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The scaling is really the question. ARM processors generally have better performance per watt because they're designed to prioritize power efficiency over absol

by zrm 7y ago

The scaling is really the question. ARM processors generally have better performance per watt because they're designed to prioritize power efficiency over absolute performance. The Intel parts Apple's ARM processors compare to on performance are the lowest power ones, which isn't exactly the sweet spot for Intel's microarchitecture. If you gave the ARM designers the (higher) laptop power budget, almost certainly they'd increase performance at the expense of performance per watt. In other words they'd take more of the trade offs that Intel and AMD do. But to justify switching architectures it can't just be the same, it would have to be enough better to be worth the transition.

amalter 7y ago
This has been exactly proven out by Amazon - https://aws.amazon.com/about-aws/whats-new/2019/12/announcing-new-amazon-ec2-m6g-c6g-and-r6g-instances-powered-by-next-generation-arm-based-aws-graviton2-processors/ https://aws.amazon.com/about-aws/whats-new/2019/12/announcin... If Amazon can make a server class ARM chip that is competitive or better with their custom designed Xeons, I take it as a truism Apple could do the same for mobile.
- wu_187 7y ago
  The problem is the use-case. The software Mac laptops run would perform horribly on ARM. A Macbook Pro is not going to have an ARM processor.
  - scarface74 7y ago
    Why do you think the software Macs run are so much different than the software that iPad Pros run? They run some of the same frameworks. Since when you run iOS apps in the simulator for Macs you actually running x86 builds of iOS apps linked against an x86 build of the iOS frameworks, it’s not hard to compare performance
  - mindajar 7y ago
    It already does, in the T2. It seems to me like future T* chips will run more and more of the system, leaving the x86 to become something like the MBP’s discrete GPU option. And then, like discrete GPUs, eventually an x86 CPU is only available in top-end models.
- zrm 7y ago
  There are a lot of reasons to expect that to work better for servers than laptops. Most server workloads scale with core count, so winning in performance per watt is winning in general because you can scale performance by adding cores. A server with twice as many cores that are each half as fast is just as good, but that doesn't work for a laptop. A server processor also doesn't have to win at every workload. If it can win at any workload, people can use it for only those, which makes it useful. That also doesn't really work for a laptop. People run Linux on servers. It's portable. The architectural transition cost there is close to zero. On top of that, Amazon is fudging the benchmarks in claiming it's faster. They're comparing performance "per-vCPU" which on Intel are hyperthreads rather than full cores. That's fine when Amazon is charging less for the ARM "vCPU" than the Intel hyperthread "vCPU", but you can't use that trick when running single-threaded workloads on a laptop.
  - scarface74 7y ago
    And OS X is portable. It’s already been ported from PPC to x86 and parts of it back and forth between ARM and x86.
    - zrm 7y ago
      The operating system itself isn't the problem, it's all the applications. And the PowerPC transition was both easier and more worth it because the x86 processors were so much faster than the PowerPC processors of the time that they were competitive even when emulating PowerPC code, which wouldn't be the case this time.
      - scarface74 7y ago
        “All the applications” don’t matter. Once you have the OS, Apple’s first party applications, Microsoft, Adobe, and a few Mac only niche apps, you cover most of your bases. During the 680x0 to PPC transition, almost all of the applications that needed performance were already ported. The same was true for the x86 transition. But more than likely, this time it will be the low end that would go ARM to optimize for battery life and the high end would stay x86. Also the difference this time is that the two largest commercial vendors - Adobe and Microsoft already have ARM versions and Apple has Catalyst to make porting iPad apps to MacOS easier. Also, during the last two translations, there was a lot more assembly code optimizations in third party apps than now. Especially going from 68K to PPC. And sadly, there are a lot more Electron apps out there that would be easy to port. Microsoft has struggled to get Windows ARM laptops because they also thought the performance/power ratio made it worth it.

by zrm 7y ago

amalter 7y ago

This has been exactly proven out by Amazon - https://aws.amazon.com/about-aws/whats-new/2019/12/announcing-new-amazon-ec2-m6g-c6g-and-r6g-instances-powered-by-next-generation-arm-based-aws-graviton2-processors/ https://aws.amazon.com/about-aws/whats-new/2019/12/announcin... If Amazon can make a server class ARM chip that is competitive or better with their custom designed Xeons, I take it as a truism Apple could do the same for mobile.

wu_187 7y ago
The problem is the use-case. The software Mac laptops run would perform horribly on ARM. A Macbook Pro is not going to have an ARM processor.
- scarface74 7y ago
  Why do you think the software Macs run are so much different than the software that iPad Pros run? They run some of the same frameworks. Since when you run iOS apps in the simulator for Macs you actually running x86 builds of iOS apps linked against an x86 build of the iOS frameworks, it’s not hard to compare performance
- mindajar 7y ago
  It already does, in the T2. It seems to me like future T* chips will run more and more of the system, leaving the x86 to become something like the MBP’s discrete GPU option. And then, like discrete GPUs, eventually an x86 CPU is only available in top-end models.
zrm 7y ago
There are a lot of reasons to expect that to work better for servers than laptops. Most server workloads scale with core count, so winning in performance per watt is winning in general because you can scale performance by adding cores. A server with twice as many cores that are each half as fast is just as good, but that doesn't work for a laptop. A server processor also doesn't have to win at every workload. If it can win at any workload, people can use it for only those, which makes it useful. That also doesn't really work for a laptop. People run Linux on servers. It's portable. The architectural transition cost there is close to zero. On top of that, Amazon is fudging the benchmarks in claiming it's faster. They're comparing performance "per-vCPU" which on Intel are hyperthreads rather than full cores. That's fine when Amazon is charging less for the ARM "vCPU" than the Intel hyperthread "vCPU", but you can't use that trick when running single-threaded workloads on a laptop.
- scarface74 7y ago
  And OS X is portable. It’s already been ported from PPC to x86 and parts of it back and forth between ARM and x86.
  - zrm 7y ago
    The operating system itself isn't the problem, it's all the applications. And the PowerPC transition was both easier and more worth it because the x86 processors were so much faster than the PowerPC processors of the time that they were competitive even when emulating PowerPC code, which wouldn't be the case this time.
    - scarface74 7y ago
      “All the applications” don’t matter. Once you have the OS, Apple’s first party applications, Microsoft, Adobe, and a few Mac only niche apps, you cover most of your bases. During the 680x0 to PPC transition, almost all of the applications that needed performance were already ported. The same was true for the x86 transition. But more than likely, this time it will be the low end that would go ARM to optimize for battery life and the high end would stay x86. Also the difference this time is that the two largest commercial vendors - Adobe and Microsoft already have ARM versions and Apple has Catalyst to make porting iPad apps to MacOS easier. Also, during the last two translations, there was a lot more assembly code optimizations in third party apps than now. Especially going from 68K to PPC. And sadly, there are a lot more Electron apps out there that would be easy to port. Microsoft has struggled to get Windows ARM laptops because they also thought the performance/power ratio made it worth it.