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2017-09-26 - 12:54
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13th Real-Time Linux Workshop from October 20 to 22 at the Faculty of Electrical Engineering, Czech Technical University in Prague

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Adaptive tickless kernel

Frederic Weisbecker

The scheduler tick is a timer that runs periodically from 100 to 1000 times per second. It acts as a kernel heartbeat to maintain the progression of walltime, jiffies, the scheduler state, rcu state, load statistics, cputime, timers, etc...

With 2.6.21 came a new feature called dynticks that shuts down the periodic tick when a CPU goes idle. The goal was to reduce CPU energy consumption and the amount of interrupt generating critical section that can hurt latencies on a real time environment.

Today, more efforts are invested to push the tickless feature further when the CPU is busy running tasks. Ie: minimizing the periodic tick as much as possible. The goal is not anymore about energy saving but rather in reducing even more the critical sections that induce latencies. Throughput may also get better without useless interrupts to handle and the amount of CPU cache they use. So this is expected to be useful for the two extreme evironments that Real Time and High Performance Computing are. And may be even for more common usecases in the middle (embedded, desktop, server,...).

Of course getting that feature properly upstream is going to be some adventure.