bcc-btrfsdist man page

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

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.

CONFIG_BPF and bcc.

-h

Print usage message.

-T

Don't include timestamps on interval output.

-m

Output in milliseconds.

-p PID

Trace this PID only.

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

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).

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.

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.

Linux

Unstable - in development.

Brendan Gregg

btrfsslower(8)