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AMD claims Arm ISA doesn't offer efficiency advantage over x86

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Re: AMD claims Arm ISA doesn't offer efficiency advantage over x86

#341

Post by jabl »

codedokode wrote: post #124
torginus wrote: post #18

Earlier quoted context omitted.

I remember reading this Jim Keller interview: https://web.archive.org/web/20210622080634/https://www.anand... Basically the gist of it is that the difference between ARM/x86 mostly boils down to instruction decode, and: - Most instructions end up being simple load/store/conditional branch etc. on both architectures, where there's literally no difference in encoding efficiency - Variable length instruction has pretty…

x86 decoding must be a pain - I vaguely remember that they have trace caches (a cache of decoded micro-operations) to skip decoding in some cases. You probably don't make such caches when decoding is easy. Also, more complicated decoding and extra caches means longer pipeline, which means more price to pay when a branch is mispredicted (binary search is a festival of branch misprediction for example, and I got 3x acc…

> x86 also has flags, which add implicit dependencies between instructions, and must make designer's life harder.

Fortunately flags (or even individual flag bits) can be renamed just like other registers, removing that bottleneck. And some architectures that use flag registers, like aarch64, have additional arithmetic instructions which don't update the flag register.

Using flag registers brings benefits as well. E.g. conditional jump distances can be much larger (e.g. 1 MB in aarch64 vs. 4K in RISC-V).

Re: AMD claims Arm ISA doesn't offer efficiency advantage over x86

#342

Post by petrichorko »

sgc wrote: post #340
petrichorko wrote: post #329

Earlier quoted context omitted.

To me it's not as simple as comparing the efficiency under full load. I imagine the efficiency on x86 as some kind of log curve, which translates to higher power consumption even on lighter loads. Apple's ARM implementation tends to eat a lot less power on tasks that happen most of the time, hence greatly improving the battery life. I've tried a Ryzen 7 that had a similar efficiency to an M1 according to some tests,…

The OS matters, and I would guess you were using two different OSes? I have no doubt macOS running on an m1 is more optimized than whatever you were using on the ryzen. I recently had to remove Windows completely from a few years old laptop with an 12th gen cpu and a Intel Iris / GeForce RTX 3060 Mobile combo because it was running very hot (90c+) and the fans were constantly running. Running Linux, I have no issues.…

Linux can definitely help with this, I had the same experience with it on Z1 (SteamOS). But even running Windows 11 in a VM on M1 does not make the machine run hot

Re: AMD claims Arm ISA doesn't offer efficiency advantage over x86

#343

Post by goalieca »

KingOfCoders wrote: post #265
jorvi wrote: post #224

Earlier quoted context omitted.

Nice followup to your link: https://chipsandcheese.com/p/arm-or-x86-isa-doesnt-matter . Personally I do not entirely buy it. Intel and AMD have had plenty of years to catch up to Apple's M-architecture and they still aren't able to touch it in efficiency. The PC Snapdragon chips AFAIK also offer better performance-per-watt than AMD or Intel, with laptops offering them often having 10-30% longer battery life at simila…

Why would they? They are dominated by gaming benchmarks in a way Apple isn't. For decades it was not efficiency but raw performance, 50% more power usage for 10% more performance was ok. "The same goes for GPUs, where Apple's M1 GPU completely smoked an RTX3090 in performance-per-watt" Gamers are not interested in performance-per-watt but fps-per-$. If some behavior looks strange to you, most probably you don't under…

> Gamers are not interested in performance-per-watt but fps-per-$.

I game a decent amount on handheld mode for the switch. Like tens of millions of others.

Re: AMD claims Arm ISA doesn't offer efficiency advantage over x86

#344

Post by mrheosuper »

audunw wrote: post #331
mrheosuper wrote: post #217

Earlier quoted context omitted.

Well, Every single CPU need some kind of voltage regulation module to work. About "fine tune" part, this does not relate to PMIC(or VRM) at all, more like CPU design: How many power domain does this CPU have ?

I don’t know how it is for Apple-M, but for chips I’ve worked on, this can definitely relate to PMIC/VRMs. You can tune the voltage you feed to the various power domains based on the clock speed required for those domains at any given time. We do it with on-chip power regulators, but I suppose for Apple M it would perhaps be off-chip PMICs feeding power into the chip.

it's the other way around. You design PMIC for a given CPU, not designing CPU for a given PMIC(but in Apple case, the engineers can work closely together to come up with something balance).

Re: AMD claims Arm ISA doesn't offer efficiency advantage over x86

#345

Post by pjmlp »

whatevaa wrote: post #319
diddid wrote: post #240

Earlier quoted context omitted.

I mean the M1 is nice but pretending that it can do in 110w what the 3090 does with 320w is Apple marketing nonsense. Like if your use case is playing games like cp2077, the 3090 will do 100fps in ultra ray tracing and an M4 Max will only do 30fps. Not to mention it’s trivial to undervolt nvidia cards and get 100% performance at 80% power. So 1/3 the power for 1/3 the performance? How is that smoking anything?

