4 ms·

> Here in this article we’ll bring together research, comments from people who are very familiar with CPUs, and a bit of our in-house data to show why focusing

by bfung 2y ago

> Here in this article we’ll bring together research, comments from people who are very familiar with CPUs, and a bit of our in-house data to show why focusing on the ISA is a waste of time Very amateur-ish question and counterpoint from me: how is Apple M1 performance and power consumption so good compared to the other laptop cpus then?

xwolfi 2y ago
The code ? Why you think Apple found a way to reverse the heat death of the universe ? They just ... do less stuff so they consume less !
twoodfin 2y ago
Apple absolutely leverages their full-stack platform control to optimize their silicon. They know with insane accuracy how many cycles would be saved across a billion phones if they added (say) another integer divide unit, and if they decide that’s worth it, they can rev every major developer’s toolchain to schedule instructions for the new ALU months before the new chip ships.
- saagarjha 2y ago
  Apple doesn’t do this, as it would reveal details about unreleased products. The scheduling model for their CPUs typically drops months after the chips ship, and even then the benefit you get from that is minor. (You can try it yourself, by comparing code generated using the “wrong” microarchitecture versus the “right” one. And also keep in mind that developers don’t always update their apps immediately to use the new toolchain.)
pizlonator 2y ago
Silicon economics mean that whoever has the highest volume can invest the most in better designs and better process. Apple gets volume from the iPhone. This is also why x86 outperformed expensive (and so low volume) RISC workstation CPUs for a long time at single thread perf, and then eventually on multi thread perf too.
- drivebycomment 2y ago
  This "why" is more "what are the underlying economics that enable the development of the better chip". Economics doesn't guarantee you'll get a better CPU. It still takes a cutting-edge engineering team with a good CPU architect to build that best chip. e.g. Intel didn't fall behind because of lack of money.
  - pizlonator 2y ago
    Intel’s revenue has been at least 4x less than Apple’s since 2015. Last year the gap was more like 7x.
- saagarjha 2y ago
  Intel has volume, though. They ship millions of expensive CPUs to servers around the world. It’s just that they dropped the ball compared to Apple.
  - pizlonator 2y ago
    Hard to find reliable numbers, but it looks like the number of x86 chips sold per year is less than the number of iPhones sold per year, based on my totally not serious research. Do you have data that says otherwise?
    - saagarjha 2y ago
      Oh, I would probably agree. I’m just saying Intel also ships a lot of chips and it’s not like they are hurting for cash from those sales. I think a direct comparison would be difficult because the BOM of the average iPhone processor is surely much less than Intel’s but they sell a lot more, but also Apple’s revenue is mixed in a lot of things so looking at just a processor is not really possible to do considering the money goes to making iPhones not just chips. I think if you looked at overall R&D investment on processors in dollars though then numbers would look a lot closer.
      - 2y ago
drivebycomment 2y ago
It's not a counter-point you think it is. ARM is not a primary reason why Apple's M series are so much better. If it is, other ARM should be able to match, but they don't. Simply put, Apple built a good microarchitecture and a pipeline - e.g. M1 has, e.g. 600 reorder buffer. Back then, this was 2x of most other CPUs, regardless of ISA. This is not something you can just throw more transistors at it - you need all the other parts of the processor optimized in order to make that useful, and Apple did. Simply, M-series are one of the best out-of-order pipelines ever built.

by bfung 2y ago

xwolfi 2y ago

The code ? Why you think Apple found a way to reverse the heat death of the universe ? They just ... do less stuff so they consume less !

twoodfin 2y ago

Apple absolutely leverages their full-stack platform control to optimize their silicon. They know with insane accuracy how many cycles would be saved across a billion phones if they added (say) another integer divide unit, and if they decide that’s worth it, they can rev every major developer’s toolchain to schedule instructions for the new ALU months before the new chip ships.

saagarjha 2y ago
Apple doesn’t do this, as it would reveal details about unreleased products. The scheduling model for their CPUs typically drops months after the chips ship, and even then the benefit you get from that is minor. (You can try it yourself, by comparing code generated using the “wrong” microarchitecture versus the “right” one. And also keep in mind that developers don’t always update their apps immediately to use the new toolchain.)

pizlonator 2y ago

Silicon economics mean that whoever has the highest volume can invest the most in better designs and better process. Apple gets volume from the iPhone. This is also why x86 outperformed expensive (and so low volume) RISC workstation CPUs for a long time at single thread perf, and then eventually on multi thread perf too.

drivebycomment 2y ago
This "why" is more "what are the underlying economics that enable the development of the better chip". Economics doesn't guarantee you'll get a better CPU. It still takes a cutting-edge engineering team with a good CPU architect to build that best chip. e.g. Intel didn't fall behind because of lack of money.
- pizlonator 2y ago
  Intel’s revenue has been at least 4x less than Apple’s since 2015. Last year the gap was more like 7x.
saagarjha 2y ago
Intel has volume, though. They ship millions of expensive CPUs to servers around the world. It’s just that they dropped the ball compared to Apple.
- pizlonator 2y ago
  Hard to find reliable numbers, but it looks like the number of x86 chips sold per year is less than the number of iPhones sold per year, based on my totally not serious research. Do you have data that says otherwise?
  - saagarjha 2y ago
    Oh, I would probably agree. I’m just saying Intel also ships a lot of chips and it’s not like they are hurting for cash from those sales. I think a direct comparison would be difficult because the BOM of the average iPhone processor is surely much less than Intel’s but they sell a lot more, but also Apple’s revenue is mixed in a lot of things so looking at just a processor is not really possible to do considering the money goes to making iPhones not just chips. I think if you looked at overall R&D investment on processors in dollars though then numbers would look a lot closer.
    - 2y ago

drivebycomment 2y ago

It's not a counter-point you think it is. ARM is not a primary reason why Apple's M series are so much better. If it is, other ARM should be able to match, but they don't. Simply put, Apple built a good microarchitecture and a pipeline - e.g. M1 has, e.g. 600 reorder buffer. Back then, this was 2x of most other CPUs, regardless of ISA. This is not something you can just throw more transistors at it - you need all the other parts of the processor optimized in order to make that useful, and Apple did. Simply, M-series are one of the best out-of-order pipelines ever built.