5 ms·

This is a great explaination of why high power CPUs are great for desktops and servers but terrible for mobile.

• gameswithgo 7y ago
  Does this actually waste power? A lot of people's intuition about what wastes power with cpus is wrong. Usually it is best to light up all the tricks, heat the cpu up, finish the work, then go back to sleep. If branch prediction helps you get back to sleep sooner, it is probably a net win.
  • dragontamer 7y ago
    My understanding of CPU-physics is as follows: https://www.ti.com/lit/an/scaa035b/scaa035b.pdf https://www.ti.com/lit/an/scaa035b/scaa035b.pdf Page 4 (page8 in PDF): > P = C * V^2 * f * N Power-used = Capacitance * Voltage^2 * Frequency * Number of Bits flipped This equation roughly holds for all CMOS circuits, from the 1970s through today's CPUs. Smaller transistors result in smaller capacitance, which is what led to Dennard scaling for the past 40 years. Otherwise, the physics are the same. Static-power consumption in CMOS is theoretically zero, and measured to be femto-amps. Static power consumption can therefore be ignored, only dynamic power matters in the real world. Assuming the same transistor size (aka: capacitance), you can see that power use is most strongly determined by voltage. Another note: higher frequencies (say 3GHz or 4GHz) requires more-and-more voltage to sustain. A mobile chip drawing 1/2 voltage at 1/2-frequency will have 1/8th the power consumption but take 2x longer to complete a task. Overall, you have 1/4th the power consumption used. ---------- This is why servers reduce frequency and voltage and save on power in practice.
    • dannyw 7y ago
      As another example, many cryptocurrency miners undervolt their cards to get better performance per unit of energy.
• gpderetta 7y ago
  all mobile cpus (at least those worth using) do exactly the same thing.