, the code may be pretty but it's put them in an ugly place.

Re:Speed versus complexity

[yakovlev]

For a "modern" CPU the instruction decoder is an absurdly tiny part. This is because the branch prediction, caches, issue queue, regfiles, etc. are all much larger or at least the same size.

This isn't nearly so true in a super-low-power mobile design. The instruction decoder size for a given instruction set architecture is pretty much a fixed size per decode pipe. This means that in one of these tiny mobile chips the relative size of the decoders is dramatically larger. A super-low-power chip dramatically reduces the sizes of the caches and branch prediction, reduces the size of the regfiles, and often eliminates the issue queue. It probably also removes a decode pipe, but the relative reduction in decode size is much smaller than the relative size reduction in other areas.

The limited register set absolutely hurts x86 on power usage, perhaps more than the decoders do, since it forces more data cache accesses for register spills and fills.

Now, I'm not saying that x86 is necessarily worse than arm on power usage, as the richer instruction set may have other advantages such as reducing instruction cache miss rate which can be used to improve IPC which can be spent to lower frequency and reduce power. Also, microcoded instructions may turn out to be more power efficient because they don't have to access the instruction cache every cycle.

None of this considers the fact that Intel has the best fab technology in the world. This means their processors will be a generation more efficient than everyone else's, which is probably more than enough to counter any "x86 tax" which the instruction set incurs.

Re:Speed versus complexity

[hairyfeet]

While this is true frankly its only been fairly recently that either AMD or Intel gave a crap about power, and look at how far they've come? Intel has gotten Atoms to less than 3w, AMD has gotten dual cores AND a decent GPU down to 9w in the C Series bobcats, and of course the Intel CULV Core chips can do a scary amount of processing on I believe their latest are sub 10w. Now according to ARM their A9 duals are just a hair under 2w. that of course isn't counting the chips like the hardware decoders typically found with ARM because it just can't do as many IPCs as X86.

So I'd say as folks demand more and more performance out of their mobile devices the advantage will probably swing to Intel.Tthey have the fabs and have been able to shrink quicker than anybody else so 1 or 2 more shrinks and its gonna be pretty damned close and with such a huge IPC difference between X86 and ARM in a damned close race I'm sure many would rather have the faster Intel chip, AMD will most likely be stuck at the niche they are now, at least as long as they stick with the faildozer "half a core" design so that just leaves Intel and ARM and with the money, the fabs, and the R&D budget that Intel has i think it'd be crazy to call it for ARM at this stage of the game.

After all it wasn't too long ago that everyone was making netburst space heater jokes and look how quickly that situation changed. I seriously doubt Intel is gonna sit this one out and when looking at their past record there is no reason to think they can't make a chip that'll compete.

Re:Speed versus complexity

[bzipitidoo]

x86 is ugly. It's one of the most screwed up, inconsistent, crufty architectures ever created. Motorola's 68000 architecture was a lot cleaner. But Intel, through sheer brute force, has managed patch up many of its shortcomings and make x86 perform well in spite of itself.

They went with a load and execute architecture for the x86 instructions. Then they didn't stick to that model for the floating point instructions, going with a stack for that. And remember they split the CPU into 2 parts. If you wanted the floating point instructions, you had to get a very expensive matching x87 chip. I still remember the week when 80387 prices collapsed from $600 to $200, and still no one would buy, not with free emulators and the 486DX nearing release. Another major bit of ugliness was the segment. Rather than a true 32bit architecture, they used this segmented architecture scheme, then buggered it up even more by having different modes. In some modes, the segment and address were simply concatenated for a 32bit address space, and in others 12 bits overlapped to give only a 20bit address space. Then you had all this switching and XMS and EMS to access memory above 1M. Nasty.

x86 has been bashed for years for not having enough registers. And for making them special purpose. For instance, only one, AX, can be used for integer multiplication. Ask some compiler designers about the x86 sometime. Bet you'll get an earful.

Few platform segregation points? Maybe, but one price is lots of legacy garbage. x86 still has to support those ancient segmented modes. Then there's junk like the ASCII adjust and decimal adjust instructions: AAA, AAS, AAD, and AAM, and DAA, and DAS. Nobody uses packed decimal any more! And hardly anyone ever used it. Those instructions were a crappy way to support decimal anyway. If they were going to do it at all, should have just had AA for ASCII Add instead of "adjusting" after a regular ADD instruction. Then there's the string search instructions, REPNE CMPSW and relatives. They're hopelessly obsolete. We have much better algorithms for string search than that. They also screwed up the instructions intended for OS support on the 286. That's one reason why the lowest common denominator is i386 and not i286. 286 is also only 16bit.

