SIMPLE SOLUTIONS

BTRFSDIST-BPFCC(8) - Linux man page online | Administration and privileged commands

Summarize btrfs operation latency. Uses Linux eBPF/bcc.

Chapter
2016-02-15
btrfsdist(8) System Manager's Manual btrfsdist(8)

NAME

btrfsdist - Summarize btrfs operation latency. Uses Linux eBPF/bcc.

SYNOPSIS

btrfsdist [-h] [-T] [-N] [-d] [interval] [count]

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.

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 btrfs operation time, and print a summary on Ctrl-C: # btrfsdist Trace PID 181 only: # btrfsdist -p 181 Print 1 second summaries, 10 times: # btrfsdist 1 10 1 second summaries, printed in milliseconds # btrfsdist -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 btrfs writes and fsyncs, as well as all system reads and opens (due to the current implementation of the btrfs_file_operations inter‐ face). 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 work‐ load; eg, 1M/sec), at which point the overhead of this tool may become noticeable. Mea‐ sure 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

btrfsslower(8)
USER COMMANDS 2016-02-15 btrfsdist(8)
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