Timer Coalescence Makes OS X Maverick Power Efficient

A
pple, with the release of its OS X Maverick, has moved Macs a notch up in terms of power efficiency by introducing a technology known as timer coalescing.  

With timer coalescing, Maverick taps the  power saving mode of the CPU by keeping it in a low-power idle state for longer durations while the machine is still running normally.

Making a CPU enter and exit the idle state is a costly affair in terms of power and latency.  The duration of the idle-state time must be long enough so as to have sufficient power savings to justify these costs.  Increasing the idle state time, however, is a little tricky.

The trick is timer coalescence. It takes a little liberty with the software timers and reduce their precision.

The execution of individual timers (for the applications and back ground tasks) are shifted by a small amount so as to synchronize different process wake ups; i.e. operations are grouped together.  The processor, therefore, begins to  execute various tasks at the same time, completes them and then goes back to its idle state before waking up again.  Compared to the more frequent wake ups in the absence of timer coalescence, this is more efficient in terms of power.

Without Timer Coalescence - More Frequent Processor Wake Ups, Less Power Efficiency

Without Timer Coalescence – More Frequent Processor Wake Ups, Less Power Efficiency

Image Source: Apple
With Timer Coalescence - Less Frequent Processor Wake Ups, More Power Efficiency

With Timer Coalescence – Less Frequent Processor Wake Ups, More Power Efficiency

Image Source: Apple
  

The overall result is that the processor is woken up less frequently from its idle low power state and relatively longer durations of idle, power saving state is achieved. Net result: CPU activity reduction up to 72%, less energy usage and a longer battery life!

 

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Tarique Haider

Tarique Haider is an engineer by training, a pacifist at heart and a teacher by choice. He believes in a better tomorrow through education and technology. Connect with him on Google+

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