Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

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

techpowerup.com

Post reply on HN
Print view View original

51–60 of 446 posts

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

#51

Post by pengaru »

gigatexal wrote: post #12

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…

Your Intel mac was stuck in the past while everyone paying attention on PCs were already enjoying TSMC 7nm silicon in the form of AMD Zen processors.

Apple Silicon macs are far less impressive if you came from an 8c/16t Ryzen 7 laptop. Especially if you consider the Apple parts are consistently enjoying the next best TSMC node vs. AMD (e.g. 5nm (M1) vs. 7nm (Zen2))

What's _really_ impressive is how badly Intel fell behind and TSMC has been absolutely killing it.

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

#52

Post by FlyingAvatar »

kccqzy wrote: post #34
gigatexal wrote: post #12

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…

That's not mostly because of a better ISA. If Intel and Apple had a chummier relationship you could imagine Apple licensing the Intel x86 ISA and the M series chips would be just as good but running x86. However I suspect no matter how chummy that relationship was, business is business and it is highly unlikely that Intel would give Apple such a license.

It's pretty difficult to imagine.

Apple did a ton of work on the power efficiency of iOS on their own ARM chips for iPhone for a decade before introducing the M1.

Since iOS and macOS share the same code base (even when they were on different architectures) it makes much more sense to simplify to a single chip architecture that they already had major expertise with and total control over.

There would be little to no upside for cutting Intel in on it.

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

#53

Post by bryanlarsen »

x0x0 wrote: post #50
kccqzy wrote: post #34

Earlier quoted context omitted.

That's not mostly because of a better ISA. If Intel and Apple had a chummier relationship you could imagine Apple licensing the Intel x86 ISA and the M series chips would be just as good but running x86. However I suspect no matter how chummy that relationship was, business is business and it is highly unlikely that Intel would give Apple such a license.

> That's not mostly because of a better ISA Genuinely asking -- what is it due to? Because like the person you're replying to, the m* processors are simply better: desktop-class perf on battery that hangs with chips with 250 watt TDP. I have to assume that amd and intel would like similar chips, so why don't they have them if not due to the instruction set? And AMD is using TSMC, so that can't be the difference.

What's it due to? At least this, probably more.

- more advanced silicon architecture. Apple spends billions to get access to the latest generation a couple of years before AMD.

- world class team, with ~25 years of experience building high speed low power chips. (Apple bought PA Semi to make these chips, which was originally the team that build the DEC StrongARM). And then paid & treated them properly, unlike Intel & AMD

- a die budget to spend transistors for performance: the M chips are generally quite large compared to the competition

- ARM's weak memory model also helps, but it's very minor IMO compared to the above 3.

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

#54

Post by exmadscientist »

x0x0 wrote: post #50
kccqzy wrote: post #34

Earlier quoted context omitted.

That's not mostly because of a better ISA. If Intel and Apple had a chummier relationship you could imagine Apple licensing the Intel x86 ISA and the M series chips would be just as good but running x86. However I suspect no matter how chummy that relationship was, business is business and it is highly unlikely that Intel would give Apple such a license.

> That's not mostly because of a better ISA Genuinely asking -- what is it due to? Because like the person you're replying to, the m* processors are simply better: desktop-class perf on battery that hangs with chips with 250 watt TDP. I have to assume that amd and intel would like similar chips, so why don't they have them if not due to the instruction set? And AMD is using TSMC, so that can't be the difference.

> I have to assume that amd and intel would like similar chips

They historically haven't. They've wanted the higher single-core performance and frequency and they've pulled out all the stops to get it. Everything had been optimized for this. (Also, they underinvested in their uncores, the nastiest part of a modern processor. Part of the reason AMD is beating Intel right now despite being overall very similar is their more recent and more reliable uncore design.)

They are now realizing that this was, perhaps, a mistake.

AMD is only now in a position to afford to invest otherwise (they chose quite well among the options actually available to them, in my opinion), but Intel has no such excuse.

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

#55

Post by John23832 »

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.

Tight integration matters.

Look at the difference in energy usage between safari and chrome on M4s.

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

#56

Post by variadix »

Instruction decode for variable length ISAs is inherently going to be more complex, and thus require more transistors = more power, than fixed length instruction decode, especially parallel decode. AFAIK modern x86 cores have to speculatively decode instructions to achieve this, compared to RISC ISAs where you know where all the instruction boundaries are and decoding N in parallel is a matter of instantiating N decoders that work in parallel. How much this determines the x86 vs ARM power gap, I don’t know, what’s much more likely is x86 designs have not been hyper optimized for power as much ARM designs have been over the last two decades. Memory order is another non-negligible factor, but again the difference is probably more attributable to the difference in goals between the two architectures for the vast majority of their lifespan, and the expertise and knowledge of the engineers working at each company.

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

#57

Post by x0x0 »

exmadscientist wrote: post #54
x0x0 wrote: post #50

Earlier quoted context omitted.

> That's not mostly because of a better ISA Genuinely asking -- what is it due to? Because like the person you're replying to, the m* processors are simply better: desktop-class perf on battery that hangs with chips with 250 watt TDP. I have to assume that amd and intel would like similar chips, so why don't they have them if not due to the instruction set? And AMD is using TSMC, so that can't be the difference.

> I have to assume that amd and intel would like similar chips They historically haven't. They've wanted the higher single-core performance and frequency and they've pulled out all the stops to get it. Everything had been optimized for this. (Also, they underinvested in their uncores, the nastiest part of a modern processor. Part of the reason AMD is beating Intel right now despite being overall very similar is their…

Not arguing, but I would think there is (and always has been) very wide demand for fastest single core perf. From all the usual suspects?

Thank you.

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

#58

Post by mmis1000 »

o11c wrote: post #19
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 ...

Current windows or linux executable format don't even list the used instruction though. And even it is listed, how about dynamic linkables? The program may decide to load library at any time it wishes, and the OS is not going to know what instruction may be used this time.

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

#59

Post by cptskippy »

The ISA is the contract or boundary between software and hardware. While there is a hardware cost to decode instructions, the question is how much?

As all the fanbois in the thread have have pointed out, Apple's M series is fast and efficient compared to x86 for desktop/server workloads. What no one seems to acknowledge is that Apple's A series is also fast and efficient compared to other ARM implementations in mobile workloads. Apple sees the need to maintain M and A series CPUs for different workloads, which indicates there's a benefit to both.

This tells me the ISA decode hardware isn't or isn't the only bottleneck.

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

#60

Post by gigatexal »

bryanlarsen wrote: post #53
x0x0 wrote: post #50

Earlier quoted context omitted.

> That's not mostly because of a better ISA Genuinely asking -- what is it due to? Because like the person you're replying to, the m* processors are simply better: desktop-class perf on battery that hangs with chips with 250 watt TDP. I have to assume that amd and intel would like similar chips, so why don't they have them if not due to the instruction set? And AMD is using TSMC, so that can't be the difference.

What's it due to? At least this, probably more. - more advanced silicon architecture. Apple spends billions to get access to the latest generation a couple of years before AMD. - world class team, with ~25 years of experience building high speed low power chips. (Apple bought PA Semi to make these chips, which was originally the team that build the DEC StrongARM). And then paid & treated them properly, unlike Intel &…

How many of those engineers remain, didn't a lot go to Nuvia that was then bought by Qualcomm?
Post reply on HN