Apple fans drinking apple juice, nothing new with fans, sadly.

Indeed, like talking as if Apple mattered at all in server space, or digital workstations (studio is not a replacement for people willing to buy Mac Pros, which still keep being built with Intel Xeons).

Re: AMD claims Arm ISA doesn't offer efficiency advantage over x86

#346

Post by pjmlp »

goalieca wrote: post #343
KingOfCoders wrote: post #265

Earlier quoted context omitted.

Why would they? They are dominated by gaming benchmarks in a way Apple isn't. For decades it was not efficiency but raw performance, 50% more power usage for 10% more performance was ok. "The same goes for GPUs, where Apple's M1 GPU completely smoked an RTX3090 in performance-per-watt" Gamers are not interested in performance-per-watt but fps-per-$. If some behavior looks strange to you, most probably you don't under…

> Gamers are not interested in performance-per-watt but fps-per-$. I game a decent amount on handheld mode for the switch. Like tens of millions of others.

While others run PlayStation and XBox.

The demographics aren't the same, nor the games.

Re: AMD claims Arm ISA doesn't offer efficiency advantage over x86

#347

Post by devnullbrain »

ben-schaaf wrote: post #263
jorvi wrote: post #224

Earlier quoted context omitted.

Nice followup to your link: https://chipsandcheese.com/p/arm-or-x86-isa-doesnt-matter . Personally I do not entirely buy it. Intel and AMD have had plenty of years to catch up to Apple's M-architecture and they still aren't able to touch it in efficiency. The PC Snapdragon chips AFAIK also offer better performance-per-watt than AMD or Intel, with laptops offering them often having 10-30% longer battery life at simila…

> Personally I do not entirely buy it. Intel and AMD have had plenty of years to catch up to Apple's M-architecture and they still aren't able to touch it in efficiency. The PC Snapdragon chips AFAIK also offer better performance-per-watt than AMD or Intel, with laptops offering them often having 10-30% longer battery life at similar performance. Do not conflate battery life with core efficiency. If you want to measu…

I want to measure the device how I use it. Race-to-sleep and power states are integral to CPU design.

Re: AMD claims Arm ISA doesn't offer efficiency advantage over x86

#348

Post by aurareturn »

exmadscientist wrote: post #247
jorvi wrote: post #224

Earlier quoted context omitted.

Nice followup to your link: https://chipsandcheese.com/p/arm-or-x86-isa-doesnt-matter . Personally I do not entirely buy it. Intel and AMD have had plenty of years to catch up to Apple's M-architecture and they still aren't able to touch it in efficiency. The PC Snapdragon chips AFAIK also offer better performance-per-watt than AMD or Intel, with laptops offering them often having 10-30% longer battery life at simila…

Yes, Intel/AMD cannot match Apple in efficiency. But Apple cannot beat Intel/AMD in single-thread performance. (Apple marketing works very hard to convince people otherwise, but don't fall for it.) Apple gets very, very close, but they just don't get there. (As well, you might say they get close enough for practical matters; that might be true, but it's not the question here.) That gap, however small it might be for…

  But Apple cannot beat Intel/AMD in single-thread performance.
AMD, Intel, Qualcomm have all reference Geekbench ST numbers. In Geekbench, Apple is significantly ahead of AMD and Intel in ST performance. So no need Apple marketing to convince us. The industry has benchmarks to do so.

Re: AMD claims Arm ISA doesn't offer efficiency advantage over x86

#349

Post by ben-schaaf »

devnullbrain wrote: post #347
ben-schaaf wrote: post #263

Earlier quoted context omitted.

> Personally I do not entirely buy it. Intel and AMD have had plenty of years to catch up to Apple's M-architecture and they still aren't able to touch it in efficiency. The PC Snapdragon chips AFAIK also offer better performance-per-watt than AMD or Intel, with laptops offering them often having 10-30% longer battery life at similar performance. Do not conflate battery life with core efficiency. If you want to measu…

I want to measure the device how I use it. Race-to-sleep and power states are integral to CPU design.

Yes they are, but only one of those is at all affected by the choice of ISA. If modern AMD chips are better at race-to-sleep than an Apple M1 and still get worse battery life then the problem is clearly not x86-64.

Re: AMD claims Arm ISA doesn't offer efficiency advantage over x86

#350

Post by boxed »

dwattttt wrote: post #325
boxed wrote: post #309

Earlier quoted context omitted.

He said "per watt", that's still true. You just talked about max throughput, which no one is discussing.

> The latest AMD under full load uses the same power as M1 and is faster, thus it has better performance per watt. He also said per watt. An AMD CPU running at full power and then stopping will use less battery than an M1 with the same task; that's comparing power efficiency.

https://techjourneyman.com/blog/m1-ultra-vs-nvidia-rtx-3090/

Look at their updated graph which has less BS. It's never close in perf/watt.

The BS part about apples graph was that they cut the graph short for the nvidia card (and bending the graph a bit at the end). The full graph still shows apple being way better per watt.

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