NAME¶

zfsdist - Summarize ZFS operation latency. Uses Linux eBPF/bcc.

SYNOPSIS¶

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

DESCRIPTION¶

This tool summarizes time (latency) spent in common ZFS 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.

This uses kernel dynamic tracing of the ZPL interface (ZFS POSIX Layer), and will need updates to match any changes to this interface.

This is intended to work with the ZFS on Linux project:

http://zfsonlinux.org

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

# zfsdist

Trace PID 181 only:

# zfsdist -p 181

Print 1 second summaries, 10 times:

# zfsdist 1 10

1 second summaries, printed in milliseconds

# zfsdist -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 ZFS 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

SEE ALSO¶

zfssnoop(8)