btrfsdist(8) System Manager's Manual btrfsdist(8)
btrfsdist - Summarize btrfs operation latency. Uses Linux eBPF/bcc.
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:
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.
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 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.
This is from bcc.
Also look in the bcc distribution for a companion _examples.txt file containing example
usage, output, and commentary for this tool.
Unstable - in development.
USER COMMANDS 2016-02-15 btrfsdist(8)