Manual: xfsslower-bpfcc

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 op‐
       erations, 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 (warn‐
       ing: 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 mea‐
	      sure 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, 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 over‐
       head 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)