ktime

ktime is a kernel-facing time representation used in the Linux kernel to store and manipulate time values with high resolution and monotonic semantics. It is part of an effort to unify timekeeping across subsystems such as timers, schedulers, and time sources, providing a common type for time operations that can be efficiently handled inside the kernel.

The ktime type is designed to be a 64-bit value that represents time in nanoseconds. This representation supports precise arithmetic and comparisons and is intended to be monotonic, meaning it progresses consistently over time without being affected by external adjustments to the system clock. This makes ktime suitable for scheduling, timeouts, and high-resolution timers where absolute wall-clock accuracy is not required.

In kernel code, ktime values are used by a variety of components, including high-resolution timers (hrtimers), timer facilities, and scheduling logic. The API provides ways to obtain the current time, perform arithmetic with durations, and convert between ktime and other time formats used internally or when interfacing with user space. Helper functions and macros enable conversions to and from nanoseconds, and to or from other representations such as timespec-like structures when necessary.

Conversions and interoperability are a core part of the design. While ktime is primarily an internal kernel construct, there are established pathways to convert to and from user-visible time formats and to interconvert with other kernel time representations. This abstraction helps minimize cross-platform differences and simplifies the handling of time in time-sensitive code paths.

See also: CLOCK_MONOTONIC, CLOCK_REALTIME, hrtimers, and kernel timekeeping infrastructure.