xfsslower(8) System Manager's Manual xfsslower(8)
NAME
xfsslower - Trace slow xfs file operations, with per-event details.
SYNOPSIS
xfsslower [-h] [-j] [-p PID] [min_ms]
DESCRIPTION
This tool traces common XFS file operations: reads, writes, opens, and
syncs. It measures the time spent in these operations, and prints de-
tails for each that exceeded a threshold.
WARNING: See the OVERHEAD section.
By default, a minimum millisecond threshold of 10 is used. If a thresh-
old of 0 is used, all events are printed (warning: verbose).
Since this works by tracing the xfs_file_operations interface func-
tions, 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
-p PID Trace this PID only.
min_ms Minimum I/O latency (duration) to trace, in milliseconds. De-
fault is 10 ms.
EXAMPLES
Trace synchronous file reads and writes slower than 10 ms:
# xfsslower
Trace slower than 1 ms:
# xfsslower 1
Trace slower than 1 ms, and output just the fields in parsable format
(csv):
# xfsslower -j 1
Trace all file reads and writes (warning: the output will be verbose):
# xfsslower 0
Trace slower than 1 ms, for PID 181 only:
# xfsslower -p 181 1
FIELDS
TIME(s)
Time of I/O completion since the first I/O seen, in seconds.
COMM Process name.
PID Process ID.
T Type of operation. R == read, W == write, O == open, S == fsync.
OFF_KB File offset for the I/O, in Kbytes.
BYTES Size of I/O, in bytes.
LAT(ms)
Latency (duration) of I/O, measured from when it was issued by
VFS to the filesystem, to when it completed. This time is inclu-
sive of block device I/O, file system CPU cycles, file system
locks, run queue latency, etc. It's a more accurate measure of
the latency suffered by applications performing file system I/O,
than to measure this down at the block device interface.
FILENAME
A cached kernel file name (comes from dentry->d_name.name).
ENDTIME_us
Completion timestamp, microseconds (-j only).
OFFSET_b
File offset, bytes (-j only).
LATENCY_us
Latency (duration) of the I/O, in microseconds (-j only).
OVERHEAD
This adds low-overhead instrumentation to these XFS operations, includ-
ing 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 (even if it prints no "slower" events)
can begin to become significant. Measure and quantify before use. If
this continues to be a problem, consider switching to a tool that
prints in-kernel summaries only.
Note that the overhead of this tool should be less than fileslower(8),
as this tool targets xfs functions only, and not all file read/write
paths (which can include socket I/O).
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
biosnoop(8), funccount(8), fileslower(8)
USER COMMANDS 2016-02-11 xfsslower(8)
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