Accurate timestamps for the ftrace ring buffer

The function tracer (ftrace) subsystem has become an essential part of the kernel's introspection tooling. Like many kernel subsystems, ftrace uses a ring buffer to quickly communicate events to user space; those events include a timestamp to indicate when they occurred. Until recently, the design of the ring buffer has led to the creation of inaccurate timestamps when events are generated from interrupt handlers. That problem has now been solved; read on for an in-depth discussion of how this issue came about and the form of its solution.

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