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There's quite a few fallacies in this article. The worst offenders being that performance scales with clockrate, that different CPU designs can scale to the sa

by sliken 8y ago

There's quite a few fallacies in this article. The worst offenders being that performance scales with clockrate, that different CPU designs can scale to the same clock rate, and that power use/heat is anywhere near linear in respect to clock rate. However it is still impressive that the A12X could hit 80% of a fairly aggressive Intel design at 60% of the same block. Certainly active cooling would help ARM chips sustain the performance they can get for short periods of time without active cooling. So Arm is closing the gap and the A12x is a pretty impressive chip. Certainly plenty for many use cases met today by Intel Desktops/Laptops. But to hit the same clock speeds Intel's using might well require Apple to add an extra stage in the pipeline and/or running cache at a lower fraction of the CPU clock. Not to mention increasing clock speeds without decreasing memory latency will also hurt IPC. Any of these changes would hurt IPC and make it that much harder to reach 100% parity with Intel.

gpderetta 8y ago
> Arm is closing the gap and the A12x s/ARM/Apple/ really. They have a great chip development team, but they are focusing, obviously, on mobile and do not seem to be interested yet in desktop, and even less in servers, except possible as a byproduct of their mobile development.
- coldcode 8y ago
  That we are aware of, Apple always looks at a long horizon. If there is an efficiency in building any kind of silicon itself, Apple will look at it.
- pault 8y ago
  > but they are focusing, obviously, on mobile Isn't it pretty much taken as a given that Apple is going to produce an ARM powered laptop in the next couple of years?
  - gpderetta 8y ago
    I'm sure they have prototypes and I'm sure they will consider releasing it if they have a design that works well, but I doubt that a laptop chip will ever be the focus of their main development team.
  - monocasa 8y ago
    It's not an obvious win like the last couple of architecture switches because of the end of Moore's law. Like the PowerPC chips they were initially using ran 68k code quicker in a non-JITing emulator than any 68k they could buy. They had to switch to a JIT with Rosetta, but that same perf distinction was still true for the high end for PowerPC/Intel during their switch. Running x86 code faster in an emulator than on a real chip might not ever happen. And in not too long the x86-64 patents will have expired all the way through SSE4... I think Apple making their own x86 chips is just as likely as switching to ARM.
BeeOnRope 8y ago
I don't think he is assuming linear scaling with any of those factors. He is saying that despite using a small fraction of the power, and running at a significantly lower frequency, the Apple chips have only a small deficit on Spec2006 (and, not noted, but for several benchmarks, no deficit at all - a lot depends on whether SIM plays a big role). Under that scenario, it is reasonable to assume that if you say tripled the power budget and adjusted the frequency to match the larger power budget and "full size" cooling solution, there would be a jump in performance. They are not claiming it would be 3 (power) x 1.5 = 4.5x times faster performance, i.e., A-series chips would be many times faster than Intel chips. I think it is entirely reasonable to assume it would be the in the range of 20% or more, however. Certainly Intel chips scale up and down based on exactly those factors. In my opinion, in the case where apples-to-oranges comparisons are possible (low TDPs), Apple's newest chips are already faster than Intel chips. In a high TDP scenario, the same would be true with basic re-targeting of voltages, frequencies, etc (no uarch changes). We don't have the latter yet, and by the time we do we will probably see Ice Lake and Sunny Cove from Intel, so the pendulum may swing back the other way.
whynotminot 8y ago
> There's quite a few fallacies in this article. The worst offenders being that performance scales with clockrate, that different CPU designs can scale to the same clock rate, and that power use/heat is anywhere near linear in respect to clock rate. I kind of hate the way you throw this out there as if it invalidates the whole point of the article. You sort of walk it back with the rest of your comments, but the damage is done within the first line, overemphasizing nitpicks at the expense of the greater picture. I guess such things should be expected on a forum filled with pedantic engineers... I'm guilty of this myself. I hope people still take the time to read what is an otherwise interesting, fair minded view that proves the central point it sets out -- that ARM is not an inherently inferior architecture and that recent designs from Apple prove this handily.

by sliken 8y ago

gpderetta 8y ago

> Arm is closing the gap and the A12x s/ARM/Apple/ really. They have a great chip development team, but they are focusing, obviously, on mobile and do not seem to be interested yet in desktop, and even less in servers, except possible as a byproduct of their mobile development.

coldcode 8y ago
That we are aware of, Apple always looks at a long horizon. If there is an efficiency in building any kind of silicon itself, Apple will look at it.
pault 8y ago
> but they are focusing, obviously, on mobile Isn't it pretty much taken as a given that Apple is going to produce an ARM powered laptop in the next couple of years?
- gpderetta 8y ago
  I'm sure they have prototypes and I'm sure they will consider releasing it if they have a design that works well, but I doubt that a laptop chip will ever be the focus of their main development team.
- monocasa 8y ago
  It's not an obvious win like the last couple of architecture switches because of the end of Moore's law. Like the PowerPC chips they were initially using ran 68k code quicker in a non-JITing emulator than any 68k they could buy. They had to switch to a JIT with Rosetta, but that same perf distinction was still true for the high end for PowerPC/Intel during their switch. Running x86 code faster in an emulator than on a real chip might not ever happen. And in not too long the x86-64 patents will have expired all the way through SSE4... I think Apple making their own x86 chips is just as likely as switching to ARM.

BeeOnRope 8y ago

I don't think he is assuming linear scaling with any of those factors. He is saying that despite using a small fraction of the power, and running at a significantly lower frequency, the Apple chips have only a small deficit on Spec2006 (and, not noted, but for several benchmarks, no deficit at all - a lot depends on whether SIM plays a big role). Under that scenario, it is reasonable to assume that if you say tripled the power budget and adjusted the frequency to match the larger power budget and "full size" cooling solution, there would be a jump in performance. They are not claiming it would be 3 (power) x 1.5 = 4.5x times faster performance, i.e., A-series chips would be many times faster than Intel chips. I think it is entirely reasonable to assume it would be the in the range of 20% or more, however. Certainly Intel chips scale up and down based on exactly those factors. In my opinion, in the case where apples-to-oranges comparisons are possible (low TDPs), Apple's newest chips are already faster than Intel chips. In a high TDP scenario, the same would be true with basic re-targeting of voltages, frequencies, etc (no uarch changes). We don't have the latter yet, and by the time we do we will probably see Ice Lake and Sunny Cove from Intel, so the pendulum may swing back the other way.

whynotminot 8y ago

> There's quite a few fallacies in this article. The worst offenders being that performance scales with clockrate, that different CPU designs can scale to the same clock rate, and that power use/heat is anywhere near linear in respect to clock rate. I kind of hate the way you throw this out there as if it invalidates the whole point of the article. You sort of walk it back with the rest of your comments, but the damage is done within the first line, overemphasizing nitpicks at the expense of the greater picture. I guess such things should be expected on a forum filled with pedantic engineers... I'm guilty of this myself. I hope people still take the time to read what is an otherwise interesting, fair minded view that proves the central point it sets out -- that ARM is not an inherently inferior architecture and that recent designs from Apple prove this handily.