These are some pointers to timing and timer related files in the Linux kernel.
kernel/time/time.c file defines basic time related system calls:
kernel/time/timer.c file implements a legacy timer subsystem based on
kernel/time/hrtimer.c file implements a high resolution timers subsystem that is the
basis for high resolution kernel timers as well as most current userspace timer iterfaces:
nanosleep, and POSIX timers.
kernel/time/tick-common.c file defines functions for generating and handling
tick events, including
for periodic tick systems.
kernel/time/tick-oneshot.c file defines functions for oneshot ticks.
kernel/time/tick-broadcast.c file defines functions for handling
the broadcast of tick events for SMP systems, including functions for
handling ticks in oneshot mode.
include/linux/ktime.h file defines the
type, which is a nanosecond representation of kernel time values.
kernel/time/timekeeping.c file several functions
for accessing, measuring, and setting time in the Linux kernel,
including several functions which return or take as parameters
variables of the