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> Intel's problem is that their CPUs were performance focused and as such didn't scale down as well Don't know the first thing about electronics, but I am inte

> Intel's problem is that their CPUs were performance focused and as such didn't scale down as well Don't know the first thing about electronics, but I am interested to learn more about what you meant here. Highly-optimized code (usually) isn't too readable or extendable, are you saying Intel has the same problem with their processor's design?

cptskippy 8y ago
There are different design considerations when designing a CPU to run in a chilled data center vs your pocket. Intel was trying to make everything x86 from data center to pocket and that just wasn't going to work.
pjc50 8y ago
There are a lot of instances in a design, both macro and micro, where you can trade off greater performance at the expense of something else - either area or power or both. Then these tradeoffs tend to multiply each other. If you have a design which is fast on branch-predicted and slow on branch-mispredicted, and you build a big branch predictor, it works well. But you're committed to powering all that. I mean, compare http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0388f/CHDHCFBC.html http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.... (few sentences) with http://www.agner.org/optimize/microarchitecture.pdf http://www.agner.org/optimize/microarchitecture.pdf (admittedly a lot more detail, but it's clearly a more complicated system too)
tlb 8y ago
Fast processors work by “speculating” — calculating several possible next steps in advance before knowing for sure what the next step will be. Modern Intel chips do this several steps ahead, at multiple levels. It uses more power, because it does work that is ultimately wasted. Large amounts of speculation makes sense for data center CPUs, but not for battery-powered devices.
- std_throwaway 8y ago
  I'd say this is a myth unless you have actual numbers.
std_throwaway 8y ago
If you compare energy per calculation intel server processors readily beat ARM server processors. When under constant high load, intel processors surely aren't bad in regards to power consumption. So that can't be it. Maybe it's more about peak performance vs. average power consumption under very low load as you usually have in a mobile phone that's only used occasionally. For example when starting an app and scrolling you need very high performance but the rest of the time the CPUs are mostly idling.

cptskippy 8y ago

There are different design considerations when designing a CPU to run in a chilled data center vs your pocket. Intel was trying to make everything x86 from data center to pocket and that just wasn't going to work.

pjc50 8y ago

There are a lot of instances in a design, both macro and micro, where you can trade off greater performance at the expense of something else - either area or power or both. Then these tradeoffs tend to multiply each other. If you have a design which is fast on branch-predicted and slow on branch-mispredicted, and you build a big branch predictor, it works well. But you're committed to powering all that. I mean, compare http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0388f/CHDHCFBC.html http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.... (few sentences) with http://www.agner.org/optimize/microarchitecture.pdf http://www.agner.org/optimize/microarchitecture.pdf (admittedly a lot more detail, but it's clearly a more complicated system too)

tlb 8y ago

Fast processors work by “speculating” — calculating several possible next steps in advance before knowing for sure what the next step will be. Modern Intel chips do this several steps ahead, at multiple levels. It uses more power, because it does work that is ultimately wasted. Large amounts of speculation makes sense for data center CPUs, but not for battery-powered devices.

std_throwaway 8y ago
I'd say this is a myth unless you have actual numbers.

std_throwaway 8y ago

If you compare energy per calculation intel server processors readily beat ARM server processors. When under constant high load, intel processors surely aren't bad in regards to power consumption. So that can't be it. Maybe it's more about peak performance vs. average power consumption under very low load as you usually have in a mobile phone that's only used occasionally. For example when starting an app and scrolling you need very high performance but the rest of the time the CPUs are mostly idling.