3 ms·

I'd say that depends on the higher end of what? Control over the firmware, understanding of the actual bits you're flipping and the architecture, power consumpt

I'd say that depends on the higher end of what? Control over the firmware, understanding of the actual bits you're flipping and the architecture, power consumption, or raw computer per clock?

mastazi 6y ago
I’m not parent but personally I’m interested in performance per Watt
- ljhsiung 6y ago
  The ISA design has very little impact on actual energy consumption rather than an actual CPU's uArch. This is a conception that hasn't been true for at least 20 years. It was somewhat true in the days where memory was expensive, and so smaller instructions were a good idea. But this came at the cost of increased area and thus energy (since you need more decoding logic). As time went on, transistors shrank, so this cost kept decreasing; at the same time, memory got better and we developed techniques to hide the latency more, so the upside also kept decreasing. Ultimately in modern times any difference in ISA results in some ~1% difference in energy consumption. You would gain far more efficiency (on the order of 2.5x) in just designing your uArch in a better way-- say, in-order vs OoO. [1] In my opinion, the reason CISC vs. RISC is still very alive today is because ARM has done a fabulous job in marketing and executing itself as energy efficient. The big.Little architectures are an example in cementing this idea. Conversely, Intel has done a similarly fabulous job in marketing and executing itself as performant, allowing both companies to live happily in their respective areas. The introduction of hyperthreading is another example of pushing this edge. But these design decisions are NOT ISA intrinsic, and these misconceptions are changing incredibly fast (though I think ARM is doing a much better job than Intel at changing these paradigms). [1] https://research.cs.wisc.edu/vertical/papers/2013/hpca13-isa-power-struggles.pdf https://research.cs.wisc.edu/vertical/papers/2013/hpca13-isa...
  - jlokier 6y ago
    > ARM has done a fabulous job in marketing and executing itself as energy efficient. To be fair to ARM, they actually have produced energy efficient processors. I don't know a lot about ARM processor internals, but I've seen some presentations from many years ago and they had clever tricks for saving power while running, such as only charging some transistors during part of a clock cycle. That doesn't mean the ISA is the reason for power efficiency, it means ARM designs have other tricks as well. Or at least, they used to.

I'd say that depends on the higher end of what? Control over the firmware, understanding of the actual bits you're flipping and the architecture, power consumption, or raw computer per clock?

mastazi 6y ago

I’m not parent but personally I’m interested in performance per Watt

ljhsiung 6y ago
The ISA design has very little impact on actual energy consumption rather than an actual CPU's uArch. This is a conception that hasn't been true for at least 20 years. It was somewhat true in the days where memory was expensive, and so smaller instructions were a good idea. But this came at the cost of increased area and thus energy (since you need more decoding logic). As time went on, transistors shrank, so this cost kept decreasing; at the same time, memory got better and we developed techniques to hide the latency more, so the upside also kept decreasing. Ultimately in modern times any difference in ISA results in some ~1% difference in energy consumption. You would gain far more efficiency (on the order of 2.5x) in just designing your uArch in a better way-- say, in-order vs OoO. [1] In my opinion, the reason CISC vs. RISC is still very alive today is because ARM has done a fabulous job in marketing and executing itself as energy efficient. The big.Little architectures are an example in cementing this idea. Conversely, Intel has done a similarly fabulous job in marketing and executing itself as performant, allowing both companies to live happily in their respective areas. The introduction of hyperthreading is another example of pushing this edge. But these design decisions are NOT ISA intrinsic, and these misconceptions are changing incredibly fast (though I think ARM is doing a much better job than Intel at changing these paradigms). [1] https://research.cs.wisc.edu/vertical/papers/2013/hpca13-isa-power-struggles.pdf https://research.cs.wisc.edu/vertical/papers/2013/hpca13-isa...
- jlokier 6y ago
  > ARM has done a fabulous job in marketing and executing itself as energy efficient. To be fair to ARM, they actually have produced energy efficient processors. I don't know a lot about ARM processor internals, but I've seen some presentations from many years ago and they had clever tricks for saving power while running, such as only charging some transistors during part of a clock cycle. That doesn't mean the ISA is the reason for power efficiency, it means ARM designs have other tricks as well. Or at least, they used to.