You might be tempted to think x86 was good for its time. Nope. Even by the standards and principles of the 1970s, x86 stinks.

Someone mentioned CISC, as if that beat out RISC? It didn't. Under the hood, modern x86 CPUs actually translate each x86 instruction to several RISC instructions. So why not just use the actual RISC instruction set directly? One argument in favor of the x86 instruction set is that it is denser. Takes fewer bytes than the equivalent action in RISC instructions. Perhaps, but that's accidental. If that is such a valuable property, ought to create a new instruction set that is optimized for code density. Then, as if x86 wasn't CISC enough, they rolled out the MMX, SSE, SSE2, SSE3, SSE4 additions.

That makes a powerful argument in favor of open source. Could drop all the older SSE versions if only all programs could be easily recompiled.

Re:Speed versus complexity

[dgatwood]

Three watts isn't even close to usable for a mobile phone. At that level of power consumption, you would either have to charge your phone every half hour (by the time you add in the chipset consumption) or build a phone that looks like one of those old portable phones from the 1980s with the small suitcase attached....

Intel's latest Atom offerings, however, claim to draw about two orders of magnitude less power than that at idle, and are thus in the ballpark for being usable for phones and similar devices. It remains to be seen who will adopt it.

BTW, last I read, a 2GHz Cortex A9 CPU based on a 40 nm process drew about 250 mW max, not 2W, though those numbers could easily be wrong.

Re:Speed versus complexity

[Dahamma]

And the most insightful post of the thread is from an AC... if you had posted non-AC I might have modded you up ;)

It also points out how the GP post talking about slow off-die IO is way overrated and really not all that relevant to the mobile/embedded space.

ARM is winning the embedded STB/TV/BD/phone wars because their core is tiny and integrates well in SoCs. Many of these SoCs have graphics, Ethernet, Wifi, USB, SATA, HW crypto, MPEG decoding, etc all on die, on a $10-20 part. Intel may have something a bit faster, but they don't have anything close in overall features for that price.

Well...

[QuietLagoon]

What did you expect him to say... that an Intel product was not suitable for the mobile marketplace? That would have been career suicide for him. He is singing from the Intel songbook. Those songs may not be sung with what is best for the customer in mind.

Turn that boat around

[busyqth]

Intel spent many years chasing performance with little thought of power draw.
Now they are putting all their engineering muscle into minimizing power requirements, while maintaining high performance.
I don't see any reason to think they won't succeed, and if they do, then ARM will end up a niche architecture.

He's mostly right

[Erich]

All those scalar processors look the same. You can trade energy efficiency for performance and end up with a lower power processor that's a lot slower. When you push the performance, the architecture doesn't matter as much, because most of the energy is spent figuring out what to run and when to run it.

Compounding this fact, ARM isn't that great of an architecture. It's got variable length instructions, not enough registers, microcoded instructions, and a horrible, horrible virtual memory architecture.

The big thing that ARM has is the licensing model. ARM will give you just about everything you need for a decent applications SOC. Processor, bus, and now even things like GPU and memory controllers. Sprinkle in your own companies' special sauce, and you have a great product. All they ask is for a little bit of royalty money for every chip you sell. And since everyone is using pretty much the same ARM core, the tools and "ecosystem" is pretty good.

But there's not much of an advantage to the architecture... the advantage is all in the business model, where everyone can license it on the cheap and make a unique product out of it.

And nowadays, the CPU is becoming less important. It's everything around it -- graphics, video, audio, imaging, telecommunications -- is what makes the difference.

Re:He's mostly right

[Darinbob]

ARM has fixed length instructions. Thumb is a separate instruction set from ARM and is also a fixed size set. You can't easily interchange ARM and Thumb without making a function call. There is Thumb 2 that interchanges them more easily now. However the instruction set decoder for Thumb to ARM is so very very simple that it could even be a standard project in an undergrad CS class. Thumb really is for people who are willing to give up some performance to save space anyway. ARM has plenty of registers compared to Thumb. I think it has the sweet spot of 16 registers which is enough to not feel cramped but not so many that context switching or interrupts get in your way. ARM is not micro-coded in any model as far as I know, it is RISC and there's no reason to do any micro-coding (maybe in an FPU coprocessor?).

However it does have a goofy MMU at times, however this is treated as a separate coprocessor and is not intrinsic to the ARM (a different ARM system-on-chip will handle memory mapping and VM differently, it is not standardized).

He's missing the point...

[romanval]

ARM works because 1) it's good enough while being 2) cheap enough. As far as I know, ARM is getting license royalties in the pennies per chip or SoC core using their design. For how much better Intel can make their low power x86 CPUs, its going to have to compete with dozens of foundries churning out millions of ARM devices when it comes to pricing...and thats where I see Intel having a hard time.