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

111–120 of 446 posts

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

#111

Post by adgjlsfhk1 »

epolanski wrote: post #105
tapoxi wrote: post #84

Earlier quoted context omitted.

Since the Pentium Pro the hardware hasn't implemented the ISA, it's converted into micro ops.

Come on, you know what I meant :) If you want to support AVX e.g. you need 512bit (or 256) wide registers, you need dedicated ALUs, dedicated mask registers etc. Ice Lake has implemented SHA-specific hardware units in 2019.

sure, but Arm has Neon/sve which impose basically the same requirements for vector instructions, and most high performance arm implimentations have a wide suite of crypto instructions (e.g. Apple's M series chips have AES, SHA1 and Sha256 instructions)

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

#112

Post by tester756 »

slimginz wrote: post #5

IIRC There was a Jim Keller interview a few years ago where he said basically the same thing (I think it was from right around when he joined Tenstorrent?). The ISA itself doesn't matter, it's just instructions. The way the chip interprets those instructions is what makes the difference. ARM was designed from the beginning for low powered devices whereas x86 wasn't. If x86 is gonna compete with ARM (and RISC-V) then…

https://chipsandcheese.com/p/arm-or-x86-isa-doesnt-matter

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

#113

Post by gigatexal »

Jensson wrote: post #96
gigatexal wrote: post #85

Earlier quoted context omitted.

Wait are you saying the diff in perf per watt from apple arm to x86 is purely on fab leading edge ness?

Basically yeah, if you compare CPU from same fab then its basically the same. Its just Apple buys next gen fabs while AMD and intel has to be on last gen, so the M computers people compare are always one fab gen ahead. It has very little to do with CPU architecture. They do have some cool stuff about their CPU, but the thing most laud them for has to do with fabs.

Man that either hella discounts all the amazing work Apple’s CPU engineers are doing or hyping up what AMD’s have done. Idk

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

#114

Post by bfrog »

Jensson wrote: post #101
bfrog wrote: post #71

Earlier quoted context omitted.

I have, the m4 is significantly ahead by any measure I’ve seen, with snapdragon just behind. https://www.xda-developers.com/tested-apple-m4-vs-intel-luna...

The m4 is not the same fab technology so not comparable. If you want to discuss the validity of some CPU architecture it needs to be between comparable fab technology, M4 being a generation ahead there makes the comparison unfair. If you compare like to like the difference almost completely disappears.

You mean how they all use tsmc n3 and the two arm parts still beat out lunar lake? It’s not like a whole generational node behind here. I get they aren’t the exact same process node but still.

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

#115

Post by bsder »

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.

> Genuinely asking -- what is it due to?

Mostly memory/cache subsystem.

Apple was willing to spend a lot of transistors on cache because they were optimizing the chips purely for mobile and can bury the extra cost in their expensive end products.

You will note that after the initial wins from putting stonking amounts of cache and memory bandwidth in place, Apple has not had any significant performance jump beyond the technology node improvements.

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

#116

Post by adgjlsfhk1 »

pablok2 wrote: post #23
azornathogron wrote: post #9

Earlier quoted context omitted.

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.

How much instruction perf analysis do they do to save 1% (compounded) on the most common instructions

it's less that and more all the peripheral things. USB, wifi, bluetooth, ram, random capacitors in the VRM etc.

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

#118

Post by tracker1 »

gigatexal wrote: post #113
Jensson wrote: post #96

Earlier quoted context omitted.

Basically yeah, if you compare CPU from same fab then its basically the same. Its just Apple buys next gen fabs while AMD and intel has to be on last gen, so the M computers people compare are always one fab gen ahead. It has very little to do with CPU architecture. They do have some cool stuff about their CPU, but the thing most laud them for has to do with fabs.

Man that either hella discounts all the amazing work Apple’s CPU engineers are doing or hyping up what AMD’s have done. Idk

I wouldn't discount what Apple has done... they've created and integrated some really good niche stuff in their CPUs to do more than typical ARM designs. The graphics cores are pretty good in their own right even. Not to mention the OS/Software integration including accelerated x86 and unified memory usage in practice.

AMD has done a LOT for parallelization and their server options are impressive... I mean, you're still talking 500W+ in total load, but that's across 128+ cores. Strix Halo scaling goes down impressively to the ~10-15W range under common usage, not as low as Apple does under similar loads but impressive in its own way.

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

#119

Post by ahartmetz »

rasz wrote: post #107
ahartmetz wrote: post #86

Earlier quoted context omitted.

Variable length decoding is more or less figured out, but it takes more design effort, transistors and energy. They cost, but not a lot, relatively, in a current state of the art super wide out-of-order CPU.

Not a lot is not how I would describe it. Take a 64bit piece of fetched data. On ARM64 you will just push that into two decoder blocks and be done with it. On x86 you got what, 1 to 15 bytes range per instruction? I dont even want to think about possible permutations, its in the 10 ^ some two digit number order.

It's a lot for a decoder, but not for a whole core. Citation needed, but I remember that the decoder is about 10% of a Ryzen core's power budget, and of course that is with a few techniques better than complete brute force.
Post reply on HN