.TH btrfsdist 8  "2016-02-15" "USER COMMANDS"
.SH NAME
btrfsdist \- Summarize btrfs operation latency. Uses Linux eBPF/bcc.
.SH SYNOPSIS
.B btrfsdist [\-h] [\-T] [\-N] [\-d] [interval] [count]
.SH DESCRIPTION
This tool summarizes time (latency) spent in common btrfs 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 btrfs_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.
.SH REQUIREMENTS
CONFIG_BPF and bcc.
.SH OPTIONS
.TP
\-h
Print usage message.
.TP
\-T
Don't include timestamps on interval output.
.TP
\-m
Output in milliseconds.
.TP
\-p PID
Trace this PID only.
.SH EXAMPLES
.TP
Trace btrfs operation time, and print a summary on Ctrl-C:
#
.B btrfsdist
.TP
Trace PID 181 only:
#
.B btrfsdist -p 181
.TP
Print 1 second summaries, 10 times:
#
.B btrfsdist 1 10
.TP
1 second summaries, printed in milliseconds
#
.B btrfsdist \-m 1
.SH FIELDS
.TP
msecs
Range of milliseconds for this bucket.
.TP
usecs
Range of microseconds for this bucket.
.TP
count
Number of operations in this time range.
.TP
distribution
ASCII representation of the distribution (the count column).
.SH OVERHEAD
This adds low-overhead instrumentation to btrfs writes and fsyncs, as well
as all system reads and opens (due to the current implementation of the
btrfs_file_operations interface). Particularly, all reads and writes from
the file system cache will incur extra overhead while tracing. 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.
.SH SOURCE
This is from bcc.
.IP
https://github.com/iovisor/bcc
.PP
Also look in the bcc distribution for a companion _examples.txt file containing
example usage, output, and commentary for this tool.
.SH OS
Linux
.SH STABILITY
Unstable - in development.
.SH AUTHOR
Brendan Gregg
.SH SEE ALSO
btrfsslower(8)