Power consumption is a hot topic — from laptop, to datacenter. Recently, the Linux kernel has made huge steps forward in power conservation. This article focuses on the so-called “tickless idle” feature being integrated into the 2.6.21 and 2.6.23 kernel versions.
Power consumption is a hot topic — from laptop, to datacenter. Recently, the Linux kernel has made huge steps forward in power conservation. This article focuses on the so-called “tickless idle” feature being integrated into the 2.6.21 and 2.6.23 kernel versions.
How to Save Power
Before explaining some of the improvements the kernel has undergone in the last few months, it’s useful to list some general power-saving strategies and techniques:
*Turn the device off when not in use. Obviously, when a component isn’t used, the operating system should turn it off as much as possible.
*Create long idle time between activities. Processors (but also disks and other components) have several degrees of power-saving when idle. If a component is idle for a long time, it can go into the deepest possible power-saving state; but if it’s only idle for a short time, it can only go into a shallow power-saving state.
Each type of component defines what’s meant by “long time.” For processors, a “long time” is roughly twenty milliseconds. For disks, a “long time” is about two seconds. While the scale differs, the net effect is the same: it’s better to do all the work in one step than to perform several smaller steps.
C-states
Several of the new kernel improvements center around processors, so it’s appropriate to explain the so-called C-states present in contemporary (mobile) processors from the various vendors.
“C-states” is a term derived from the ACPI specification. The basic idea is that…
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