Running a processor at high clock speeds allows for better performance. However, when the same processor is run at a lower frequency (speed), it generates less heat and consumes less power. In many cases, the core voltage can also be reduced, further reducing power consumption and heat generation. By using SpeedStep, users can select the balance of power conservation and performance that best suits them, or even change the clock speed dynamically as the processor burden changes.
The power consumed by a CPU with a capacitance C, running at frequency f and voltage V is approximately:[3]
- P = C V 2 f {\displaystyle P=CV^{2}f}
For a given processor, C is a fixed value. However, V and f can vary considerably. For example, for a 1.6 GHz Pentium M, the clock frequency can be stepped down in 200 MHz decrements over the range from 1.6 to 0.6 GHz. At the same time, the voltage requirement decreases from 1.484 to 0.956 V. The result is that the power consumption theoretically goes down by a factor of 6.4. In practice, the effect may be smaller because some CPU instructions use less energy per tick of the CPU clock than others. For example, when an operating system is not busy, it tends to issue x86 halt (HLT) instructions, which suspend operation of parts of the CPU for a time period, so it uses less energy per tick of the CPU clock than when executing productive instructions in its normal state. For a given rate of work, a CPU running at a higher clock rate will execute a greater proportion of HLT instructions. The simple equation which relates power, voltage and frequency above also does not take into account the static power consumption of the CPU. This tends not to change with frequency, but does change with temperature and voltage. Hot electrons, and electrons exposed to a stronger electric field are more likely to migrate across a gate as "gate leakage" current, leading to an increase in static power consumption.
Older processors such as the Pentium 4-M, which use older versions of SpeedStep, have fewer clock-speed increments. SpeedStep technology is partly responsible for the reduced power consumption of Intel's Pentium M processor, part of the Centrino brand.
---In Avid-L2@yahoogroups.com, <mactvman@...> wrote :
On Dec 26, 2018, at 2:46 PM, John Moore bigfish@... [Avid-L2] <Avid-L2@yahoogroups.com> wrote:For the fun I often open Acitvity Monitor when transcoding or other processor intensive processes to see how much of the 12 core is being used.I can get up to 2,000 percent usage on Avid Transcodes depending on the codec and perhaps other factors I'm unaware of. Today it CC 2015 Adobe Media Encoder and the CPU Usage window is screaming with all 24 bars up to the top. The second bar of the core hyper thread is just a little below top and the first bars are all to the top. My visual math would suggest approx 2,100 cpu percentage but in the Activity monitor window the %CPU is bouncing around 1,400 to 1,600 %CPU. Curious why CPU Usage bars look like more core is being used? IIRC with Avid it's more visually bar graph and %CPU comparable. Is there something about how AME processes that would cause the perceived discrepancy. I am running parallel encoding with ProResHQ and 2 H_264 encodes for each file. Not a broke but makes me curious.John Moore Barking Trout Productions Studio City, CA bigfish@...
Posted by: bigfish@pacbell.net
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