NAME¶

xfsdist.bt - Summarize XFS operation latency. Uses bpftrace/eBPF.

SYNOPSIS¶

xfsdist.bt

DESCRIPTION¶

This tool summarizes time (latency) spent in common XFS file operations: reads, writes, opens, and syncs, and presents it as a power-of-2 histogram. It uses an in-kernel eBPF map to store the histogram for efficiency.

Since this works by tracing the xfs_file_operations interface functions, it will need updating to match any changes to these functions.

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

REQUIREMENTS¶

CONFIG_BPF and bpftrace.

EXAMPLES¶

Trace XFS operation time, and print a summary on Ctrl-C:

# xfsdist.bt

FIELDS¶

0th

The operation name (shown in "@[...]") is printed before each I/O histogram.

1st, 2nd

This is a range of latency, in microseconds (shown in "[...)" set notation).

3rd

A column showing the count of operations in this range.

4th

This is an ASCII histogram representing the count column.

OVERHEAD¶

This adds low-overhead instrumentation to these XFS operations, including reads and writes from the file system cache. Such reads and writes can be very frequent (depending on the workload; eg, 1M/sec), at which point the overhead of this tool may become noticeable. Measure and quantify before use.

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.

This is a bpftrace version of the bcc tool of the same name. The bcc tool may provide more options and customizations.

https://github.com/iovisor/bcc

OS¶

Linux

STABILITY¶

Unstable - in development.

AUTHOR¶

Brendan Gregg

SEE ALSO¶

biolatency.bt(8)