function::cpu_clock_ns - Linux

Overview

cpu_clock_ns provides the current CPU clock, expressed as nanoseconds since system boot. This command is useful for measuring the elapsed time of code execution, collecting precise performance metrics, and synchronizing across multiple threads or processes.

Syntax

cpu_clock_ns [[ [-]specs] ]

Options/Flags

  • -d: Display the elapsed time in seconds since boot.
  • -f: Display the result in floating-point format.
  • -h: Display usage help and exit.

Examples

Measure the time taken by a sleep command:

cpu_clock_ns -d
sleep 2
cpu_clock_ns -d

Measure the elapsed time between two events:

start=$(cpu_clock_ns)
sleep 5
end=$(cpu_clock_ns)
elapsed=$((end - start))
echo "Elapsed time: ${elapsed}ns"

Common Issues

  • Error: math: underflow: This occurs when the clock has overflowed and the elapsed time is larger than 2^63.
  • Incorrect values: Ensure that the system clock is set correctly using date or a related tool.

Integration

Combine with time command:

time cpu_clock_ns [-d] command

This executes the provided command and displays the elapsed time in seconds or nanoseconds.

Use in scripts:

#!/bin/bash

start=$(cpu_clock_ns)
# Perform some operations here
end=$(cpu_clock_ns)

elapsed=$((end - start))
echo "Elapsed time: ${elapsed}ns"

Related Commands

  • clock_gettime: Gets the current time using a specified clock.
  • time: Measures the execution time of a command.