NAME

ext4dist - Summarize ext4 operation latency. Uses Linux eBPF/bcc.

SYNOPSIS

ext4dist [-h] [-T] [-m] [-p PID] [interval] [count]

DESCRIPTION

This tool summarizes time (latency) spent in common ext4 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 ext4_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 bcc.

OPTIONS

-h: Print usage message.
-T: Don't include timestamps on interval output.
-m: Output in milliseconds.
-p PID: Trace this PID only.

EXAMPLES

Trace ext4 operation time, and print a summary on Ctrl-C:: # ext4dist
Trace PID 181 only:: # ext4dist -p 181
Print 1 second summaries, 10 times:: # ext4dist 1 10
1 second summaries, printed in milliseconds: # ext4dist -m 1

FIELDS

msecs: Range of milliseconds for this bucket.
usecs: Range of microseconds for this bucket.
count: Number of operations in this time range.
distribution: ASCII representation of the distribution (the count column).

OVERHEAD

This adds low-overhead instrumentation to these ext4 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 bcc.

: https://github.com/iovisor/bcc

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

OS

Linux

STABILITY

Unstable - in development.

AUTHOR

Brendan Gregg