From: david.brown@hesbynett.no   
      
   On 22/09/2025 21:36, MitchAlsup wrote:   
   >   
   > David Brown  posted:   
   >   
   >> On 22/09/2025 17:28, Stefan Monnier wrote:   
   >>>> But, AFAIK the ARM cores tend to use significantly less power when   
   >>>> emulating x86 than a typical Intel or AMD CPU, even if slower.   
   >>>   
   >>> AFAIK datacenters still use a lot of x86 CPUs, even though most of them   
   >>> run software that's just as easily available for ARM.  And many   
   >>> datacenters care more about "perf per watt" than raw performance.   
   >>>   
   >>> So, I think the difference in power consumption does not favor ARM   
   >>> nearly as significantly as you think.   
   >>>   
   >>   
   >> Yes, I think that is correct.   
   >>   
   >> A lot of it, as far as I have read, comes down to the type of   
   >> calculation you are doing.  ARM cores can often be a lot more efficient   
   >> at general integer work and other common actions, as a result of a   
   >> better designed instruction set and register set.  But once you are   
   >> using slightly more specific hardware features - vector processing,   
   >> floating point, acceleration for cryptography, etc., it's all much the   
   >> same.  It takes roughly the same energy to do these things regardless of   
   >> the instruction set.  Cache memory takes about the same power, as do PCI   
   >> interfaces, memory interfaces, and everything else that takes up power   
   >> on a chip.   
   >>   
   >> So when you have a relatively small device - such as what you need for a   
   >> mobile phone - the instruction set and architecture makes a significant   
   >> difference and ARM is a lot more power-efficient than x86.  (If you go   
   >> smaller - small embedded systems - x86 is totally non-existent because   
   >> an x86 microcontroller would be an order of magnitude bigger, more   
   >> expensive and power-consuming than an ARM core.)  But when you have big   
   >> processors for servers, and are using a significant fraction of the   
   >> processor's computing power, the details of the core matter a lot less.   
   >   
   > Big servers have rather equal power in the peripherals {DISKs, SSDs, and   
   > NICs} and DRAM {plus power supplies and cooling} than in the cores.   
      
   Yes, all that will be independent of the type of cpu core.   
      
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