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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

#11

Post by YetAnotherNick »

mananaysiempre wrote: post #8
exmadscientist wrote: post #2

This is an entirely uncontroversial take among experts in the space. x86 is an old CISC-y hot mess. RISC-V is a new-school hyper-academic hot mess. Recent ARM is actually pretty good. And none of it matters, because the uncore and the fabrication details (in particular, whether things have been tuned to run full speed demon or full power sipper) completely dominate the ISA. In the past x86 didn't dominate in low powe…

> x86 didn't dominate in low power because Intel had the resources to care but never did Remember Atom tablets (and how they sucked)?

> how they sucked

Care to elaborate. I had the 9" mini laptop kind of device based on Atom and don't remember Atom to be the issue.

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

#12

Post by gigatexal »

You’ll pry the ARM M series chips of my Mac from my cold dead hands. They’re a game changer in the space and one of the best reasons to use a Mac.

I am not a chip expert it’s just so night and day different using a Mac with an arm chip compared to an Intel one from thermals to performance and battery life and everything in between. Intel isn’t even in the same ballpark imo.

But competition is good and let’s hope they both do —- Intel and AMD because the consumer wins.

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

#13

Post by SushiHippie »

azornathogron wrote: post #9
w4rh4wk5 wrote: post #6

Ok. When will we get the laptop with AMD CPU that is on par with a Macbook regarding battery life?

How much of the Mac's impressive battery life is due purely to CPU efficiency, and how much is due to great vertical integration and the OS being tuned for power efficiency? It's a genuine question; I'm sure both factors make a difference but I don't know their relative importance.

I just searched for the asahi linux (Linux for M Series Macs) battery life, and found this blog post [0].

> During active development with virtual machines running, a few calls, and an external keyboard and mouse attached, my laptop running Asahi Linux lasts about 5 hours before the battery drops to 10%. Under the same usage, macOS lasts a little more than 6.5 hours. Asahi Linux reports my battery health at 94%.

[0] https://blog.thecurlybraces.com/2024/10/running-fedora-asahi...

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

#15

Post by wlesieutre »

exmadscientist wrote: post #2

This is an entirely uncontroversial take among experts in the space. x86 is an old CISC-y hot mess. RISC-V is a new-school hyper-academic hot mess. Recent ARM is actually pretty good. And none of it matters, because the uncore and the fabrication details (in particular, whether things have been tuned to run full speed demon or full power sipper) completely dominate the ISA. In the past x86 didn't dominate in low powe…

VIA used to make low power x86 processors

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

#16

Post by nottorp »

Irrelevant.

There are two entities allowed to make x86_64 chips (and that only because AMD won the 64 bit ISA competition, otherwise there'd be only Intel). They get to choose.

The rest will use arm because that's all they have access to.

Oh, and x86_64 will be as power efficient as arm when one of the two entities will stop competing on having larger numbers and actually worry about power management. Maybe provide a ?linux? optimized for power consumption.

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

#17

Post by tinktank »

bfrog wrote: post #4

And yet... the world keeps proving Intel and AMD wrong on this premise with highly efficient Arm parts. While sure, there's bound to be improvements to make on x86 ultimately its a variable length opcode encoding with a complex decoder path. If nothing else, this is likely a significant issue in comparison to the nicely word aligned op code encoding arm has and surely given apples to apples core designs, the opcode d…

PPA results comparing x86 to ARM say otherwise; take a look at Ryzen's embedded series and Intel's latest embedded cores.

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

#18

Post by torginus »

exmadscientist wrote: post #2

This is an entirely uncontroversial take among experts in the space. x86 is an old CISC-y hot mess. RISC-V is a new-school hyper-academic hot mess. Recent ARM is actually pretty good. And none of it matters, because the uncore and the fabrication details (in particular, whether things have been tuned to run full speed demon or full power sipper) completely dominate the ISA. In the past x86 didn't dominate in low powe…

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 much been figured out on x86 that it's no longer a bottleneck

Also my personal addendum is that today's Intel efficiency cores are have more transistors and better perf than the big Intel cores of a decade ago

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

#19

Post by o11c »

WithinReason wrote: post #10

Since newer CPUs have heterogeneous cores (high performance + low power), I'm wondering if it makes sense to drop legacy instructions from the low power cores, since legacy code can still be run on the other cores. Then e.g. an OS compiled the right way can take advantage of extra efficiency without the CPU losing backwards compatibility

We've seen CPU-capability differences by accident a few times, and it's always a chaotic mess leading to SIGILL.

The kernel would need to have a scheduler that knows it can't use those cores for certain tasks. Think about how hard you would have to work to even identify such a task ...

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

#20

Post by mort96 »

exmadscientist wrote: post #2

This is an entirely uncontroversial take among experts in the space. x86 is an old CISC-y hot mess. RISC-V is a new-school hyper-academic hot mess. Recent ARM is actually pretty good. And none of it matters, because the uncore and the fabrication details (in particular, whether things have been tuned to run full speed demon or full power sipper) completely dominate the ISA. In the past x86 didn't dominate in low powe…

This matches my understanding as well, as someone who has a great deal of interest in the field but never worked in it professionally. CPUs all have a microarchitecture that doesn't look like the ISA at all, and they have an instruction decoder that translates ISA one or more ISA instructions into zero or more microarchitectural instructions. There are some advantages to having a more regular ISA, such as the ability to more easily decode multiple instructions in parallel if they're all the same size or having to spend fewer transistors on the instruction decoder, but for the big superscalar chips we all have in our desktops and laptops and phones, the drawbacks are tiny.

I imagine that the difference is much greater for the tiny in-order CPUs we find in MCUs though, just because an amd64 decoder would be a comparatively much larger fraction of the transistor budget

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