5 ms·

Anybody knows if Apple's ARM chips (iPhone) have better thermal efficiency (watts/GFLOPs) than the chips in this latest gen? If this is the case, I think it's

by llekn 8y ago

Anybody knows if Apple's ARM chips (iPhone) have better thermal efficiency (watts/GFLOPs) than the chips in this latest gen? If this is the case, I think it's just a matter of time for Apple replacing Intel with their own custom ARM chips.

lykr0n 8y ago
You can't really compare ARM and x86_64 chips. I'm going to use a crude example. Think of the ARM chip being one of those USPS Trucks (https://upload.wikimedia.org/wikipedia/commons/3/37/Small_USPS_Truck.jpg https://upload.wikimedia.org/wikipedia/commons/3/37/Small_US...) while the x86_64 is a F150 pickup. Both can drive around and transport things, but the USPS Truck is purpose build to deliver mail, stop and start frequently, and be reliable. It does a few things well. On the other hand the F150 is widely produced, can be customized in many different ways, and is general purpose vehical. Could it do the function of the USPS Truck? Sure, but it would be slower, cost more to run, and be less efficient. Could the USPS Truck haul a trailer? Maybe, but it wouldn't be very good at it. Both are a truck, but both are designed to different things and excel at different things. That crude comparison is ARM vs x86_64. ARM is getting there, and for the specific ARM functions it's more performant than the equivalent x86_64 functions. But once you go outside of what the ARM chip has been specifically designed for, your performance takes a massive hit. Will ARM be able to take off in a Macbook? Maybe in a few years, but Apple would need to dump a massive amount of R&D into their designs before I would think they would consider it (but who knows?)
- shub 8y ago
  What? They're CPUs. They're designed to run instructions. Intel's chips spend more energy on the really fancy stuff like huge reorder buffers and extensive speculation. They get higher IPC at lower MIPS/watt. An i7 isn't going to run iOS more slowly than whatever Apple calls their latest ARM SoC. It _is_ going to blow its lid without a big ole heatsink brick on there and a fan too, which is why smartphones use ARM cores designed for efficiency. P.S. if anything, ARM is the "general purpose vehicle" in your analogy. x64 is all about high throughput and high power on a chip you buy and plug in. ARM is the one where you can get an architecture license and customize the shit out of it.
  - ldh 8y ago
    Not all instructions (or instruction sets) are equivalent.
    - shub 8y ago
      They're not that different, either. It's been a long time since high-performance cores were executing the instructions as fetched and not translating into µops. The stuff Intel does on their chips works on ARM too. People are doing it, and it's working[0]. That makes a hell of a lot more difference on throughput than what ISA is implemented. [0] https://fuse.wikichip.org/news/1316/a-look-at-caviums-new-high-performance-arm-microprocessors-and-the-isambard-supercomputer/ https://fuse.wikichip.org/news/1316/a-look-at-caviums-new-hi...
      - ebikelaw 8y ago
        Actually the x86 instruction format is key to Intel's performance dominance. It happens to be rather dense in terms of instruction per byte, and it turns out that instruction cache hit rate (and iTLB hit rate) are extremely important to high performance. Rather than the naive view that x86 is somehow saddled with its ancient and ugly instruction set, it's actually all of the RISC-like architectures that turn out to be hampered by their overly beautiful instructions.
        StillBored 8y ago
        The other way to think about it is like the v7 thumb modes in comparison to the original 32-bit predicated instruction set. X86 has a lot of less than ideal instructions, but they are uncommonly used. So the core instruction set is quite dense and high performance. Intel is learning (or knows, depending on your perspective, see goldmont) how to build highly efficient cores too, but like ARM haven't quite figured out how to build a super high performance one that is crazy efficient. ARM's continue to be quite efficient but not particularly performant, while intel's continue to be quite peformant but not particularly efficient. Either way, the trend is pretty clear at this point more power dissipation=more performance.
deleted 8y ago
[deleted]

by llekn 8y ago

lykr0n 8y ago

You can't really compare ARM and x86_64 chips. I'm going to use a crude example. Think of the ARM chip being one of those USPS Trucks (https://upload.wikimedia.org/wikipedia/commons/3/37/Small_USPS_Truck.jpg https://upload.wikimedia.org/wikipedia/commons/3/37/Small_US...) while the x86_64 is a F150 pickup. Both can drive around and transport things, but the USPS Truck is purpose build to deliver mail, stop and start frequently, and be reliable. It does a few things well. On the other hand the F150 is widely produced, can be customized in many different ways, and is general purpose vehical. Could it do the function of the USPS Truck? Sure, but it would be slower, cost more to run, and be less efficient. Could the USPS Truck haul a trailer? Maybe, but it wouldn't be very good at it. Both are a truck, but both are designed to different things and excel at different things. That crude comparison is ARM vs x86_64. ARM is getting there, and for the specific ARM functions it's more performant than the equivalent x86_64 functions. But once you go outside of what the ARM chip has been specifically designed for, your performance takes a massive hit. Will ARM be able to take off in a Macbook? Maybe in a few years, but Apple would need to dump a massive amount of R&D into their designs before I would think they would consider it (but who knows?)

shub 8y ago
What? They're CPUs. They're designed to run instructions. Intel's chips spend more energy on the really fancy stuff like huge reorder buffers and extensive speculation. They get higher IPC at lower MIPS/watt. An i7 isn't going to run iOS more slowly than whatever Apple calls their latest ARM SoC. It _is_ going to blow its lid without a big ole heatsink brick on there and a fan too, which is why smartphones use ARM cores designed for efficiency. P.S. if anything, ARM is the "general purpose vehicle" in your analogy. x64 is all about high throughput and high power on a chip you buy and plug in. ARM is the one where you can get an architecture license and customize the shit out of it.
- ldh 8y ago
  Not all instructions (or instruction sets) are equivalent.
  - shub 8y ago
    They're not that different, either. It's been a long time since high-performance cores were executing the instructions as fetched and not translating into µops. The stuff Intel does on their chips works on ARM too. People are doing it, and it's working[0]. That makes a hell of a lot more difference on throughput than what ISA is implemented. [0] https://fuse.wikichip.org/news/1316/a-look-at-caviums-new-high-performance-arm-microprocessors-and-the-isambard-supercomputer/ https://fuse.wikichip.org/news/1316/a-look-at-caviums-new-hi...
    - ebikelaw 8y ago
      Actually the x86 instruction format is key to Intel's performance dominance. It happens to be rather dense in terms of instruction per byte, and it turns out that instruction cache hit rate (and iTLB hit rate) are extremely important to high performance. Rather than the naive view that x86 is somehow saddled with its ancient and ugly instruction set, it's actually all of the RISC-like architectures that turn out to be hampered by their overly beautiful instructions.
      - StillBored 8y ago
        The other way to think about it is like the v7 thumb modes in comparison to the original 32-bit predicated instruction set. X86 has a lot of less than ideal instructions, but they are uncommonly used. So the core instruction set is quite dense and high performance. Intel is learning (or knows, depending on your perspective, see goldmont) how to build highly efficient cores too, but like ARM haven't quite figured out how to build a super high performance one that is crazy efficient. ARM's continue to be quite efficient but not particularly performant, while intel's continue to be quite peformant but not particularly efficient. Either way, the trend is pretty clear at this point more power dissipation=more performance.

deleted 8y ago

[deleted]