In previous versions of Red Hat Enterprise Linux, the kernel used a timer-based mechanism that continuously produced a system interrupt. During each interrupt, the system polled; that is, it checked to see if there was work to be done.
Depending on the setting, this system interrupt or timer tick could occur several hundred or several thousand times per second. This happened every second, regardless of the system's workload. On a lightly loaded system, this impacts power consumption by preventing the processor from effectively using sleep states. The system uses the least power when it is in a sleep state.
The most power-efficient way for a system to operate is to do work as quickly as possible, go into the deepest sleep state possible, and sleep as long as possible. To implement this, Red Hat Enterprise Linux 6 uses a tickless kernel. With this, the interrupt timer has been removed from the idle loop, transforming Red Hat Enterprise Linux 6 into a completely interrupt-driven environment.
The tickless kernel allows the system to go into deep sleep states during idle times, and respond quickly when there is work to be done.