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I've noticed that CPU companies are focusing more and more on power efficiency to compete with ARM potentially. Maybe turning off the features described in the

I've noticed that CPU companies are focusing more and more on power efficiency to compete with ARM potentially. Maybe turning off the features described in the OP makes lower end CPUs run faster? That might be significant since i also presume most laptops use those same lower end CPUs. Laptops being the ones that need to save energy much of the time. (Desktops are obviously plugged in). This is probably most significant in the Microsoft Surface (it uses a real intel CPU if i recall correctly). I wonder which features it has marked "off" , and what impact that has on battery power.

icegreentea 12y ago
The "lowest" end of the CPUs that the OP discusses are low end desktop/laptop parts. Furthermore, the biggest criticism of the author isn't the feature disabling per se, but how inconsistently Intel applies it across their overall performance bins. For example, the lack of TXT support in high end i7 parts when its there for middle tier i5 parts. Why the i7-3990K has VT-d and the i7-3770K doesnt(which really should just be distinguished by their clock/cache/TDP).
- ptysiu 12y ago
  3770K cpu has basic version 3770, which has the VT-d ext. There is no such thing like 3990k.
wtallis 12y ago
Remember, within a generation these chips are almost all made from the same set of masks. None of these disabled features save any transistors or die area; the disabling just leaves you with a dead spot on the chip. So the real question is if you've got the hardware in place to provide these special features, can you save any power by not using those features? The answer is that you only save power by not doing at all the things those features accelerate. It's never more efficient to implement AES through general-purpose instructions than using the fixed-function hardware. If you've got a workload that can benefit from the wider SIMD units, it won't save any energy to only use the narrower instructions. If you're trying to secure or virtualize your OS, doing it with VT-x and VT-d will be so much faster than emulating it in software that even if those features added several watts to the chips power consumption you would still save energy. Doing less can save power, but doing the same amount of stuff the hard way doesn't help anything.
- tanderson92 12y ago
  That's only true if you are using those features 100% of the time though, right ? By which I mean, there is no doubt a trade-off in play when you only use the features for 15% of your workload. This is because the chip must be powered on all the time but, say, the software implementation of AES doesn't always have to be running.
  - wtallis 12y ago
    No, special-purpose functional units are very well power-gated on modern chips. They don't draw appreciably more power when not in use than when fused off.
    - rasz_pl 12y ago
      you say that, but in practice Intel is still 5-10x off ARM when it comes to idle power.
      - wmf 12y ago
        Is that true for Merrifield/Moorefield? AFAIK they're pretty close, but only in the phone chips.
      - wtallis 12y ago
        Register renaming and instruction reordering and things like that can't be selectively powered down, and are very power-hungry. But if you were talking about when the entire core is suspended, then that's largely unrelated to the high-level feature set of the processor. It's about things like the analog characteristics of the transistors used: Intel builds their mainstream CPUs using circuits that can run at 4-5GHz without trouble while none of the mobile SoCs can come close regardless of exotic cooling.
- dippyskoodlez 12y ago
  You can also disable defective components without being forced to bin the entire chip to a recycle bin. That is honestly probably more of a factor than anything for the segregation between models. Get that yield up to improve margins significantly.

icegreentea 12y ago

The "lowest" end of the CPUs that the OP discusses are low end desktop/laptop parts. Furthermore, the biggest criticism of the author isn't the feature disabling per se, but how inconsistently Intel applies it across their overall performance bins. For example, the lack of TXT support in high end i7 parts when its there for middle tier i5 parts. Why the i7-3990K has VT-d and the i7-3770K doesnt(which really should just be distinguished by their clock/cache/TDP).

ptysiu 12y ago
3770K cpu has basic version 3770, which has the VT-d ext. There is no such thing like 3990k.

wtallis 12y ago

Remember, within a generation these chips are almost all made from the same set of masks. None of these disabled features save any transistors or die area; the disabling just leaves you with a dead spot on the chip. So the real question is if you've got the hardware in place to provide these special features, can you save any power by not using those features? The answer is that you only save power by not doing at all the things those features accelerate. It's never more efficient to implement AES through general-purpose instructions than using the fixed-function hardware. If you've got a workload that can benefit from the wider SIMD units, it won't save any energy to only use the narrower instructions. If you're trying to secure or virtualize your OS, doing it with VT-x and VT-d will be so much faster than emulating it in software that even if those features added several watts to the chips power consumption you would still save energy. Doing less can save power, but doing the same amount of stuff the hard way doesn't help anything.

tanderson92 12y ago
That's only true if you are using those features 100% of the time though, right ? By which I mean, there is no doubt a trade-off in play when you only use the features for 15% of your workload. This is because the chip must be powered on all the time but, say, the software implementation of AES doesn't always have to be running.
- wtallis 12y ago
  No, special-purpose functional units are very well power-gated on modern chips. They don't draw appreciably more power when not in use than when fused off.
  - rasz_pl 12y ago
    you say that, but in practice Intel is still 5-10x off ARM when it comes to idle power.
    - wmf 12y ago
      Is that true for Merrifield/Moorefield? AFAIK they're pretty close, but only in the phone chips.
    - wtallis 12y ago
      Register renaming and instruction reordering and things like that can't be selectively powered down, and are very power-hungry. But if you were talking about when the entire core is suspended, then that's largely unrelated to the high-level feature set of the processor. It's about things like the analog characteristics of the transistors used: Intel builds their mainstream CPUs using circuits that can run at 4-5GHz without trouble while none of the mobile SoCs can come close regardless of exotic cooling.
dippyskoodlez 12y ago
You can also disable defective components without being forced to bin the entire chip to a recycle bin. That is honestly probably more of a factor than anything for the segregation between models. Get that yield up to improve margins significantly.