The kernel's lowest-level primitives can be called thousands of times (or more) every second, so, as one might expect, they have been ruthlessly optimized over the years. To do otherwise would be to sacrifice some of the system's performance needlessly. But, as it happens, hard-won performance can slip away over the years as the code is changed and gains new features. Often, such performance loss goes unnoticed until a developer decides to take a closer look at a specific kernel subsystem. That would appear to have just happened with regard to how the kernel handles preemption. <p> Click below (subscribers only) for the full article from this week's Kernel Page.