Man pages sections > man8 > xfsslower-bpfcc

xfsslower - Trace slow xfs file operations, with per-event details.

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 details for each that exceeded a threshold.
 
WARNING: See the OVERHEAD section.
 
By default, a minimum millisecond threshold of 10 is used. If a threshold of 0 is used, all events are printed (warning: verbose).
 
Since this works by tracing the xfs_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

-p PID Trace this PID only.
min_ms
Minimum I/O latency (duration) to trace, in milliseconds. Default 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 inclusive 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_iname).
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, including 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)
2016-02-11 USER COMMANDS