Summary

This chapter covered the Linux scheduler, preemption in Linux, and the Linux system clock and timers.

More specifically, we covered the following topics:

• We introduced the new Linux 2.6 scheduler and outlined its new features.

• We described how the scheduler chooses the next task from among all tasks it can choose and the algorithms the scheduler uses to do so.

• We discussed the context switch that the scheduler uses to actually swap a process and traced the function into the low-level architecture-specific code.

• We covered how processes in Linux can yield the CPU to other processes by calling schedule() and how the kernel then marks that process as "to be scheduled."

• We delved into how the Linux kernel calculates dynamic priority based on the previous behavior of an individual process and how a process eventually gets removed from the scheduling queue.

• We then moved on and covered implicit and explicit user- and kernel-level preemption and how each is dealt with in the 2.6 Linux kernel.

• Finally, we explored timers and the system clock and how the system clock is implemented in both x86 and PPC architectures.