NAME¶

loads.bt - Prints load averages. Uses bpftrace/eBPF.

SYNOPSIS¶

loads.bt

DESCRIPTION¶

These are the same load averages printed by "uptime", but to three decimal places instead of two (not that it really matters). This is really a demonstration of fetching and processing a kernel structure from bpftrace.

Since this uses BPF, only the root user can use this tool.

REQUIREMENTS¶

CONFIG_BPF and bpftrace.

EXAMPLES¶

Print system load averages every second:

# loads.bt

FIELDS¶

HH:MM:SS

Each output line includes time of printing in "HH:MM:SS" format.

load averages:

These are exponentially-damped moving sum averages of the system loads. Load is a measurement of demand on system resources, which include CPUs and other resources that are accessed with the kernel in an uninterruptible state (TASK_UNINTERRUPTIBLE), which includes types of disk I/O and lock accesses. Linux load averages originally reflected CPU demand only, as it does in other OSes, but this was changed in Linux 0.99.14. This demand measurement reflects not just the utilized resource, but also the queued demand (a saturation measurement). Finally, the three numbers are called the "one-", "five-", and "fifteen-minute" load averages, however these times are constants used in the exponentially-damping equation, and the load averages reflect load beyond these times. Were you expecting an accurate description of load averages in the man page of a bpftrace tool?

OVERHEAD¶

Other than bpftrace startup time, negligible.

SOURCE¶

This is from bpftrace.

https://github.com/iovisor/bpftrace

Also look in the bpftrace distribution for a companion _examples.txt file containing example usage, output, and commentary for this tool.

REFERENCE¶

For more on load averages, see:

http://www.brendangregg.com/blog/2017-08-08/linux-load-averages.html

OS¶

Linux

STABILITY¶

Unstable - in development.

AUTHOR¶

Brendan Gregg

SEE ALSO¶

uptime(1)