Thomas Gleixner and Ingo Molnar [interview] posted an update of their high-res timers kernel patches for the 2.6.17 kernel, "upon which we based a tickless kernel (dyntick) implementation and a 'dynamic HZ' feature as well". The patch currently works for x86, with ports to x86_64, PPC and ARM in the works. Thomas explains, "the high-res timers feature (CONFIG_HIGH_RES_TIMERS) enables POSIX timers and nanosleep() to be as accurate as the hardware allows (around 1usec on typical hardware). This feature is transparent - if enabled it just makes these timers much more accurate than the current HZ resolution." He goes on to discribe the tickless kernel:

"The tickless kernel feature (CONFIG_NO_HZ) enables 'on-demand' timer interrupts: if there is no timer to be expired for say 1.5 seconds when the system goes idle, then the system will stay totally idle for 1.5 seconds. This should bring cooler CPUs and power savings: on our (x86) testboxes we have measured the effective IRQ rate to go from HZ to 1-2 timer interrupts per second.

"This feature is implemented by driving 'low res timer wheel' processing via special per-CPU high-res timers, which timers are reprogrammed to the next-low-res-timer-expires interval. This tickless-kernel design is SMP-safe in a natural way and has been developed on SMP systems from the beginning."