Instead, the kernel will only awaken the processor when an event is scheduled, and will try to schedule multiple events to process together–thus allowing the processor to remain in its sleep state for longer intervals and consume less power. Linux made a big step forward in this area with the introduction of the “ tickless idle” feature of kernel 2.6.21 in 2007.Įnabling the tickless idle feature prevents the kernel (and thus the processor) from waking up at regular intervals to increment counters and check for application events waiting to be processed. Since the kernel determines when to put the processor to sleep and when to wake it up, good idle state management can make a tremendous difference in overall power consumption. Modern CPUs have multiple sleep states (also known as C-states), each of which uses successively less power than the one before. Check your distribution’s documentation to see what is included.Įven running at its lowest frequency the processor consumes more power than it does in an idle state. There are several applications to help you make use of cpufreq, including panel applets for KDE and GNOME and command-line utilities. More flexible policies exist, too, such as “ondemand” which increases CPU speed when the load increases, and “userspace” which defers the decision to an interactive application. You can tell cpufreq to use different strategies for selecting processor speed, such as always using the highest speed available (the “performance” policy) or the lowest (the “powersave” policy). CPU scaling uses the cpufreq module, which is provided by default in most consumer Linux distributions.
Usbextreme saving portable#
For many day-to-day computing tasks, running at a lower processor speed will have no discernible effect, and on portable devices can greatly increase battery life.
The first technique is called CPU frequency scaling, and the second takes advantage of a feature called “tickless idle” in recent kernels.įrequency scaling adjusts the speed at which the processor’s clock runs (also known as the processor’s P-states). Linux can conserve processor power in two ways: throttling back the frequency at which the processor runs when active, and better managing the idle state of the processor when it isn’t. Other tools allow you to audit which applications wake up the processor unnecessarily, so you can tune your system accordingly. Recent advances in the kernel have brought energy-saving to a new level for Linux systems, enabling better control over power usage at the processor and on the motherboard.
Regardless of the state of the economy, price of electricity, or proximity to Earth Day, saving power is always a good idea.
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